Lang 2002

OCCURRENCE PATTERNS, SITE FIDELITY, AND MOVEMENTS OF PACIFIC COAST BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) IN THE SOUTHERN CALIFORNIA BIGHT _______________

A Thesis Presented to the Faculty of San Diego State University

_______________

In Partial Fulfillment of the Requirements for the Degree Master of Science in Interdisciplinary Studies: Animal Behavior _______________

by Aimée R. Lang Spring 2002

THE UNDERSIGNED FACULTY COMMITTEE APPROVES THE THESIS OF AIMÉE R. LANG:

___________________________________________ R. H. Defran, Chair Department of Psychology

___________________________________________ Vanessa Malcarne Department of Psychology

___________________________________________ David W. Weller Department of Biology

SAN DIEGO STATE UNIVERSITY Spring 2002

____________ Date

iii

ACKNOWLEDGEMENTS

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TABLE OF CONTENTS PAGE ACKNOWLEDGEMENTS..................................................................................................... iii LIST OF TABLES.................................................................................................................. vii LIST OF FIGURES ............................................................................................................... viii INTRODUCTION .....................................................................................................................1 Space-Use Patterns………………………………………………………………………...1 Ecological Factors..........................................................................................................2 Internal Constraints........................................................................................................5 Pacific Coast Bottlenose Dolphin Research ........................................................................6 Objectives ..........................................................................................................................10 METHODS…. .........................................................................................................................12 Photographic Survey Procedure.........................................................................................16 Photo-Identification Procedures.........................................................................................17 Computer Analysis.............................................................................................................19 Occurrence Patterns .....................................................................................................20 Distribution ..................................................................................................................21 Site Fidelity..................................................................................................................21 Movements...................................................................................................................22 Rate of Discovery Curves ............................................................................................22 RESULTS ……........................................................................................................................24 Occurrence .........................................................................................................................24 Distribution ........................................................................................................................25 Site Fidelity........................................................................................................................25 Movements.........................................................................................................................30 Rate of Discovery ..............................................................................................................32 Comparisons with Past Studies..........................................................................................32 Occurrence Patterns .....................................................................................................32 El Niño .........................................................................................................................37

v PAGE RESULTS (continued) Distribution ..................................................................................................................40 Site Fidelity..................................................................................................................40 Movements...................................................................................................................43 Rate of Discovery ........................................................................................................43 DISCUSSION ..........................................................................................................................46 Occurrence Patterns ...........................................................................................................47 Distribution ........................................................................................................................51 Site Fidelity........................................................................................................................54 Movements.........................................................................................................................57 Rate of Discovery Curve....................................................................................................59 Comparisons with Other Study Areas................................................................................61 CONCLUSIONS......................................................................................................................66 REFERENCES ........................................................................................................................69 APPENDIX PHOTOGRAPHIC QUALITY CRITERIA........................................................................79 ABSTRACT ..........................................................................................................................82

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LIST OF TABLES TABLE

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1. Habitat Features of Study Area Zones in San Diego and Santa Barbara........................29 2. Summary Information on Survey Effort, Study Period, and Photographic Results from San Diego Between 1984 and 1989...........................................................34 3. Summary Information on Survey Effort, Study Period, and Photographic Data for Southern California Bight Study Areas 1982-1999 ..........................................44

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LIST OF FIGURES FIGURE

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1. Map of the Southern California Bight .............................................................................13 2. Map of the San Diego Study Area...................................................................................14 3. Map of the Santa Barbara Study Area.............................................................................15 4. Computation of the Dorsal Ratio.....................................................................................18 5. Mean Number of Dolphins Observed per Complete Survey as a Function of Oceanographic Season in San Diego and Santa Barbara between April 1998 and August 1999..............................................................................................................26 6. Mean School Size as a Function of Oceanographic Season for San Diego and Santa Barbara between April 1998 and August 1999 ...............................................................27 7. Number of Dolphins Observed in 1 Km Zones of the San Diego and Santa Barbara Study Areas Divided by the Number of Surveys Covering Each Zone ..........................28 8. Number of Dolphins Identified in San Diego and Santa Barbara between April 1998 and August 1999 with Sighting per Kilometer Surveyed Ratios in Specified Categories ........................................................................................................................31 9. Cumulative Number of Dolphins Identified in San Diego and Santa Barbara between April 1998 and August 1999 ...........................................................................................33 10. Mean School Size across Years for All Schools Sighted in San Diego between 1984-1999 .........................................................................................................35 11. Mean Number of Dolphins Sighted per Complete Survey in San Diego between 1984 and 1999 ...................................................................................................36 12. Mean Number of Dolphins per Complete Survey as a Function of Oceanographic Season in San Diego between 1984 and 1999.................................................................38 13. Mean School Size as a Function of Oceanographic Season for Surveys Conducted in San Diego between 1984-1999 .................................................................39 14. Number of Dolphins Observed per Unit Survey Effort over 1 Km Segments of the San Diego Study Area between 1984-1999 ..........................................................41 15. Sighting Frequencies of Dolphins Identified in San Diego between 1984-1999 ............42 16. Rate of Discovery Curve Showing the Cumulative Number of Dolphins Identified over Blocks of Five Surveys ...........................................................................45

1

INTRODUCTION The objective of this research was to study space-use patterns of Pacific bottlenose dolphins (Tursiops truncatus) in two coastal areas of the Southern California Bight: San Diego and Santa Barbara, California. Results from this study expanded on findings obtained from long-term photo-identification studies of bottlenose dolphins along the Pacific coast, which began in 1981 and continued through 1999 (Hansen 1990, Wells et al. 1990, Weller 1991, Caldwell 1992, Feinholz 1996, Defran and Weller 1999, Defran et al. 1999, Dudzik 1999, Marsh 2000, Defran et al. In prep). Bottlenose dolphins occurring along the west coast of North America generally remain within 1 km of shore (Hanson and Defran 1993, Caretta et al. 1998, Defran and Weller 1999) and are known to have a coastal range of at least 830 km, from Ensenada, Baja California, Mexico to Monterey Bay, California (Wells et al. 1990, Defran et al. 1999). Members of this population demonstrate little site fidelity to any one coastal area within their range (Defran and Weller 1999, Defran et al. 1999) and live in a highly dynamic social system characterized by fluid social affiliations between dolphins (Weller 1991, Marsh 2000). Past research on Pacific coast bottlenose dolphins has been largely centered in San Diego, with more limited survey effort conducted off three coastal California areas: Orange County, Santa Barbara, and Monterey Bay; and two coastal regions along the Pacific coast off Baja California Norte, Mexico: Ensenada and San Quintín. This study used both Santa Barbara and San Diego as primary study areas, allowing direct interstudy area comparisons to be made. Primary objectives were to document bottlenose dolphin site fidelity and occurrence patterns, as well as to describe the distribution and movement patterns within and between these coastal areas. Information gathered during the study offers a broader understanding of the ecological and biological factors affecting space-use patterns of coastal bottlenose dolphins inhabiting the Southern California Bight. Space-use Patterns Information regarding the movements of animals within their environment plays an important role in understanding the behavioral ecology of a species or population. For most mammalian species, individuals are not distributed randomly but instead form characteristic

2 patterns of distribution, grouping, ranging, and association (Crook et al. 1976). These behavioral patterns are shaped not only by spatial and temporal changes in the environment but also by internal biological constraints of individuals, such as age and sex. In the context of ecological and internal influences, behavioral strategies evolve to optimize the conditions under which individuals can perform vital functions to maximize fitness (Crook et al. 1976). Vital functions include resource exploitation, predator avoidance, and reproduction. Movement is an important and necessary component of these vital functions; without movement it would be difficult to procure food, avoid predators, or find mates with which to reproduce. Traditionally, studies of animal space-use patterns have focused on documenting the home range of individuals. Home range refers to the area an animal normally uses for routine activities, such as feeding, mating, and care of young (Burt 1943, Jewell 1966). More recently, studies have focused on how animals use space within their home range. Most animals do not use all areas of their home range with the same intensity; instead, it is more common for certain regions to be occupied with greater frequency than others (Dixon and Chapman 1980). Areas of concentrated use are termed “core areas” (Burt 1943, Kaufmann 1962, Samuel et al. 1985). Studying core areas and movements within the range is an important part of understanding factors determining space-use and in helping to understand interactions with other individuals and the environment (Samuel et al. 1985). Ecological Factors On an ecological time scale (i.e., the lifespan of an individual), fitness is defined by survival and reproduction. Survival necessitates extracting life-sustaining energy from resources within the environment, while simultaneously avoiding being killed by predators. Reproduction requires finding receptive individuals with which to mate. Since resource availability, predation pressure, and access to mates vary across environments, they represent ecological constraints that influence the behavioral strategies animals adopt to maximize fitness given the specific structure of the habitat in which they live (Crook et al. 1976). Resource availability has a fundamental ecological influence on the behavior of animals, as an individual must first obtain sufficient food resources to satisfy metabolic requirements before it is able to avoid predation or find mates. On the most basic level, the home range of an animal must be large enough to provide adequate food resources to satisfy

3 energetic requirements (McNab 1963). Abundance, distribution, and predictability of food resources influence both the size of the area needed, and the way space within that area is used (Davies and Houston 1984). Optimal foraging theory, which states that an individual will maximize food intake while minimizing the amount of energy used to obtain food (Krebs and McCleery 1984), has been used to draw several generalizations about the interaction between resource availability and space-use patterns. Where food resources are abundant, animals tend to use smaller ranges than in areas where resources are limited and individuals must travel farther to obtain food (Schoener 1968, Clutton-Brock 1975). Abundant resources dispersed into patches, however, may also result in increased range sizes, as animals must travel between patches (Orians 1961, Schoener 1968, Geist 1974, Jarman 1974, Clutton-Brock 1975, Hladik 1975). Resource predictability may further affect the distribution of individuals (Brown 1964). Resources which are dispersed into patches of consistent abundance and distribution often favor the development of territorial strategies, as an individual can survive on one patch and will expend less energy in defending that patch than in traveling between patches. Unpredictable resources, however, are difficult to defend and tend to favor more wide-ranging space-use strategies. Competitive interactions between individuals of the same species or different species occupying the same ecological niche may further modify the abundance and spatial and temporal distribution of resources and thereby influence space-use strategies. As more individuals exploit an area of initially abundant resources, the resource value of the area declines until it becomes more beneficial for an individual to move to another area (Milinski and Parker 1991). Space-use patterns, which maximize resource exploitation, may vary on both a temporal and spatial scale in response to changes in resource availability. Bottlenose dolphins off the west coast of California shifted their range northward during the 1982-1983 El Niño. Prior to 1983, the northern range boundary for Pacific coast bottlenose dolphins was considered to be San Pedro, California (Hansen 1990). Following the El Niño event, dolphins identified off San Diego were subsequently sighted as far north as Monterey Bay (Wells et al. 1990); this range extension appears to be long-term, as dolphins have continued to use the Monterey Bay area through 2001 (Fienholz 1996; Pacific Cetacean Group, personal communication). The spatial shift in the range of Pacific coast bottlenose dolphins

4 was thought to be in response to shifts in prey distribution due to changing water temperatures and oceanic currents brought by the El Niño. Similar shifts in territory use have also been documented for red foxes (Vulpes vulpes) living in Oxford, England (Doncaster and MacDonald 1991). Red foxes live in social groups, with each group inhabiting an exclusive territory. In neighboring suburban areas of Oxford, group territories were primarily stable. However, within the city of Oxford red fox groups demonstrated a pattern of “drifting territoriality”, where territories shifted in a directional, fixed spatial arrangement across the landscape. Territory shifts were considered to be a behavioral response to the instability of the urban environment, where food resources fluctuated rapidly and unpredictably (Doncaster and MacDonald 1991). Predation pressure is another environmental constraint influencing space-use patterns. Predation has an obvious and direct correlation with fitness; there are few failures more detrimental to fitness than being killed. Predation may affect not only where an animal feeds, but also how it feeds. Studies of foraging behavior in gray squirrels (Sciurus carolinensis) indicated that individuals fed preferentially in patches closest to cover (Newman and Caraco 1987) and increased travel speed between and time spent in patches offering little cover (Newman et al. 1988). Access to mates, and thereby the opportunity to reproduce, acts as an additional environmental parameter thought to influence behavioral patterns. While space-use strategies used to satisfy metabolic demands or avoid being killed by predators may increase chances of survival, maximizing fitness also entails passing genes on to the next generation. Strategies to increase access to mates are often integrated with strategies to exploit food resources. For example, in some species males may attempt to control access to valuable food resources, as females will be drawn to areas of high resource quality. Male territorial systems evolve in areas where resources are easily defended, such as environments with stable, abundant, and dispersed food resources. In areas where the costs of territoriality are high (i.e., areas of unstable and/or limited resources), males may attempt to control access to females by preventing other males from mating with females of his group, often using aggression (Orians 1961, Brown 1964, Emlen and Oring 1977). Space-use patterns developed to maximize opportunities to mate may also be expressed in sex-based differences among space-use patterns, which are discussed in the following section.

5 Internal Constraints Within the context of ecological variation, internal constraints reflect individual requirements for energy and may be influenced by a range of biological factors, including size, sex, age, and reproductive condition. Body size represents one of the most obvious correlations with movements, as an individual of larger size requires more energy to survive. As such, large animals may require a greater area to provide enough energy for metabolic requirements (McNab 1963). Space-use patterns may also be influenced by demographic factors such as age and sex of individuals. Sex-specific differences in space-use patterns of mammals often result because some resources may be more important to one sex than to the other. Since most male mammals are not involved in rearing young, access to mates and increased opportunity to reproduce are in some respects more important determinants of reproductive success than survival of offspring. Reproductive success of females, however, is dependent on the number of young produced and raised to maturity. Thus female space-use patterns may be more directly correlated with access to resources necessary for producing and caring for young, such as food, shelter, and water; while male space-use patterns may be more closely associated with distribution of potential mates (Brown 1966, Eisenberg 1966, Trivers 1972, Bradbury and Vehrencamp 1977, Emlen and Oring 1977). Reproductive condition, particularly of females, may further shape movement patterns. A female that is pregnant or nursing a calf will have increased energetic demands. A study of coyotes (Canis latrans) in Nebraska found that females had smaller home ranges during gestation and nursing periods than during pre-breeding and breeding seasons (Andelt and Gipson 1979). Similar results were found in a study of roe deer (Capreolus capreolus), where females with fawns had smaller ranges than females without fawns, presumably because of increased energetic demands (Tufto et al. 1996). Space-use patterns may also vary with age of individuals. In a radio-tracking study of opossums (Didelphis marsupialis) in Kansas, immature opossums covered a smaller area on a daily basis than adult opossums did (Fitch and Shirer 1970). Immature opossums, however, did occasionally make dispersive movements, presumably to explore their environment, and progressively extended their range of movements with age. These range extensions suggested that young animals simply needed time to discover the limitations of

6 their environment. A similar trend was found in white-crowned sparrows (Zonotrichia leucophrys nutalli) where first year male sparrows had significantly smaller territories than mature males (Ralph and Pearson 1971). Differences in territory sizes were correlated with breeding success, however, and suggested that younger sparrows lacked the experience to defend more optimal territories. Pacific Coast Bottlenose Dolphin Research Boat-based photo-identification studies of Pacific coast bottlenose dolphins were started by Hansen (1990) in 1981 and continued through 1999. While Hansen’s research was concentrated in the San Diego area, photo-identification studies have since incorporated several other areas of the Pacific coast, ranging as far south as San Quintín, Baja California Norte, Mexico (30°15’N, 121°48’W) north to Monterey Bay, California (36°48’N, 121°48’W) (Wells et al. 1990, Weller 1991, Caldwell 1992, Feinholz 1996, Defran and Weller 1999, Defran et al. 1999, Dudzik 1999, Marsh 2000, Defran et al. In prep). Studies of Pacific coast bottlenose dolphins have spanned almost two decades, and the longitudinal nature of the research has provided a relatively detailed understanding of the interaction between the highly dynamic environment found along the Pacific coast and the behavior of bottlenose dolphins inhabiting the area. Hansen’s (1990) study included 22 boat-based photo-identification surveys conducted between September 1981 and January 1983. Surveys covered the area extending from Scripps Pier in La Jolla, California north to Oceanside Harbor (See Figure 2). Dolphins were sighted on 86% (n = 12) of all surveys encompassing the entire study area, with most sightings occurring between Torrey Pines State Beach and south Carlsbad. All sightings were made within 1 km of shore. One hundred twenty-three dolphins were photographically identified, with 42% (n = 52) sighted only one time and the remainder sighted between two and nine times during the study. A small subset of identified individuals (n = 21) were sighted five or more times throughout the study. Closed population models estimated that between 173 – 240 dolphins used the area. Seven aerial surveys, covering all (n = 5) or part (n = 2) of the area between the Mexican border and Long Beach Harbor, were also conducted as part of Hansen’s (1990) study. Dolphins were encountered on all aerial surveys, with the number of dolphins counted per survey ranging from 55 to 128.

7 Based on the results from his study, Hansen (1990) considered the range of Pacific coast bottlenose dolphins to include an area of at least 155 km between La Jolla and San Pedro. While dolphins were present in the San Diego study area year-round, sighting frequencies of individuals varied considerably, and Hansen concluded that the San Diego area was part of a seasonal range for some individuals and a permanent range for the small subset of the population (n = 21) sighted most often. Defran and colleagues (Defran and Weller 1999, Defran et al. 1999) continued research on Pacific coast bottlenose dolphins between 1984 and 1989. One hundred forty-six boat-based photo-identification surveys were conducted in San Diego between January 1984 and December 1989. The study area used was slightly smaller than Hansen’s study area, and extended 32 km from Scripps Pier in La Jolla to south Carlsbad. Dolphins were sighted on 72% (n = 79) of all surveys covering the entire area, but encounter percentages varied annually, ranging from a low of 60% in 1987 to a high of 95% in 1989. Both number of dolphins encountered per survey (mean = 26.8, SD = 22.30) and school size (mean = 19.8, SD = 18.40) were also variable. While sightings were made within 1 km of the coastline and were distributed throughout the study area, the majority (70% of dolphins, 67% of schools) of sightings were concentrated in the southern portion of the study area, between Torrey Pines State Park and Solana Beach. Three hundred seventy-three individual dolphins were identified between 1984 and 1989. New dolphins were continually being identified throughout the study, although the rate at which previously unidentified dolphins were photographed had begun to decrease by 1989. Identified individuals were sighted between one and twenty-four times, with an average of 4.6 sightings. The majority (66%) of identified dolphins were resighted six times or less, for an average of less than one time per year. Sighting per opportunity ratios were calculated to reflect sightings per unit effort, and were derived by dividing the number of sightings for each individual by the number of surveys on which dolphins were encountered. The overall mean sighting per opportunity ratio was 0.09. Association patterns of identified dolphins were analyzed by Weller (1991) using the half-weight index, which yields values ranging from 0.00 for animals never sighted together, to 1.00 for animals always sighted together. Ninety-five percent of the calculated coefficients of association were between 0.00 and 0.39, and mean levels of association for

8 individual dolphins ranged from 0.14 to 0.29. The mean number of affiliates ranged from 124, with the number of affiliates increasing with the number of sightings of each individual. The low coefficients of association and high number of affiliates indicated that Pacific coast bottlenose dolphins are members of a fluid and dynamic social system. Twenty-nine percent (n = 30) of the dolphins sighted by Hansen were not photographed by Defran and Weller (1999) between 1984 and 1989. Of Hansen’s subset of frequently (>5 times) sighted dolphins (n = 21), four were not photographed during Defran and Weller’s study, and six were seen less than once per year. One of Hansen’s frequently sighted dolphins, however, was the most frequently sighted dolphin between 1984 and 1989. Photographic survey efforts in San Diego ceased in 1989 but were resumed by Dudzik (1999) between March 1996 and August 1998. She conducted 66 photographic surveys, during which 233 dolphins were identified. Fifty-six percent (n = 131) of these dolphins had been previously identified during the 1984-1989 study by Defran and Weller (1999). Comparison of occurrence patterns, as measured by the percentage of surveys on which dolphins were encountered, the number of dolphins per complete survey, and average school size, between the 1984-1989 surveys and the 1996-1998 surveys showed no significant differences, suggesting that occurrence of dolphins was stable over time. Population size estimates were also compared across study periods, using Chao’s Mth model. Given the low sighting frequencies of most identified dolphins in the population, this model was considered the most appropriate because it allowed capture probabilities to vary by both time and individual. Estimates were derived for three different study periods (1984-1986, 1987-1989, 1996-1998) and ranged from 289 to 356. Similar estimates across study periods suggested that population size also remained stable across the eleven year time span. Regional studies have also been carried out in other areas of the range of Pacific coast bottlenose dolphins. Between 1981 and 1989, boat-based photo-identification surveys were conducted in three secondary study areas within the Southern California Bight: Orange County and Santa Barbara, California; and Ensenada, Baja California Norte, Mexico (Defran et al. 1999). The majority of dolphins identified in Santa Barbara (88%), Orange County (92%), and Ensenada (88%) were also photographed in San Diego. One hundred twenty (58%) of the 207 dolphins identified in the three secondary study areas were documented to

9 move between areas. Within each study area, most individuals were sighted only one time, and the majority of resightings were made within days or weeks. During the 1982–1983 El Niño, Pacific coast bottlenose dolphins were documented to shift the northward limit of their range (Wells et al. 1990, Feinholz 1996). Bottlenose dolphins were first sighted north of Point Conception in May 1983 (Wells et al. 1990). Opportunistic sightings indicated bottlenose dolphins traveled as far north as Monterey Bay between 1983 and 1988, and several of these sightings included dolphins previously identified within the Southern California Bight (Wells et al. 1990). Systematic photo-identification surveys of Monterey Bay began in 1990. Feinholz (1996) conducted 84 boat surveys between October 1990 and November 1993. Bottlenose dolphins were sighted on 79% (n = 66) of all surveys. Sixty-eight individual dolphins were identified; 63% (n = 43) of the dolphins identified had previously been sighted within the Southern California Bight. Two dolphins sighted within Monterey Bay had previously been sighted as far south as Ensenada, a distance approximately 830 km south of Monterey Bay. Twenty-six percent (n = 18) of the dolphins identified were sighted only one time. Feinholz (1996) considered 13 individuals (19% of identified dolphins) to demonstrate some level of site fidelity to the Monterey Bay area, based on sighting frequencies and presence in the area at least once during each year of the study. Eight boat-based photo-identification surveys were conducted in San Quintín, Baja California Norte, Mexico between April and August 1990 (Caldwell 1992, Defran et al. In prep) to determine a southern range boundary for Pacific coast bottlenose dolphins. One hundred five dolphins were identified. The majority (62%) of dolphins identified were sighted only one time, with most resightings occurring within days of the first sighting. Only one dolphin had previously been sighted within the Southern California Bight. Dolphin #006 was sighted 5 times in San Diego and twice in Ensenada prior to being photographed on two consecutive days in San Quintín. Subsequent to its sighting in San Quintín, dolphin #006 was also photographed several times in San Diego. While survey effort in San Quintín was relatively limited, comparable effort in Santa Barbara and Ensenada was sufficient to detect movements of known individuals between areas. Thus, results from the San Quintín study indicated that a probable southern range boundary for Pacific coast bottlenose dolphins exists between Ensenada and San Quintín. The boundary was unlikely to represent physical

10 limitations of distance dolphins were able to cover, since Santa Barbara and San Quintín are roughly the same distance from San Diego. The exact nature of the boundary, and any causal mechanisms, have yet to be determined (Caldwell 1992, Defran et al. In prep). Results from studies spanning many years and several different study areas have illustrated the complexity of interactions between the dynamic environment found along the Pacific coast and bottlenose dolphin behavior. Coastal California waters experience significant daily, monthly, and yearly variability, creating patchy and unpredictable patterns of resource availability (Cross and Allen 1993, Dailey et al. 1993). The high mobility, extensive coastal distances traveled, variable school sizes, and apparent lack of site fidelity demonstrated by Pacific coast bottlenose dolphins may be a reflection of patchy and unpredictable abundance and distribution of prey fish along the Pacific coast (Defran and Weller 1999, Defran et al. 1999). Changes in prey distribution and abundance are also presumed to have affected range boundaries, demonstrated both by the northward range extension of Pacific coast bottlenose dolphins following the 1982-1983 El Niño (Wells et al. 1990), and by the existence of a probable southern range boundary north of San Quintín (Caldwell 1992, Defran et al. In prep). The high degree of behavioral variation over both time and space that has been demonstrated by Pacific coast bottlenose dolphins would have been difficult to document in a study of more limited scope, and emphasizes the importance of conducting studies covering broad temporal and geographic scales. Objectives While research on Pacific coast bottlenose dolphins was conducted for almost two decades prior to this study, important questions remained unanswered. The extension of research efforts between 1998 and 1999 offered further opportunity to examine the stability of behavioral patterns over time, allowing more detailed information on the ecological and biological factors influencing individual behavior to be obtained. Research presented here involved the continuation of boat-based photo-identification studies of Pacific coast bottlenose dolphins in San Diego, California, as well as the inclusion of an additional study area in Santa Barbara, California, 271 km to the north of San Diego and near the northern terminus of the Southern California Bight. While Pacific coast bottlenose dolphins had been studied in areas other than San Diego before, such studies had never been conducted over the

11 same time span and with comparable effort. The addition of regular survey effort in Santa Barbara in combination with continued survey effort in San Diego allowed movements of individuals, occurrence patterns, and individual sighting frequencies to be compared between areas, and permitted more detailed examination of the effect that ecological variables may have on space-use patterns of Pacific coast bottlenose dolphins. Further study in both areas also allowed determination of sex and reproductive state of more individuals. Comparison of behavioral patterns of individuals of known sex and reproductive state to the rest of the identified population permitted preliminary analyses of how internal differences factored into behavioral variation between individuals. Furthermore, comparison of results from this study to results from prior datasets allowed documentation of any changes in occurrence patterns or individual sighting frequencies of Pacific coast bottlenose dolphins that may have occurred over time in response to ecological variation. The strength of the study was derived from the many comparisons that could be made. As such, the objectives of the study were classified into three categories: (1) within study area comparisons, (2) between study area comparisons, and (3) past-to-present comparisons. Within each study area, documentation of the occurrence of bottlenose dolphins throughout the year-long study allowed comparison of space-use patterns over seasons. Comparisons of the results from surveys in San Diego and Santa Barbara permitted documentation of movements between areas and analysis of space-use patterns of each area by individuals. The distribution of sightings within each area was also compared to determine if regions of heavy use within study areas shared similar ecological features. Patterns of occurrence, distribution, and individual sighting frequencies between 1998 and 1999 were further compared to past research conducted on Pacific coast bottlenose dolphins to determine the stability of usage patterns over time.

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METHODS The research presented here utilized two coastal areas within the Southern California Bight: San Diego and Santa Barbara, California. The Southern California Bight (Figure 1) extends 732 km from Point Conception (34º33’N, 120º28’W) in the north to Punta Colnett (30º57’N, 116º20’W) in the south. The coastal environment within the Southern California Bight can be characterized as open and dynamic. Point Conception marks a sharp eastward break in the coastline which interrupts the flow of the California current system, resulting in the creation of the Southern California Countercurrent and producing a region where northern, southern, western, and upwelling bottom waters converge. Converging waters create a marked change in coastal climate and marine fauna within the Bight. Waters of the Southern California Bight are subject to both short- and long-term temperature fluctuations dependent on oceanic currents, with average maximum surface temperatures peaking at 19°C between July and September, and falling to an average minimum temperature of 14.5°C in late winter. Nearshore salinities vary slightly, with a high of 33.6 ppt in July and a low of 33.4 ppt in late winter (Dailey et al. 1993). The San Diego study area (Figure 2) consisted of a narrow strip of coastline extending from Scripps Pier in La Jolla (32º52’N, 117º15’W) 32 km north to Tamarack in south Carlsbad (32º08’N, 117º20’W). Nearshore underwater topography was variable, ranging from submerged reefs, dense kelp beds, and sea grass flats to barren sandy bottoms. Beaches also varied in composition, with gently sloping sand, steeply inclined cobblestone, estuary mouths, and rocky outcrops. Low levels of commercial and recreational vessel traffic were present. The study area was similar to the area used by Hansen (1990), and identical to that used by Defran and Weller (1999) and Dudzik (1999). The Santa Barbara study area (Figure 3) extended from the Santa Barbara Harbor (34º 25’N, 119º 42’W) in the north 38 km southeast to Emma Wood State Beach (34º18’N, 119º21’W) in Ventura County. While Santa Barbara and San Diego were similar in nearshore underwater topography and beach composition, the Santa Barbara coastline is oriented northwest to southeast, as opposed to the more direct north-south orientation of the San Diego coastline. Much of the Santa Barbara area is also sheltered by the Channel Islands

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Point Conception Santa Barbara

34 Orange County

33 San Diego

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Figure 1. Map of the Southern California Bight.

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Figure 3. Santa Barbara study area.

34o00'

16 (San Miguel, Santa Rosa, and Santa Cruz islands), which provided relief from wind and sea conditions and resulted in generally calmer waters than in the San Diego study area. Photographic Survey Procedure Photo-identification surveys were conducted twice a month in San Diego and four times a month in Santa Barbara. San Diego surveys used a 5.8 m powerboat equipped with a 115 hp engine, while Santa Barbara surveys utilized a 4.6 m inflatable boat with a 40 hp engine. All surveys were conducted in Beaufort sea state of ≤3, to ensure conditions adequate for sighting, observing, and photographing dolphins. Boat surveys consisted of travel 90-180 m outside of the surf line while systematic observations from the beach to 2 km offshore were conducted. When a school of dolphins was detected, time and location (using Global Positioning System) where the school was initially sighted were recorded. Attempts were then made to photograph all dolphins present in the school. After all dolphins in the school were thought to have been photographed, location and time where observations were terminated were recorded, and school composition (i.e., number of calves present) and school size were noted. The survey then proceeded until the next sighting was made or the end of the study area was reached. All surveys attempted to cover the entire study area. Surveys covering the entire study area were labeled as complete surveys and were used in all analyses. Surveys that failed to cover the entire study area due to weather, sea state, or equipment failure were labeled as partial surveys and were used in selected analyses. Definitions of schools, calves, and probable mothers followed those used by Weller (1991), Defran and Weller (1999), Defran et al. (1999), and Dudzik (1999) so that data could be compared. Schools were defined as any dolphins observed in close proximity to one another and usually moving in the same direction and engaged in similar behavior. Calves were defined using three criteria: (1) an animal consistently demonstrating close affiliation with a larger dolphin; (2) an animal displaying an awkward and immature surfacing pattern; and (3) an animal small in size, possessing fetal folds, and/or distinct neonatal coloration. Probable mothers were defined as in Weller (1991): a larger dolphin exhibiting prolonged and exclusive or near-exclusive association with a dolphin identified as a calf. In addition, those dolphins defined as probable mothers (n = 12) by Weller (1991) between 1984 and

17 1989 were combined with those dolphins defined as probable mothers during the present study to represent a subset of females in the population. Photo-identification Procedures A Canon A-1 35 mm camera equipped with a 400-mm lens and high-speed motor drive was used to photograph dolphin dorsal fins. Kodak Tri-X 400 ISO black and white film was used for all photographs. Methods used to sort, match, identify, and catalog dorsal fin photographs are described in detail elsewhere (Defran et al. 1990) but are briefly summarized as follows. After developing film from each survey, the resulting negatives were assessed for photographic quality and notch pattern distinctiveness. Photographic quality was evaluated on the basis of focus, clarity, lighting, and parallax of the image; any negative not meeting the pre-set criteria was excluded from analyses. Only dorsal fins containing a notch pattern allowing unequivocal identification from other fins in the database were used. Once usable negatives were sorted out, negatives from each school were grouped according to recognizable individuals. The best negative (based on photographic criteria presented in Appendix) of each dorsal fin was considered the type specimen and was placed in a slide mount labeled with date, school number, area of sighting, and a temporary identification number. Type specimens were projected and enlarged to fit a 10x17 cm frame and subsequently traced by hand onto white paper. The tracing process allowed all traced fins to be standardized for size and orientation. After tracing, dorsal ratios were calculated for all dorsal fins with two or more notches on the trailing edge. Dorsal ratios were computed by dividing the distance between the two largest notches on the trailing edge of the fin by the distance between the top of the fin and the notch nearest the bottom of the fin (Figure 4). If the fin contained notches of similar size, the notches furthest apart were used for the dorsal ratio. Tracings of previously identified dolphins were placed into one of four catalogs: (1) dorsal fins with a single notch; (2) dorsal fins with a notch in the top of the fin; (3) dorsal fins with two to three notches; and (4) dorsal fins with four or more notches. Within catalogs, tracings were organized numerically according to dorsal ratios. Organization of identified individuals by number of notches and dorsal ratios facilitated the cataloging process. The

18

TOP A B

Computation of the dorsal ratio (from Defran et al. 1990). Figure 4. Computation of the dorsal ratio

Dorsal Ratio 19 mm 44 mm

A to B

=

B to Top

=

.439

19 analyst first searched for matches of the unidentified dolphins under the appropriate catalog and dorsal ratio. Upon finding a match, slides of the new dolphin and all slides of the previously identified dolphin were compared. If all slides matched, the image was then labeled and filed with the identification number of the previously identified dolphin. If no matches were made, all catalogs were searched twice before the dolphin was considered a new sighting and given a permanent identification number. For all steps of the cataloging process, three people must either have agreed to the match or have searched all catalogs twice before the process was considered complete. All negatives were given a photographic quality rating based on four factors (see Appendix): focus of fin image, contrast between fin image and background, proportion of fin visible in image, and size of fin image. Negatives given the lowest rating on any one of these factors were not used for any analysis. Computer Analysis Data collected in San Diego and Santa Barbara between April 1998 and August 1999 were stored in two Excel databases: a photographic database consisting of date and area of sightings of all individuals; and a sighting database, in which the date, time, and location of sightings, as well as estimated school size and number of calves present, were recorded. These databases are referred to as the short-term photographic and sighting databases. Within the short-term databases, data collected in San Diego by Dudzik (1999) between April 1998 and August 1998 were consolidated with data collected in San Diego for this study Data collected in San Diego between 1998 and 1999 were then combined with data collected in San Diego between January 1984 and December 1989 (Defran and Weller 1999) and between March 1996 and March 1998 (Dudzik 1999) to form a long-term dataset consisting of all bottlenose dolphin sightings and identifications in San Diego between 1984 and 1999. This dataset was also divided into a photographic database, containing the dates of sighting for all dolphins, and a sighting database with the date, time, location, and composition of all schools. These databases are referred to as the long-term photographic and sighting databases, respectively.

20 The sighting databases (both long and short-term) were used in analysis of occurrence patterns and distribution of sightings. The photographic databases were used to examine site fidelity and movement patterns, as well as to construct rate of discovery curves. Occurrence Patterns Occurrence patterns were measured in several ways: total number of dolphins observed in the study area per survey, percentage of surveys encountering dolphins, and size of schools encountered. The first three parameters were analyzed using data from the survey database. Only complete surveys were used to analyze the number of dolphins observed per survey and the number of surveys encountering dolphins, while all surveys were used for school size analyses. Occurrence pattern parameters were analyzed using analysis of variance methods (ANOVAs) generated by SPSS 7.5. Although the Santa Barbara study area is larger than the San Diego study area, the difference is slight (~ 6 km), and occurrence patterns were compared directly between the two areas. Within each study area, occurrence patterns were also compared between oceanographic seasons, which were defined by Hickey et al. (1993) to include the Upwelling period (March -July), Oceanic period (August-October), and Davidson current period (November-February). The oceanographic seasons are defined by water temperatures and as such may more directly influence dolphin and prey distribution than would traditional solar seasons. The final comparisons of occurrence patterns were made by combining data collected in San Diego between 1998 and 1999 with data collected in San Diego between 1984 and 1989 (Defran and Weller 1999) and between 1996 and 1998 (Dudzik 1999). Occurrence patterns were then compared across years, as well as across oceanographic seasons, to determine the stability of occurrence patterns over time. The long-term survey database was also used to compare occurrence patterns across El Niño, La Niña, and normal months. Months were classified into categories using the Bivariate Enso time series index (Smith and Sardeshmukh 2000), which is based on both sea surface temperature anomalies and atmospheric pressure differences.

21 Distribution Distribution of sightings within each study area was examined by dividing each area into zones of 1 km² and calculating a ratio of the number of dolphins observed in each zone divided by the number of surveys covering that zone. Location where dolphins were first sighted was used in order to avoid potential influences on dolphin behavior by boat interaction. Zones were then classified as follows: (1) low if the usage ratio was below the mean minus the standard deviation (for both areas this was a negative number, so zones with no usage were classified as low), (2) high if the usage ratio was above the mean plus the standard deviation, and (3) moderate for all other ratios. Although this analysis is recognized as being preliminary, ratios were employed to provide a rough comparison of usage between zones. Within San Diego, ratios were calculated using both 1998-1999 sightings and 19841999 sightings to examine consistency of patterns over time. Site Fidelity For the 1998-1999 study, the degree of site fidelity to each area was examined. This analysis calculated a ratio of sightings per kilometer surveyed for all identified individuals in each area as a way to account for unequal survey effort between areas. The number of kilometers covered in each survey was determined by plotting the GPS location where surveys were terminated onto the 1 km zones used for distribution analyses. The last 1 km zone completely covered by the survey was considered the number of kilometers covered. Kilometers covered in surveys of each area were then summed, and the number of sightings of identified dolphins in each area was divided by the corresponding sum of kilometers covered for each area. An ANOVA was then used to compare sighting per kilometer ratios between areas to determine if mean levels of site fidelity differed. As previously mentioned, since the majority of consecutive day surveys occurred in Santa Barbara, sightings on consecutive days were excluded from the analysis (and effort calculations were adjusted) to eliminate any potential bias introduced if dolphins were more likely to be resighted on consecutive day surveys rather than surveys separated by a week or more. A preliminary analysis of biological constraints contributing to individual variation in site fidelity characteristics was also conducted, by subdividing the population by sex and lactational state. Dolphins identified as probable mothers (i.e., lactating dolphins) between 1998 and 1999 represented one subset, and their sightings per kilometer ratios in each area

22 were compared to those of the rest of the identified population. Probable mothers identified between 1998 and 1999 were combined with dolphins identified by Weller (1991) as probable mothers between 1984 and 1989 to represent a subset of females. The sightings per kilometer ratios of all females were then compared with the ratios of the remainder of the population. These analyses were considered preliminary, as they represent only one subset of each factor (i.e., only females or only lactating dolphins) and are made up of a small fraction of those subsets. However, these analyses may provide a basis for generating ideas for future study. Movements The movements of identified dolphins between San Diego and Santa Barbara between 1998 and 1999 were documented. The mean, range, and standard deviation of interval of days between sightings in different areas were analyzed by calculating the maximum travel speed between areas. The number of dolphins sighted in both areas over the long-term study period between 1984 and 1999 was also calculated. Rate of Discovery Curves Rate of discovery curves, which plot the number of dolphins identified in an area over time or effort, were generated for both the short- and long-term photographic datasets. For the short-term study, separate rate of discovery curves were generated for the San Diego and Santa Barbara study areas by plotting the cumulative number of dolphins identified over each month of the study. Curves were then compared between the two areas in order to determine if similar rates of acquiring previously unidentified dolphins existed in each area. The slope of each curve was also examined to provide further information on occurrence patterns. While a continuously rising slope would indicate that previously unidentified dolphins are moving into an area at a steady rate, an irregular slope, with periods of rapid increase interspersed with periods of little or no increase, would be indicative of pulses of new dolphins moving into the area over certain months or seasons. A collective rate of discovery curve for the San Diego study area was also generated using dolphins identified in San Diego between 1984 and 1999. This curve was plotted using the cumulative number of dolphins identified over blocks of five surveys on which at least one dolphin was identified. The curve was then examined to determine the point at which it

23 began to reach an asymptote, which was used as an indication that the majority of dolphins in the population had been identified.

24

RESULTS Between April 1998 and August 1999, 43 surveys were conducted in San Diego coastal waters, and 61 surveys were conducted in Santa Barbara waters. Of these surveys, 65.1% (n = 28) in San Diego and 70.5% (n = 43) in Santa Barbara covered the entire study area and are termed “complete” surveys. Occurrence A total of 912 dolphins in 58 schools were observed in San Diego, while 915 dolphins in 72 schools were observed in Santa Barbara. Calves represented 8.3% (n = 76) of all dolphins observed in San Diego and 7.8% (n = 71) of all dolphins observed in Santa Barbara. In both study areas between one and four schools were observed per survey, with 42.9% (n = 12) of complete surveys in San Diego and 27.9% (n = 12) of complete surveys in Santa Barbara encountering only one school. Both complete and partial surveys were used to compare school sizes between areas. Mean school size was slightly lower in Santa Barbara (mean = 12.7, SD = 8.27, range 2-35) than in San Diego (mean = 15.7, SD = 8.26, range 196), but these differences were not significant (F(1, 128) = 1.49, P>0.05). The number of dolphins sighted during complete surveys in San Diego ranged from 1 to 135 (mean = 20.6, SD = 28.50), and dolphins were encountered on 82.1% (n = 23) of complete surveys. In Santa Barbara, 67.4% (n = 29) of complete surveys encountered dolphins, with the number of dolphins sighted per survey ranging from 2 to 54 (mean = 15.7, SD = 15.02). No significant differences were observed in the number of dolphins observed per survey (F(1, 69) = 0.89, P>0.05) or the percentage of surveys encountering dolphins ( ² = 1.84, df = 1, P>0.05). Seasonal patterns of occurrence were examined using the oceanographic seasons defined by Hickey (1993), which include: Upwelling (March through July), Oceanic (August through October), and Davidson (November through February). Using only complete surveys of each study area, no significant difference across oceanographic seasons was observed in the number of dolphins per survey in Santa Barbara (F(2,40) = 0.41, P>0.05) (Figure 5). In San Diego, however, the number of dolphins observed per complete survey

25 was significantly greater (F(2,25) = 10.712, P<0.001) during the Davidson period than in either the Oceanic or Upwelling period (Figure 5). The number of complete surveys on which dolphins were encountered did not show significant variation across oceanographic seasons in Santa Barbara (X² = 0.35, df = 2, P>0.05) but was significantly higher during the Upwelling season than during the Oceanic season in San Diego (X² = 6.26, df = 2, P = 0.044). Both complete and partial survey data were combined to compare school size (Figure 6). While school size did not differ across oceanographic seasons in Santa Barbara (F(2, 69) = 0.17, P>0.05), school sizes in San Diego were significantly larger during the Davidson period than during either the Oceanic or Upwelling periods (F(2, 55) = 5.48, P = 0.007). Distribution Ratios of total dolphins observed per unit effort were graphed for 1 km² zones in each study area (Figure 7). In San Diego, the mean number of dolphins observed in each zone per unit survey effort was 0.7 (SD = 0.95, range 0-4.3), while in Santa Barbara the mean number of dolphins per unit survey effort was 0.5 (SD = 0.41, range 0-1.4). Zones of low usage in San Diego included zones 5, 11, 13, 17, 20, and 24; while zones of high usage included zones 1, 2, and 6. In Santa Barbara, zones of low usage included zones 10-12, 14, 20, 30, and 36-38; and zones of high usage included 1, 4, 5, 17, 28, and 31. Table 1 details some of the zones containing topographical or environmental features that might affect dolphin distribution. Site Fidelity Between April 1998 and August 1999, 204 dolphins were identified in San Diego, and 178 dolphins were identified in Santa Barbara. In San Diego, dolphins were sighted between one and eight times, and the mean number of sightings per dolphin was 2.0 (SD = 1.49). One hundred five dolphins (51.5%) were sighted only one time. In Santa Barbara, dolphins were identified between one and seven times, and the mean number of sightings was 2.1 (SD = 1.30). Eighty-two dolphins (46.1%) were sighted only one time. The mean interval between sightings of the same individual was 97.8 days (SD = 95.11) in San Diego

26 100 Mean Number of Dolphins

90 80 70

San Diego Santa Barbara

60 50 40 30 20 10 0 Upwelling

Oceanic

Davidson

Oceanographic Season Figure 5. Mean number of dolphins observed per complete survey as a function of oceanographic season in San Diego and Santa Barbara between April 1998 and August 1999. Error bars represent standard deviations.

27

Mean School Size

45 40

San Diego

35

Santa Barbara

30 25 20 15 10 5 0 Upwelling

Oceanic

Davidson

Oceanographic Season Figure 6. Mean school size as a function of oceanographic season for San Diego and Santa Barbara between April 1998 and August 1999. Error bars represent standard deviations.

4.5 4 3.5 3 2.5 2 1.5 1 0.5 31

29

27

25

23

21

19

17

15

13

11

9

7

5

3

0 1

Dolphins Per Unit Survey Effort

28

1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 37

34

31

28

25

22

19

16

13

10

7

4

0 1

Dolphins Per Unit Survey Effort

San Diego 1 km Zones

Santa Barbara 1 km Zones

Figure 7. Number of dolphins observed in 1 km zones of the San Diego and Santa Barbara study areas divided by the number of surveys covering each zone. Zones run from south to north in San Diego and from southeast to northwest in Santa Barbara.

29 Table 1. Habitat features of study area zones in San Diego and Santa Barbara. Study Area San Diego

Santa Barbara

Zone 1-2 5-6 8-9 13-14 18-19 26-27 1 9-11 15-16 21-23 38

Habitat Feature Scripps Canyon Rocky reef (Ward 1999) Los Penasquitos lagoon San Dieguito river mouth San Elijo lagoon Batiquitos lagoon ~ 1 km northwest of the Ventura Estuary Oil piers Rincon Creek mouth El Estero lagoon <1 km southeast of the Santa Barbara Harbor

30 and 96.5 days (SD = 88.27) in Santa Barbara, and was not significantly different between areas (F(1,397) = .02, P>0.05). To compare sighting frequencies across areas with unequal survey effort, a ratio of number of sightings per km surveyed was calculated for individual dolphins identified in each area (Figure 8). Sighting per km ratios were significantly higher for dolphins identified in San Diego than for those identified in Santa Barbara (F(1,380) = 59.77, P<0.001). The greatest number of dolphins identified in any one month of the study occurred in January 1999 in the San Diego study area, when 79 dolphins (38.7% of all dolphins identified in San Diego) were identified. Forty percent (n = 164) of all identifications made in San Diego accrued between the months of November 1998 and January 1999 (no surveys were conducted in December in San Diego). In Santa Barbara, the highest number of dolphins identified during any one month occurred in June 1999 and included 40 dolphins (23% of the total number of dolphins identified in Santa Barbara). Analyses of the effect of sex and lactational state on sighting frequencies were also run for each area. No significant differences were found in sighting ratios for probable mothers (F(1, 202) = 0.20, P>0.05) or females (F(1, 202) = 2.99, P>0.05) and the remainder of identified dolphins within the San Diego study area between 1998-99. In Santa Barbara, females (F(1, 176) = 12.80, P<0.001) and probable mothers (F(1,176) = 10.42, P = 0.001) showed significantly higher sightings per kilometer surveyed than did other dolphins in the population. Due to small sample sizes in the number of known females and probable mothers, these results should be considered preliminary. Movements A total of 293 dolphins were identified during the study, with 30.4% (n = 89) of identified dolphins sighted in both study areas between April 1998 and August 1999. One hundred thirty-one inter-study area movements were documented, with individual dolphins moving between study areas between one and four times. Fifty-five (61.8%) of the dolphins sighted in both areas were documented to move between study areas only one time. Sixtynine (52.7%) of the observed movements were from San Diego north to Santa Barbara. Of those dolphins sighted in only one area, 115 were identified in San Diego and 89 in Santa Barbara.

31 120 51%

San Diego Santa Barbara

Number of Dolphins

100 80

44%

60 40 20

24% 22% 13%

11%

11% 6% 1% 1%

4%

5%

2%

2%

0 0.00- 0.50- 1.00- 1.50- 2.00- 2.50- 3.00- 3.50- 4.00- 4.50- 5.00- 5.50- 6.00- 6.50- 7.000.49 0.99 1.49 1.99 2.49 2.99 3.49 3.99 4.49 4.99 5.49 5.99 6.49 6.99 7.49

Sightings Per Km Surveyed (x10-3)

Figure 8. Number of dolphins identified in San Diego and Santa Barbara between April 1998 and August 1999 with sighting per kilometer surveyed ratios in specified categories. Numbers above bars represent percent of the total number of dolphins identified in each area with ratios in each category. Consecutive day sightings of the same individual have been removed.

32 The mean number of days between sightings in different areas was 96.0 days (SD = 73.04) and ranged from five to 383 days. The fastest travel speed recorded averaged 61.6 km/day and was displayed by one dolphin first identified in San Diego on 28 February 1999 and subsequently resighted in Santa Barbara on 5 March 1999. Rate of Discovery Rate of discovery curves were generated for both areas using the cumulative number of dolphins identified per month (Figure 9). By the last month of the study, only two new dolphins (15% of all dolphins identified that month) were identified in San Diego, and one new dolphin (8% of all dolphins identified that month) was identified in Santa Barbara. However, the rate at which new dolphins were identified each month fluctuated considerably, and survey effort differed between months as well as between study areas. The curves showing the cumulative number of dolphins identified in each area shows a slight leveling trend in both areas by the end of the study. Comparisons with Past Studies Sighting history and survey data collected in San Diego between April 1998 and August 1999 were pooled with data collected in San Diego between January 1984 and December 1989 (Defran and Weller 1999) and between March 1996 and April 1998 (Dudzik 1999) to allow comparisons to be made over time. Information on survey effort for each study is presented in Table 2. Occurrence patterns Occurrence patterns, as measured by encounter rate, total number of dolphins encountered, school size, and percentage of calves per school, were compared across years. All observed schools were used to compare school size, which yielded no significant difference across years (F(9, 256) = 1.641, P>0.05) (Figure 10). Both the encounter rate (X² = 23.181, df = 9, P = 0.006) and the number of dolphins observed per survey (F(9, 255) = 4.300, P<0.001) were significantly different across years (Figure 11). With the exception of 1997, which contained both the lowest encounter rate and the lowest number of dolphins

33

Cumulative Number of Dolphins Identified

250 SB SD

200

150

100

50

0 Apr- May- Jun98 98 98

Jul- Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun98 98 98 98 98 98 99 99 99 99 99 99

Jul- Aug99 99

Month

Figure 9. Cumulative number of dolphins identified in San Diego and Santa Barbara between April 1998 and August 1999. Thin dotted line (between December 1998 and January 1999 in San Diego) denotes month with no survey effort.

34 Table 2. Summary information on survey effort, study period, and photographic results from San Diego between 1984 and 1989. Photographic results differ from those given in Defran and Weller 1999 and Dudzik 1999 due to revision of the dataset over time and elimination of sightings not meeting the specified photographic quality criteria.

Number Number Sighting School Size Dolphins Frequency ResightingsResightings Number of of of Surveys Dolphins Schools Mean±SD Identified Mean±SD from from (Number Complete) (Range) (Range) 1984-1989 1996-1998 January 1984 146 (109) 2869 145 19.8 ± 18.41 323 4.6 ± 3.25 December 1989 (2 - 90) (1 - 19) Study Period

March 1996 March 1998

52 (20)

1233

63

19.6 ± 25.19 (1 - 140)

206

2.0 ± 1.21 (1 - 7)

108

April 1998 August 1999 Total

43 (28)

912

58

204

5014

266

2.0 ± 1.49 (1 - 8) 5.0 ± 4.21 (1 - 24)

103

241 (157)

15.7 ± 18.83 (1 - 96) 18.9 ± 20.29 (1 - 140)

468

124

Mean School Size

35 45 40 35 30 25 20 15 10 5 0 1984 1985 1986 1987 1988 1989

1996 1997 1998 1999

Year Figure 10. Mean school size across years for all schools sighted in San Diego between 19841999. Error bars represent standard deviations.

Mean Number of Dolphins Per Survey

36 60 50 40 30 20 10 0

1984 1985 1986 1987 1988 1989

1996 1997 1998 1999

Year Figure 11. Mean number of dolphins sighted per complete survey in San Diego between 1984 and 1999. Error bars represent standard deviations.

37 observed per survey, both of these parameters were higher in the latter years of the study (1988-1989, 1996-1999) than during the earlier years (1984-1987). Occurrence patterns were also compared across oceanographic seasons for the longterm database. When data from all complete surveys were pooled, the mean number of dolphins observed per complete survey (F(2,154) = 5.31, P = 0.006) was lower during the Oceanic season than during the other two seasons (Figure 12). Dolphins were also encountered significantly less often on complete surveys during the Oceanic season than during the Upwelling season (X² = 10.94, df = 2, P = 0.004), though no significant difference was found between the Oceanic and Davidson period. School size was significantly greater (F(2,263) = 12.50, P<0.001) during the Davidson season when compared with other oceanographic seasons (Figure 13). Each year with observations across all three oceanographic seasons was also examined individually for evidence of seasonal occurrence patterns. Results varied, with some years demonstrating no evidence of seasonal patterns or showing seasonal patterns inconsistent with those observed in 1998-1999. In general, however, the seasonal pattern of increased usage of the San Diego study area during the Davidson period was more marked during the latter years of the study (1996-1999) than during the earlier years (1984-1989). El Niño The influence of El Niño events on occurrence patterns of Pacific coast bottlenose dolphins was examined using data collected in San Diego between 1984 and 1999. This period encompassed a relatively mild El Niño/La Niña event between 1987 and 1988 and a stronger El Niño/La Niña event between 1997 and 1999. For the 1987-1988 El Niño/La Niña event, no significant differences between El Niño, La Niña, and normal months were found in school size (F(2, 207) = 0.27, P>0.05), number of dolphins observed per survey (F(2,127) = 1.71, P>0.05), or number of surveys encountering at least one group of dolphins (X² = 5.36, df = 2, P>0.05). Similarly, no significant differences between El Niño, La Niña, or normal months were found in school size (F(2, 213) = 0.52, P>0.05), number of dolphins observed per survey (F(2, 116) = 0.47, P>0.05), or number of surveys encountering at least one group of dolphins (X² = 3.56, df = 2, P>0.05) for the 1997-1999 El Niño/La Niña event.

38

Mean Number of Dolphins

45 40 35 30 25 20 15 10 5 0

Upwelling

Oceanic

Davidson

Oceanographic Seasons Figure 12. Mean number of dolphins per complete survey as a function of oceanographic season in San Diego between 1984 and 1999. Error bars represent standard deviations.

Mean School Size

39 45 40 35 30 25 20 15 10 5 0

Upwelling

Oceanic

Davidson

Oceanic Season

Figure 13. Mean school size as a function of oceanographic season for surveys conducted in San Diego between 1984-1999. Error bars represent standard deviations.

40 Distribution Distribution of sightings was examined using the 1984-1999 dataset in the San Diego study area. The mean number of dolphins found in each 1 km segment per unit survey effort was 0.5 (SD = 0.26) (Figure 14). This ratio of dolphins per unit effort was used to classify each zone as one of low, moderate, or high usage according to the same criteria used for the short-term database. Zones of low usage included zones 19 and 17, while zones of high usage included zones 1, 6, 8, and 14. In general, zones located in the southern half of the study area (zones 1-16) were used more heavily than those in the northern portion (zones 1732). Table 1 shows some of the important topographical or environmental features in each zone. Site Fidelity A total of 468 dolphins were identified in the San Diego study area between 1984 and 1999. The number of sightings per dolphin (Figure 15) ranged from one to 24, and the mean number of sightings per dolphin was 5.0 (SD = 4.21). One hundred four (22.2%) of the dolphins identified were sighted only one time. Of the 204 dolphins identified in San Diego between 1998-1999, 77.0% (n = 157) had been identified in previous studies. Only 15.0% (n = 70) of the dolphins identified were sighted during all three study periods. The sighting histories of the dolphins (n = 63) sighted ten or more times in the San Diego study area, and therefore considered to be “frequently sighted”, were examined in detail. Fifty-three (84.1%) of these dolphins were identified in all seasons, with the remaining 15.9% (n = 10) being sighted in both the Upwelling and Davidson seasons but not the Oceanic season. Forty-eight (76.2%) of these dolphins were sighted in areas other than San Diego. The mean number of years this subset of frequently sighted dolphins was identified was 5.8 (SD = 1.58) and ranged between two and nine years. The number of sightings of dolphins identified as females (n = 22) during any part of the study was compared with the number of sightings of the remainder of identified dolphins. Females had higher sighting frequencies (F(1,466) = 19.64, P<0.001) than other identified dolphins.

1.4 1.2 1 0.8 0.6 0.4 0.2 31

29

27

25

23

21

19

17

15

13

11

9

7

5

3

0 1

Dolphins Per Unit Survey Effort

41

1 km Zones Figure 14. Number of dolphins observed per unit survey effort over 1 km segments of the San Diego study area between 1984-1999. Segments run south to north.

42

Number of Dolphins

120 100 80 60 40 20 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Number of Sightings Figure 15. Sighting frequencies of dolphins identified in San Diego between 1984-1999.

43 Movements Movements between areas were examined by comparing the San Diego 1984-1999 dataset with the Santa Barbara 1998-1999 dataset as well as with datasets from surveys conducted in Santa Barbara, Orange County, and Ensenada between 1982 and 1989 by Defran and colleagues (see Defran et al. 1999). Survey effort and number of dolphins identified in each area are shown in Table 3. Two hundred fifty-four (54.3%) of the dolphins identified in San Diego were seen in at least one other study area. Five dolphins were identified in all four study areas, and 59 dolphins were seen in at least three study areas. Of the 47 dolphins identified in Santa Barbara in 1987 and 1989, 34.0% (n = 16) were resighted in Santa Barbara between 1998 and 1999. Rate of Discovery A rate of discovery curve plotting the cumulative number of dolphins identified in the San Diego study area between 1984-1989 is shown in Figure 16. Survey effort was divided into blocks of 5 surveys on which at least one dolphin was identified (n = 162 surveys), with the exception of block 19 and block 33 which contained only four and three surveys, respectively. A break in survey effort of over six years occurred between block 19, which ended in December 1989, and block 20, which began in March 1996. The curve shows a continual increase throughout most of the study but begins to reach an asymptote toward the end of the study period, with only one new dolphin identified in San Diego during the final months of the study.

CumulativeNumber of Dolphins Identified

44 500 450 400 350 300 250 200 150 100 50 0 1

3

5

7

9 11 13 15 17 19 21 23 25 27 29 31 33

Survey Blocks Figure 16. Rate of discovery curve showing the cumulative number of dolphins identified over blocks of five surveys on which at least one dolphin was identified. Block 19 includes only 4 surveys, and Block 33 contains only 3 surveys. A break in survey effort (shown with dotted line) from Dec 1989 to Mar 1996 occurs after block 19.

45 Table 3. Summary information on survey effort, study period, and photographic data for Southern California Bight study areas 1982-1999. Photographic data differ slightly from information presented in Defran et al. 1999 due to revision of the dataset over time and the elimination of sightings not meeting the specified photographic quality criteria.

Study Area

Dates

San Diego 1984-1989, 1996-1999 Santa Barbara 1987, 1989, 1998-1999 Orange County 1982-1989 Ensenada 1985-1986 Total 1982-1999

Number of Surveys 241 73 44 11 346

Number of Dolphins Identified 468 209 118 66 533

Number of Dolphins Resighted in San Diego -----------------------------------75.6% (n=158) 82.2% (n=97) 80.3% (n=53) ------------------------------------

46

DISCUSSION This study analyzed the occurrence patterns, site fidelity, and movements of coastal bottlenose dolphins within two areas of the Southern California Bight. Although Pacific coast bottlenose dolphins have been studied since 1981 (Hansen 1990, Wells et al. 1990, Weller 1991, Caldwell 1992, Feinholz 1996, Defran and Weller 1999, Defran et al. 1999, Dudzik 1999, Marsh 2000, Defran et al. In prep), many questions remain about the effect of ecological and environmental variables on their behavior. The present study contributed to our understanding of the behavioral ecology of the population by allowing comparisons to be made over both space and time. The extension of previous studies of Pacific coast bottlenose dolphins in San Diego coastal waters permitted temporal changes in behavior to be examined. Bottlenose dolphins are long-lived mammals, existing in complex societies and exhibiting a high degree of behavioral flexibility. Long-term studies allow documentation of the persistence of behavioral patterns in the population as a whole over time, offering further understanding of the effect of environmental variables on behavior. Longitudinal studies also present an opportunity to observe changes in the behavior of individuals over time, providing an indication of the effect of internal constraints on behavior. In addition, concentrated study of Pacific coast bottlenose dolphins in Santa Barbara waters provided a spatial dimension for comparison, by allowing dolphin behavior from the same population in two different parts of their range to be compared. While both areas share similar types of habitats, some differences in topography and temperature exist between the two areas (Dorman and Palmer 1981). Santa Barbara lies approximately 270 km to the north of San Diego and is somewhat sheltered from prevailing wind and sea conditions by the Channel Islands. The San Diego coastline, however, is fully exposed to direct western swells (Littler 1980). The continental slope also drops more rapidly and steeply off the San Diego coastline than in Santa Barbara, where the slope is more gradual (Dorman and Palmer 1980). Furthermore, the southernmost end of the San Diego study area contains a submarine canyon, providing an area of increased topographical relief. These differences in topography and openness are unlikely to affect dolphin behavior directly. They may influence the

47 distribution of prey resources, however, and thereby provide an indirect index of the effect of subtle habitat differences on dolphin behavior. Additionally, continued study of Pacific coast bottlenose dolphins has allowed more direct comparisons to be made with other long-term studies of coastal bottlenose dolphins in Sarasota Bay, Florida (Wells 1986) and in Aransas Pass, Texas (Weller 1998, Maze and Würsig 1999). Geographic comparisons of this nature allow the effects of large-scale habitat differences on behavior of bottlenose dolphins to be explored. Occurrence Patterns Examination of the occurrence patterns of Pacific coast bottlenose dolphins within the Southern California Bight can provide one indication of the effect of environmental factors on the behavior of the population. Occurrence patterns are primarily influenced by a combination of direct limitations to environmental characteristics (e.g. water temperature and salinity), predation pressure, the need to reproduce, and prey distribution and abundance. Bottlenose dolphins within the Southern California Bight live in a temperate environment, while populations in other regions, such as off the coast of Scotland, are known to withstand more extreme oceanographic conditions (Wilson et al. 1997a). Thus, variables such as water temperature and salinity should not directly limit dolphin movements within the coastal Southern California Bight environment. Predation pressure, as well, probably provides minimal influence on the behavior patterns of coastal California bottlenose dolphins (Weller 1991). The shark species most commonly associated with bottlenose dolphin predation, which include tiger (Galeocerdo cuvier), dusky (Carcharhinus obscurus), bull (Carcharhinus leucas) and great white (Carcharadon carcharias) sharks (Wood et al. 1970, Corkeron et al. 1987), are rarely found within the coastal Southern California Bight environment (Barnhart 1936). Killer whales, considered to be another dolphin predator (Würsig and Würsig 1979), are also infrequently sighted in the area. Influences associated with the need to reproduce would be reflected in behavioral differences between individuals of different sex, age, or reproductive classes, and will be discussed in later sections. Given these factors, occurrence patterns of the population as a whole are most likely to be influenced by prey distribution and abundance. Little direct information, however, is available about the diet of Pacific coast bottlenose dolphins. Walker (1981) analyzed the

48 stomach contents of nine southern California coastal bottlenose dolphins and concluded that the primary prey species of coastal dolphins were fish and invertebrates inhabiting the littoral and sublittoral zones. The diet was diverse, with fish from 12 families and invertebrates from six families represented in the stomachs, but the majority (62%) of the species ingested came from two families of fish, Sciaenidae (croakers) and Embioticidae (perches). These results were based primarily on stomach contents of stranded animals, however, and as such may not have reflected the typical diet of healthy animals. Despite the paucity of direct information on the diet of coastal bottlenose dolphins within the Southern California Bight, indirect information on the influence of prey distribution and abundance on dolphin behavior can be provided by examining occurrence patterns across study areas, seasons, and years. Between 1998 and 1999, occurrence patterns of bottlenose dolphins in San Diego and Santa Barbara coastal waters were similar, indicating that dolphins used both of these areas with comparable intensity. When occurrence patterns were compared across oceanographic seasons, however, only San Diego showed evidence of seasonal patterns of occurrence. While dolphins were present in San Diego waters year-round, the number of dolphins observed per survey as well as the size of observed schools was greatest during the Davidson season. Similar results were found during behavioral studies by Ward (1999) between 1996 and 1997, who postulated that the larger school sizes of coastal bottlenose dolphins in San Diego during late fall and winter were correlated with the presence of market squid (Loligo opalescens) off La Jolla during winter months. While market squid spend much of their life cycle in offshore waters, they move inshore to spawn, often forming large aggregations near marked submarine topographic features (Recksiek and Frey 1978). In southern California spawning is most evident between December and February (Fields 1965, Recksiek and Frey 1978) and has been observed near La Jolla Canyon (McGowan 1954, Limbaugh and Shepard 1957, Fields 1965), which is adjacent to Scripps Canyon and the southern terminus of the San Diego study area. The influx of dolphins into the San Diego study area during the Davidson period, as reflected by both greater numbers of dolphins within the study area as well as larger school sizes, may represent dolphins taking advantage of this concentrated prey resource. While this short-term exploitation may entail dolphins feeding directly on squid

49 aggregations, the spawning squid may also be attracting predatory fish that are important prey of the dolphins. Increased usage of the San Diego study area during the Davidson oceanographic season was not as evident over the long-term dataset (1984-1999) as it was during the shortterm study (1998-1999). While school sizes remained significantly higher during the Davidson period than during other oceanographic seasons, numbers of dolphins in the area were similar during the Davidson and Upwelling seasons and decreased during the Oceanic season. Less marked increase in the number of dolphins using the area during the Davidson season over the long-term study may be further related to exploitation of market squid. Because squid have a relatively short life span, generally less than two years, they are extremely responsive to inter-annual fluctuations in biological and physical variables (Boyle and Boletzky 1996), and their impact on the ecosystem as both predator and prey varies considerable from year to year (Beddington et al. 1990, Rodhouse and Nigmatullin 1996). Those years with no pattern of increased usage of the San Diego study area during the Davidson period may represent years in which the size of market squid spawning aggregations was reduced, resulting in more widespread distribution of dolphins. As well, variation in the degree of upwelling across oceanographic seasons may affect prey distribution and abundance and thereby influence seasonal occurrence patterns of dolphins. May and June are the maximum upwelling periods in the vicinity of Scripps Pier (Dailey et al. 1993), which are often correlated with the presence of unusually high concentrations of demersal fish nearshore (Moyle and Cech 1988). Additionally, the majority of coastal marine fish species in southern California, including those consumed by bottlenose dolphins, aggregate in spring and summer to spawn (Hansen and Defran 1993). The overall increased availability of prey in San Diego during the Upwelling season may serve to bring high numbers of dolphins into the area, but dolphins may be dispersed into smaller groups as a reflection of abundant and more evenly dispersed prey resources (Weller 1991). Seasonal occurrence patterns during the long-term study (1984-1999) supported this hypothesis, as the numbers of dolphins in the area were similar during the Davidson and Upwelling seasons, while school sizes were greater in the Davidson period than in the Upwelling season. During the Davidson season, when overall productivity within the Southern California Bight is reduced, prey resources may be less evenly distributed and more

50 difficult to find. Larger schools may be beneficial in this situation, as dolphins may integrate their sensory capabilities in order to increase the probability of finding food (Norris and Dohl 1980). Annual variation in occurrence patterns of Pacific coast bottlenose dolphins in the San Diego study area was also evident. While school size did not differ significantly across years (1984-1999), both the number of dolphins observed per survey and the number of surveys encountering at least one school varied across years. Variation in dolphin occurrence patterns may be a reflection of the highly dynamic ecosystem of the Southern California Bight, which undergoes significant daily, monthly, seasonal, and yearly fluctuations (SCCWRP 1973, Dailey et al. 1993). The effect of such environmental variability can be seen at the lowest trophic levels, with changes in both phytoplankton and zooplankton biomass thought to be correlated with yearly changes in the flow of the California Current system as well as with changes in the intensity and timing of local coastal upwelling events (Tont 1976, 1981; Roesler and Chelton 1987). The influence of environmental variability is further manifested in the recruitment and spawning success of some species of fish. For example, rockfish recruitment within the Southern California Bight increases during warmer years, when both transport by the California Current and upwelling are lower, and decreases during colder years when transport and upwelling are higher (Norton 1987). As well, during the latter years of the study (1997-1999), the Southern California Bight was being affected by an El Niño event of similar strength to that of 1982-1983 (Wolter and Timlin 1998). During El Niño events, water temperatures within the Southern California Bight are elevated several degrees above normal (Dailey et al. 1993). While it is unlikely that changing water temperatures affect Pacific coast bottlenose dolphins directly, changes in distribution and abundance patterns (Fiedler et al. 1986, Bragg 1991, Hollowed and Wooster 1992, Ainley et al. 1995, Stull and Tang 1996) as well as species composition (Westerhagen 1993) of marine biota are known to occur as a consequence of changes in habitat quality (Woodbury 1999) and direction of currents (Yoklavich et al. 1996, Connolly and Roughgarden 1999). As mentioned previously, the range of Pacific coast bottlenose dolphins was extended following the 1982-83 El Niño, presumably in response to changing prey distributions (Wells et al. 1990). El Niño events have also been documented to affect foraging in California sea lions (Zalophus californianus). During the 1982-83 El Niño, the

51 relative contributions of different food types in the diet of California sea lions was altered, apparently in response to changing availability of prey (DeLong et al. 1991). California sea lions were also affected by the 1997-1998 El Niño, when pup production decreased by 64%, presumably due to nutritional stress (Forney et al. 2000). Based on the Bivariate Enso time series index (Smith and Sardeshmukh 2000), however, the occurrence patterns of Pacific coast bottlenose dolphins did not vary between El Niño, La Niña, and normal months. While it is possible that Pacific coast bottlenose dolphin occurrence patterns did not shift in response to El Niño conditions, the index used, which was based on sea surface temperature and atmospheric pressure, may not have accurately reflected environmental cues dolphins use to change behavior, or some lag time might have existed before changing conditions were reflected in dolphin behavior. Distribution While comparison of occurrence patterns between years, seasons, and study areas has provided information on large-scale environmental factors affecting the behavioral ecology of Pacific coast bottlenose dolphins, examination of sightings within each study area can offer an indication of more finely scaled variables shaping dolphin behavior. Although characterizing all potentially influential habitat variables was beyond the scope of this study, some general patterns emerged when the distribution of sightings was examined. As demonstrated in previous studies of Pacific coast bottlenose dolphin distribution (Hansen 1990, Caldwell 1992, Hanson and Defran 1993, Feinholz 1996, Caretta et al. 1998, Defran and Weller 1999, Defran et al. 1999, Ward 1999, Dudzik 1999), the majority of sightings in both study areas were made within 0.5 km from shore, and no dolphins were sighted beyond 1 km of the coastline. Nearshore waters of the Southern California Bight are biologically rich and diverse, supporting numerous trophic levels and a wide diversity of habitats including submarine canyons, sandy bottoms, rocky reefs, and kelp beds. Coastal waters also receive a greater supply of nutrients than do waters further from the coast, due to terrestrial runoff and increased vertical mixing of nutrients caused by upwelling and tidal cycling. The productive waters, in combination with the low levels of predation and interspecific competition thought to exist in coastal waters (Weller 1991), make the nearshore zone a favorable environment for Pacific coast bottlenose dolphins.

52 Within the San Diego study area, the most prominent distributional pattern was heavy usage of areas associated with submarine canyon habitat, both in the long-term (1984-1999) and short-term (1998-1999) datasets. Behavioral studies by Ward (1999) found increased feeding of Pacific coast bottlenose dolphins in canyon versus non-canyon habitat during his behavioral study between 1996 and 1997. Submarine canyons are nutrient rich areas due to increased levels of upwelling, which are generated as tide-driven water masses flow up and down the canyon walls (Svedrup et al. 1942). The topography of submarine canyons also produces a diversity of microhabitats, ranging from rocky canyon shoulders to dense mats of surf grass and kelp detritus. This diversity hosts organisms of many different trophic levels, beginning with amphipods and invertebrates inhabiting mats and attracting both demersal and pelagic fish (Vetter 1994). These fish may provide a prey resource for Pacific coast bottlenose dolphins. Increased usage of canyon habitat during this study was also consistent with the observed occurrence patterns, which indicated that dolphins use the San Diego study area heavily during winter months when market squid are spawning near the canyon. The combination of both consistent prey resources, in the form of fish attracted to the area by the diversity of micro-habitats and increased levels of nutrients due to upwelling, and temporally abundant resources, represented by aggregations of market squid during spawning season in some years, probably makes areas surrounding the canyon preferential habitat for Pacific coast bottlenose dolphins. Areas of heavy use within both the San Diego and Santa Barbara study areas were also examined for correlations with estuaries. Estuaries are sites of high concentrations of nutrients, which support large numbers of invertebrates and fish (Vannucci 1969, Thomson 1973, Moyle and Cech 1988). Previous studies comparing Pacific coast bottlenose dolphin use of estuarine areas within the San Diego study area have had mixed results. Although no formal analysis was conducted, Hansen (1990), whose study area extended north to Oceanside, observed that the distribution of Pacific coast bottlenose dolphins was concentrated between Torrey Pines State Reserve and south Carlsbad and attributed this in part to the presence of lagoon mouths providing nutrient rich areas. Hanson (1990), however, found the proportion of time spent feeding to be greater in areas containing reefs than in those surrounding estuarine areas. Results from this study were inconclusive. While several small lagoon estuaries exist within both the San Diego and Santa Barbara study areas,

53 most estuarine areas showed only low to moderate levels of usage between 1998 and 1999. When data collected in San Diego between 1984 and 1999 were combined, however, zones associated with the San Dieguito and Los Penasquitos lagoons demonstrated moderate to high levels of usage, while zones associated with the San Elijo and Batiquitos lagoons exhibited low to moderate levels of usage. Many of the small lagoon estuaries along the California coast are closed to the sea for most of the year by wave built sand spits, which are only breached during winter when rainfall is highest (Elwaney et al. 1998, Emmett et al. 2000). Without consistent contact with the surrounding ocean, the high levels of productivity typically associated with estuaries may be too unpredictable to attract dolphins on a regular basis. Two 3 km stretches containing no sightings existed within the Santa Barbara study area and included the zones lying directly southeast of the Santa Barbara Harbor and the zones surrounding a pier used by ships associated with oil well operations. Both areas contain high levels of large vessel traffic. While bottlenose dolphins in this study area have been observed bow-riding in front of large boats, they may avoid use of these areas for activities other than traveling and playing due to the increased levels of disturbance as well as higher levels of pollution in the water associated with boats and oil well operations. Comparison of the distribution of dolphin sightings in the San Diego study area between 1998 and 1999 with the distribution of sightings during the combined 1984-1999 period demonstrated that sightings were spread more evenly throughout the study area over the long-term study. The more regularly dispersed sightings over the long-term study indicate that most portions of the study area are valuable to Pacific coast bottlenose dolphins in some capacity and may be related to prey distribution. The high daily, monthly, and annual variability in the coastal ecosystem of the Southern California Bight creates patchy and unpredictable patterns of distribution of marine organisms, including prey species of the bottlenose dolphin (SCCWRP 1973, Mearns 1974, DeMartini and Allen 1984, Ware and Thompson 1991, Cross and Allen 1993, Dailey et al. 1993). Over longer time scales, however, prey patches would occur over most portions of the study area, resulting in more uniform usage of the entire area by bottlenose dolphins. As expected, these results indicate that habitat usage by Pacific coast bottlenose dolphins in the Southern California Bight is determined by a combination of many different

54 factors. More complete analysis of habitat usage should incorporate not only more extensive documentation of the habitats within the coastal Southern California Bight, but also behavioral observations within different habitat types, extending the work done by Ward (1999). Currently, Geographic Information System mapping techniques are often used in both terrestrial and marine systems to overlay animal sightings with an array of different habitat variables. The application of such techniques to the habitat of Pacific coast bottlenose dolphins would provide a much more thorough understanding of the complex factors affecting dolphin distribution. Site Fidelity Previous studies of Pacific coast bottlenose dolphins have reported low sighting frequencies of individuals in San Diego coastal waters (Defran and Weller 1999, Dudzik 1999) as well as in less extensively studied secondary areas within the Southern California Bight (Defran et al. 1999). Regional studies within the Southern California Bight further indicated that the majority of dolphins identified in Santa Barbara (76%) and Orange County (82%), California and Ensenada (80%), Baja California Norte, Mexico had also been sighted within the San Diego study area. Taken together, these observations suggested that Pacific coast bottlenose dolphins range over extensive coastal areas, demonstrating little preference for any one area (Defran and Weller 1999, Defran et al. 1999, Dudzik 1999). Results from the present study further indicated that Pacific coast bottlenose dolphins are essentially transient within the Southern California Bight. Dolphins identified in both study areas had an average of only two sightings despite the high number of surveys conducted. Lack of site fidelity among Pacific coast bottlenose dolphins has been attributed to the patchy and unpredictable distribution of prey (Defran and Weller 1999, Defran et al. 1999). Within the coastal Southern California Bight environment, most fish species either are found in temporary local concentrations or are widely but sparsely distributed (SCCWRP 1973, Mearns 1974, DeMartini and Allen 1984, Ware and Thomson 1991, Cross and Allen 1993, Dailey et al. 1993). The patchy or sparse distributions of dolphin prey may be a factor in the long distances traveled by Pacific coast bottlenose dolphins (Defran et al. 1999), as patchy and sparse resource distributions necessitate that animals range widely to locate sufficient prey (Krebs and Davies 1981). As well, Pacific coast bottlenose dolphin school

55 sizes are large when compared with most other coastal bottlenose dolphin populations (Wells et al. 1987, Corkeron 1990, Shane 1990, Smolker et al. 1992, Bräger et al. 1994, Fertl 1994), which may be a further indication of patchy resource distribution within the Southern California Bight. Large school sizes are thought to increase sensory integration and thereby aid in locating difficult to find resources (Norris and Dohl 1980), and they may represent an adaptation by Pacific coast bottlenose dolphins to increase efficiency in locating patchily distributed prey (Weller 1991, Defran and Weller 1999, Defran et al. 1999). The combined long-term database yielded further evidence that dolphins demonstrate only low levels of site fidelity to the San Diego study area, with individual dolphins sighted an average of only five times over the ten-year period of study. More detailed examination of sighting patterns also indicated that lack of site fidelity was not correlated with seasonal movements within the range, as most of those dolphins with the highest sighting frequencies were observed in the San Diego study area over all three oceanographic seasons. While dolphins in both study areas were sighted infrequently, sightings as a function of effort were significantly higher within the San Diego study area. Higher ratios may reflect the influx of dolphins into the San Diego study area during the Davidson season rather than increased site fidelity to the area over the entire study period. The number of dolphins identified in San Diego during January 1999 was almost twice as high as the greatest number of dolphins identified during any one month in Santa Barbara, despite higher survey effort in Santa Barbara than in San Diego for the months compared. Thus the higher levels of site fidelity observed in the San Diego study area between 1998 and 1999 may not be an indication of consistent and long-term differences in site fidelity patterns between the two areas but may instead reflect differences in prey resource distribution during the Davidson oceanographic season of this particular study period. Individual differences in site fidelity were explored by comparing dolphins identified as probable mothers and females to the rest of the population. Between 1998 and 1999, dolphins identified as females, as well as the subset of those females identified as probable mothers, had higher sighting per kilometer ratios than did other dolphins identified in Santa Barbara. Females and probable mothers in San Diego did not demonstrate increased site fidelity between 1998 and 1999; however, females in San Diego did have higher sighting per kilometer ratios over the long-term study (1984-1999). Higher site fidelity of females and

56 probable mothers is likely related to differences in reproductive strategies between sexes. In most mammals, males provide no parental care and focus on impregnating as many females as possible to maximize their reproductive success. Female reproductive success, however, relies on raising young to maturity. The higher energetic demands of both pregnancy and lactation may require that females maximize energy intake while minimizing movements within the range. As such, female distribution, when compared with that of males, is often more closely linked with resource distribution (Bradbury and Vehrencamp 1977, Emling and Oring 1977, Wrangham 1980). The higher levels of site fidelity in females not identified as mothers may reflect formation of groups of females to protect calves, as has been observed in sperm whales (Whitehead and Weilgart 2000). Evidence of increased levels of association between probable mothers in the Santa Barbara study area between 1998 and 1999 was documented (Marsh 2000), indicating that at least those dolphins with calves may group together over relatively short time spans. However, predation pressure on coastal bottlenose dolphins within the Southern California Bight is thought to be low (Weller 1991), and no evidence of long-term stable associations between individuals has been observed (Weller 1991, Marsh 2000). The higher levels of site fidelity of females over the long-term study in San Diego may simply reflect that these females were pregnant or were, although not identified as such, associated with calves during the study. Bottlenose dolphin calves generally remain with their mothers for three to four years after birth (Wells et al. 1987, Smolker et al. 1992) and often are not weaned until the female is in the latter stages of her next pregnancy (Mann et al. 2000). Thus, most females of reproductive age in the population would probably have been either pregnant or lactating during the study, and as such would have been under increased nutritional demands when compared to the remainder of the population. The lack of increased site fidelity in probable mothers and females observed in San Diego during the short-term study may be due to several factors. While a higher number of total dolphins were identified in San Diego than in Santa Barbara coastal waters, fewer probable mothers and females were documented in San Diego during the short-term study. This difference is probably not due to greater number of females or probable mothers using the Santa Barbara study area but rather is related to the more strenuous survey conditions found in the San Diego study area. Calf behavior was observed closely before observers

57 made decisions on which adult would be identified as the probable mother. The calmer and more protected waters of the Santa Barbara study area facilitated close and lengthy observations of dolphins, while more direct exposure to swells within San Diego coastal waters often prevented the close and prolonged observations necessary to identify probable mothers. While these same conditions might be responsible for true differences between areas, with mothers with calves preferring the more sheltered waters provided by the Santa Barbara coastline, the higher levels of site fidelity observed in females over the long-term study in San Diego argue against any consistent differences between the two areas. In general, however, ambiguity in results from analyses of female site fidelity between and within areas may be due in part to the small number of dolphins identified as females and as probable mothers relative to the total number of identified dolphins and illustrates the need for further studies to be conducted before any conclusions are drawn. While females and probable mothers did demonstrate increased site fidelity when compared to other identified individuals, levels of site fidelity in both female and other Pacific coast bottlenose dolphins are low when compared to other populations containing more residential dolphins (e.g. Wells et al. 1987). Dolphins identified as females in San Diego coastal waters were identified a mean of only nine times over the ten-year span of the study, and all except two identified females (10%) had been sighted in other study areas. Thus while female occurrence patterns may be more closely linked with prey resource distribution than those of males, females must still range over extensive areas to meet nutritional demands. Movements Between 1998 and 1999, 89 dolphins were documented to move between San Diego and Santa Barbara, representing 50% and 44% of the number of dolphins identified in Santa Barbara and San Diego, respectively. Since the study areas were not surveyed on a daily basis, these percentages likely underestimate the actual number of individuals moving between the two areas. They can, however, be considered a minimum estimate of the number of dolphins moving between the two areas during the seventeen months of the study. The frequency of documented movements between the two areas was even higher, with some individuals moving between areas as many as four times. The high percentage of individuals

58 documented to move between the two areas, combined with the large number of observed movements, provides further evidence that Pacific coast bottlenose dolphins are highly mobile within the Southern California Bight. When the long-term dataset was used to examine movements of dolphins between areas, over half of the dolphins identified in San Diego between 1984 and 1999 had been sighted in at least one other region of the Southern California Bight. Even among the subset of most frequently sighted dolphins, most were sighted in other study areas, indicating that even those dolphins with relatively high sighting frequencies in San Diego waters range widely throughout the Southern California Bight. Results obtained by combining data collected between 1996 and 1999 in San Diego and Santa Barbara with that obtained in San Diego, Orange County, and Santa Barbara, California and Ensenada, Baja California Norte, Mexico between 1982 and 1989 (Defran et al. 1999) demonstrates the effect of continued survey effort on resighting percentages. In both Ensenada and Orange County, where survey effort was discontinued after 1989, the percent of dolphins identified in those areas and resighted in at least one other study area increased (from 88% to 91% in Ensenada and from 92% to 95% in Orange County) with the addition of the 1996 through 1999 surveys. The high percentages indicate that even without coverage of most parts of the range of Pacific coast bottlenose dolphins, continued survey effort over time in only small parts of the range is sufficient to identify the majority of dolphins in the population. The fastest travel speed documented during the seventeen-month study was 61.6 km/day, reached by one dolphin moving between San Diego and Santa Barbara over five days. This speed is higher than the maximum speed previously observed, in which three dolphins averaged 47 km/day over 2 days when moving between San Diego and Orange County, California (Defran et al. 1999). Bottlenose dolphins in other areas have been observed to travel at similar or faster speeds. One dolphin off the southwest coast of Britain traveled 1076 km over 20 days, for an average of 53.8 km/day (Wood 1998). Two stranded and rehabilitated bottlenose dolphins were released into the wild off the west coast of Florida and subsequently tracked using satellite tags to determine the success of their release (Wells et al. 1999). One individual traveled at an average of 48 km/day, covering 2050 km over the first 43 days after his release and attaining speeds of at least 75 km/day as he rounded the tip

59 of Florida. The second dolphin traveled 4200 km over 47 days, for an average of 89 km/day. Both dolphins were thought to have been of the offshore ecotype, which may range over greater distances than coastal dolphins. However, they illustrate the fact that bottlenose dolphins are capable of covering great distances in a short amount of time. Rate of Discovery Curve Rate of discovery curves represent the cumulative number of individual dolphins identified within a study area, generally plotted against either survey effort or time. These curves never flatten out entirely due to new dolphins being “born” (i.e., becoming marked and thereby identifiable) into the population; however, when the majority of individuals have been identified the curve begins to reach an asymptote which can be roughly correlated with the number of marked individuals in the population. Previous studies of the Pacific coast bottlenose dolphin population by Defran and Weller (1999) between 1984 and 1989 and by Dudzik (1999) between 1996 and 1998 have demonstrated that the rate at which new dolphins are first identified in the San Diego study area continues to increase with effort even over extended periods of time. The rate of discovery curve generated by Defran and Weller (1999) began to reach a possible asymptote only after 146 surveys across six years of study, during which a total of 373 dolphins were identified. Dudzik (1999) identified a total of 233 dolphins over 66 surveys, with only a slight leveling of the curve after 29 months of study. While several methods have been employed to estimate the size of the population of Pacific coast bottlenose dolphins (Hansen 1990, Defran and Weller 1999), the most recent calculations by Dudzik (1999) estimated that between 289 and 356 dolphins use the San Diego study area as part of their range. These estimates used sighting data between 1984 and 1998 and indicated that the population size of Pacific coast bottlenose dolphins over the fourteen -year period was relatively stable. Abundance estimates have also been generated using tandem aerial surveys covering the area between the U.S. Mexican border and Point Conception. This method, which represents not population size but rather abundance of dolphins using the study area, yielded estimates ranging between 78 and 271 dolphins (Caretta et al. 1998). Rate of discovery curves can also be used to provide rough estimates of the number of identifiable individuals within a population. The rate of discovery curve generated for San

60 Diego between 1984 and 1999 showed a continual increase throughout most of the study, although the curve flattened out over the last four months, during which time only one previously unidentified dolphin was photographed. By the end of the study, a total of 468 dolphins had been photographed in the San Diego coastal waters, and the increased leveling of the curve over the summer of 1999 indicated that the majority of dolphins in the population had been identified. Estimates of the number of identifiable dolphins within a population, as determined through rate of discovery curves, are not directly comparable with population estimates for two reasons. First, rate of discovery curves do not account for unmarked (and thus unidentifiable through photo-identification) dolphins in the population. Along the Pacific coast, Hansen and Defran (1990) estimated that approximately 35% of coastal bottlenose dolphins were unmarked, and thereby not represented in the curve. The rate of discovery curve also does not account for mortality of any identified dolphins over the sixteen-year span of the study. Wells and Scott (1990) determined the mortality rate for bottlenose dolphins in Sarasota Bay, Florida, to be between 0.010 and 0.038 per year. If mortality rates for the Pacific coast population are consistent with those observed in Florida, and the population estimates of Dudzik (1999) are assumed to be accurate, then between 46 and 216 dolphins may have died between 1984 and 1999. Incorporation of both these factors with the number of identified individuals determined by the rate of discovery curve would produce estimates more closely corresponding to those calculated by Dudzik (1999). Rate of discovery curves produced from data collected in San Diego and in Santa Barbara between 1998 and 1999 were compared to determine if any differences existed in the rate at which dolphins were identified in each area. Both rate of discovery curves continued to increase throughout the study, with only a slight leveling trend in both curves toward the end of the study. While the curves are not entirely equivalent due to differences in survey effort in each area, some interesting patterns emerged when the curves were compared. The curve produced for Santa Barbara, which demonstrated no differences in seasonal occurrence patterns during the study, increased at a relatively consistent rate throughout the study, with the largest increase in the number of new dolphins identified in Santa Barbara occurring between August and September 1998. The curve for San Diego, however, showed more dramatic fluctuations in the rate of increase, with a leveling trend observed between July and October 1998 followed by a sharp increase from October 1998 to January 1999. This pattern

61 is consistent with the observed seasonal occurrence patterns, in which school size and total number of dolphins using the area were highest during the Davidson season and lowest during the Oceanic season. Decrease in the number of previously unidentified dolphins using the San Diego study area during the Oceanic season corresponded with an increase, although less marked than the seasonal pulse observed in San Diego, of new dolphins into the Santa Barbara study area. Comparisons with Other Study Areas On an even larger scale, comparisons between bottlenose dolphin populations occupying different habitats can help identify the selective environmental factors shaping behavior and ecology. For this purpose, results obtained through long-term study in the Southern California Bight have been contrasted with those from two other studies of bottlenose dolphins in Sarasota Bay, Florida, and Aransas Pass, Texas. Studies in these two areas were chosen for comparison because they represent longitudinal research in environments with habitat characteristics different from those found along the Pacific coast. Studies in all three areas have been ongoing for many years. Research conducted in Sarasota Bay began in 1970, and continues to date (Irvine and Wells 1972, Wells et al. 1980, Irvine et al. 1981, Wells et al. 1987, Scott et al. 1990, Wells 1991, Barros and Wells 1998). This study is impressive not only in its longitudinal scope but also in the diversity of work conducted in the area. The sheltered and shallow waters of the inner bays have allowed dolphins to be temporarily captured, and as a result age, sex, reproductive condition, and familial relationships are known for many members of the Sarasota community. This information, in conjunction with knowledge of individual sighting histories and occurrence patterns obtained through boat-based photo-identification studies, has been used not only in studies of behavior and ecology but also in research on the acoustics, genetics, and physiology of the population (Hohn et al. 1989, Sayigh et al. 1990, Duffield and Wells 1991, Tolley et al. 1995). The integration of knowledge gained from such a range of biological disciplines has led to one of the most comprehensive pictures of a dolphin society available today. Work in both the Southern California Bight and along the Texas coast has been more limited in duration and scope, in part because of the inaccessibility of these environments relative to that found in Sarasota. Work along the Southern California Bight began in 1981

62 and has continued through 1999 (Hansen 1990, Wells et al. 1990, Weller 1991, Caldwell 1992, Feinholz 1996, Defran and Weller 1999, Defran et al. 1999, Dudzik 1999, Marsh 2000, Defran et al. In prep). Initial work along the Texas coast consisted of several short-term studies in different areas along the coastline (Shane 1980, Shane and Schmidly 1978, Gruber 1981, Jones 1988, Henningsen 1991, Bräger 1993, Bräger et al. 1994, Fertl 1994, Lynn 1995, Maze and Würsig 1999). The first comprehensive effort, however, which covered four different study areas along the Texas coast, was begun by Weller (1998) in 1991. Although work from other areas is still ongoing, results from surveys of Aransas Pass, Texas, between 1991 and 1997, are presented in Weller (1998) and are used for the comparisons made here. The environments found within the Southern California Bight, Sarasota Bay, and Aransas Pass study areas differ in both habitat structure and oceanography. The environment of the Southern California Bight is characterized as open, exposed, and highly dynamic, with current-driven variation in water properties on daily, seasonal, and annual scales (Dailey et al. 1993). Water temperatures vary from 14.5° C in late winter to 19°C in summer and early fall, with corresponding changes in salinity from a low of 33.4 ppt to a high of 33.6 ppt (Dailey et al. 1993). The distribution of dolphin prey species within the Bight is thought to be patchy and unpredictable, as a response to the high variability in oceanographic variables (Defran et al. 1999). At the other extreme, waters of Sarasota Bay, located on the western coast of Florida, are sheltered by a series of barrier islands, containing a system of large bays and inlets connected to the open ocean by channels and passes. Inner waters consist primarily of shallow seagrass beds, and waters remain relatively calm due to the protection of the barrier islands (Wells et al. 1987). Although fish distribution and abundance in most marine systems is patchy at some spatial scale (Nybakken 1993), the small size (approximately 125 km²) of the dolphins’ range within Sarasota Bay precludes wide dispersal of patches, and the primary dolphin prey species are thought to be present year-round (Barros and Wells 1998). The habitat structure of Aransas Pass, Texas, closely resembles that of Sarasota Bay, with a series of bays and inner waters sheltered by barrier islands and connected to the open ocean via dredged shipping lanes (Weller 1998). However, seasonal variability in both salinity and temperature is more pronounced within Aransas Pass when compared with the variability typical of Florida (Weller 1998). Sea surface temperatures

63 range from a high of 30.0°C in the summer and a low of 8.3°C in the winter, while salinity ranges from a high of 40 ppt in the summer to a low of 17 ppt in the spring (Copeland 1965). The occurrence patterns and site fidelity characteristics of bottlenose dolphins in each area reflect these differences in habitat structure and oceanography. Within the Southern California Bight, between 289 and 356 dolphins (Dudzik 1999) range over an area of at least 830 km², demonstrating little site fidelity to any one area and exhibiting frequent movements between different parts of their range (Defran and Weller 1999, Defran et al. 1999, Dudzik 1999). These frequent movements and the lack of site fidelity are thought to be an adaptation to patchy and unpredictable distribution of prey, which necessitates that dolphins range widely to locate prey resources (Defran et al. 1999). Relatively large group sizes, averaging 19 dolphins, are also thought to be an adaptation to patchily distributed prey, as larger groups may be able to locate prey resources more efficiently (Norris and Dohl 1980, Weller 1991, Marsh 2000). Although seasonal patterns were not evident in all parts of the dolphins’ range, dolphins were more abundant during the Davidson (November through February) and Upwelling (March through July) seasons over the long-term study in San Diego. This seasonal flux may be due to the presence of temporally abundant prey resources, represented by semi-annual aggregations of spawning squid within the study area, during the Davidson season as well as increased levels of prey concentration around upwelling areas during spring and early summer. Dolphins within Sarasota Bay, however, exhibit markedly different behavioral patterns. Approximately 100 dolphins have been identified as year-round residents within an area of approximately 125 km² (Wells et al. 1980, Irvine et al. 1981, Wells 1986, Scott et al. 1990). Site fidelity of dolphins and the relatively small home-range dimensions of the community indicates that prey species are consistently available across seasons and years. School sizes are small, averaging 7 dolphins (Wells et al. 1987), which is considered a reflection of feeding on solitary and non-obligate schooling prey (Wells 1991, Barros and Wells 1998). Although dolphins remain in the area year-round, some seasonal shifts in distribution within the study area occur, as dolphin abundance is highest in channels, passes, and offshore areas during fall and winter and increases within the inner waters of the bays during spring and summer (Scott et al. 1990). These seasonal shifts have been linked to

64 changes in water temperatures, either through the thermal requirements of dolphins or as a response to changes in prey and predator distribution (Irvine et al. 1981, Wells et al. 1980). Given the similarity in habitat structure between the two areas, dolphin behavioral patterns within Aransas Pass, Texas, were expected to parallel those in Sarasota Bay (Weller 1998). However, longitudinal research in the area indicated behavior was more similar to that observed on the Pacific coast. Dolphins belonged to a large and open population, with 782 dolphins identified over a four-year period. While most dolphins demonstrated no evidence of site fidelity to the area, a small proportion of the population appeared to be semiresidential within the area. Short-term studies in both Aransas Pass and other areas along the Texas coast have also identified small groups of resident or semi-resident dolphins (Shane 1977, Gruber 1981, Bräger 1992, Fertl 1994, Lynn 1995, Maze and Würsig 1999), suggesting that the population of bottlenose dolphins off the Texas coast may be separated into semi-residential subpopulations inhabiting bays and inner waters, and a larger group of transient animals traveling extensive distances along the coast. Dolphins were present in the Aransas Pass study area year-round, but abundance peaked in late fall and winter and correspondingly decreased in spring and summer. Seasonal sighting patterns were also evident among individual dolphins, with most identified during only one season. Research along the Texas coast provided an interesting contrast with results generated by work conducted in Sarasota Bay and along the Pacific coast (Weller 1998). Past studies along the Pacific coast and in Sarasota Bay have presented what were generally considered to be two extremes of intraspecific variation in bottlenose dolphin behavior. This variation has been attributed in large part to differences in habitat structure between the two areas (Defran et al. 1999). At one extreme, small groups of residential dolphins, such as those of Sarasota Bay, are known to inhabit protected bays and inlets thought to contain relatively abundant and spatially stable prey resources. At the other end of the continuum, larger populations of essentially transient dolphins inhabit the more open and dynamic environment of the Pacific coast, ranging widely in search of unpredictable and patchily distributed prey resources. Research in Aransas Pass, however, illustrated the importance of other ecological variables in the relationship between habitat and behavior. While habitat structure within Aransas Pass most closely resembles that of Sarasota Bay, dolphin behavioral patterns were more similar to those observed along the Pacific coast. Weller (1998) theorized that the more pronounced

65 seasonal variability in water temperatures and prey availability along the Texas coast, which resembles that of the Pacific coast, might account for similarities in dolphin movements along the Texas and Pacific coastlines. Within the Texas coast population, however, a small proportion of individuals do exhibit site fidelity characteristics more similar to dolphins of Sarasota Bay. Residential or semi-residential dolphins are primarily found in protected bays and inlets of the Texas coast, which closely resemble the bays and barrier islands of the Sarasota study area. Thus, the variability of bottlenose dolphin behavioral patterns along the Texas coast may reflect the effect of both large-scale (habitat structure) and small-scale (temperature variability) ecological differences on behavior of bottlenose dolphins, as well as illustrating the complexity of determining which environmental factors are important in shaping behavior.

66

CONCLUSIONS The primary objectives of this study were to examine the occurrence patterns, site fidelity, and movements of Pacific coast bottlenose dolphins over both space and time. Bottlenose dolphins, which can be found in most of the world’s oceans and in a wide variety of different habitats, have demonstrated a high degree of behavioral flexibility in response to environmental variables (Shane et al. 1986). This study was able to examine Pacific coast bottlenose dolphin behavior across three different spatial scales. At the finest scale, distribution of sightings within the San Diego and Santa Barbara study areas were examined for correlations with habitat characteristics. While some behavior patterns were stable at this scale (e.g., dolphins always remained within 1 km of shore), other patterns, such as increased sightings in canyon habitat of San Diego, provided evidence of differential use of habitats within study areas. At the next level, behavioral patterns were compared between the San Diego and Santa Barbara study areas between 1998 and 1999. While analysis of occurrence patterns indicated that dolphins used these two areas with comparable intensities, dolphin occurrence in the Santa Barbara study area was similar across oceanographic seasons, while dolphins utilized the San Diego study area most heavily during the Davidson season. More intense usage of the San Diego study area during this season suggested that dolphins were exploiting a temporally abundant resource, in the form of aggregations of spawning squid near Scripps Canyon. Comparison of site fidelity patterns indicated that dolphins were sighted more often in San Diego than in Santa Barbara during the seventeen-month study, and closer examination of sighting patterns indicated that increased levels of site fidelity in San Diego might also have been correlated with seasonal usage patterns. Thus comparison of occurrence and site fidelity patterns between areas indicated that dolphins do use portions of their range differently, at least over time scales of 1-2 years, and suggested that exploitation of temporally abundant resources may play an important role in shaping occurrence patterns of Pacific coast bottlenose dolphins. At the broadest spatial scale, continued and long-term study of bottlenose dolphins along the Pacific coast allowed comparisons with longitudinal studies in other areas. Two such areas, Sarasota Bay, Florida, and Aransas Pass, Texas, were chosen for comparison

67 because of the large-scale differences in habitat structure and oceanography of both areas when compared to the Southern California Bight. While Sarasota Bay and Aransas Pass are similar in habitat structure, containing relatively protected inner waters sheltered from the open ocean by barrier island chains, they differ oceanographically, with Aransas Pass undergoing more intense seasonal fluctuations than those occurring in Sarasota Bay. The habitat structure of the Southern California Bight, on the other hand, is quite different from both Sarasota Bay and Aransas Pass, with coastal waters open and exposed to the full force of the ocean. Although seasonal fluctuations in temperature and salinity are not as marked as those found in Aransas Pass, waters of the Southern California Bight are highly dynamic and undergo daily, seasonal, and annual fluctuations in response to changes in the California Current system. In Sarasota Bay, where waters are protected and resources are considered to be abundant and evenly distributed, dolphins are residential within a small area year-round. In the more open, exposed, and spatially variable environment of the Southern California Bight, however, dolphins travel extensive coastal differences and exhibit little site fidelity within their range, presumably as an adaptation to widely distributed and unpredictable prey resources. Dolphins in Aransas Pass seem to employ both behavioral strategies, with small groups of semi-residential dolphins, similar to those in Sarasota Bay, inhabiting protected bays while a larger subset of the population ranges widely and exhibits seasonal shifts in distribution. Thus comparison of these three areas indicates that while habitat structure may play a significant role in shaping behavioral patterns of bottlenose dolphins, variation in oceanographic characteristics also has considerable influence on occurrence patterns, site fidelity, and movements of dolphins. Comparisons of behavioral patterns over time were also valuable in illuminating environmental factors influencing dolphin behavior. Over the sixteen-year span of the study, some patterns remained consistent over time, while others fluctuated on both a yearly and/or seasonal basis. For example, over the course of the long-term study dolphins were most often observed within 0.5 km of the coastline, and were always within 1 km of shore. This pattern likely developed due to a combination of abundant nearshore prey resources and limited predation pressure and interspecific competition. Within the range of Pacific coast bottlenose dolphins, these factors are consistent over time and space and as such lead to the development of stable behavioral strategies. The number of dolphins observed within the

68 study area, however, varied with both season and year. Thus, while the environmental forces shaping latitudinal distribution may remain constant over time, those factors influencing alongshore distribution may be inconsistent over both short (within year) and long (between years) time scales, making a behaviorally flexible strategy most effective in exploiting resources within the 1 km² zone. In summary, extension of photo-identification studies of Pacific coast bottlenose dolphins over both time and space provided the opportunity to learn more about the forces shaping behavior in this coastal predator. Understanding behavior and the factors influencing it are important from a conservation and management viewpoint. While the coastal bottlenose dolphin population in the Southern California Bight appears stable, other populations (e.g. Moray Firth , Wilson et al. 1997b; mid-Atlantic seaboard of the United States, Wang et al. 1994) might be considered threatened (Connor et al. 2000), and knowledge of the factors influencing behavior in Pacific coast bottlenose dolphins may provide valuable insight into risks facing other populations. As well, the coastal environment of bottlenose dolphins is exposed to high levels of anthropogenic impacts, including boat traffic, pollution, and habitat alteration. By providing information on baseline dolphin behavior, long-term studies allow any changes in behavior, which could be a response to such impacts, to be detected. The health of bottlenose dolphins, as top-level predators within the coastal environment, may also provide a valuable indication of the overall health of the habitat and ecosystem (Tyack et al. 2000).

69

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80

APPENDIX PHOTOGRAPHIC QUALITY CRITERIA*

Negatives were be judged for quality based upon the following parameters: 1) Focus (Sharpness) - The focus of a photograph will be assessed using the following 3-point scale: 3 = Blurry but general outline visible. 2 = Questionable whether small nicks can be detected. (slightly blurred edge or “soft” edge) 1 = Adequate to detect small nicks. (sharp edge)

2) Exposure - The contrast of a photograph will be assessed using the following 3point scale: 3 = Fin and background (or glare) similar in shading so that notch pattern is not easily distinguished. 2 = Fin somewhat lighter than background (or glare) but notch pattern can still be distinguished. (For color: fin somewhat darker than background.) 1 = Fin very light against a dark background with fin still lighter in color than glare: notches are very easily distinguished. (For color: fin very dark against light background.) 3) Proportion of Fin/ID area visible - The percentage of the dorsal fin region visible in each negative will be assessed and labeled using the following 3 point scale: Note: consult reference diagram for this measure. 3 = 1/3-2/3 of the fin is visible 2 = 2/3 or more of the fin is visible 1 = All or nearly all of the fin is visible (more than 2/3)

*

Adapted from Dudzik 1999

81 4) The area that a dorsal fin occupies on a given negative will be assessed using transparent grids designed specifically for this task. The following three-point scale will be used for this measure: 4 = fin occupies box containing 4 squares 3 = fin occupies box containing 9 grid squares 2 = fin occupies box containing 16 squares 1 = fin larger than box containing 16 squares If any portion of the fin is outside of the box, then designate the fin as occupying the next larger box.

ABSTRACT

ABSTRACT OF THE THESIS Occurrence Patterns, Site Fidelity, and Movements of Pacific Coast Bottlenose Dolphins (Tursiops truncatus) by Aimée R. Lang Master of Science in Interdisciplinary Studies: Animal Behavior San Diego State University, Spring 2002 Boat-based photo-identification surveys conducted over a seventeen-month period off San Diego (n=43) and Santa Barbara (n=61), California were used to study occurrence patterns, site fidelity and movements of Pacific coast bottlenose dolphins (Tursiops truncatus). Within the Santa Barbara study area, mean size of observed dolphin schools was 12.7, with 67.4% of surveys encountering dolphins and an average of 15.7 dolphins sighted per survey. Although mean school size ( x =15.7), mean number of dolphins observed per survey ( x =20.6), and percent of surveys encountering dolphins (82.1%) were higher in the San Diego study area, these differences were not significant, indicating that dolphins used both areas with similar intensities. When occurrence patterns were compared across oceanographic seasons, only San Diego demonstrated evidence of seasonal patterns. Both school sizes and number of dolphins observed per survey were significantly higher during the Davidson oceanographic season than during all other seasons (P<0.01), which was attributed in part to the presence of aggregations of spawning squid within the San Diego study area between November 1998 and February 1999. Squid aggregations likely represented a temporally abundant prey resource that was exploited either directly or indirectly by dolphins during this time period. Over the seventeen-month study, 204 dolphins were photographically identified in San Diego, while 178 dolphins were identified in Santa Barbara. Dolphins demonstrated little site fidelity in either area, with a mean of 2.1 sightings per individual in Santa Barbara and a mean of 2.0 sightings per individual in San Diego. Eighty-nine dolphins were photographed in both areas, with a total of 131 documented inter-study area movements. The mean number of days between sightings in different areas was 96.0 days. One dolphin was documented to move between areas over only five days, for a mean travel speed of 61.6 km/day. Data collected in the San Diego study area during the seventeen-month study was combined with that collected in San Diego waters by Defran and Weller between 1984 and 1989 and by Dudzik between 1997 and 1999 to examine the stability of occurrence patterns and site fidelity of dolphins over time. A total of 241 surveys were conducted during the combined study period and were used to compare dolphin occurrence patterns across years and oceanographic seasons. While school sizes did not vary significantly across years, the encounter rate (P =0.006) and the number of dolphins sighted per survey (P <0.001) were significantly different across years, with a general trend of higher occurrence of schools during the latter years of the study. Increased dolphin occurrence during the Davidson oceanographic season was not as marked over the long-term dataset; instead, seasonality in

occurrence patterns was reflected in decreased encounter rates and number of dolphins per survey during the Oceanic season. No effect of the 1987-88 El Niño or the stronger 19971998 El Niño on dolphin occurrence patterns was detected. Four hundred sixty-eight dolphins were photographed in San Diego between 1984 and 1999, and identified individuals were sighted a mean of five times. Of the subset of most frequently sighted dolphins, the majority had been sighted in other study areas of the Southern California Bight, providing further evidence that dolphins are highly mobile within their range. As well, the majority of dolphins in this subset were photographed during all three oceanographic seasons, indicating that the lack of observed site fidelity in Pacific coast bottlenose dolphins was not correlated with seasonal movements within the range. The high mobility and lack of site fidelity demonstrated by identified dolphins, in combination with the observed variability in occurrence patterns over seasonal and annual time scales, were considered a reflection of the highly dynamic nature of the coastal environment of the Southern California Bight.