Defran Et Al

Defran, Caldwell, Lang and Weller 1

PHOTOGRAPHIC EVIDENCE FOR GEOGRAPHIC BOUNDARIES IN BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) ALONG THE PACIFIC COASTS OF CALIFORNIA AND BAJA CALIFORNIA NORTE

Bottlenose dolphins (Tursiops truncatus) off the Pacific coast of California and Baja California Norte are highly nomadic, regularly ranging over extensive distances (Wells et al. 1990, Defran et al. 1999). Recent investigations have shown that a majority of dolphins in this coastal population utilize an area extending from at least Ensenada, Baja California Norte in the south, to Monterey Bay, California in the north (Feinholz 1996, Defran and Weller 1999, Defran et al. 1999). Historical records suggest this species once occurred as far north as San Francisco Bay, California (Orr 1963); however, more contemporary accounts have considered southern Los Angeles County, with occasional sightings extending as far north as Point Dume, California (Dohl et al. 1981), to be the typical northern distribution limit (Norris and Prescott 1961, Leatherwood and Reeves 1982, Hansen 1990). Following the 1982-1983 El Niño event, bottlenose dolphins extended their northern distribution to Monterey Bay, and perhaps as far as San Francisco (Wells et al. 1990, Feinholz 1996). This range extension appears permanent, as dolphins continue to regularly occur off central California1 and occasional sightings further north suggest that the distribution of this population may have returned to its known historical limit (Ferrero and Tsunoda 1989, Feinholz 1996, Wells and Scott 1999). While the northern range limit for bottlenose dolphins along the California coast may be determined by cold water tolerance limits, such a temperature barrier does not

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Personal Communication from Lisa Giesick and Tom Kieckhefer, Pacific Cetacean Group, 3239 Imjin Road #122, Marina, CA 93933, January 2000.

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occur to the south until the presumed southern extent of bottlenose dolphin distribution off central Chile (Jefferson et al. 1993, Wells and Scott 1999). Research by Curry (1997) found no genetic differences between bottlenose dolphins off California and South America, indicating that some level of population mixing was probably occurring along the entire range of the species. Population distinctions within this distribution, however, remains poorly understood. To better determine the southern movement patterns for dolphins photographically identified in several study sites off southern and central California (Fig. 1), a series of photo-identification surveys were conducted off Ensenada, Baja California Norte (Defran et al. 1999). A high percentage (88%) of 68 dolphins identified off Ensenada (Table 1) were matched to a catalog of 516 known individuals identified during a long-term study (1981-1998) off San Diego (Hansen 1990, Weller 1991, Defran and Weller 1999, Dudzik 1999). In addition, a high number of dolphins sighted in Ensenada were also sighted in more northern study sites off Orange County, Santa Barbara, and Monterey Bay (Feinholz 1996, Defran et al. 1999). These results suggested that if a southern range boundary for coastal bottlenose dolphins off California existed, it was likely to be south of Ensenada. The research presented here was conducted in the coastal waters 32 km south of San Quintín, Baja California Norte (30o 18’ N, 115o 50’ W) between April and August 1990. Our San Quintín study area was located approximately 376 km south of San Diego and 200 km south of Ensenada. The study area consisted of a 38 km coastal region from Punta Azufre, near the entrance to San Quintín Bay, to Cañon del Rosario, and extended 2 km offshore (Fig. 1). Survey and photo-identification procedures were identical to

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those employed during similar studies off California and Baja California Norte, and are detailed elsewhere (Defran et al. 1990, Weller 1991, Defran and Weller 1999). A total of eight boat-based photo-identification surveys were conducted in the San Quintín study area during three sampling periods: April 9 to 12 (n = 2); June 13 to 16 (n = 3); and August 8 to 11 (n = 3). During the first survey on 9 April 1990, the research boat was launched at Punta Azufre, and the survey track extended south to El Socorro (Fig. 1). For all subsequent surveys, the boat was launched from the beach off our base camp, and surveyed south to Cañon del Rosario. Two hundred bottlenose dolphins in 14 schools were observed during the study. The average school size was 14.3 dolphins (SD = 7.53), and ranged from 5 - 30 individuals. A total of 105 individual dolphins were identified, and 38% (n = 40) of these dolphins were photographed on two or more surveys. In most cases, resightings of an individual were obtained during a single sampling period (i.e., within days), reflecting short-term site fidelity similar to that displayed by dolphins off more northern study sites (Defran and Weller 1999, Defran et al. 1999). Dorsal fin photographs collected during each survey in San Quintín were compared to an existing catalog of 545 dolphins identified in southern and central California and off Ensenada from 1981 to 1998 (Hansen 1990, Weller 1991, Feinholz 1996, Defran and Weller 1999, Defran et al. 1999, Dudzik 1999). In contrast to the high levels of photographic match-up reported for dolphins identified in study sites between Ensenada and Monterey Bay (Table 1), only two (2%) of the 105 dolphins identified in San Quintín were previously or subsequently identified in any northern study site. Dolphin 006, first photographed in 1982 off San Diego by Hansen (1990), was also photographed twice in

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Ensenada and five times in San Diego between 1982-1989. This dolphin was then photographed twice in San Quintín during August 1990, twice in San Diego during February 1991, and eight times in San Diego between March 1996 and August 1998. Dolphin 739, first photographed in San Quintín in June 1990, was subsequently photographed in the same school as dolphin 006 off San Diego on 14 August 1998. Several aspects of the present study may have contributed to the low level of photographic mixing observed between coastal locations. For example, the limited number of surveys (n = 8) conducted in San Quintín may not have been adequate to document photographic matches between regions. However, earlier studies in Baja California Norte and in Southern California (Defran and Weller 1999, Defran et al. 1999) indicated that the San Quintín sample size was sufficient to detect photographic matches between coastal locations. For example, a relatively low number of surveys were also conducted off Santa Barbara (n = 12) and Ensenada (n = 11). When photographs from each of these study sites were compared to a catalog of 516 dolphins identified off San Diego between 1981-1998 (Caldwell 1992, Defran and Weller 1999, Dudzik 1999), resighting rates of 88% (Ensenada) and 92% (Santa Barbara) were documented (Table 1). Further, more dolphins were identified in San Quintín (n = 105) than in either Santa Barbara (n = 49) or Ensenada (n = 68) (Table 1), making the probability of finding an inter-study area match more likely. The spring-summer seasonal sampling bias off San Quintín was also unlikely to have had a significant influence on the low photographic overlap detected between coastal study areas, because the occurrence and distribution patterns for dolphins off San Diego, our most intensively sampled study area (Table 1), were not seasonally-based (Defran

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and Weller 1999). Therefore, we conclude that the photo-identification techniques employed during the present study were sufficient to detect greater inter-study area overlap had it existed. It is also improbable that the 376 km distance between the northern San Quintín and southern San Diego study area borders represented a significant barrier. Coastal movements of 450 km were commonly observed for dolphins off Baja California Norte and California (Defran et al. 1999), and travel distances in excess of 900 km were recorded for dolphins moving between Ensenada and Monterey Bay (Feinholz 1996). The findings presented here, in combination with results from previous longitudinal research on Pacific coast bottlenose dolphins (Defran and Weller 1999, Defran et al. 1999), suggest that at least two Tursiops populations may occur off the coastline of California and Baja California Norte. We hypothesize that the coastal region between Ensenada and San Quintín functions as the southern range boundary for most members of a “California” population of bottlenose dolphins that range between Ensenada and Monterey Bay, and as the northern range boundary for a “Baja California Norte” population. Range boundaries typically occur where there are breaks in resources, where environmental conditions become inhospitable, or where geographic features deter movement (Mayr 1970). Our review of the literature regarding the ecology, oceanography, and marine geology of the eastern Pacific seaboard between San Quintín and Ensenada2 (see also Caldwell 1992) revealed no apparent explanation for the range

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Personal Communication from Eduardo Morteo, Ciencias Marinas, Universidad Autónoma de Baja California, Km 103 Carr. Tijuana-Ensenada, 22800 Ensenada, Baja California Norte, January 2000.

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boundary proposed here. The determination of two potentially discrete Tursiops populations along the Pacific coast of California and Baja California Norte provides the basis for better defining management and conservation efforts regarding this delphinid species, and functions as an important reference point in continued basic science studies of bottlenose dolphin behavioral ecology. Future research programs incorporating genetic comparisons along the California and Baja California Norte coast, and boat-based photo-identification surveys between Ensenada and San Quintín may help to better clarify the apparent population distinctions reported here.

ACKNOWLEDGEMENTS The authors extend their sincere gratitude to the many individuals who made important contributions to the field, laboratory, and manuscript phases of this research. A. Sandoval and D. Holmgren of Centro De Investigación Científica Y De Educación Superior De Ensenada, Ensenada, Baja California Norte, and J. Bullis and A. French of San Diego State University provided essential logistical support in the field. A. Bassett, L. Barre, and numerous members of the Cetacean Behavior Laboratory maintained and updated our photographic catalogs and associated databases. E. Morteo critically reviewed Spanish language publications on the marine biology of the Southern California Bight and San Quintín regions and J. Barlow made valuable suggestions about terminology. This study was conducted under the provisions of a research permit issued by the Secretaría de Medio Ambiente Recursos Naturales Y Pesca to Dr. G. Hamman, Faculdad de Ciencias Marinas, Universidad Autónoma de Baja California, Km 103 Carr. Tijuana-Ensenada, 22800 Ensenada, Baja California Norte.

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LITERATURE CITED Caldwell, M. 1992. A comparison of bottlenose dolphins identified in San Quintín and the Southern California Bight. M.S. thesis, San Diego State University, San Diego, CA. 59 pp. Curry, B. 1997. Phylogenetic relationships among bottlenose dolphins (Genus Tursiops) in a worldwide context. Ph.D. dissertation, Texas A&M University, College Station, TX. 138 pp. Defran, R. H., G. M. Shultz and D. W. Weller. 1990. A technique for the photographic identification and cataloging of dorsal fins of the bottlenose dolphin (Tursiops truncatus). Report of the International Whaling Commission (Special Issue 12):5355. Defran, R. H., and D. W. Weller. 1999. The occurrence, distribution, site fidelity and school size of bottlenose dolphins (Tursiops truncatus) off San Diego, California. Marine Mammal Science 15:366-380. Defran, R. H., D. W. Weller, D. L. Kelly and M. A. Espinosa. 1999. Range characteristics of Pacific coast bottlenose dolphins in the Southern California Bight. Marine Mammal Science 15:381-393. Dohl, T. P., K. S. Norris, R. C. Guess, J. D. Bryant and M. W. Honig. 1981. Summary of marine mammal and seabird surveys of the Southern California Bight area, 19751978. Volume III. Investigator’s Reports. Part II. Cetacea of the Southern California Bight. National Technological Information Service. 434 pp. Available from National Technical Information Service, Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.

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Dudzik, K. J. 1999. Population dynamics of the Pacific coast bottlenose dolphins (Tursiops truncatus). M.S. thesis, San Diego State University, San Diego, CA. 63 pp. Feinholz, D. M. 1996. Pacific coast bottlenose dolphins (Tursiops truncatus gilli) in Monterey Bay, California. M.S. thesis, San Jose State University, San Jose, CA. 78 pp. Ferrero, R. C., and L. M. Tsunoda. 1989. First record of a bottlenose dolphin (Tursiops truncatus) in Washington State. Marine Mammal Science 5:302-305. Hansen, L. J. 1990. California coastal bottlenose dolphins. Pages 403-420 in S. Leatherwood and R. R. Reeves, eds. The bottlenose dolphin. Academic Press, San Diego, CA. Jefferson, T. A., S. Leatherwood and M. A. Webber. 1993. Marine mammals of the world. FAO species identification guide. FAO, Rome, 320 pp. Leatherwood, S., and R. R. Reeves. 1982. Bottlenose dolphin (Tursiops truncatus) and other toothed cetaceans. Pages 369-414 in J. A. Chapman and G. A. Feldhammer, eds. Wild mammals of North America: Biology, management, economics. The John Hopkins University Press, Baltimore, MD. Mayr, E. 1970. Population, species, and evolution: an abridgment of animal species and evolution. Belknap Press of Harvard University Press, Cambridge, MA. Norris, K. S., and J. H. Prescott. 1961. Observations on Pacific cetaceans of California and Mexican waters. University of California Publications of Zoology 63:291-402.

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Orr, R. T. 1963. A northern record of the Pacific bottlenose dolphin. Journal of Mammalogy 44:424. Weller, D. W. 1991. The social ecology of Pacific coast bottlenose dolphins. M.S. thesis, San Diego State University, San Diego, CA. 93 pp. Wells, R. S., and M. D. Scott. 1999. Bottlenose dolphin Tursiops truncatus (Montagu, 1821). Pages 137-182 in S. H. Ridgway and R. Harrison, eds. Handbook of marine mammals. Volume 6. The second book of dolphins and the porpoises. Academic Press, San Diego, CA. Wells, R. S., L. J. Hansen, A. Baldridge, T. Dohl, D. L. Kelly and R. H. Defran. 1990. Northward extension of the range of bottlenose dolphins along the California coast. Pages 421-431 in S. Leatherwood and R. R. Reeves, eds. The bottlenose dolphin. Academic Press, San Diego, CA.

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R. H. Defran3, Marthajane Caldwell 4, Aimée R. Lang, and David W. Weller5, Cetacean Behavior Laboratory, Department of Psychology, San Diego State University, San Diego, California 92182-4611, U.S.A.; e-mail: [email protected].

Author to whom correspondence should be addressed. Current Address: Department of Biology, University of Miami, P.O. Box 249118, Coral Gables, FL 33124, U.S.A 5 Current Address: Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, P.O. Box 271, La Jolla, CA 92038-0271, U.S.A. 3 4

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Table 1. Summary information on survey effort, study period, and photographic data for San Quintín and other Pacific coast study areas.

a

Study area

Number of surveys

Study period

Number of dolphins identified

Number resighted to San Diego

San Diego Orange County Ensenada Santa Barbara Monterey Baya San Quintín

245 44 11 12 52 8

1981 - 1991, 1996 - 1998 1982 - 1989 1985 - 1986 1987 & 1989 1990 - 1993 1990

516 133 68 49 58 105

------123 (92%) 60 (88%) 45 (92%) 47 (81%) 2 (2%)

Reflects our reanalysis of the Feinholz (1996) photographic data.

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FIGURE CAPTION Figure 1. San Quintín study area. Inset shows Pacific coast study area locations mentioned in the text.

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