Defran In Prep

Panama Dolphin Abundance Project: A Research Proposal R.H. Defran, Ph.D. Wildlife International Network, Inc. November 21, 2005

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Introduction This proposal describes a plan for carrying out a dolphin abundance study in the Bocas del Toro (Bocas) area of the Republic of Panama (Figs. 1A, 1B). The species of interest to this Panama Dolphin Abundance Project (PDAP) is the common bottlenose dolphin (Tursiops truncatus – Fig. 2). The primary objectives of this study will be to first define the geographical boundaries (i.e., home range) of the bottlenose dolphins which are found in the Bocas area, and then to carry out seasonal and annual assessments of the size of this population (i.e., abundance). An effective and well-developed technique for assessing the home range and abundance of a cetacean species, such as bottlenose dolphins, involves boat-based surveys in which photographic (photo-identification) and observational data are collected Photo-identification techniques have been successfully used to study the abundance and behavioral ecology of bottlenose dolphins in a number of coastal and offshore island locations, including the west coast of Canlifornia and North Baja California, as well as in the Turneffe and Drowned Cayes archipelagos of Belize in Central America. (Defran and Weller 1999, Campbell et al. 2002, Kerr et al. 2005). During boat-based photoidentification surveys, researchers attempt to photograph each dolphin’s dorsal fin, which often contains naturally occurring and distinctive notches (Fig. 3). Dorsal fin images are used to identify, and reidentify individuals, over time and in varying locations. The temporal and spatial sighting patterns of individuals allows a determination of their geographic range (home range), as well as their fidelity to this range (site fidelity). Both home range and site fidelity are important dimensions used to determine membership in a

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population. Ultimately, the photographic history of a dolphin’s sightings may be used in the calculation of mark-recapture estimates of dolphin abundance. The Research Plan Research on the PDAP will occur in two phases. Phase I involves a somewhat informal determination of the home range of dolphins in the Bocas area that is accomplished by carrying out meandering boat-based surveys throughout the area. These boat surveys will serve a number of functions including: a determination of the locations favored by bottlenose dolphins in the Bocas area; the exploration and recording of habitat types represented in the Bocas area and their navigability, including deep and shallow areas, windward and leeward exposures, coral reef, sea grass and sandy bottom infrastructure, etc. (see Fig. 4 for an example of such habitat mapping in Turneffe Atoll, Belize); the determination of survey routes which will efficiently and comprehensively sample a significant spatial representation of the Bocas area, which includes all major habitat types. Fig. 5 shows a hypothetical array of four survey routes in the Bocas area which sample a variety of habitat types and is included for illustrative purposes. Phase II involves a formal and systematic application of photo-identification methodology using well developed survey routes over seasons and across years. Photographic Survey Procedure Boat-based photo-identification surveys will be carried out four times per year: twice during the dry season (January to mid-April) and twice during the rainy season (mid-April to December). A complete survey will consist of completing each of the designated survey routes developed during Phase I (home range, see Fig. 5 for examples

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of hypothetical survey routes in the Bocas area). Two or three complete surveys may be completed during each of the quarterly sampling periods. During surveys, observers on the survey vessel will search for dolphins groups and then attempt to obtain the dorsal fins of all members of the group. The survey vessel will be a 8 m boat equipped with an outboard engine. On photo-identification surveys, the vessel will proceed along the designated survey route at 30 – 33 km/hr with the pilot and two additional onboard research observers will visually search a 180º area around the boat until dolphins are sighted. Immediately after a sighting, the sighting location will be marked by recording it as a GPS waypoint (latitude and longitude). This GPS waypoint, as well as information on group size and composition, behavior, direction of movement, environmental conditions, and time will be recorded on a Sighting Form (Fig. 6). Dolphin groups will be defined as all dolphins in close proximity (<100 m) to one another, generally moving in the same direction and engaging in similar behavior (Quintana-Rizzo and Wells 2001, Urian and Wells 1996). Group size estimates will include the total number of dolphins, neonates and calves. Neonates have darker coloration than non-calves, exhibit characteristic head-up surfacing patterns, and may exhibit fetal folds that remain evident for several weeks as neonatal stripes. Calves are small dolphins, larger than neonates, not exhibiting fetal folds and up to about 75% of the presumed mother's length. Calves consistently travel alongside their presumed mothers, in the baby position. Adults (non-calves or neonates) are large dolphins that exceed approximately 2 m in length. An attempt will also be made, through photography and accompanying field notes, to identify probable females by noting their association with

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neonates or calves who accompany them while maintaining the ‘baby position’. A similar effort will be made to document males who display their penis. Upon completion of initial data collection, the vessel will be maneuvered to within 2 – 10 m of the dolphin group and individual dorsal fins will be photographed with a Canon EOS 20D digital camera equipped with a Canon 400mm telephoto lens. Effort will be made to acquire high quality photographs of the left and right side of each individual’s dorsal fin, without regard to apparent distinctiveness. After completion of all photographic data collection, the survey vessel will return to the original sighting location or to the closest point on the original survey route, and identical procedures will be repeated as additional dolphin groups are encountered. Sighting and photographic data collected while completing the designated survey route will be regarded as ‘on-effort data’. Similar data collected while returning along an already completed survey route component or during other opportunistic survey encounters will be labeled as ‘off-effort data’. Notations about survey route components that involve on- or off-effort data collection are recorded on the Survey Form (Fig. 6). Analysis and Interpretation Photo-identification Data Photo-identification analyses involving the sorting of digital dorsal fin images will generally follow the techniques described by Mazzoil et al. (2004). Procedures for matching and cataloging digital dorsal fin images will be implemented by FinBase (Adams 2005). These sorting, matching and cataloging procedures are briefly summarized as follows. Clear digital photographs of distinctively marked dorsal fins will be sorted by recognizable notch patterns, and the best photograph for each dolphin will

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be selected as the “type specimen” to which all other photographs will be compared. Subsequently, only unambiguous matches with the “type specimen” will be accepted as reidentifications of a known individual. Group Size and Composition Accumulated data on group size will be partitioned by location within different habitats of the Bocas. Such data can reflect foraging strategies and associated prey item abundance, density and distribution (Campbell et al. 2002). Similarly, areas frequented by ‘nursery groups’ may reflect higher or selective productivity as well as protection from predation by sharks. Group size and composition data will also be examined for seasonal (wet, dry, transitional) effects which may be related to prey item characteristics, but also incursions from transients. Sighting Frequency and Distribution Sighting frequency data for individual dolphins and its seasonal and annual distribution may be used to asses the resident or transient status of individuals. The criteria used for identifying a resident varies widely across photo-identification studies. However, the most convincing criteria are usually associated with studies that have broad geographic coverage of the study area, frequent surveys across years, and a longer rather than shorter study period. In the current study, the criteria used to identify a dolphin as a resident is yet to be determined but will be based on the number of sightings across seasons and years. Rate of discovery (ROD) data will provide an empirical view of the closed, open or mixed status of the Bocas study area dolphins (Fig. 7 presents an example of a rate of discovery function – Campbell et al. 2002). Finding a high proportion of resident dolphins within the Bocas study area should lead to a flattening of the ROD

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curve. Sudden increases in the slope of the ROD curve, followed by a rapid return to asymptote could reflect seasonal incursions by transients (possibly seasonal migrants) into the Bocas study area. Other combinations of a mix between resident and transient dolphins are possible, and the characteristics of this mix will also be reflected in the slope of the ROD curve. Population Estimation Standard mark-recapture models for estimating abundance assume that, within a sample, a marked animal will be recognized with certainty if recaptured (Pollock et al. 1990). If the probability of capture is not equal among members of a population then the resulting abundance estimates will be negatively biased (Hammond 1986). This assumption can be violated if poor quality photographs are used to identify individuals (Hammond 1986). Several cetacean mark-recapture studies have addressed the issue of photographic quality through the development and application of photo quality rating systems (Arnbom 1987, Whitehead et al. 1998, Wilson et al. 1999, Friday et al. 2000). In order to reduce bias toward highly distinctive individuals in our analyses, the photographic quality rating system adapted from Friday et al. (2000) will be applied. Mark-recapture animal abundance estimator models are classified as either closed or open (Pollock et al. 1990). Closed models assume that no births, deaths, immigration or emigration occur during the study period, while open models disregard these assumptions (Otis et al. 1978). Advantages of closed models include higher precision and, if desired, allowances for heterogeneity of capture probabilities (Otis et al. 1978). Currently, there are no existing data to suggest whether a closed or open population estimate would be appropriate for the Bocas area population of bottlenose dolphins. Since

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the bottlenose dolphins exhibit a long life span and low reproductive rate (Wells and Scott 1999), births and deaths will assumed to be infrequent. Inherent differences in individual behaviors, such as preferences for certain portions of the Bocas study area, are assumed to affect the probability of identifying individuals during sampling periods. In addition, individual variations in boat avoidance techniques and surfacing rates will be assumed to affect the probability of capture during encounters (Hammond 1986, Wilson et al. 1999). Therefore, Chao’s closed model Mth (time and heterogeneity) which allows capture probabilities to vary with time (sampling period) and by individual (Chao et al. 1992) will be considered as a population estimator. In conjunction with this estimator, short sampling periods will be selected in order to minimize the probability of changes in the population size. Abundance estimators such as Chao’s closed model Mth only provide an index of the size of the distinctively marked population. The proportion of distinctly versus non-distinctly marked dolphins in the Bocas population will be estimated from dolphin groups in which all distinctively and non-distinctively marked individuals are photographed (Wells et al. 1996). The precision of these estimators will ultimately be linked to the quality and comprehensiveness with which dolphin groups are photographed in the field. Once the distinct-non-distinct proportion estimator is developed, it will then be combined with Chao’s closed model Mth estimate to provide a comprehensive estimate of the Bocas population.

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Literature Cited Adams, J.D. 2005. FinBase photo-identification database and mapping tool. Retrieved 06 October 2005 from http://www.chbr.noaa.gov/FinBase/ Arnbom, T. 1987. Individual identification of sperm whales. Reports of the International Whaling Commission 37:201-204. Campbell, G.S., B.A. Bilgre and R.H. Defran. 2002. Bottlenose dolphins (Tursiops truncatus) in Turneffe Atoll, Belize: occurrence, site fidelity, group size and abundance, Aquatic Mammals 28:170-180. Chao A., M.S. Lee, and S.L. Jeng. 1992. Estimating population size for capturerecapture data when probabilities vary by time and individual animal. Biometrics 48:201-216. Defran, R.H. and D.W. Weller. 1999. Occurrence, distribution, site fidelity, and school size of bottlenose dolphins (Tursiops truncatus) off San Diego, California. Marine Mammal Science 15:366-380. Friday, N., T.D. Smith, P.T. Stevick and J.A. Allen. 2000. Measurement of photographic quality and distinctiveness for the photographic identification of humpback whales, Megaptera noveangliae. Marine Mammal Science 16:355-374. Hammond, P.S. 1986. Estimating the size of naturally marked whale populations using capture-recapture techniques. Reports of the International Whaling Commission (Special Issue 8) 2553-282. Kerr, K., R.H. Defran and G.S. Campbell. 2005. Bottlenose dolphins (Tursiops truncatus) in the Drowned Cayes, Belize: group size, site fidelity and abundance. Caribbean Journal of Science 41:172-177.

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Mazzoil, M., S.D. McCulloch, R.H. Defran and E. Murdoch. 2004. The use of digital photography and analysis for dorsal fin photo-identification of bottlenose dolphins. Aquatic Mammals 30:209-219. Pollock, K.H., J.D. Nichols, C. Brownie, and J.E. Hines. 1990. Statistical inference for capture-recapture experiments. Wildlife Monographs 107:1-97. Quintana-Rizzo, E. and R. Wells. 2001. Resighting and association patterns of bottlenose dolphins (Tursiops truncatus) in the Cedar Keys, Florida: insights into social organization. Canadian Journal of Zoology 79:447-456. Urian, K.W. and R.S. Wells. 1996. Bottlenose dolphin photo-identification workshop: March 21-22, 1996, Charleston, South Carolina. NOAA Tech. Mem. NMFSSEFSC-393. Wells, R.S., K.W. Urian, A.J. Read, M.K. Bassos, W.J. Carr, and M.D. Scott. 1996. Lowlevel monitoring of bottlenose dolphins, Tursiops truncatus, in Tampa Bay, Florida: 1988-1993. NOAA Technical Memorandum NMFS-SEFSC-385. Wells, R.S. and M.D. Scott. 1999. Bottlenose dolphins. Pages 137-182 in S.H. Ridgway and R. Harrison, eds, Handbook of marine mammals, Vol. 6, the Second book of dolphins and porpoises. Academic Press, San Diego, CA. Whitehead, H.S., S. Gowns, A. Falconer and S.W. McCrery. 1998. Population analysis of northern bottlenose whales in the Gully, Nova Scotia. Marine Mammal Science 13:173-185. Wilson, B., P. S. Hammond and P. S. Thompson. 1999. Estimating size and assessing trends in a coastal bottlenose dolphin population. Ecological Applications 9:288-300.

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Figure 1A and 1B. Map of the Panama. Inset shows detail for Bocas del Toro area, including Colon, Cristobal, Bastimentos and Pope Islands, as well as the Chiriqui Lagoon, Malaita and Florida Islands, as well as the oceanic passages and corridors which separate them. 11

Figure 2. Common bottlenose dolphin (Tursiops truncatus).

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Figure 3. Distinctively marked dorsal fins from common bottlenose dolphins in the coastal waters of north San Diego County (Defran and Weller 1999).

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Figure 4. Habitat mapping of Turneffe Atoll in Belize.

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Figure 5. Hypothetical photo-identification survey routes in the Bocas study area. The details of these survey routes were arbitrarily selected to illustrate in this proposal how such routes are planned an how they are designed to sample coastal area on the windward and leeward sides of the Bocas islands, as well as mainland areas and the more open waters between islands and the mainland coastline.

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Figure 6. Panama Dolphin Abundance Project photo-identification sighting form. This form is completed during and following each dolphin group sighting.

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Figure 7. Rate of discovery curve for Turneffe Atoll in Belize, Central America, Campbell et al. 2002. This form of expressing photo-identification data is often used to determine whether or not a significant portion of a population has been photographed (sampled). Extended flat portions of the ROD curve suggest that most members of a population have been photographed.

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