2001 Marine Mammal Conference Abstracts

Bottlenose Dolphins in the Drowned Cayes, Belize: Occurrence, School Size, Abundance, and Site Fidelity

Kerr, K.A., Campbell, G.S., AND Defran, R.H.

Cetacean Behavior Laboratory, Department of Psychology, San Diego State University,
San Diego, CA 92182-0350, and Oceanic Society Expeditions,
Fort Mason Center, Bldg E, San Francisco, CA 94123

Bottlenose dolphin (Tursiops truncatus) occurrence, school size, site fidelity, and abundance in the Drowned Cayes, Belize, were examined based on data from 392 photo-identification surveys conducted between February 1997 and December 1999. A total of 2150 dolphins were observed across 737 schools. School size ranged from 1 to 20 ( = 2.9, D = 2.32) with single dolphins comprising 31% (n = 229) of all sightings. Sighting frequencies for the 115 photographically identified individuals ranged from 1 to 50 (= 8.3, SD = 12.51). Twenty-four percent (n = 27) of the identified individuals were photographed only once, while 27% (n = 31) were photographed 10 or more times.

Seventy-three dolphins were newly identified during the first 80 surveys in which at least one distinctively marked individual was photographed. However, only 41 new dolphins were identified during the remaining 182 surveys, and no new individuals were identified during the last 32 surveys. Residents were defined as individuals photographed a minimum of 2 times across each of the three study years or 4 or more times in each of two successive years and constituted 30% (n = 34) of the identified dolphins. Abundance was estimated at 122 95% CI = 114 - 140) using Chao's closed model Mth. Photographic comparisons between the Drowned Cayes catalog and 81 individuals from a four-year data set collected at nearby Turneffe Atoll showed no overlap despite close proximity and apparent occasional use of each study area by a high proportion of identified dolphins. Considered together, the very low average school size, early leveling of the rate of discovery curve and relatively low percent of dolphins showing site fidelity suggest that prey availability in this coral reef, mangrove, sea grass environment is low and that this population of dolphins should be considered vulnerable to anthropogenic impacts.