Abstract:
In 1987 I established a research program on the behavioral ecology of spinner dolphins in the nearshore waters of Mo'orea, French Polynesia. Objectives were to describe dolphin distribution in varying environmental conditions; typify dolphins' critical habitat; describe school sizes among locations, environmental conditions, and habitats; examine school size data for monthly or seasonal variations; determine individuals' home range characteristics and movement patterns; monitor immigration of individuals from outside Mo'orea's waters; produce population estimates for each field season; and compare results with data from studies of conspecifics at Hawaii. Shore and boat surveys were conducted on 435 days from 1987-1992. Dolphins were observed on 315 days. They regularly utilized as rest areas nine of Mo'orea's twelve pass/bay complexes. Within each complex, salient features of dolphin distribution were dolphins' preferences for passes and bay mouths, their cavalier utilization of lagoon evacuation channels, and their disdain of bays' head regions. Dolphins preferred areas with clear water over a light colored substrate. More dolphins were found along the leeward side of Mo'orea than along the sideshore or windward sides. Distribution around the island often changed with shifts in wind direction, but some movements were not in response to wind. Overall mean school size with 95% CI was 31 ± 2.6 dolphins. The largest schools were found in April; this may reflect seasonality in the dolphins' reproductive physiology. Mo'orea's dolphins comprise a closed, resident community of often geographically segregated individuals. Some dolphins prefer the west coast; others prefer the north shore or east coast. Home ranges include all of Mo'orea, and on occasion, may include the northwest coast of Tahiti. The daily total number of dolphins observed around Mo'orea was invariably less than 100; likewise, the largest single schools contained approximately 100 individuals. Population estimates (with 95% Likelihood Intervals) for the two most intensive field seasons, 1988 and 1989, were 150[less than or equal to]N[less than or equal to]172 and 125[less than or equal to]N[less than or equal to]144 dolphins, respectively. These data suggest that Mo'orea has a carrying capacity of approximately 150 dolphins.
