Behavioral ecology and social structure of coastal bottlenose dolphins in South Carolina

I investigated the roles of geographic and social factors in determining habitat use and ranging patterns, foraging specializations, and social structure of two stocks of Atlantic bottlenose dolphins which have overlapping ranges but different seasonal patterns of residency in Calibogue Sound, S.C. and adjoining coastal and inland waters. From October 1994 through December 1998, 1 conducted 209 surveys in Calibogue Sound, South Carolina and adjoining coastal waters. Surveys were conducted quarterly from 1994 to 1996 and year round in 1997 and 1998. Individual dolphins were identified by distinctive fin characteristics and were categorized as year round (resident) or seasonal (transient) inhabitants of the area based on overall resighting patterns. Transient dolphins were generally present from May through December. Groups in which resident dolphins were identified were only sighted in the inland waters of the study area while groups with transients were observed throughout the inland and oceanic waters. Transient individuals used larger ranges within the study area than did residents. There were complex habitat use patterns reflecting interactions among group size, behavior, residency status and habitat type. Resident dolphins occurred in inshore waters, ranged over moderate distances, exhibited strong site fidelity and showed distinct patterns of core use within their home ranges. Social variables such as group composition and behavior had a strong influence on sequences of behavioral states and interactions of these dolphins. Resident and transient dolphins differed in the specific foraging behaviors they used as weft as the number of behaviors used by individuals. My results suggest that resident and transient dolphins had high rates of interaction when transients were present in the study area. Environmental and behavioral conditions did not affect the association rates of resident dolphins. Among resident dolphins, associates were most likely chosen for reasons other than current conditions and likely reflected long term social affiliations.; My results confirm the distinct yet overlapping ranges of residents and transients along the coast and suggest that geographic, social and behavioral factors contributed to the observed stranding patterns during a mass mortality event in 1987 and 1988. Cultural traditions passed between generations within each stock could account for the existence and maintenance of different behavioral patterns of residents and transients. Social and environmental factors influenced many aspects of the social, foraging and ranging behaviors of these dolphins, potentially impacting all aspects of group living including the social and mating systems of the population, communication, disease transmission, learning and predator avoidance and defense.