Date of Award
1995
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Oceanography
Department
Oceanography
First Advisor
Howard Winn
Abstract
During studies of bottlenose dolphins (Tursiops truncatus) in Bull Creek, a natural tidal channel in the Spartina marsh system of the Calabogue Sound estuary in South Carolina, 46 individual bottlenose dolphins were identified photographically between August 1988 and July 1993. Twenty-two of these were judged to be permanent or year-round residents of the site based on resightings in 70% or more of the 17 surveyed seasons. Five hundred thirty-eight dedicated boat-based surveys revealed an average density of 3.9 dolphins/km2. Small, but statistically significant, differences in mean dolphin densities were noted between years and seasons of the study (p < 0.05). Inter-year seasonal differences were not statistically significant (p > 0.05). Nine dolphins in the resident population produced 14 calves during this study, all of which disappeared and presumably died within three to nine months of initial sighting. Group sizes averaged 2.4 dolphins although the mode was single individuals (33.6%), and were not statistically significant between years and seasons (p > 0.05 level). Five groups were determined to be affiliates based on analysis of association patterns using the half-weight association index. Displacement patterns suggest the dolphins move with the tidal currents in the study area.
Groups of two or more dolphins, in synchronized efforts, forced schools of fish onto mud banks, stranding themselves in the process. While on the banks, the dolphins picked up and ate the stranded prey. Observations, during all seasons over a five-year period, revealed that this "strand-feeding" behavior was limited to animals that were long-term or permanent residents of the study area. Analysis of association patterns between individuals revealed that the foraging groups were composed of stable subgroups within the population.
Strand-feeding events occurred at all hours of the night and day, but only within three hours of the time of low water when the banks were exposed. Use of the technique of strand-feeding was independent of water temperature, which ranged from 9-33 °C, but only occurred when water clarity (Secchi depth) was less than 66 cm.
Detailed sonar profiles of bottom topography at consistently used strand-feeding sites revealed the existence of "structures" that resulted in concentrations of the prey fish (mullet, Mugil sp. And Atlantic menhaden, Brevoortia tyrannus). Selections of strand-feeding sites were decided by prey location, and did not involve herding of the prey by the dolphins.
Recommended Citation
Petricig, Richard Oliver, "BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) IN BULL CREEK, SOUTH CAROLINA" (1995). Open Access Dissertations. Paper 1631.
https://digitalcommons.uri.edu/oa_diss/1631