Delphinus

Abstract: A total of 297 common dolphin (Delphinus delphis) stomachs was used for these diet analyses. All originated from common dolphins incidentally captured in Natal, where their occurrence is strongly associated with an annual, northward fish migration, the sardine run, along the east coast. Thirty-six fish and four cephalopod prey species were identified. Though 86.9% by weight of the diet was made up of only five prey species, common dolphins appear to feed opportunistically, their diet reflecting local prey abundance and availability. Prey were primarily small, easily-caught, pelagic shoaling species, with the main prey being South African pilchard (Sardinops ocellatus). Although pilchard dominated the diet between 1974 and 1992, there were marked annual and seasonal fluctuations in dietary composition, reflecting changes in prey availability and abundance. There were clear differences in the contribution of particular prey species to the diet of different sex and size groups, with strong evidence for resource partitioning between groups. The influence of the annual ‘sardine run’, and the fish predators associated with it, on the diet, feeding biology and distribution of common dolphins is discussed.

Abstract: During the first months of operation (March, 1954 to Sept. 1955) of the new oceanarium, Marineland of the Pacific, we have had numerous opportunities to observe the dolphins and porpoises of California waters. In addition, we have recorded the behavior of captive Atlantic bottlenose dolphins ( Tursiops truncatus ). Many members of the staff at Marineland have assisted in making these observations. We are particularly grateful to Frank Brocato, Captain of the collecting vessel, Geronimo , and his assistant, Frank Calandrino, for their help in compiling the field observations. We wish to thank Dr. Leonard L. Mortimer D.V.M., for his assistance and suggestions during treatment of captive animals. Dr. Raymond Gilmore has given us much assistance and has critically reviewed the manuscript. We follow Norman and Fraser (1940) in their definition of the terms porpoise and dolphin; porpoise refers to members of the Delphinidae which are small, beakless, and with triangular dorsal fins and tricuspid teeth. Dolphin is used for the remainder of the family, except those larger forms dignified by the name, whale . This species ( Lagenorhynchus obliquidens Gill, Pl. I, Top) and the common dolphin ( Delphinus bairdi ) have been observed many times more than these data indicate, particularly during the months before Marineland of the Pacific was completed. These observations serve to strengthen the conclusions we draw here. Plate 1 Top: Captive Lagenorhynchus obliquidens , in company with Tursiops truncatus , in the circular tank at Marineland of the Pacific. Bottom: Transporting a specimen of Delphinus bairdi . Photo by William Eccles. Seasonal movements .—The Pacific white-sided dolphin is probably the most common cetacean species in southern California waters. Schools scattered over areas as large as four square miles that numbered an estimated 1000 animals have been sighted in the channel between Santa Catalina Island and the mainland. Diffuse schools such …