RELATIONSHIPS OF THE BLUE SHARK, PRZONACE GLAUCA, AND ITS PREY SPECIES NEAR SANTA CATALINA ISLAND, CALIFORNIA'

Small fishes and cephalopds associated with both pelagic and inshore habitats composed the major prey for the blue shark, Prionace glauca, near Santa Catalina Island, Calif. The northern anchovy, Engraulis mordm, was the predominant prey for sharks in the immediate study area while at least 13 species of pelagic cephalopdsconstituted major prey for sharks in more distant oceanic waters. Inshore species taken by sharks included pipefish, Syngnathus californiensis; jack mackerel, Trachurus symmetricus; and blacksmith, Chromispunctipinnis. In addition, sharks moved inshore to feed on winter spawning schools of market squid, Loligo opalescens. Digestive rate studies and telemetric monitoring of activity patterns indicate that sharks forage in waters near the surface from around midnight through dawn. Die1 activities of prey species were examined and show that most prey dispersed in the upper water column at night and refuged during the day either by schooling (anchovies and jack mackerel) or by retreating to deeper waters (pelagic cephalopods). Field observations of shark feeding behavior indicate that predatory modes vary in response to prey behavior. The blue shark,Prionace glauca (Carcharhinidae) (Figure 11, is a pelagic carnivore cosmopolitan in tropical and warm temperate seas. Because of its pelagic habits, the majority of ecological studies on this species have been predicated on data from sharks captured by sport and commercial fisheries. As a result data has been largely qualitative, and the shark's role as a predator in the epipelagic habitat has remained unclear.