Tuna aggregation and feeding near fronts observed in satellite imagery

Stomach contents of albacore (Thunnus alalunga) and skipjack (Katsuwonus pelamis) caught off California in August 1983 showed they were feeding on juvenile northern anchovy (Engraulis mordax), other fishes, and planktonic crustaceans. The distribution and diet of these predators were related to mesoscale frontal features visible in satellite sea surface temperature and phytoplankton pigment imagery. Albacore were caught in the vicinity of a filament of cold, pigment-rich surface water that varied with the intensity of coastal upwelling on time scales of several days. Stomachs of albacore caught closer to the filament contained relatively more juvenile anchovy and fewer pelagic red crabs (Pleuroncodes planipes). Skipjack were caught in warm water in the Southern California Bight, north of their normal range due to El Nin˜o warming. They appeared to be feeding most successfully near the strong frontal boundary of a productive, cold water mass south of Pt. Conception, where dense patches of euphausiids were available. Both species were feeding near variable, mesoscale centers of high productivity where prey abundance may be enhanced.