Fish Bulletin 152. Food Habits of Albacore, Bluefin Tuna, and Bonito In California Waters

The authors investigated food habits of albacore, Thunnus alalunga, bluefin tuna, Thunnus thynnus, and bonito, Sarda chiliensis, in the eastern North Pacific Ocean during 1968 and 1969. While most stomach samples came from fish caught commercially off southern California and Baja California, some came from fish taken in central California, Oregon, and Washington waters. Standard procedures included enumeration of food items, volumetric analysis, and measure of frequency of occurrence. The authors identified the majority of forage organisms to the specific level through usual taxonomic methods for whole animals. Identification of partially digested animals was accomplished through the use of otoliths for fish, beaks for cephalopods, and the exoskeleton for invertebrates. A pictorial guide to beaks of certain eastern Pacific cephalopods was prepared and proved helpful in identifying stomach contents. This guide is presented in this publication. The study indicates the prominent forage for bluefin tuna, bonito, and albacore in California waters is the northern anchovy, Engraulis mordax.