FEEDING-HABITS OF YELLOWFIN TUNA ASSOCIATED WITH FISH AGGREGATION DEVICES IN AMERICAN-SAMOA

In American Samoa, Fish Aggregation Devices (FADs) provide target fishing locations with high catch rates, but little is known about their ecological impact. The effect on the diet of yellowfin tuna associating with FADs has been examined in the Philippines, French Polynesia and Hawaii, but results differ among the regions. Diel patterns of movement around FADs appear to be consistent among regions. The stomach contents of yellowfin tuna were compared from FADs, offshore banks, areas away from these features and from before FADs were deployed in American Samoa. Differences were minimal among these four groups of yellowfin tuna in the frequency of occurrence of important prey in their diets. Diurnal patterns in the stomach fullness and the frequency of occurrence of some prey in the diet indicate that these yellowfin tuna are not feeding at night and that they may prey on vertically migrating mesopelagic organisms during crepuscular periods. FAD- and bank-associated yellowfin tuna probably follow the diel movement patterns observed in other areas. The regional differences in the apparent effect of FAD association on the diet of yellowfin tuna are discussed and possible explanations are given.