TROPHIC RELATIONSHIPS OF ALBATROSSES ASSOCIATED WITH SQUID AND LARGE-MESH DRIFT-NET FISHERIES IN THE NORTH PACIFIC-OCEAN

The diets of Laysan (Diomedea immutabilis) and black-footed albatrosse s (D. nigripes) killed in squid and large-mesh drift nets in the trans itional zone of the North Pacific Ocean were investigated by examining the contents of the digestive tracts and determining delta(13)C and d elta(15)N values in breast-muscle tissue. The results show that (i) th e combined prey of the two species of albatross consists of over 46 sp ecies of marine organisms including coelenterates, arthropods, mollusk s, fish, and marine mammals; (ii) both species supplement their tradit ional diets with food made available by commercial fishing operations (e.g., net-caught squid and offal); (iii) while obtained from drift ne ts, diets of nonbreeding Laysan and black-footed albatrosses are domin ated by neon flying squid (Ommastrephes bartrami); (iv) in the absence of drift-net-related food, Laysan albatrosses feed most heavily on fi sh and black-footed albatrosses feed most heavily on squid; and (v) ba sed on delta(15)N values, nonbreeding adult Laysan albatrosses from th e transitional zone of the North Pacific Ocean and Laysan albatross ne stlings fed by adults from Midway Island in the subtropical Pacific fe ed at one trophic level and one-third of a trophic level lower than bl ack-footed albatrosses, respectively.