THE FISH DIET OF BLACK-BROWED ALBATROSS DIOMEDEA-MELANOPHRIS AND GREY-HEADED ALBATROSS DIOMEDEA-CHRYSOSTOMA AT SOUTH-GEORGIA

The fish component of the diet of black-browed and grey-headed albatro sses at South Georgia was investigated by intercepting 155 meals from adults arriving to feed chicks during February 1986 and 1994. Fish rep resented 30% and 72% by mass of the diet of black-browed albatrosses a nd 14% and 60% by mass of the diet of grey-headed albatrosses in 1986 and 1994 respectively. We determined the identity and quantified the c ontribution (by numbers, size and mass) of fish species mainly by usin g otoliths (54 representing 9 taxa and 57 representing 17 taxa in blac k-browed and grey-headed albatross samples respectively). For black-br owed albatrosses in 1986 the main fish prey was Patagonotothen gunther i (77% of otoliths, 51% of estimated fish biomass) and a single large specimen of Icichthys australis (40% estimated biomass), whereas in 19 94 Pseudochaenichthys georgianus was the main fish prey (57% of estima ted biomass) with Magnisudis prionosa (30%) and Champsocephalus gunnar i (12%) also making substantial contributions. Grey-headed albatross s amples from 1986 were dominated by southern lampreys (40% by number, 7 9% of estimated biomass), lanternfish (32% of numbers, 9% by mass) and Patagonotothen guntheri (11% by mass); in 1994 Champsocephalus gunnar i (42% by numbers, 24% by mass), Magnisudis prionosa (13% by number, 3 6% by mass), Muraenolepis microps (90% by number), Pseudochaemichthys georgianus (15% by mass) and lanternfish (18% by number but only 1% by mass) were the main prey. The importance of Patagonotothen guntheri t o both species in 1986 and its absence in 1994 probably reflect albatr osses obtaining it from the commercial fishery, which was active in 19 86 but closed in 1994. Otherwise the fish diet of black-browed albatro sses is dominated by krill-feeding fish, characteristic of the waters of the South Georgia shelf. In contrast, the grey-headed albatross die t comprises deeper water mesopelagic species, especially lanternfish, which reflect its affinity for the Antarctic Polar Frontal Zone and as sociated oceanic upwellings.