The fish diet of black-browed albatross Diomedea melanophris and grey-headed albatrossD. Chrysostoma at South Georgia
The fish component of the diet of black browed and grey-headed albatrosses at South Georgia was investigated by intercepting 155 meals from adults arriving to feed chicks during February 1986 and 1994. Fish represented 30% and 72% by mass of the diet of black-browed albatrosses and 14% and 60% by mass of the diet of grey-headed albatrosses in 1986 and 1994 respectively. We determined the identity and quantified the contribution (by numbers, size and mass) of fish species mainly by using otoliths (54 representing 9 taxa and 57 representing 17 taxa in black-browed and greyheaded albatross samples respectively). For blackbrowed albatrosses in 1986 the main fish prey wasPatagonotothen guntheri (77% of otoliths, 51% of estimated fish biomass) and a single large specimen ofIcichthys australis (40% estimated biomass), whereas in 1994 Pseudochaenichthys georgianus was the main fish prey (57% of estimated biomass) withMagnisudis prionosa (30%) andChampsocephalus gunnari (12%) also making substantial contributions. Grey-headed albatross samples from 1986 were dominated by southern lampreys (40% by number, 79% of estimated bio mass), lanternfish (32% of numbers, 9% by mass) andPatagonotothen guntheri (11% by mass); in 1994Champsocephalus gunnari (42% by numbers, 24% by mass),Magnisudis prionosa (13% by number, 36% by mass),Muraenolepis microps (90% by number),Pseudochaenichthys georgianus (15% by mass) and lanternfish (18% by number but only 1% by mass) were the main prey. The importance ofPatagonotothen guntheri to both species in 1986 and its absence in 1994 probably reflect albatrosses obtaining it from the commercial fishery, which was active in 1986 but closed in 1994. Otherwise the fish diet of black-browed albatrosses is dominated by krill-feeding fish, characteristic of the waters of the South Georgia shelf. In contrast, the grey-headed albatross diet comprises deeper water mesopelagic species, especially lanternfish, which reflect its affinity for the Antarctic Polar Frontal Zone and associated oceanic upwellings.