Trophic interactions between the Patagonian toothfish, its fishery, and seals and seabirds around Macquarie Island

Macquarie Island is a small subantarctic island that supports a variety of breeding seabird and marine mammal populations, A fishery targeting the Pat agonian toothfish Dissostichus elegenoides was established around the islan d in 1994. For ecological sustainable development (ESD) of the fishery, thi s study investigated the trophic interactions based on diet composition and annual consumption between Patagonian tooth-fish, its fishery, and seals a nd seabirds within the Macquarie Island Exclusive Economic Zone (MI-EEZ). A nnual consumption rates for each predator were estimated from dietary data (mostly published sources), energetic budgets, prey energy content, and pop ulation size. Results indicated little predation on toothfish by seals or s eabirds, or prey competition between toothfish and other marine predators. The greatest dietary overlap with toothfish was with gentoo penguins (21 % dietary overlap) and southern elephant seals (19 %). These overlaps in diet were small relative to those among fur seals (3 species, greater than or e qual to 90 %), giant petrels (84 %), royal and rockhopper penguins (65 %), and king and royal penguins and fur seals (> 60 %). The total annual prey b iomass consumed by seabirds, seals, toothfish and the fishery within the MI -EEZ was estimated to be 419 774 t, with the greatest consumption in Januar y, at 2779 t d(-1). Pelagic fish (61 %, mostly myctophids), followed by pel agic crustaceans (28 %, mostly euphausids) and cephalopods (7 %) were the m ajor prey, Most prey biomass was consumed by penguins (88 %), with comparat ively small amounts by toothfish (8 %), seals (3 %) other seabirds (<1 %) a nd the fishery (0.1 %). These results indicate weak trophic linkages betwee n the toothfish, its fishery, and seabirds and seals around Macquarie Islan d.