MEPS 218:283-302 (2001)  -  doi:10.3354/meps218283

ABSTRACT: Macquarie Island is a small subantarctic island that supports a variety of breeding seabird and marine mammal populations. A fishery targeting the Patagonian toothfish Dissostichus elegenoides was established around the island in 1994. For ecological sustainable development (ESD) of the fishery, this study investigated the trophic interactions based on diet composition and annual consumption between Patagonian toothfish, its fishery, and seals and seabirds within the Macquarie Island Exclusive Economic Zone (MI-EEZ). Annual consumption rates for each predator were estimated from dietary data (mostly published sources), energetic budgets, prey energy content, and population size. Results indicated little predation on toothfish by seals or seabirds, 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, ≥90%), giant petrels (84%), royal and rockhopper penguins (65%), and king and royal penguins and fur seals (>60%). The total annual prey biomass consumed by seabirds, seals, toothfish and the fishery wit the MI-EEZ was estimated to be 419774 t, with the greatest consumption in January, at 2779 t d^-1. Pelagic fish (61%, mostly myctophids), followed by pelagic crustaceans (28%, mostly euphausids) and cephalopods (7%) were the major prey. Most prey biomass was consumed by penguins (88%), with comparatively small amounts by toothfish (8%), seals (3%) other seabirds (<1%) and the fishery (0.1%). These results indicate weak trophic linkages between the toothfish, its fishery, and seabirds and seals around Macquarie Island.

KEY WORDS: Patagonian toothfish · Seabirds · Seals · Dietary overlap · Trophic interactions · Prey consumption · Commercial fisheries · Macquarie Island