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CSIRO Marine and Atmospheric Research
Past Seminars

Seminar Abstract

Feeding ecology of neritic pelagic fishes in northern Australia: predation of commercially important species in the Northern Prawn Fishery

Ecosystem-based management is becoming an increasingly popular management tool for Australian fisheries, such as the Northern Prawn Fishery (NPF), to demonstrate ecologically sustainability.

Some ecosystem models used to quantify fishing impacts on an ecosystem (e.g. ECOPATH/ECOSIM) require a good understanding of species composition in the ecosystem and their trophic relationships. This knowledge is lacking for complex ecosystems of northern Australia, prompting a quantitative pilot study of the diets of pelagic fishes, ranging from large tunas to small scads.

We found marked differences in the diet breadth (Ba = 0.003-0.063) and diet overlap (Ro = 0-0.895) among the ten species analysed. Species with overlapping diets (tunas and bonitos) appear to partition resources by prey size. Most species mainly consumed small pelagic fishes (Engraulids and Clupeids) and small pelagic crustaceans (Brachyuran megalopa), but also demersal prey items suggesting some degree of benthic-pelagic coupling. Notably, commercially important penaeids such as Penaeus merguiensis and cephalopods (eg. Photololigo spp) comprised a reasonable percentage of the diets of cobia (19% and 18%), longtail tuna (6% and 3%), and golden trevally (8%).

By estimating the biomass of longtail tuna from aerial surveys in the NPF during 1982-1984 (1.9 kg per km2), we estimate that up to 1000 tonnes yr-1 of commercially important penaeids may be consumed by longtail tuna alone on the NPF trawl grounds; 13% of the average annual commercial catch. This study has shown that pelagic fish may have a substantial impact on demersal assemblages, including commercially important species in the NPF, and such impacts need to be considered in ecosystem models.

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CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Peter Oke, (Oceanographic seminars) CSIRO Marine Research (03) 6232 5387
Keith Hayes, (Biological seminars) CSIRO Marine Research (03) 6232 5298
Katrina Nitschke, Antarctic Climate and Ecosystems CRC (03) 6226 2265 & IASOS, University of Tasmania (03) 6226 2509