ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Are Seals Bad for Fisheries and Fisheries Bad for Seals? Trophic Interactions between Pinnipeds and Commercial Fisheries in Australia

Simon Goldsworthy, Cathy Bulman, Xi He, James Larcombe and Charles Littnan

La Trobe University, BUNDOORA, AUSTRALIA

THEME: ASFB

The extent of ecological or trophic interactions between marine mammals and fisheries is becoming an increasingly important conservation and fisheries management issue. In Australia there are economic concerns that increasing pinniped populations (and consumption) will reduce fisheries production, and conservation concerns that increased fishing effort will impact on the recovery and status of pinniped species. This study represents the first effort to synthesize information on these trophic interactions in Australia, and provides a framework by which the nature and extent of trophic interactions between marine mammals and fisheries can be more objectively assessed. Here we develop population, biomass and prey consumption models for the three Australian pinniped populations, in conjunction with fisheries catch data and foraging models to identify regions where the spatial distribution of consumption overlap by pinnipeds and fisheries are greatest. We then use ecological modelling (ECOPATH and ECOSIM), to simulate the outcomes of different scenarios of seal and fisheries consumption. The estimated total annual consumption by pinnipeds in southern Australia is 475,000t/year, more than double Australia’s total annual fisheries production. The greatest pinniped consumption effort occurred in Bass Strait in south-eastern Australia, where estimated consumption exceeded 2t/km2/year. The greatest spatial overlap in consumption by pinnipeds and fisheries was in eastern Bass Strait. Ecological models were developed using pinniped diet and food web data on over 100 fish species, and fishery catch data for the region. Simulations were run over a 30 year period to investigate the impacts of increased fishing effort on seal biomass, and increasing seal populations on the biomass of 8 commercially fished species. Simulations produced some unexpected outcomes. Seal biomass was found to be relatively insensitive to changes in fishing effort, while increasing seal populations produced positive changes in five commercial species, neutral in one species, and negative changes in the biomass in two other species.