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    Ecosystem modelling for the Antarctic krill fishery

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    T. Antezana, J. Cornejo, E. Bredesen, P. Faundez (Chile), A.W. Trites and T. Pitcher (Canada)
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    Euphausia superba Dana (Antarctic Krill) has been recognized as a key forage species in the Antarctic ecosystem. This species serves as prey for many organisms in the ecosystem and has also been the target of an small industrial fishery since the mid 1970s. New quotas have recently been set but there is concern that the reduction in krill biomass due tome fishery may have impacts on other krill predators such as penguins, seals and whales.
    In order to evaluate the effects of krill fishing on the trophic web, it is necessary to have better knowledge of the ecosystem structure and dynamics. This can be achieved by studying community interactions, such as those between predators and preys, as well as competitors for a common resource. In this context we aim to investigate whether the krill fishery and the top predators are competing for krill biomass. This is a cooperative pilot project led by University of Concepcion, Chile with the Fisheries Centre at University of British Columbia, Canada.
    In a pilot study Ecopath with Ecosim 4.0 is being used to develop two mass-balance models of the Antarctic ecosystem, one for CCAMLR area 48.1 and another for areas 48.2 and 48.3 combined. Organisms in the system were combined into groups (of one or more species) on the basis of their feeding behavior, growth rate and their present or potential fishing importance, in order to simulate the trophic interactions of the system. Both models are being constructed with the same structure to allow comparisons between the two. Although this modeling tool has some limitations and several assumptions, the construction of these models is a step towards investigating and identifying major gaps in knowledge and potential impacts of krill fishing upon the ecosystem.