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    Modelling the impact of krill fishing on seal and penguin colonies

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    É.E. Plagányi and D.S. Butterworth (South Africa)
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    A key area of concern highlighted by the Scientific Committee of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) concerns the potential overlap of the krill fishery with the foraging area of land-based predators such as seals and penguins in the Antarctic Peninsula region. The dynamics of krill in this region are strongly influenced by advective processes. A key question is therefore whether or not limitations on fishing activities (reducing their economic efficiency) are necessary given that there is a flux of krill through this region with its islands habited by predator colonies. In order to estimate the krill production actually available for predator consumption, it is necessary not only to consider “snapshot” survey estimates of krill abundance in the vicinity of a breeding colony but also the flux of krill through such areas. This paper outlines a proposed spatial modelling framework that could be used to couple flux estimates with estimates of removals by both the fishery and predators, in an attempt to quantify what level and localisation of the fishing effort might impact the predators negatively. The approach described represents work still in progress as the focus thus far has been on first developing a model of the possible impact of pelagic fishing on seal and penguin colonies on the South African west coast. The latter ecosystem shares a number of common features with the Antarctic Peninsula ecosystem in that there is a substantial advective flux of either pelagic fish or of krill, with both species serving as dominant prey items for colonies of land-based predators in the region concerned. Subject to the availability of data from both predator studies and krill surveys, the West Coast model methodology could thus straightforwardly (initially at least) be adapted to the Antarctic Peninsula region. This would permit the evaluation of a wide range of management options pertaining to the issue of taking into account the needs of other species when setting precautionary krill catch limits at an appropriate spatial scale.