Friday, November 27, 2009

Deep-water fisheries are relatively new but they have had a significant impact, with commercial species harvested ‘outside safe biological limits’ and some species regarded as critically endangered. The long term future of these fisheries, and the communities that depend on them for economic and social stability, looks bleak.

An ‘ecosystem approach’ to fisheries management has been called for globally, but how do you do it? Modelling predator-prey-environmental-fisheries interactions is one way. By constructing a foodweb model, with fisheries as top predator one can identify the impacts of changes in fishing effort or catch on other species.

One technique used for modelling multiple species fisheries (Ecopath with Ecosim) has been employed on the oldest deepwater fishery in the world: the Rockall Trough, which is one of the most well studied deep-sea regions in the world with datasets starting prior to the fishery.

Best estimates of the changes that took place over the past 40 years in this foodweb show a declining trend in most species since the onset of fishing but newly lowered TACs should lead to recovery of some species, while others will need further intervention.

Mixed impacts in fisheries have caused many an unexpected result from brute force management, which we modelled here: The hypothetical removal of the blue whiting fishery from 2007 to 2020 will increase blue whiting in the model, impacting species that compete with them for food (roundnose grenadier), and benefiting those species that prey on blue whiting (blue ling).

This project has demonstrated that a more holistic approach can reveal more about the complex fisheries interactions that would not be apparent through more traditional approaches to fisheries management. Ecosystem modelling, while not the single answer to deep-water fisheries management, certainly needs to be included in the tool kit available to fisheries managers.

See report here.

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