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11-08-2010, 02:52 PM #1
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Managing the exploitation of migratory salmonids
By E. C. E. Potter, J. C. MacLean, R. J. Wyatt, R. N. B. Campbell
Fisheries Research, Volume 62, Issue 2, The Scientific Basis for Management of Salmonid stocks in the British Isles, May 2003, Pages 127-142, ISSN 0165-7836, DOI: 10.1016/S0165-7836(02)00159-5.
The control of exploitation in fisheries for Atlantic salmon (Salmo salar L.) and trout (S. trutta L.) has both biological and socio-economic objectives, the former relating to the protection of the productive capacity and diversity of the resource and the latter to issues such as the allocation of any harvestable surplus to different user groups. In fulfilling the biological aims, managers can restrict catches or fishing effort to ensure that sufficient fish from each population are permitted to spawn; they may also consider options for increasing the production of the stock, such as habitat improvement or stocking. Biological reference points (e.g. limits and targets) are increasingly being used to provide an objective measure of the status of stocks and determine the possible need for management actions, although a range of other stock indicators may be required to fully protect the diversity of our stocks. This is consistent with the application of a precautionary approach to salmon fishery management as adopted by the North Atlantic Salmon Conservation Organisation (NASCO). NASCO has agreed that a limit reference point (or conservation limit) for Atlantic salmon should be set at the spawning stock size that will give maximum sustainable yield (SMSY). Fisheries should therefore be managed to ensure that there is a high probability that these limits are exceeded, and actual escapement should usually be higher than these thresholds. NASCO has proposed that stocks should be maintained above their conservation limits by setting higher, and thus more precautionary, management targets, although alternative approaches are possible. ICES and NASCO have favoured a fixed escapement strategy for the management of salmon fisheries, although in practice, this strategy is being implemented in a variety of ways. In many fisheries, approaches more akin to `floor policies' or `proportional threshold harvesting' are being employed although the merits of different strategies for the management of commercial and recreational salmon fisheries have yet to be fully explored. Scientists still have some way to go in fully incorporating uncertainty into their management advice, but the objective must be to utilise the best information available to them, regardless of its imperfections, in developing management options and to account explicitly in their advice for the various sources of uncertainty both in the current state of scientific knowledge and in our ability to control fisheries. These management approaches have mainly been developed for the management of Atlantic salmon, but there would clearly be merits in developing similar approaches to protect production of both migratory and non-migratory trout stocks.
Keywords: Salmo salar; Salmo trutta; Exploitation; Management; Stock-recruitment; Harvest strategies; Biological reference points