© 2003 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
A large-mesh salmon trap: a way of mitigating seal impact on a coastal fishery
a National Board of Fisheries, Tjärnö Marine Biological Laboratory SE-452 96 Strömstad, Sweden
b National Board of Fisheries SE-178 93 Stockholm, Sweden
c National Board of Fisheries Box 423, SE-401 26 Gothenburg, Sweden
*Correspondence to S. G. Lunneryd; tel: +46 526 686 25; fax: +46 526 686 07. e-mail: sven-gunnar.lunneryd{at}fiskeriverket.se.
A new design for a salmon trap aimed at minimizing damage to catch and gear caused by grey seals was tested. The traditional trap design used in the northern Baltic permits an efficient hunting strategy by seals, whereby chased fish entangle themselves in the side panels and can then easily be taken, with associated damage to the net. The side panels of the test trap (excluding the fish chamber) are made of large-mesh (400 mm) netting compared to 
200 mm in traditional traps. This should allow seal-chased and panicking salmon to pass through, while less stressed individuals should still be guided efficiently towards the fish chamber. Trials with the two trap types were performed at the mouth of the river Indal (northern Sweden) in a comparative test programme. Catches of salmon and trout in the test trap were larger than in the standard trap. We estimated that 65% of the potential catch was lost in the standard trap owing to seal predation, while escape rate through the large meshes in the test trap was 52%. The standard trap had a total of 269 holes owing to seal damage, while only six holes were found in the test trap. Seal activity in and around the standard trap was up to 16 times higher compared with the test trap and decreased considerably during the following year when only large-meshed traps were used in the area. We suggest that seals are difficult to deter from fishing gear as long as they get a reward in terms of food and propose that a strategy that deprives seals of a reward will make the gear uninteresting to them and may have long-term mitigation effects.
Keywords: conflict, fishery, grey seal, mitigate, predation, salmon, trap
Received 8 July 2002; accepted 15 July 2003.
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