A large-mesh salmon trap: a way of mitigating seal impact on a coastal fishery

Published source details Lunneryd S.G., Fjälling A & Westerberg H. (2003) A large-mesh salmon trap: a way of mitigating seal impact on a coastal fishery. ICES Journal of Marine Science, 60, 1194-1199.
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This study is summarised as evidence for the following.

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	Use a larger mesh size for fishing trap-nets Action Link

Use a larger mesh size for fishing trap-nets

A controlled study in 2000–2001 at the mouth of the River Indal, northern Sweden (Lunneryd et al. 2003) found that a fishing trap-net with a larger mesh size in the first two sections had fewer grey seals Halichoerus grypus feeding around it and less damage by seals than a conventional trap-net. Fewer seals were observed surfacing (average 0.2 seals/h) and feeding on fish (0 seals) around the modified trap-net than a conventional trap-net (surfacing: average 1.6–4.1 seals/h, feeding: 0.1–0.3 seals/h). The modified trap-net had fewer holes caused by seals (total 6) than the conventional trap-net (total 269), although statistical significance was not assessed. Catches of target salmon Salmo salar and trout Salmo trutta were higher in the modified trap-net during one trial, and similar in modified and conventional trap-nets during two trials (see original paper for data). A modified and conventional trap-net were alternated between two fishing sites on opposite sides of a river mouth during three trials (each lasting 15–25 days). Both had a 100-m leader net with 3–4 funnel-shaped sections leading to a ‘seal-safe’ fish chamber. The first two sections had mesh sizes of 400 mm (modified trap-net) or 200 mm (conventional trap-net). Target fish catches and holes were recorded every other day during each of the three trials in June–August 2000. Seals were observed daily from the shore and with a video camera above each trap-net during two of the three trials in July–August 2001.

(Summarised by: Anna Berthinussen)