Mitigation of seal-induced damage in salmon and whitefish trapnet fisheries by modification of the fish bag

• Published in: ICES Journal of Marine Science
• Main Authors: Lehtonen, Esa, Suuronen, Petri
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2004
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Oceanography; Salmo salar
• Online Access: http://dx.doi.org/10.1016/j.icesjms.2004.06.012; http://academic.oup.com/icesjms/article-pdf/61/7/1195/29122511/61-7-1195.pdf

Abstract During the past decade, seal-induced gear and catch damage has increased dramatically in the Baltic Sea. The problems are most severe in the coastal trapnet fisheries for salmon (Salmo salar) and whitefish (Coregonus lavaretus), where grey seals (Halichoerus grypus) in particular frequently visit the traps. There is an acute need for gear modifications and other solutions that can prevent seals from entering the fish bag of the traps. Modifications that have been tested in Finland include a wire grid installed in the funnel of the trap and a fish bag made of extra-strong netting material. In comparative fishing experiments conducted in 2001 in the Gulf of Finland the grid was made of 2-mm steel wires with 175-mm spacing. The average undamaged salmon catch per haul in the fish bag of modified trapnets was significantly higher (70%) than that of traditional traps (Mann–Whitney, p < 0.01). In the whitefish experiments, the average undamaged catch of whitefish per haul was 16% higher in modified trapnets than in traditional traps, but the difference was not significant (Mann–Whitney, p > 0.05). These results indicate that the wire grid did not prevent fish from swimming into the fish bag. Experiments also suggest that the wire grid and the extra-strong netting prevented seals from entering the bag. However, on some occasions seals were able to tear the fish through the netting. Underwater observations confirmed that the wire grid kept adult seals outside the bag while salmon and whitefish could be seen entering through the grid into the bag.