Temporal and regional patterns in seal-induced catch and gear damage in the coastal trap-net fishery in the northern Baltic Sea: effect of netting material on damage

Abstract

Seal-induced damage in the traditional trap-net fishery increased dramatically during the 1990s in the northern Baltic Sea. Most damage is induced by a rapidly growing grey seal (Halichoerus grypus) population. We evaluated seal damage in the coastal trap-net fishery of the Gulf of Bothnia, where different gear constructions and netting materials are used. A total of 72 commercial fishermen with 136 trap-nets were involved in the study. Catch and gear-damage observations made by fishermen were consistent with our own. The largest catch losses of salmon (Salmo salar) were recorded in the Bothnian Sea, where seals damaged at least 37% of salmon catch (by number). In other regions, losses were notably smaller, at between 3 and 9%. The number of salmon caught in a trap on any one occasion correlated significantly with the number of damaged salmon. However, the more salmon were present in a trap, the smaller was the proportion damaged by seals. Observed catch losses in the whitefish (Coregonus sp.) fishery varied between regions from 5 to 7%. Gear damage was observed in 2-15% of trap-net emptyings, depending largely on region. The extent of gear damage followed the trend of catch damage in each region. Fish entanglement in trap-nets increased the amount of gear damage. The type of netting material significantly affected gear-damage frequencies and salmon entanglement. Seal-induced catch and gear damage could be reduced by gear modification and operational changes. The choice of suitable netting materials and the development of seal-safe fish-bags are essential in protecting the gear and catch from seals. © 2005 Elsevier B.V. All rights reserved