Cod pots in a Baltic fishery: are they efficient and what affects their efficiency?

Sara J Königson,Ulf M Bergström,Sven-Gunnar Lunneryd,Patrick Strömberg,Ronny E Fredriksson

doi:10.1093/icesjms/fsu230

Abstract

Abstract With the growing grey seal population in the Baltic Sea, the inshore cod fishery has suffered dramatic increases in both catch losses and damage to fishing gear. To mitigate this situation, cod pots were evaluated as an alternative to traditional gillnets and longlines. During a 3-year study, cod pots were used by commercial fishers in two areas off the coast of Sweden. Using the data from this study, we evaluated catches from pots in relation to other gear types and investigated the effects of environmental and fisheries-related variables such as depth and soak time. The comparison of pots with other gear types showed that, during the first half of the year, the pot fishery generated lower daily catches than the gillnet and longline fisheries at comparable fishing efforts. During the second half of the year, catches in the pot fishery exceeded or were equal to those in the traditional fisheries. Using generalized additive models to evaluate the impact of environmental and fisheries-related variables on pot catches, we showed that, in both areas, the catch per unit effort (cpue) of legal-sized cod was affected by the water depth, the time of year (months), and the soak time. In one of the areas, cpue was also affected by the direction of the water current in relation to the orientation of the string of pots. The cpue of undersized cod was affected by topographic variables such as the slope and the complexity of the bottom, in addition to the water depth, month of the year, and soak time. The results from the study indicate that pots can be a useful alternative gear in the Baltic cod fishery, at least during part of the year. By using our information on how catches are affected by environmental and fisheries-related variables, the pot fishery may be further optimized to increase catches.

Highlights

Seal-inflicted damage to fishing gear and catch losses have increased rapidly along the coast of the Baltic Sea, and many small-scale coastal fisheries have been severely affected (Westerberg et al, 2006; Bruckmeier and Hoj Larsen, 2008; Hemmingsson et al, 2008)
The gillnet and longline fisheries for Atlantic cod (Gadus morhua) have experienced extensive surges in damage caused by grey seals (Halichoerus grypus) since around the year 2000 (Konigson et al, 2009)
Cod pots are preferable to traditional methods in areas prone to seal predation, as they enclose the caught fish in a compartment which can be made seal-safe, meaning that it is much harder for the seals to get at the fish than when they are caught in a gillnet or hooked on a line (Konigson, 2011; Ovegard et al, 2011)

Summary

Introduction

Seal-inflicted damage to fishing gear and catch losses have increased rapidly along the coast of the Baltic Sea, and many small-scale coastal fisheries have been severely affected (Westerberg et al, 2006; Bruckmeier and Hoj Larsen, 2008; Hemmingsson et al, 2008). The gillnet and longline fisheries for Atlantic cod (Gadus morhua) have experienced extensive surges in damage caused by grey seals (Halichoerus grypus) since around the year 2000 (Konigson et al, 2009). This has led to the development of seal-safe alternative fishing gear, such as baited cod pots. The environmental impact of traps and pots is considered less severe than that of trawls and other active fishing gear (Jennings et al, 2001; Thomsen et al, 2010). Pots are classified as LIFE (low impact and fuel efficient) fishing gear due to their low

Methods

Results

Conclusion