Bioeconomic modelling of grey seal predation impacts on the West of Scotland demersal fisheries

Vanessa Trijoulet,Steven J Holmes,Helen Dobby,Robin M Cook,Raúl Prellezo

doi:10.1093/icesjms/fsx235

Vanessa Trijoulet, Steven J Holmes + Show 3 more

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https://doi.org/10.1093/icesjms/fsx235

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Abstract

Abstract The role grey seals have played in the performance of fisheries is controversial and a cause of much debate between fishers and conservationists. Most studies focus on the effects of seal damage to gears or fish and on prey population abundance but little attention is given to the consequences of the latter for the fisheries. We develop a model that quantifies the economic impact of grey seal predation on the West of Scotland demersal fisheries that traditionally targeted cod, haddock and whiting. Three contrasting fishing strategy scenarios are examined to assess impacts on equilibrium fleet revenues under different levels of seal predation. These include status quo fishing mortality (SQF, steady state with constant fishing mortality), open access fishing (bioeconomic equilibrium, BE) and the maximum economic yield (MEY). In all scenarios, cod emerges as the key stock. Large whitefish trawlers are most sensitive to seal predation due to their higher cod revenues but seal impacts are minor at the aggregate fishery level. Scenarios that consider dynamic fleet behaviour also show the greatest effects of seal predation. Results are sensitive to the choice of seal foraging model where a type II functional response increases sensitivity to seal predation. The cost to the fishery for each seal is estimated.

Highlights

There has long been controversy concerning the potential impact seals have on commercial fisheries (Lambert, 2001; Lavigne, 2003; Read, 2008), especially those where traditionally cod (Gadus morhua) formed a large portion of catches or revenues
A number of studies have evaluated the predation mortality rate of seal populations on cod both off the Canadian coast (Mohn and Bowen, 1996; Trzcinski et al, 2006; O’Boyle and Sinclair, 2012) and in European waters (Alexander et al, 2015; Cook et al, 2015). These studies primarily consider the dynamics of the resource and the role seal predation may have played in the decline of cod stocks or their failure to recover
The estimated equilibrium haddock spawning stock biomass (SSB) is little changed in all three scenarios even for large changes in seal population

Summary

Introduction

There has long been controversy concerning the potential impact seals have on commercial fisheries (Lambert, 2001; Lavigne, 2003; Read, 2008), especially those where traditionally cod (Gadus morhua) formed a large portion of catches or revenues. A number of studies have evaluated the predation mortality rate of seal populations on cod both off the Canadian coast (Mohn and Bowen, 1996; Trzcinski et al, 2006; O’Boyle and Sinclair, 2012) and in European waters (Alexander et al, 2015; Cook et al, 2015). These studies primarily consider the dynamics of the resource and the role seal predation may have played in the decline of cod stocks or their failure to recover. Regardless of any role seal predation has had on the decline in fish stocks, there is a widely held perception that seals represent direct competition with commercial fisheries and are

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