Assessing fishery and ecological consequences of alternate management options for multispecies fisheries

Robert Brian Thorpe,Stuart Reeves,Simon Jennings,Paul James Dolder,Peter Robinson

doi:10.1093/icesjms/fsw028

Abstract

AbstractDemands for management advice on mixed and multispecies fisheries pose many challenges, further complicated by corresponding requests for advice on the environmental impacts of alternate management options. Here, we develop, and apply to North Sea fisheries, a method for collectively assessing the effects of, and interplay between, technical interactions, multispecies interactions, and the environmental effects of fishing. Ecological interactions involving 21 species are characterized with an ensemble of 188 plausible parameterizations of size-based multispecies models, and four fleets (beam trawl, otter trawl, industrial, and pelagic) characterized with catch composition data. We use the method to evaluate biomass and economic yields, alongside the risk of stock depletion and changes in the value of community indicators, for 10 000 alternate fishing scenarios (combinations of rates of fishing mortality F and fleet configuration) and present the risk vs. reward trade-offs. Technical and multispecies interactions linked to the beam and otter trawl fleets were predicted to have the strongest effects on fisheries yield and value, risk of stock collapse and fish community indicators. Increasing beam trawl effort led to greater increases in beam trawl yield when otter trawl effort was low. If otter trawl effort was high, increases in beam trawl effort led to reduced overall yield. Given the high value of demersal species, permutations of fleet effort leading to high total yield (generated primarily by pelagic species) were not the same as permutations leading to high catch values. A transition from F for 1990 to 2010 to FMSY, but without changes in fleet configuration, reduced risk of stock collapse without affecting long-term weight or value of yield. Our approach directly addresses the need for assessment methods that treat mixed and multispecies issues collectively, address uncertainty, and take account of trade-offs between weight and value of yield, state of stocks and state of the environment.

Highlights

Mixed-fisheries catch different species and stocks with the same gears at the same time
Technical interactions are an important issue for managers of the international demersal fisheries of the North Sea, because multiple stocks are exploited in mixed-fisheries
For the beam and otter trawl fleets, increasing beam trawl effort is predicted to result in greater increases in beam trawl yield when otter trawl effort is low

Summary

Introduction

Mixed-fisheries catch different species and stocks with the same gears at the same time. The need for management to address the poor conservation status of North Sea cod while still allowing fishing on other, less depleted stocks caught in the same fisheries, has stimulated several analyses of the consequences of technical interactions (Vinther et al, 2004; Reeves et al, 2009; Ulrich et al, 2011) Such analyses have sought to identify trade-offs and their consequence and to define alternate options for balancing conflicting objects

Methods

Results

Conclusion