The necessity of a holistic approach when managing marine mammal\u2013fisheries interactions: Environment and fisheries impact are stronger than seal predation

David Costalago,Maciej T Tomczak,Monika Winder,Barbara Bauer,Karl Lundström

doi:10.1007/s13280-018-1131-y

Abstract

Seal populations are recovering in many regions around the world and, consequently, they are increasingly interacting with fisheries. We used an Ecopath with Ecosim model for the offshore Central Baltic Sea to investigate the interactions between the changes in fish stocks and grey seal (Halichoerus grypus) population under different fishing and environmental scenarios for the twenty-first century. The assumed climate, eutrophication and cod (Gadus morhua) fisheries scenarios modified seal predation impacts on fish. Fish biomass and catches are more affected by fishing mortality and the environment than by seal predation. Our results highlight that the impacts of the increasing seal population on lower trophic levels are complex; thus, we emphasize the need to consider a range of possible ecosystem contexts when evaluating potential impacts of top predators. Finally, we suggest that an increasing seal population is not likely to hinder the preservation of the main Baltic fish stocks.

Highlights

During the second half of the twentieth century, conservation efforts led to the improvement of the status of numerous marine mammal populations worldwide (Lotze et al 2011; Magera et al 2013; Chasco et al 2017)
Our results showed that predation mortality of Baltic fish by grey seals was higher in the Env0 scenario, in which cod, sprat and herring abundances had their lowest values
This work shows that the impacts of the increasing Baltic grey seal population on fish stocks are complex

Summary

Introduction

During the second half of the twentieth century, conservation efforts led to the improvement of the status of numerous marine mammal populations worldwide (Lotze et al 2011; Magera et al 2013; Chasco et al 2017). Many studies quantify the losses to fishery without taking into account that (1) not every fish is caught, even if predators are lacking (Yodzis 2001; Heikinheimo et al 2016), and (2) there might be several confounding factors shaping the seals’ potential for predation (e.g. climate change, competitors and diseases (O’Boyle and Sinclair 2012; Morissette and Brodie 2014). It is necessary to develop tools that allow us to understand and to predict the effects of a changing environment on marine mammals and the interactions between their populations and fish stocks. This understanding can inform the debate on the conservation and management of marine mammals and fisheries and alleviate conflicts

Methods

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Discussion

Conclusion