Herring supports Northeast Pacific predators and fisheries: Insights from ecosystem modelling and management strategy evaluation

Mimi E Lam,Andrea Belgrano,Rajeev Kumar,Evgeny A Pakhomov,Tony J Pitcher,Divya Varkey,Szymon Surma

doi:10.1371/journal.pone.0196307

Abstract

This paper analyzes the trophic role of Pacific herring, the potential consequences of its depletion, and the impacts of alternative herring fishing strategies on a Northeast Pacific food web in relation to precautionary, ecosystem-based management. We used an Ecopath with Ecosim ecosystem model parameterized for northern British Columbia (Canada), employing Ecosim to simulate ecosystem effects of herring stock collapse. The ecological impacts of various herring fishing strategies were investigated with a Management Strategy Evaluation algorithm within Ecosim, accounting for variability in climatic drivers and stock assessment errors. Ecosim results suggest that herring stock collapse would have cascading impacts on much of the pelagic food web. Management Strategy Evaluation results indicate that herring and their predators suffer moderate impacts from the existing British Columbia harvest control rule, although more precautionary management strategies could substantially reduce these impacts. The non-capture spawn-on-kelp fishery, traditionally practiced by many British Columbia and Alaska indigenous peoples, apparently has extremely limited ecological impacts. Our simulations also suggest that adopting a maximum sustainable yield management strategy in Northeast Pacific herring fisheries could generate strong, cascading food web effects. Furthermore, climate shifts, especially when combined with herring stock assessment errors, could strongly reduce the biomasses and resilience of herring and its predators. By clarifying the trophic role of Pacific herring, this study aims to facilitate precautionary fisheries management via evaluation of alternative fishing strategies, and thereby to inform policy tradeoffs among multiple ecological and socioeconomic factors.

Highlights

Forage fish constitute an important energy conduit from zooplankton to higher predators [1,2,3,4]
Explicit incorporation of fisheries into food webs makes ecosystem modelling in a framework such as Ecopath with Ecosim (EwE) a useful tool for examining ecosystem impacts of management strategies [2, 44], as well as potential precautionary reference points and ecosystem-based fisheries management (EBFM) approaches [2, 18, 45]
Ecosim and EwE management strategy evaluation (MSE) results show that Pacific herring is an important prey item for various Northeast Pacific predators, marine mammals, and that its depletion could have notable cascading effects on predator populations and food web structure

Summary

Introduction

Forage fish constitute an important energy conduit from zooplankton to higher predators [1,2,3,4]. Exploiting forage fish may reduce the ecosystem services they provide to charismatic and fished predators. The importance of forage fish to predators and fisheries is noticeable in temperate and upwelling ecosystems [1,2,3,4,5]. The occurrence and magnitude of yield tradeoffs between predator and forage fish fisheries vary greatly across ecosystems due to predator trophic ontogeny (juveniles of predatory fish species are largely planktivorous), as well as food web redundancy and complexity [6,7,8,9]. There are indications that many forage fish exert bottom-up control over their predators [1, 2, 5]. Several fish and seal species in the North Sea [5] and humpback whales (Megaptera novaeangliae) in the Northeast Pacific [11, 12] may exert moderate top-down control over forage fish, as has recently been predicted in a theoretical model [6]

Objectives

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Results

Discussion

Conclusion