Signatures of the collapse and incipient recovery of an overexploited marine ecosystem.

Eric J Pedersen,Charlotte Moritz,Hedvig Nenzen,Ryan R E Stanley,Marie-Josée Fortin,Tarik C Gouhier,R Aaron Ball,Andrew Gonzalez,Zofia E Taranu,Heike Link,Pierre Pepin,Patrick L Thompson,Frédéric Guichard

doi:10.1098/rsos.170215

Abstract

The Northwest Atlantic cod stocks collapsed in the early 1990s and have yet to recover, despite the subsequent establishment of a continuing fishing moratorium. Efforts to understand the collapse and lack of recovery have so far focused mainly on the dynamics of commercially harvested species. Here, we use data from a 33-year scientific trawl survey to determine to which degree the signatures of the collapse and recovery of the cod are apparent in the spatial and temporal dynamics of the broader groundfish community. Over this 33-year period, the groundfish community experienced four phases of change: (i) a period of rapid, synchronous biomass collapse in most species, (ii) followed by a regime shift in community composition with a concomitant loss of functional diversity, (iii) followed in turn by periods of slow compositional recovery, and (iv) slow biomass growth. Our results demonstrate how a community-wide perspective can reveal new aspects of the dynamics of collapse and recovery unavailable from the analysis of individual species or a combination of a small number of species. Overall, we found evidence that such community-level signals should be useful for designing more effective management strategies to ensure the persistence of exploited marine ecosystems.

Highlights

Overexploitation has led to the collapse of many of the world’s fisheries [1]
Ecologists and managers responsible for keeping track of marine fish populations have historically focused on the population dynamics of one or a few commercially important species, paying little attention to the dynamics of connected predator, competitor and prey species [6]
The collapse caused a compositional reorganization of the community, and a loss of its spatial structure and functional diversity

Summary

Introduction

Overexploitation has led to the collapse of many of the world’s fisheries [1]. many fisheries have successfully recovered following reductions in fishing pressure [2], recovery rates are often slow and unpredictable [3,4]. Sustainable fisheries management requires a better understanding of the health of marine ecosystems, and indicators that can allow us to detect when changes are occurring. Ecologists and managers responsible for keeping track of marine fish populations have historically focused on the population dynamics of one or a few commercially important species, paying little attention to the dynamics of connected predator, competitor and prey species [6]. These approaches have provided deep insights into the dynamics of commercially important species [7] and, when applied effectively, have led to successful stock recoveries. Single-species management has not always been effective at predicting recovery rates [4], and has failed to restore stock biomass in some major fisheries [8,9]

Methods

Results

Conclusion