Cascading ecological effects of eliminating fishery discards.

Michael R Heath,Robin M Cook,Angus I Cameron,David J Morris,Douglas C Speirs

doi:10.1038/ncomms4893

Abstract

Discarding by fisheries is perceived as contrary to responsible harvesting. Legislation seeking to end the practice is being introduced in many jurisdictions. However, discarded fish are food for a range of scavenging species; so, ending discarding may have ecological consequences. Here we investigate the sensitivity of ecological effects to discarding policies using an ecosystem model of the North Sea—a region where 30–40% of trawled fish catch is currently discarded. We show that landing the entire catch while fishing as usual has conservation penalties for seabirds, marine mammals and seabed fauna, and no benefit to fish stocks. However, combining landing obligations with changes in fishing practices to limit the capture of unwanted fish results in trophic cascades that can benefit birds, mammals and most fish stocks. Our results highlight the importance of considering the broader ecosystem consequences of fishery management policy, since species interactions may dissipate or negate intended benefits.

Highlights

Discarding by fisheries is perceived as contrary to responsible harvesting
To address the ecological consequences of a change in discarding policy, we need to consider both direct effects on scavenging species, and the cascading of indirect effects through the entire food web; the network of species interconnected by predator–prey relationships
Detailed information on the quantities of all species of fish discarded by fisheries in the North Sea as a whole are available only for 1991

Summary

Introduction

Discarding by fisheries is perceived as contrary to responsible harvesting. Legislation seeking to end the practice is being introduced in many jurisdictions. The North Sea is a relevant region in which to study the ecological effects of discard regulations It is a prime example of a heavily exploited continental shelf ecosystem with well-documented landings by both pelagic and demersal fisheries[20,24,25]. It is difficult to conceive of a large-scale field experiment with sufficient controls to study the cascading indirect effects of alternative implementations of landing obligation policies in a large natural ecosystem such as the North Sea. As an alternative, we investigated the sensitivity to alternative implementations using a previously validated food web simulation model (StrathE2E). Maximum likelihood parameters of the model have been determined by statistical fitting to an array of observational data from the North Sea[30], and the fitted model has been demonstrated to realistically simulate both bottom-up and top-down trophic cascades[14]

Methods

Results

Conclusion