Potential Consequences of Climate and Management Scenarios for the Northeast Atlantic Mackerel Fishery

Robin Boyd,Robert Thorpe,Nicola Walker,Shovonlal Roy,Kieran Hyder,Richard Sibly

doi:10.3389/fmars.2020.00639

Abstract

Climate change and fishing represent two of the most important stressors facing fish stocks. Forecasting the consequences of fishing scenarios has long been a central part of fisheries management. More recently, the effects of changing climate have been simulated alongside the effects of fishing to project their combined consequences for fish stocks. Here, we use an ecological individual-based model (IBM) to make predictions about how the Northeast Atlantic mackerel (NEAM) stock may respond to various fishing and climate scenarios out to 2050. Inputs to the IBM include Sea Surface Temperature (SST), chlorophyll concentration (as a proxy for prey availability) and rates of fishing mortality F at age. The climate scenarios comprise projections of SST and chlorophyll from an earth system model GFDL-ESM-2M under assumptions of high (RCP 2.6) and low (RCP 8.5) climate change mitigation action. Management scenarios comprise different levels of F, ranging from no fishing to rate Flim which represents an undesirable situation for management. In addition to these simple management scenarios, we also implement a hypothetical area closure in the North Sea, with different assumptions about how much fishing mortality is relocated elsewhere when it is closed. Our results suggest that, over the range of scenarios considered, fishing mortality has a larger effect than climate out to 2050. This result is evident in terms of stock size and spatial distribution in the summer months. We then show that the effects of area closures are highly sensitive to assumptions about how fishing mortality is relocated elsewhere after area closures. Going forward it would be useful to incorporate: 1) fishing fleet dynamics so that the behavioural response of fishers to area closures, and to the stock’s spatial distribution, can be better accounted for; and 2) additional climate-related stressors such as ocean acidification, deoxygenation and changes in prey composition.

Highlights

Mackerel (S. scombrus, Northeast Atlantic mackerel (NEAM)) is among the most widelydistributed and economically valuable fish stocks in the Northeast Atlantic (Trenkel et al, 2014; Jansen et al, 2016)
To test how the NEAM stock size and associated yield from the fishery may respond to future climate change and management options, we compared future spawning stock biomass (SSB) and annual catch from multistressor scenarios 1–6 (Table 2 and Figure 3)
Environmental inputs to the individual-based model (IBM) were obtained from the Earth System Models (ESMs) GFDL-ESM-2M assuming high and low levels of climate change mitigation action

Summary

Introduction

Mackerel (S. scombrus, NEAM) is among the most widelydistributed and economically valuable fish stocks in the Northeast Atlantic (Trenkel et al, 2014; Jansen et al, 2016). Current stock size is high, it is estimated that recent levels of exploitation will lead to suboptimal yield in the long-term due to overfishing (ICES, 2019c). Management of NEAM is further complicated by the fact that the spatial distribution of the stock in the summer months has recently expanded (Berge et al, 2015; Ólafsdóttir et al, 2018) It is found in substantial numbers in the jurisdictions of Iceland and Greenland which previously had no share of the catch (Kooij et al, 2015; Olafsdottir et al, 2016). Given the commercial value of the NEAM stock it is crucial that the fishery is managed appropriately in order to preserve the economic benefits it currently provides

Methods

Results

Conclusion