Long-Term Retrospective Analysis of Mackerel Spawning in the North Sea: A New Time Series and Modeling Approach to CPR Data

Teunis Jansen,Kasper Kristensen,Corinna Schrum,Mark Payne,Sophie Pitois,Martin Edwards,Inés Álvarez

doi:10.1371/journal.pone.0038758

Abstract

We present a unique view of mackerel (Scomber scombrus) in the North Sea based on a new time series of larvae caught by the Continuous Plankton Recorder (CPR) survey from 1948-2005, covering the period both before and after the collapse of the North Sea stock. Hydrographic backtrack modelling suggested that the effect of advection is very limited between spawning and larvae capture in the CPR survey. Using a statistical technique not previously applied to CPR data, we then generated a larval index that accounts for both catchability as well as spatial and temporal autocorrelation. The resulting time series documents the significant decrease of spawning from before 1970 to recent depleted levels.Spatial distributions of the larvae, and thus the spawning area, showed a shift from early to recent decades, suggesting that the central North Sea is no longer as important as the areas further west and south. These results provide a consistent and unique perspective on the dynamics of mackerel in this region and can potentially resolve many of the unresolved questions about this stock.

Highlights

Mackerel (Scomber scombrus) is one of the most abundant and widely distributed fish species in the North East Atlantic [1]
Hydrographic drift simulations showed that advection of the larvae between the estimated spawning time and capture by the Continuous Plankton Recorder (CPR) was generally minor (Figure 3a). 90% of the larvae caught by the CPR had drifted less than 60 km from the spawning site and 75% have drifted less than 35 km (Figure 3b)
The CPR larval observations can be used as proxies for the spawning distribution of North Sea mackerel

Summary

Introduction

Mackerel (Scomber scombrus) is one of the most abundant and widely distributed fish species in the North East Atlantic [1]. Mackerel plays an important ecological role by feeding on zooplankton and on the pelagic larval and juvenile stages of a number of commercially important fish stocks [2]. Mackerel is caught by a large pelagic fishery with annual landings between 500 and 1000 thousand tonnes [1]. Large changes in mackerel abundance and distribution have significant effects on ecosystems as well as economies. The ecological impact through altered predation pressures on secondary production and fish recruits are likely large, but currently not assessed [2]. More observed are the political and economic consequences [3,4]

Methods

Results

Conclusion