Influence of larval transport and temperature on recruitment dynamics of North Sea cod (Gadus morhua) across spatial scales of observation

Giovanni Romagnoni,Nils Chr Stenseth,Trond Kristiansen,Øystein Langangen,Knut‐Frode Dagestad,Kristina Øie Kvile,Anne Maria Eikeset

doi:10.1111/fog.12474

Abstract

AbstractThe survival of fish eggs and larvae, and therefore recruitment success, can be critically affected by transport in ocean currents. Combining a model of early‐life stage dispersal with statistical stock–recruitment models, we investigated the role of larval transport for recruitment variability across spatial scales for the population complex of North Sea cod (Gadus morhua). By using a coupled physical–biological model, we estimated the egg and larval transport over a 44‐year period. The oceanographic component of the model, capable of capturing the interannual variability of temperature and ocean current patterns, was coupled to the biological component, an individual‐based model (IBM) that simulated the cod eggs and larvae development and mortality. This study proposes a novel method to account for larval transport and success in stock–recruitment models: weighting the spawning stock biomass by retention rate and, in the case of multiple populations, their connectivity. Our method provides an estimate of the stock biomass contributing to recruitment and the effect of larval transport on recruitment variability. Our results indicate an effect, albeit small, in some populations at the local level. Including transport anomaly as an environmental covariate in traditional stock–recruitment models in turn captures recruitment variability at larger scales. Our study aims to quantify the role of larval transport for recruitment across spatial scales, and disentangle the roles of temperature and larval transport on effective connectivity between populations, thus informing about the potential impacts of climate change on the cod population structure in the North Sea.

Highlights

Recruitment of fish stocks depends largely on survival during the first year and in particular during the pelagic early-life stages (ELS) in broadcast spawning teleost fish (Houde, 2008;Leggett & Deblois, 1994)
We combined long-term observational data with modelled estimates of larval transport to quantitatively assess the effect of transport on recruitment across spatial scales of observation, and we propose a novel approach for measuring effective biomass contributing to recruitment
We instead incorporate estimates of the proportion of cod larvae retained within a population and the influx of larvae from neighbouring populations, that is a more direct proxy for the effect of larval transport (Hidalgo et al, 2019), and apply this approach to the North Sea cod

Summary

| INTRODUCTION

Recruitment of fish stocks depends largely on survival during the first year and in particular during the pelagic early-life stages (ELS) in broadcast spawning teleost fish (Houde, 2008;Leggett & Deblois, 1994). A number of factors affect the ELS survival, including temperature, food availability and predation (Folkvord, 2005;Peck & Hufnagl, 2012) In addition to these factors, the interannual variability in recruitment can be influenced by advective transport of eggs and larvae from spawning to nursery areas (Bailey, 1981;Henriksen et al, 2018). We initially include retention anomaly as an environmental covariate in traditional parametric stock–recruitment model formulations and compare its effect to alternative covariates, namely sea surface temperature (SST) and the North Atlantic Oscillation index (NAO). We propose a novel approach for inclusion of the effect of larval transport in stock–recruitment models by weighting spawning stock biomass (SSB) according to yearly retention and advection rates, providing a measure of “effective biomass.”. We quantify temporal patterns in population connectivity and their relationship with SST and NAO

| MATERIALS AND METHODS

Findings

| DISCUSSION