Long-term interplay between harvest regimes and biophysical conditions may lead to persistent changes in age at sexual maturity of Northeast Arctic cod (Gadus morhua)

Carl Jakob Rørvik,Geir Ottersen,Olav Sigurd Kjesbu,Bjarte Bogstad

doi:10.1139/cjfas-2021-0068

Carl Jakob Rørvik, Geir Ottersen + Show 2 more

Open Access

https://doi.org/10.1139/cjfas-2021-0068

Copy DOI

Abstract

This investigation commenced by constructing principal maturation schedule equations as a function of fishing mortality (F), key biophysical factors and a term attributed to fisheries-induced adaptive change (FIAC). Following the onset of industrial trawl fishery on the model stock, Northeast Arctic cod (NEAC; Gadus morhua) (1934–2020), F on immature age group 5–8 years (F5-8) increased and mean age at 50% maturity (A50) decreased from ≈10 years in the late 1940s to ≈7 years today. Large annual fluctuations in total stock biomass (TSB), sea temperature (KolaT) and F5-8 were used to better understand A50 responses. In the model, the annual accumulation of F5-8 drives FIAC. The model includes the option that NEAC may sustain F5-8 up to a certain level (F_bal) before FIAC becomes statistically evident, with F_bal falling between 0.00 and 0.40 for A50. This dynamic range in F_bal indicates a sophisticated, underlying adaptive response. Independent of F_bal, our analysis clarifies that FIAC is necessary to explain the observed changes in A50.

Highlights

Fisheries exploitation changes the age and body size structure of harvested populations (Ottersen et al 2006; Shelton et al 2015)
Our analysis of the maturation traits of Northeast Arctic cod (NEAC) had the advantage of data from more than eight decades
fisheries-induced adaptive change (FIAC) is our primary explanation for why the present value of age at 50% maturity (A50) has not recovered to its pre-war level

Summary

Introduction

Fisheries exploitation changes the age and body size structure of harvested populations (stocks) (Ottersen et al 2006; Shelton et al 2015). There are associated trends towards an increased prevalence of early sexually mature individuals, as seen in, e.g., Canadian cod stocks (Trippel 1995). Whereas these changes could reflect genetic responses to fishing mortality (F) (Law and Grey 1989; Heino 1998; Heino and Godø 2002), they may possibly occur without any underlying changes in the genome as such, e.g. by epigenetic, transgenerational modifications (Heckwolf et al 2020). I.e. N3 divided by parent SSB, showed a declining trend since the 1950s (Fig. 6B)

Methods

Results

Discussion

Conclusion