Temporal trends in probabilistic maturation reaction norms and growth of Atlantic cod (Gadus morhua) on the Icelandic shelf

Abstract

Decreasing temporal trends in probabilistic maturation reaction norm (PMRN) midpoints, symptomatic of earlier maturation despite environmentally induced variation in growth, have been observed in many exploited fish stocks. Here, we studied the growth and maturation trends of female and male Icelandic cod ( Gadus morhua ) by estimating PMRN midpoints for cohorts 1964–1999 and found evidence that a shift towards maturation at smaller sizes and younger ages has occurred independently of changes in growth, condition, and temperature. Weighting the data with regional survey abundance estimates to account for spatial heterogeneity in maturity status and sampling intensity did not qualitatively affect the temporal trends. Length-at-age also decreased through the study period, which, through simulations, could be attributed to the energetic costs of earlier maturity at maturing age groups but not at younger ages. These findings support the hypothesis that such changes in maturation schedules are not caused by environmental factors alone but could also reflect a genetic change, potentially in response to intensive fishing.

Roles of density-dependent growth and life history evolution in accounting for fisheries-induced trait changes

“…Model Description), lending good empirical support to this model and providing evidence for more strongly density-dependent growth. However, aquaculture studies of Atlantic cod (62,63) suggest a high genetic variance in growth, and previous studies of other species found evidence for harvest-induced evolution of growth (10,29,64,65), suggesting that weaker density dependence and more evolution of growth are possible. Another possibility is that the strength of density-dependent growth has varied over time, which could happen if, for example, ecosystem conditions have changed (66,67).…”

Fisheries-Induced Evolution

“…The selection represents our best knowledge about relevant studies, but probably many studies have been missed, particularly when results were inconclusive or negative and not reported among the main results. There are seven studies of marine fish species that have all found positive evidence, but in all but two (Pardoe et al 2009, Swain et al 2008) changes in growth are attributed to changes in maturation. Studies on freshwater or anadromous species have covered 13 species, mostly salmonids.…”

Temporal trends in age and size at maturation of four North Sea gadid species: cod, haddock, whiting and Norway pout

“…Since cod, female whiting and haddock PMRNs have varied, demography and growth-dependent plasticity cannot fully explain temporal changes in their maturity ogives: changes in maturation propensity due to growth-independent plasticity in response to environmental conditions and/or fisheries-induced evolution in maturation are likely to have also played a role. Negative temporal trends in PMRN midpoints have already been observed for inshore haddock along the Scottish coast (Wright et al 2011a, but see Devine & Heino 2011) as well as for other cod stocks (Heino et al 2002b, Olsen et al 2004, 2005, Yoneda & Wright 2004, Pardoe et al 2009 Table 2. Regression coefficients and their standard errors (SE) for cod L p50 at age 3, haddock L p50 at age 2 and whiting L p50 at age 2, obtained from transforming back to the original set of axes the principal component regression coefficients and their SEs.…”

“…Gadid stocks have been shown to be prone to fisheries-induced changes in their life history (Jørgensen 1990, Olsen et al 2004, Pardoe et al 2009, Devine & Heino 2011, Wright et al 2011a. North Sea gadids therefore provide an adequate study system for a comparative analysis of fisheries-induced changes in maturation.…”