Maturation of Newfoundland American plaice (Hippoglossoides platessoides): long-term trends in maturation reaction norms despite low fishing mortality?

Abstract

U. 2005. Maturation of Newfoundland American plaice (Hippoglossoides platessoides): long-term trends in maturation reaction norms despite low fishing mortality? e ICES Journal of Marine Science, 62: 56e64.To interpret long-term trends in age and size at maturation, new statistical methods have recently been devised for estimating probabilistic maturation reaction norms based on data collected for the management of fisheries. Here we apply these methods to three Newfoundland stocks of American plaice (NAFO Divisions 2J3K, 3LNO, 3Ps) and report a clear long-term shift in the maturation reaction norms of these stocks towards maturation at younger age and smaller size. Theory predicts that such trends could result from fishing acting as a selective force, inducing evolutionary changes in the life histories of exploited populations. Matching long-term trends in maturation reactions norms have already been documented for several stocks that have experienced high fishing pressures (Gulf of Maine and Georges Bank cod, Northeast Arctic cod, North Sea plaice). Our results add a new dimension to these earlier findings: since fishing pressures for two stocks of Newfoundland plaice (2J3K and 3Ps) have been relatively low, our results imply that fishing is likely to result in the evolution of life histories even when fishing mortality is low, or that natural mortality has played an important role in determining selective pressures in these populations. Both options suggest that conditions for rapid life-history evolution in exploited stocks are less restrictive than previously appreciated.

Assessing changes in age and size at maturation in collapsing populations of Atlantic cod (Gadus morhua)

“…Similar findings have been obtained for North Sea plaice (Grift et al 2003; also see Rijnsdorp 1993) and American plaice (Hippoglossoides platessoides) (Barot et al 2005). These studies provide evidence for adaptive changes in maturation schedules that point in the very same direction as those documented in this study of Labrador and Newfoundland cod.…”

Does the probabilistic maturation reaction norm approach disentangle phenotypic plasticity from genetic change?

“…Application of the PMRN method provided support for the hypothesis that fisheries-induced evolutionary changes in age and size at maturation have occurred in some important exploited fish populations on contemporary time scales, e.g. in Atlantic cod (Heino et al 2002a, Barot et al 2004, Olsen et al 2004, North Sea plaice (Grift et al 2003) and American plaice (Barot et al 2005). Fisheries management bodies are being advised to consider these effects of fishing (Rijnsdorp 1993, Browman 2000, Law 2000, Pauly et al 2002 because a shift towards earlier maturation will lead to smaller average adult size, thereby lowering yields.…”

Changes in size at maturity of European hake Atlantic populations in relation with stock structure and environmental regimes

“…Morgan and Brattey (2005) propose two possible explanations; on the one hand, they consider that this may be the response to a stock biomass reduction, and on the other, suggest it could be a genetic response to increased mortality. Stressing factors, like fishing, exert a biased selection of individuals, and if they continue for a long time, can fix genetic changes that are reflected in variations of reaction norm (Jørgensen, 1990;Engelhard and Heino, 2004b;Ernande et al, 2004;Barot et al, 2005). This seems to be the case for Flemish Cap cod whose size and age at maturity have decreased, and show no signs of recovery despite the moratorium on fishing only for cod (Saborido-Rey and Junquera, 1999).…”