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Marine Ecology Progress Series

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MEPS 257:247-257 (2003)  -  doi:10.3354/meps257247

Fisheries-induced trends in reaction norms for maturation in North Sea plaice

R. E. Grift1,2,*, A. D. Rijnsdorp1, S. Barot2,4, M. Heino2,3, U. Dieckmann2

1Netherlands Institute for Fisheries Research, Animal Sciences Group, Wageningen UR, PO Box 68, 1970 AB, IJmuiden, The Netherlands
2Adaptive Dynamics Network, International Institute for Applied Systems Analysis, Schlossplatz 1, 2361 Laxenburg, Austria
3Institute of Marine Research, PO Box 1870, Nordnes, 5817, Bergen, Norway
4Present address: IRD-LEST, 32 Avenue H. Varagnat, 93143 Bondy Cedex, France

ABSTRACT: We analyse how intensive exploitation may have caused evolutionary changes in the age and length at maturation in North Sea plaice Pleuronectes platessa. Such evolutionary change in the onset of maturation is expected, given that fishing mortality is more than 4 times higher than natural mortality. In order to disentangle phenotypic plasticity from evolutionary change, we employ the probabilistic reaction-norm approach. This technique allows us to estimate the probabilities of maturing at each relevant age and size, and to disentangle the plasticity in age and size at maturation that results from changes in growth rates from evolutionary changes in maturation propensities themselves. This recently developed method is applied here to females of 41 cohorts (1955 to 1995) of North Sea plaice. We focus on trends in fishing mortality, in growth rates, and in the probabilities of maturing, and test the hypothesis that the decrease in age and length at maturation is partly caused by fisheries-induced adaptive change. We find that the reaction norm for age and length at maturation has indeed significantly shifted towards younger age and smaller length. The reaction-norm analysis suggests a picture in which short-term fluctuations originating from plastic responses are superimposed on a persistent long-term trend resulting from genetic responses and higher body growth.

KEY WORDS: Fisheries-induced change · Phenotypic plasticity · Evolution · Growth rates

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