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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on December 2, 2008
ICES Journal of Marine Science: Journal du Conseil 2009 66(2):248-257; doi:10.1093/icesjms/fsn199
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© 2008 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Two- and three-dimensional maturation reaction norms for the eastern Baltic cod, Gadus morhua

Anssi Vainikka1, Anna Gårdmark1, Barbara Bland2 and Joakim Hjelm2

1 Institute of Coastal Research, Swedish Board of Fisheries, Box 109, SE-742 22 Öregrund, Sweden
2 Institute of Marine Research, Swedish Board of Fisheries, Box 4, SE-45321 Lysekil, Sweden

Correspondence to A. Vainikka: tel: +46 173 46479; fax: +46 173 46490; e-mail: anssi.vainikka{at}fiskeriverket.se.

Vainikka, A., Gårdmark, A., Bland, B., and Hjelm, J. 2009. Two- and three-dimensional maturation reaction norms for the eastern Baltic cod, Gadus morhua. – ICES Journal of Marine Science, 66: 248–257.

Industrial fisheries have caused decreases in the size and age at maturation in several stocks of cod (Gadus morhua). Although earlier maturation can be a phenotypic response to improved growth conditions, estimation of probabilistic maturation reaction norms (PMRNs) can remove most impacts of growth and demography from maturation schedules and has often revealed a residual, potentially genetic, trend. In this study, size- and condition-based PMRNs were estimated for eastern Baltic cod cohorts from 1987 to 2003. The PMRNs suggested that both length and condition at 50% probability of maturing (Lp50 and Cp50) had decreased by 15–20%, more notably in females. Simultaneously with changes in maturation schedules, the length-at-age of mature fish decreased for most combinations of age and sex. Decrease in growth may be partly explained by advanced maturation, but temporal fluctuations in PMRNs suggest also a residual environmental impact on both growth and maturation. The results may indicate a genetic change in the eastern Baltic cod stock, adding pressure to reduce fishing mortality on it.

Keywords: fisheries selection, fishing-induced evolution, growth, maturation schedule, PMRN

Received 19 April 2008; accepted 2 November 2008; advance access publication 2 December 2008.


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