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

• Published in: ICES Journal of Marine Science
• Main Authors: Vainikka, Anssi, Gårdmark, Anna, Bland, Barbara, Hjelm, Joakim
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2008
• Subjects: Gadus morhua
• Online Access: http://dx.doi.org/10.1093/icesjms/fsn199; http://academic.oup.com/icesjms/article-pdf/66/2/248/29132758/fsn199.pdf

Abstract 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.