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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on January 16, 2007
ICES Journal of Marine Science: Journal du Conseil 2007 64(2):357-368; doi:10.1093/icesjms/fsl027
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© 2007 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

The effect of including length structure in yield-per-recruit estimates for northeast Arctic cod

Cecilie Kvamme and Bjarte Bogstad

Institute of Marine Research, PO Box 1870 Nordnes, N–5817 Bergen, Norway

Correspondence to C. Kvamme: tel: +47 55 23 85 00; fax: +47 55 23 53 93; e-mail: cecilie.kvamme{at}imr.no

Kvamme, C., and Bogstad, B. 2007. The effect of including length structure in yield-per-recruit estimates for northeast Arctic cod. – ICES Journal of Marine Science, 64: 357–368.

For northeast Arctic cod (Gadus morhua), traditional age-based estimates of yield per recruit (YPR) are compared with alternative, though comparable, YPR estimates calculated using an age–length-structured model. In the age–length-structured model, growth, fishing mortality, and natural mortality depend only on length, not on age. This model considers possible changes in size-at-age caused by, for example, a length-selective fishery, and therefore, by comparing the different YPR estimates, the importance of considering the stock's length structure can be evaluated. Length- and weight-at-age of stock and catches were influenced by exploitation pattern and pressure. Such changes are not considered in traditional estimates of YPR, for which weight-at-age is fixed and strictly speaking only representative for the current fishery. Consequently, traditional YPR estimates were somewhat higher than the age–length-based estimates for exploiting smaller fish than at present, and the other way round for exploiting larger fish. Both models indicated a gain in YPR for reducing just exploitation pressure (traditional YPR, 13%; alternative model, 20%) or both reducing exploitation pressure and postponing exploitation (traditional YPR, 23–31%; alternative model, 33–48%), compared with the current fishery.

Keywords: age–length-structured population model, age-structured population model, Gadget, Gadus morhua, yield per recruit

Received 1 November 2005; accepted 6 November 2006; advance access publication 16 January 2007.


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