Journal Article

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

Cecilie Kvamme and Bjarte Bogstad

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 64, issue 2, pages 357-368
Published in print March 2007 | ISSN: 1054-3139
Published online January 2007 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1093/icesjms/fsl027
The effect of including length structure in yield-per-recruit estimates for northeast Arctic cod

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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

Journal Article.  7844 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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