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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on January 25, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(2):206-215; doi:10.1093/icesjms/fsm192
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Crown Copyright © 2008. Published by Oxford Journals on behalf of the International Council for the Exploration of the Sea. All rights reserved

Evidence from survey data for regional variability in cod dynamics in the North Sea and West of Scotland

Steven J. Holmes, Peter J. Wright and Robert J. Fryer

FRS Marine Laboratory, Aberdeen AB9 11DB, UK

Correspondence to S. J. Holmes: tel: +44 1224 295507, fax: +44 1224 295511; e-mail: s.holmes{at}marlab.ac.uk

Holmes, S. J., Wright, P. J., and Fryer, R. J. 2008. Evidence from survey data for regional variability in cod dynamics in the North Sea and West of Scotland. – ICES Journal of Marine Science, 65: 206–215.

Although cod (Gadus morhua) in the North Sea and ICES Division VIa are assessed as single units, recent research suggests that the stocks consist of reproductively isolated subpopulations within a metapopulation. We investigate whether temporal trends in stock indicators are asynchronous across subpopulations, which would support the metapopulation hypothesis. First quarter trawl survey data for the years 1983–2005 were aggregated into putative areas of high spawner fidelity (three in VIa, seven in the North Sea) to obtain indices of spawning–stock biomass (SSB) and recruitment (numbers-at-age 1). Asynchrony was investigated by fitting a smoother to the data for each of the ten spawning areas and testing whether the smoothers were parallel. Trends in SSB differed between spawning areas in both VIa and the North Sea. In VIa, SSB collapsed in the most southwesterly area, but remained more constant elsewhere. In the North Sea, there was a general decline in SSB, but areas thought to contain resident inshore populations showed more rapid declines than those in adjacent offshore areas. Recruitment results offered less support for a metapopulation, although recruitment in the southern North Sea declined rapidly before any trend was seen for the North Sea as a whole.

Keywords: cod, metapopulation, recruitment, smoothers, SSB, survey indices

Received 21 June 2007; accepted 3 December 2007; advance access publication 25 January 2008.


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