Community Research and Development Information Service - CORDIS

Evaluation of stock management hypotheses and model assumptions

Most cod stocks in the CODYSSEY project are assessed and managed using the virtual population assessment (VPA) methodology. This method can be modified to take account of stock structure and changes in catchability between seasons, but most often doesn't and instead uses broad and largely untested assumptions about the rates of population movements between management areas. Stock hypotheses and model assumptions have been reviewed in each ecosystem and tested against the observations from the CODYSSEY project.

The data from the CODYSSEY project show that cod stocks are often partitioned into a migratory and resident component, and that the characteristics of the migratory component vary considerably between stocks (Iceland, Barents Sea, North Sea) and also between years (Baltic). Catchability of cod depends critically upon ecosystem, time of year and migratory strategy, and can therefore have consequences for the relative mortality of different stock components. It is therefore recommended that stock assessments take more account of population movements, and their consequences for determining abundance, sub-population identity and mixing.

Reported by

CENTRE FOR THE ENVIRONMENT, FISHERIES & AQUACULTURE SCIENCE
LOWESTOFT LABORATORY, PAKEFIELD ROAD
NR 33 0HT LOWESTOFT
United Kingdom
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