Work package 1.

“Common currency” of F

Fishing mortality for a stocks is often taken as the mean F at age over some age groups. Sometimes these represent the flat part of the exploitation-by-age curve, sometimes it includes only partly recruited age groups to the fishery if these are an important part of the catch, and sometimes it is based on production models where it cannot in a simple way be related to F by age groups. Furthermore, some stocks are fished with a small mesh size others with a large one and the corresponding Fmsy will depend on this. Therefore, exploitation pattern will also be considered. For meta-analysis attempted in the current project it is important to define a common “currency” so to say, for F.

A related issue is the link between Total and Spawning Stock Biomasses (TSB and SSB) and biomasses from production models. The former are well defined based on biomass-at-age and maturity-at-age, but the latter one is trickier to define. Biomasses from production models are probably exploitable biomass, which is biomass-at-age multiplied by the exploitation pattern. This also needs to be clarified properly in order to resolve the F “common currency” issue.

Key persons: Daniel, Henrik, Gunnar, Jan