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Size Matters, even with F = F msy

Size Matters, even with F = F msy. Rainer Froese rfroese@geomar.de Brussels, WWF Office, 6th March 2013. Maximum Cohort Biomass. Fish reach maximum growth rate at about 2/3 of maximum length Mortality and growth have coevolevd such that cohort biomass peaks at that size

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Size Matters, even with F = F msy

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  1. Size Matters, even with F = Fmsy Rainer Froese rfroese@geomar.de Brussels, WWF Office, 6th March 2013

  2. Maximum Cohort Biomass • Fish reach maximum growth rate at about 2/3 of maximum length • Mortality and growth have coevolevd such that cohort biomass peaks at that size • Here, fish have spawned several times, and a given catch has the least impact on biomass Froese, R., A. Stern-Pirlot, H. Winker and D. Gascuel. 2008. Size Matters: How Single-Species Management Can Contribute To Ecosystem-based Fisheries Management. Fisheries Research 92:231-241, doi:10.1016/j.fishres.2008.01.005. PDF

  3. Different Scenarios for Baltic Cod

  4. Bottom Line • For true recover and healthy stocks sensu MSFD, F = Fmsy is not enough • Size at first capture has to be gradually increase towards Lopt ~ 2/3 max length • This will minimize impact of a given catch (kill fewer fish) • Minimze unnatural selection • Restore size & age structure (many big fish) • Improve catches for a given F

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