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An assessment of Icelandic flatfish stocks Valtysson, Hreidar Tor

Abstract

Multispecies, multispatial assessment is provided for megrim, witch flounder, American plaice, dab, lemon sole, and plaice in Icelandic waters. Information used as input are logbook records on individual sets from the Danish seine fleet, biological samples mostly from port of landing, and information on individual tows from annual trawl surveys since 1985. Results are compared to commercial CPUE from the English trawler fleet that used to operate in Icelandic waters. Where data allowed the stocks were analysed with a delay difference model, cohort analysis, yield per recruit, and catch curve analysis. These models treated each species as a single stock. The condition of the flatfish stocks vary. All models indicate that the megrim stock is declining to a very low level. Megrim is however historically the smallest of the flatfish stocks and is almost exclusively caught as bycatch. Because of this, ways to protect the stock are few. The current catches of the witch flounder are close to estimated maximum sustainable yield. Some signs however indicate that the stock might be overexploited. The American plaice and dab stocks seem to be in good condition and trawl surveys do not show any decline with time. Uncertainties are large for these species and their real size can therefore not be evaluated. Using the same logic, no specific total allowed catch could be recommended. The lemon sole stock seems to be declining in most areas, how much and from what level is however difficult to judge since the models contradict each other. Information used here for the lemon sole might not be sufficient for stock evaluation. No specific TAC could therefore be advised, but on precautionary grounds, since some models estimate the stock to be on a very low level, all direct target fisheries should be limited. The plaice stock has been declining on most of the major grounds for about a decade. The stock is now at a very low level and all fishery should be reduced considerably.

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