Estimation of discard of cod (Gadus morhua) in Norwegian gillnet fisheries
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Estimates have suggested that around 10 % of global marine fisheries-catches are discarded at sea, instead of landed and utilized. Since 1987, Norway has gradually implemented a Discard ban, which prohibits the act, but also makes it hard to obtain data from discarding. The unreported discarding adds to the total fishing mortality in the stock and might lead to uncertainties in stock assessments. Estimations of discard of cod in coastal cod-fisheries with gillnets, in three statistical areas in Northern Norway, were conducted using reported data from a selection of vessels working with the Institute of Marine Research, called the Coastal Reference Fleet. Data on landings and number of sales notes from the official landing statistics were used to upscale the estimated discards to the whole coastal fleet fishing with gillnets in the areas, with two different approaches. The mean annual discard rates of cod were less than or equal to 0.73 % of total catch in weight for vessels under 15 meters in the statistical areas 00, 05 and 06 combined, irrespective of calculation method. Estimated mean discard rates per annual quarter in each area were generally higher in quarters 3 and 4, than in quarters 1 and 2. Comparisons of length distributions for landed and discarded fish showed occasional signs of high grading in the fishery (discarding smaller legal-sized cod), especially in quarter 1 and 2. The study relies on the assumption that the data from the Coastal Reference Fleet are representative for the whole coastal fishing fleet. If this is true, the annual mean discard rates for cod in coastal fisheries with gillnets are relatively small. This indicates that the additional mortality from discarding in this coastal gillnet fishery will not have large impacts on the stock assessments. The generally higher mean discard rates from quarter 3 and 4 will be from catches mainly consisting of Norwegian coastal cod. Further studies concerning discarding in this part of the fishery is recommended.