A method of detecting patterns in mean lengths of samples of discarded fish, applied to the self-sampling programme of the Dutch bottom-trawl fishery

Sebastian S. Uhlmann, Stijn M. Bierman, Aloysius T M Van Helmond

    Onderzoeksoutput: Bijdrage aan tijdschriftA1: Web of Science-artikelpeer review

    Uittreksel

    In 2009, a self-sampling programme was organized in the Netherlands, fishers sampling ca. 80 kg of discards from randomly selected bottom trawls in the North Sea. A statistical procedure is proposed to highlight samples, trips (with multiple samples), or vessels (which may have multiple trips within a year) where extreme mean lengths of discarded fish were observed. Randomization methods were used to test for evidence of non-randomness in patterns of highlighted discard samples, e.g. repeated observations of extreme mean lengths for consecutive discard samples across trips from the same vessel. European plaice (Pleuronectes platessa), common dab (Limanda limanda), grey gurnard (Eutrigla gurnardus), and whiting (Merlangius merlangus) were considered because these were the most abundant species in most of the discard samples. A linear mixed model was used to estimate randomsample effects on the estimated mean lengths by species. These random effects were incorporated into uni- and bivariate procedures to identify extreme samples that were summed for each vessel, and the probability of observing such numbers was estimated. Excluding these samples from the dataset had marginal effects on estimated size distributions of fish.
    Oorspronkelijke taalEngels
    TijdschriftICES Journal of Marine Science
    Volume68
    Exemplaarnummer8
    Pagina's (van-tot)1712-1718
    Aantal pagina’s7
    ISSN1095-9289
    DOI's
    PublicatiestatusGepubliceerd - sep-2011

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