Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

    We have a manual that explains all the features 

Record number 438973
Title A protocol for data exploration to rapidly identify bias in at-sea observer or self-sampling program
Author(s) Uhlmann, S.S.; Helmond, A.T.M. van
Event 7th International Fisheries Observers and Monitoring Conference, Vina del Mar, Chile, 2013-04-08/2013-04-12
Department(s) IMARES Vis
IMARES Visserij
Publication type Abstract in scientific journal or proceedings
Publication year 2013
Abstract To detect and subsequently minimise bias, this study investigates the utility of simple and universally-applicable quality indicators for two at-sea sampling techniques of Dutch demersal beam trawlers. We compared measures of proportionality of sampling on temporal, spatial and biological (i.e. catch composition) scales to evaluate how well observed trawls, trips and vessels represent their respective total populations. Between 2009 and 2011, vessels were sampled independently by using either observer-based or self-sampling techniques on different trips. Compared with self-sampling, observer sampling clustered in the Southern North Sea. During both observer- and self-sampled trips, sampling frequency was low at night, and on certain weekdays. Observers tended to overestimate total catch volumes, and seemed to underestimate numbers of benthic invertebrate discards. Using this protocol as a template to identify and reduce bias in at-sea monitoring schemes will be a useful tool to eventually improve the accuracy of observations.
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