Journal Article

Disentangling the effects of capture efficiency and population abundance on catch data using random effects models

Verena M. Trenkel and Hans J. Skaug

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 62, issue 8, pages 1543-1555
Published in print January 2005 | ISSN: 1054-3139
Published online January 2005 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/j.icesjms.2005.05.010
Disentangling the effects of capture efficiency and population abundance on catch data using random effects models

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We propose a random effects model for disentangling population abundance and capture efficiency effects on bottom-trawl catches. The spatial distribution of individual fish is assumed random leading to a Poisson distribution for the number of individuals in the trawl path (no schooling). Capture efficiency, i.e. the proportion of individuals in the trawl path being retained by the gear, is modelled as a random variable. We propose model extensions that include the effects of body size on haul efficiency. We applied the models to several species from the Celtic Sea groundfish community based on small-scale repetitive hauls. The resulting abundance estimates allowed us to study population abundance ratios; the estimated capture efficiencies were comparable between species and showed that generally gear efficiency increases for larger species with the exception of haddock (Melanogrammus aeglefinus), which had low estimated gear efficiency despite its large body size. Model identifiability was studied using simulations and an independent trawl data set from the same area.

Keywords: abundance; catchability; Celtic Sea; Poisson distribution; trawl survey

Journal Article.  6489 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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