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

Type Article
Date 2005-12
Language English
Author(s) Trenkel VerenaORCID1, Skaug Hans2
Affiliation(s) 1 : IFREMER, Dept EMH, F-44311 Nantes, France.
2 : IMR, N-5817 Bergen, Norway.
Source ICES Journal of Marine Science (1054-3139) (Elsevier), 2005-12 , Vol. 62 , N. 8 , P. 1543-1555
DOI 10.1016/j.icesjms.2005.05.010
WOS© Times Cited 15
Keyword(s) Trawl survey, Poisson distribution, Celtic Sea, Catchability, Abundance
Abstract 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 (Melallogrannnils 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.
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