Journal Article

Estimating end effects in trawl catches

André Battaglia, Verena M. Trenkel and Marie-Joëlle Rochet

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 63, issue 5, pages 956-959
Published in print January 2006 | ISSN: 1054-3139
Published online January 2006 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/j.icesjms.2006.03.002
Estimating end effects in trawl catches

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The end effect in trawl catches is defined as the proportion of the fish catch taken during shooting and hauling of the net, a period excluded from that nominally referred to as haul duration. If important, this effect will lead to biased abundance estimates, because the swept area will be underestimated. An experimental survey was carried out to compare catch numbers obtained in standard research 30-min hauls with those from 0-min hauls, the latter referring to the trawl being hauled as soon as the trawl geometry stabilized on the seabed. Average catch ratios (0-min/30-min hauls) ranged from 0.05 (s.d. 0.06) for sole to 0.34 (s.d. 0.64) for hake, indicating that the end effect might be more important and more variable for highly mobile species. As a consequence, the bias in abundance indices derived from swept area estimates that ignore end effects will be species-dependent.

Keywords: abundance index; bias; trawl survey

Journal Article.  1784 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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