Estimating end effects in trawl catches

Type Article
Date 2006-06
Language English
Author(s) Battaglia Andre2, Trenkel VerenaORCID1, Rochet Marie-Joelle1
Affiliation(s) 1 : IFREMER, Dept EMH, F-44311 Nantes 03, France.
2 : IFREMER, Dept HGS, F-17137 Lhoumeau, France.
Source ICES Journal of Marine Science (1054-3139) (Elsevier), 2006-06 , Vol. 63 , N. 5 , P. 956-959
DOI 10.1016/j.icesjms.2006.03.002
WOS© Times Cited 7
Keyword(s) Trawl survey, Bias, Abundance index
Abstract 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. (c) 2006 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.
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