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ICES Journal of Marine Science: Journal du Conseil 2006 63(5):956-959; doi:10.1016/j.icesjms.2006.03.002
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© 2006 International Council for the Exploration of the Sea

Estimating end effects in trawl catches

André Battagliaa, Verena M. Trenkelb and Marie-Joëlle Rochetb,*

a Département HGS IFREMER, 7 Place du séminaire, BP 7, 17137 L'Houmeau, France
b Département EMH, IFREMER Rue de l'Ile d'Yeu, B.P. 21105, 44311 Nantes, Cedex 03, France

*Correspondence to M-J. Rochet: tel: +33 240 374000; fax: +33 240 374075. e-mail: mjrochet{at}ifremer.fr.

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

Received 22 June 2005; accepted 14 March 2006.


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