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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 3, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(6):873-881; doi:10.1093/icesjms/fsn072
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© 2008 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Calibration of bottom trawls for northern shrimp

Michael C. S. Kingsley1, Kai Wieland1,2, Bo Bergström1 and Michael Rosing1

1 Greenland Institute of Natural Resources, PO Box 570, DK-3900 Nuuk, Greenland
2 Danmarks Fiskeriundersøgelser, PO Box 104, DK-9850 Hirtshals, Denmark

Correspondence to M. C. S. Kingsley: tel: +299 36 1200/6; fax: +299 36 1212; e-mail: mcsk{at}natur.gl

Kingsley, M. C. S., Wieland, K., Bergström, B., and Rosing, M. 2008. Calibration of bottom trawls for northern shrimp. – ICES Journal of Marine Science, 65: 873–881.

The Skjervøy 3000 trawl used since 1988 in the West Greenland bottom-trawl survey has been replaced by a Cosmos 2000. To be able to compare old data on the northern shrimp (Pandalus borealis) with new data, calibration experiments were carried out by trawling twice consecutively along the same track, using either the same gear twice or the two different gears in one order or the other. Catch models were fitted to the shrimp data—both size-aggregated catch weights and size-specific counts—by likelihood and Bayesian methods. The catch in the second haul relative to that in the first depended not only on the gear used in the two hauls, but also on density, the second catches being a smaller proportion of first catches when densities were high, and often larger than the first catches at low-density stations. This density-dependence of the catch ratio was larger for small shrimp than for big ones. The Cosmos trawl was estimated to fish with ~87% of the catchability of the Skjervøy trawl after correction for its greater wingspread. Catchability ratio varied with the size of shrimp caught, but the differences were not statistically significant.

Keywords: Bayesian modelling, gear calibration, Pandalus borealis, trawl survey

Received 3 July 2007; accepted 30 March 2008; advance access publication 3 May 2008.


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