Calibration of bottom trawls for northern shrimp

• Published in: ICES Journal of Marine Science
• Main Authors: Kingsley, Michael C. S., Wieland, Kai, Bergström, Bo, Rosing, Michael
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2008
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Oceanography; Greenland; Skjervøy; northern shrimp; Pandalus borealis
• Online Access: http://dx.doi.org/10.1093/icesjms/fsn072; http://academic.oup.com/icesjms/article-pdf/65/6/873/29130079/fsn072.pdf

Abstract 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 The Skjervøy 3000 trawl used since 1988 in the West Greenland bottom-trawl survey has been replaced by a Cosmos 2000.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.