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ICES Journal of Marine Science: Journal du Conseil Advance Access published online on September 23, 2009
ICES Journal of Marine Science: Journal du Conseil, doi:10.1093/icesjms/fsp236
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© 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Capture efficiency and size selectivity of hydraulic clam dredges used in fishing for ocean quahogs (Arctica islandica): simultaneous estimation in the SELECT model

Gudrun G. Thorarinsdóttir1,*, Larry Jacobson2, Stefan Áki Ragnarsson1, Elena Guijarro Garcia1 and Karl Gunnarsson1

1 Marine Research Institute, PO Box 1390, Skúlagata 4, 121 Reykjavík, Iceland
2 National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, USA

Correspondence to G. G. Thorarinsdóttir: tel: +354 575 2000; fax: +354 575 2001; e-mail: gutho{at}hafro.is.

Thorarinsdóttir, G. G., Jacobson, L., Ragnarsson, S. Á., Garcia, E. G., and Gunnarsson, K. 2010. Capture efficiency and size selectivity of hydraulic clam dredges used in fishing for ocean quahogs (Arctica islandica): simultaneous estimation in the SELECT model. – ICES Journal of Marine Science, 67: 000–000.

Estimates of capture efficiency and size selectivity for commercial dredges are important in estimating stock biomass and setting catch limits for the ocean quahog off Iceland and the United States. Ocean quahogs are long-lived, slow-growing, and sensitive to overharvest resulting from poor estimates of capture efficiency and stock biomass. Capture efficiency and size selectivity were estimated simultaneously in mixed-effect SELECT models using diver and commercial dredge experiment data from the shallow-water habitats off Iceland. Estimated capture efficiency for the commercial dredge E = 92% (CV = 8%) was high for large [107.5 mm shell length (SL)] ocean quahogs. Size selectivity followed an ascending logistic curve, with L50 = 70.5 mm SL (CV 4%), a selectivity range of 17.6 mm SL, and substantial variability among experimental dredge tows. Estimated capture efficiency was higher than that for ocean quahogs in US waters, possibly because of the deep habitats off the United States or uncertainty about dredge position during US depletion experiments. Scaling maximum selectivity from the SELECT model to one reduces correlations between size-selectivity and capture-efficiency parameters and may enhance the utility of selectivity estimates in stock assessment modelling. Our experimental and modelling approach may be useful for studies with other non-mobile benthic species.

Keywords: Arctica islandica, hydraulic dredge capture efficiency, ocean quahog, SELECT model, size selectivity

Received 2 October 2008; accepted 23 July 2009.


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