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Marine Ecology Progress Series

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MEPS 414:249-256 (2010)  -  DOI:

Shark aggregation in coastal waters of British Columbia

Rob Williams1,2,*, Thomas A. Okey3,4, S. Scott Wallace5, Vincent F. Gallucci6

1Marine Mammal Research Unit, Room 247, AERL, 2202 Main Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
2The Henry M. Jackson School of International Studies, University of Washington, Box 353650, Seattle, Washington 98195-3650, USA
3School of Environmental Studies, University of Victoria, PO Box 3060 STN CSC, Victoria, British Columbia V8W 3R4, Canada
4West Coast Aquatic, #3 4310 10th Avenue, Port Alberni, British Columbia V9Y 4X4, Canada
5David Suzuki Foundation, 2211 West 4th Avenue, Vancouver, British Columbia V6K 4S2, Canada
6School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, Washington 98195-5020, USA

ABSTRACT: A concentration of pelagic sharks was observed in an area of western Queen Charlotte Sound, British Columbia, during systematic shipboard line-transect surveys conducted (2004 to 2006) for marine mammals throughout coastal waters of British Columbia. Surveys allowed only brief observations of sharks at the surface, providing limited opportunity to confirm species identity. Observers agreed, however, that salmon sharks Lamna ditropis (Lamnidae) were most common, followed by blue sharks Prionace glauca (Carcharhinidae). Both conventional and model-based distance sampling statistical methods produced large abundance estimates (~20000 sharks of all species combined) concentrated within a hotspot encompassing ~10% of the survey region. Neither statistical method accounted for submerged animals, thereby underestimating abundance. Sightings were made in summer, corresponding with southern movement of pregnant salmon sharks from Alaska. The previously undocumented high density of these pelagic sharks in this location has implications for understanding at-sea mortality of returning Pacific salmon Oncorhynchus spp. (Salmonidae) and for assessing conservation status of sharks in Canada and beyond. We recommend that a dedicated Canada-US sightings and biological sampling programme be considered, perhaps under the UN Transboundary Species Fishery programme.

KEY WORDS:Abundance · Density · Distance sampling · Distribution · Elasmobranch · Line transect · Salmon mortality · Shark · Spatial model

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Cite this article as: Williams R, Okey TA, Wallace SS, Gallucci VF (2010) Shark aggregation in coastal waters of British Columbia. Mar Ecol Prog Ser 414:249-256.

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