Occurrence and biological characteristics of broadnose sevengill sharks (Notorynchus cepedianus) in Pacific Northwest coastal estuaries |
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Authors: | Gregory D Williams Kelly S Andrews Deborah A Farrer Gregory G Bargmann and Phillip S Levin |
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Institution: | (1) Pacific States Marine Fisheries Commission, 2725 Montlake Boulevard East, Seattle, WA 98112, USA;(2) Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration, 2725 Montlake Boulevard East, Seattle, WA 98112, USA;(3) Marine Fish Program, Washington Department of Fish and Wildlife, PO Box 1100, La Conner, WA 98257, USA;(4) Marine Fish Program, Washington Department of Fish and Wildlife, 600 Capital Way N., Olympia, WA 98501, USA |
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Abstract: | The broadnose sevengill shark (Notorynchus cepedianus) is a high-order marine predator distributed worldwide in shallow coastal waters of temperate seas. Recent reports have suggested
it may be a prevalent component of Pacific Northwest coastal estuarine communities, although biological characteristics of
the shark population remain undocumented despite growing interest in recreational harvest of the species. Longline sampling
was conducted in Willapa Bay and Grays Harbor, Washington, USA seasonally during 2003–2006 to collect sevengill shark size,
maturity, and sex ratio data, and establish some baseline catch rate information. Sevengill sharks were collected on 65% of
longline sets and catches were composed of subadult and mature individuals (122–283 cm TL) of both sexes. Most male sevengill
sharks were large sexually mature adults, based on external clasper calcification levels, whereas most comparably sized females
were considered subadults, based on literature-based size-at–maturity estimates. Neonates and young sharks <120 cm were not
collected, nor have they been reported in other historic estuary sampling efforts. Sex ratios were skewed toward males in
Willapa Bay and suggest some degree of sexual segregation for the species, as has been shown for populations elsewhere. We
suggest sevengill sharks are a largely ignored but potentially important predator in Pacific Northwest estuaries. This study
therefore provides some of the first, basic information for guiding management decisions associated with a late-maturing,
slow-growing shark species in these coastal habitats. |
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