Age and Growth of the Common Thresher Shark in the Western North Atlantic Ocean

Abstract

Age and growth estimates were generated for the Common Thresher Shark Alopias vulpinus in the western North Atlantic (WNA) using vertebral centra from 173 females and 135 males ranging in size from 56 to 264 cm FL. Assuming that vertebral band pairs were deposited annually, we estimated ages up to 22 years (228 cm FL) for males and 24 years (244 cm FL) for females. The growth of both sexes was similar until approximately age 8 (185 cm FL), after which male growth slowed. The growth of females slowed at a later age (∼age 12) than that of males. Relative goodness of fit for all candidate models supported the separate modeling of sexes. For males, von Bertalanffy growth parameters generated from the vertebral data using a set size at birth (81 cm FL) provided the best fit for the band counts (asymptotic length [L_∞ ] = 225.4 cm FL; growth coefficient [k] = 0.17). For females, the standard three-parameter von Bertalanffy growth model provided the best fit to the band counts (L_∞ = 274.5 cm FL; k = 0.09; theoretical age at a length of zero [t ₀] = −4.82). These are the first growth parameters generated for Common Thresher Sharks in the WNA and can be used to make informed decisions for the management of this species.

Received August 22, 2012; accepted June 4, 2013

ACKNOWLEDGMENTS

This study would not have been possible without the staff of the NMFS Apex Predators Program (Narragansett, Rhode Island), including Nancy Kohler, Pat Turner, Ruth Briggs, Cami McCandless, Dave McElroy, Jeff Kneebone, Bryan DeAngelis, and Karen Tougas. We also thank Greg Skomal, John Carlson, Chris Jensen, and Steve McCandless for collecting samples. We are indebted to the thousands of tournament fishermen who voluntarily provided samples from shark tournaments and who tagged and returned sharks for the NMFS Cooperative Shark Tagging Program. This study was partially funded by a grant from the Lerner–Gray Foundation. Reference to trade names does not imply endorsement by the National Marine Fisheries Service.