Abstract

The common thresher shark (Alopias vulpinus) supports important commercial and recreational fisheries in the northeastern Pacific Ocean. It is a relatively long-lived species with a late age-at-maturity, thus a comprehensive under-standing of the status of the thresher shark population is essential to guiding sustainable management decisions. The pur-pose of this study was to use oxytetracycline (OTC) tagging to validate the band pair deposition rate in thresher shark vertebrae. OTC is absorbed by calcifying structures in the thresher shark vertebrae so that time-at-liberty can be corre-lated to the number of band pairs deposited post tagging for direct validation. OTC tagging occurred off southern California from 1998-2012. A total of 2,137 thresher sharks were tagged with conventional tags and 1,445 of these animals, ranging in size from 56 to 309 cm fork length (FL), were injected with OTC. Vertebrae from 57 OTC-tagged and recaptured animals ranging from 58 to 168 cm FL at the time of tagging have been returned. Twenty-six of these samples are from individuals at-liberty for over one year, with a maximum time-at-liberty of 1,389 days (3.8 years). An-nual vertebral band pair deposition rates are currently being determined and will be used to estimate growth rates of the thresher shark at multiple life stages. This information can be used to provide accurate age and growth models for the common thresher shark in the northeast Pacific Ocean and provide information necessary for accurate stock assess-ments.

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