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    A study of Patagonian toothfish (Dissostichus eleginoides) post tagging survivorship in Subarea 48.3

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    D. J. Agnew, J. Moir Clark, P.A. McCarthy, M. Unwin, M. Ward, L. Jones (United Kingdom), G. Breedt, S. Du Plessis, J. Van Heerdon (South Africa) and G. Moreno (Spain)
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    During the 2005 fishing season experiments on the survivorship of post-tag toothfish were carried out on 8 different vessels fishing in 48.3. Toothfish were selected for tagging as normal, and then were kept in tanks with varying degrees of seawater replacement for at least 12 hours after tagging. On one vessel fish with a variety of injuries were selected to see if this affected recovery. 395 animals were included in the final analysis, with an overall survivorship of 89%. There were significant differences between vessels, and smaller animals and animals in better initial condition had a slightly higher survivorship.
    There are indications that survivorship rates may be lower while observers are learning how to tag effectively and, perhaps, in experiments such as this if handling stress is increased. The results suggest that experienced observers using animals in good condition would normally achieve a survivorship of 95% or more. An assumption of 90% post-tagging survivorship would appear to be an appropriate, conservative, parameter to use in population estimators such as CASAL and mark-recapture.