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    An interlaboratory comparison of ages estimated for Dissostichus eleginoides from the Argentine Sea, southwest Atlantic Ocean

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    Numéro du document:
    M.C. Cassia (Argentina), P.L. Horn (New Zealand) and J.R. Ashford (USA)
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    To examine consistency among laboratories in age estimation of Patagonian toothfish and the effects on readings of different otolith processing methods, scales and otoliths were taken from 124 fishes caughts in Argentine Sea ( South West Atlantic)
    Ages were estimated by readers from National Institute for Fisheries Research and Development (INIDEP) Argentine, National Institute of Water and Atmospheric Research, Nelson, New Zealand (NIWA), and Centre for Quantitative Fisheries Ecology, Old Dominion University, Norfolk, Virginia, United States of America. (CQFE).
    As a consequence of the exchange of otoliths carried out with NIWA, and the results presented, it is apparent that the NIWA preparation method produced a clearer section. More hyaline bands were visible in the NIWA preparations, particularly near the otolith margin where the zones can be very narrow. Consequently, INIDEP has adopted the NIWA method to process otoliths of the Patagonian toothfish from the Argentine Sea.
    So even though Patagonian toothfish otoliths could not be classified as easy to read, the clarity of their zones is quite similar in the South Atlantic, the waters south of New Zealand, and CCAMLR subarea 48.3.
    The comparisons of age data produced by three readers indicate a reasonable consistency for otoliths. The indices of average percent error for comparisons between R1 and R2 are satisfactory. Reader R3 generally produced older age because he has a different interpretation of the first few increments.
    Comparisons of age estimations derived from scales and otoliths are less consistent.There were significant differences in age determinations from scales between R1 and R3, and between scales and otoliths by R1 and R3. Clearly, there are differences between these readers in the interpretation of these structures, and also difficulties reconciling the counts derived from otoliths and scales from individual fish. Further work is necessary on this issue to develop consistent interpretations for age readings.