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    UPDATED BIOLOGICAL PARAMETERS FOR THE ANTARCTIC STARRY SKATE, AMBLYRAJA GEORGIANA, FROM THE ROSS SEA

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    Numéro du document:
    WG-FSA-08/20
    Auteur(s):
    M.P. Francis and S. Mormede (New Zealand)
    Point(s) de l'ordre du jour
    Résumé

    Photographs of skates taken by observers on New Zealand toothfish longliners in the Ross Sea were identified to species. Sample sizes were small, but indicated a ratio of 10.75:1 of Amblyraja georgiana to B. cf. eatonii, which is consistent with a previous estimate based on a large sample of tagged skates. Biological parameters were reviewed and updated for Amblyraja georgiana. Revised length-weight regression relationships for male and female A. georgiana confirmed that male and female relationships differ significantly. Better estimates of median length at maturity were made possible through a combination of improved observer staging of skates, and a moderate-sized sample of whole skates that was examined in the laboratory. There was no significant difference between the median length at maturity for male and female A. georgiana, which was estimated to be 67.3 cm pelvic length (= 96.5 cm total length). Nearly all of the skates caught were returned to the sea (discarded or tagged). A considerable proportion of these were returned in good condition and were considered likely to survive. Estimates of the proportion released in good condition are in the range 50–80%, depending on assumptions about whether skates were double counted, and whether all tagged skates were in good condition. Improved data recording using new fate and condition classes and a new data logsheet should provide better estimates of this parameter next year.