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    AN ASSESSMENT OF ARTIFICIAL BAIT (NORBAIT™) AS A MEANS OF REDUCING THE INCIDENTAL CATCH OF MACROURUS AND OTHER BYCATCH SPECIES IN HIGH LATITUDE TOOTHFISH FISHERIES

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    Numéro du document:
    WG-FSA-08/52
    Auteur(s):
    J.M. Fenaughty (New Zealand)
    Point(s) de l'ordre du jour
    Résumé

    The New Zealand fishing company Sanford Limited has initiated a research project to assess the effectiveness of artificial bait as a means of reducing the incidental catch of Macrouridae (rattails) and other bycatch species in the toothfish autoline longline fishery. A company vessel carried out some initial experimental work in the western Ross Sea (CCAMLR Statistical Subarea 88.1) in 2007 to assess basic requirements such as ease of use, bait longevity on the hook, and catchability (defined here as a measure of a baited hook to attract and catch a given species of fish) of target and incidental species. This is a preliminary report based on subsequent trials carried out aboard the vessel San Aspiring operating in the waters of South Georgia and the South Sandwich Islands (CCAMLR Statistical Subareas 48.3 and 48.4) during early 2008. During the period 12 April and 14 May 2008 seventeen trial lines were set in both Subareas; a total of 137,000 experimental hooks. The evaluation was based on alternating sections (magazines or mags - there are approximately 1024 hooks per magazine on San Aspiring) of line with control mags baited with squid, the vessel’s preferred bait for toothfish and alternating mags using an artificial or reconstituted bait (Norbait 800C™). Results from Subarea 48.4 indicated that catches of both the target Patagonian toothfish and bycatch of Macrourus whitsoni were reduced using Norbait when compared to the conventionally used squid bait. The reduction in rattail catches however was proportionally much greater than that of the toothfish and points to a potentially useful means of limiting Macrourid bycatch. This is similar to results obtained by another Sanford vessel San Aotea II in the Ross Sea in early 2007. This was not the case in Subarea 48.3, the other area where trials were carried out. In this area although Norbait reduced the incidental bycatch of Macrourus, an overall virtually identical reduction in the target catch of Patagonian toothfish negated any benefit. These reductions effectively meant an increase in fishing effort and time to achieve the same target catch result. Other than the obvious geographical differences between the two trial Subareas there were differences in both the Macrourus species caught and the size of toothfish caught in each. These factors may individually or in combination provide some explanation for the observed dissimilarities. There are a large numbers of variables involved in such comparative trials making definitive analysis difficult and precluding clearly defensible results. In such cases the collection of large amounts of base data in all circumstances and environments is the only way of reducing uncertainty and understanding the variability. For this reason it is necessary to stress that these results are preliminary and further work is indicated. Although increased and continuing data collection is an ideal, it must be highlighted that there are both clear and concealed costs involved in undertaking such trials. Obvious expenses are incurred in the purchase and transport of the trial bait. There are however hidden costs incurred in the additional time on the grounds and additional gear deployed to catch the same amount of fish when the bait used is less effective than the current standard.