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    Performance assessment of underwater setting chutes, side setting and blue-dyed bait to minimize seabird mortality in hawaii longline tuna and swordfish fisheries – Final Report August 2003

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    Número de documento:
    E. Gilman (USA), N. Brothers (Australia), D. Kobayashi, S. Martin, J. Cook, J. Ray, G. Ching and B. Woods (USA)
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    Mortality in longline fisheries is a critical global threat to some seabird species. Identifying
    andmainstreaming seabird avoidance methods that not only have the capacity to minimize bird interactions, but
    are also practical and convenient, providing crew with incentives to employ them consistently and effectively,
    will help resolve this global problem. Cooperative research and a commercial demonstration were conducted to
    assess three methods’ effectiveness at avoiding incidental seabird capture, commercial viability, and practicality
    in the Hawaii pelagic longline fisheries. A seabird avoidance method called side setting, which entails setting
    gear from the side of the vessel, with other gear design the same as conventional approaches when setting from
    the stern, had the lowest mean seabird contact and capture rates of treatments tested. Because side setting
    promises to provide a large operational benefit for longline vessels, the incentive for broad industry uptake and
    voluntary compliance is realistic. After making the initial conversion to side setting, there is no additional
    effort required to employ the method. A seabird avoidance method called an underwater setting chute also
    holds high promise, but requires additional research and evaluation to correct design problems, after which it
    can be considered being made commercially available. Two chutes, one 9m long and one 6.5m long, which
    deployed baited hooks 5.4m and 2.9m underwater, respectively, were used in this trial. The 9m chute had the
    second lowest mean seabird interaction rates when used with swordfish gear, and the 6.5m chute had the second
    lowest mean seabird interaction rates when used with tuna gear. A third seabird avoidance method, which
    entails thawing and dying bait dark blue to attempt to reduce seabirds’ ability to see the baits by reducing the
    bait’s contrast with the sea surface, was found to be less effective than the other two methods and was found to
    be relatively impractical and inconvenient. If pre-dyed bait were commercially available, use of blue-dyed bait
    in combination with other methods, such as side setting and adequate line weighting, has high promise.