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    Seabird mortality on longlines in Australian waters: a case study of progress and policy

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    R. Gales, N. Brothers, T. Reid, D. Pemberton and G.B. Baker (Australia)
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    Seabird bycatch arising from longline fishing is known to kill tens of thousands of seabirds each year, and is now acknowledged as representing the most pervasive threat to seabirds, particularly albatrosses, causing widespread declines in populations across the world. However the extent of seabird mortality is poorly known for most of the world's longline fisheries. Information on bird bycatch in the Southern Oceans is best known for the Australian and New Zealand regions. The 10 year evolution of the seabird bycatch issue in the Australian Fishing Zone (AFZ), where the magnitude of the impact of longline fishing on seabirds was first documented, is presented as a case study. Most of the birds killed in the tuna longline fishery operating around Australia are albatrosses, including species recently listed as threatened and endangered. Analyses of the trends of seabird catch rates in the AFZ by Japanese longliners over 10 years show an apparent fall from the 1988 bycatch figure of 0.4 birds/1000 hooks to levels of between 0.1 to 0.2 birds/1000 hooks. Based on current fishing levels, these recent rates equate to between 1000 to 3500 birds being killed year. Although the initial fall in bycatch rate was achieved rapidly, the rate has plateaued, or risen slightly since then, indicating that there may have been changes to fishing practices or equipment which are detrimental to efforts to minimise seabird bycatch and/or adoption of mitigation methods has been slow. This is a cause for concern given that awareness of the seabird bycatch issue has risen rapidly in ten years.
    In analysing seabird bycatch data it is important to understand the limitations of observer derived data sets. In particular, large amounts of data are necessary to gain clear insights into the suite of species impacted by a fishery, and the effect of different fishing gear, environmental variables, and the mitigation measures employed. In many cases, it is unlikely that such data will be available for a fishery. To overcome some of these problems, we recommend the retention of all seabird carcases for accurate identification and processing of samples, and also a pragmatic approach to the assessment and implementation of mitigation measures.
    The implementation and efficacy of the existing mitigation measures are discussed, together with the approach taken by Australia in preparing a Threat Abatement Plan to mitigate the threat posed to seabirds by oceanic longline fishing. In recognising the need for international action to address the decline in albatross populations, the Australian Government is pursuing such action through international fora such as the Convention for Conservation of Migratory Species of Wild Animals, the Ecologically Related Species Working Group of the Commission for the Conservation of Southern Bluefin Tuna and the IMALF of the Convention for the Conservation of Antarctic Marine Living Resources.