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    Seabird by-catch in the Patagonian toothfish longline fishery at the Prince Edward Islands: 1997–1998

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    P.G. Ryan and M.G. Purves (South Africa)
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    Longline fishing for Patagonian toothfish Dissostichus eleginoides in the South African Exclusive Economic Zone around the Prince Edward Islands commenced in 1996. This paper summarises seabird bycatch during the year July 1997-June 1998. Data on seabird bycatches were obtained from fishery observers aboard all 11 sanctioned fishing trips, representing a fishing effort of 4.3 million hooks. This is 13% more than the number of hooks reported set in 1996-97, but total effort probably declined during 1997-98 as a result of a decrease in the number of unsanctioned vessels operating in the area. Observers reported 498 birds of five species killed. White-chinned Petrels Procellaria aequinoctialis predominated (96%), followed by giant petrels Macronectes spp. (3%), with Yellow-nosed Mollymawks Thalassarche chlororhynchos and crested penguins Eudyptes spp. each contributing <1 % of birds killed. Average seabird bycatch rate by sanctioned vessels was 0.117 birds per 1 000 hooks, less than half that reported in 1996-97. The greatest improvement in bycatch relative to 1996-97 was among mollymawks, and resulted primarily from a decrease in daytime setting and increased use of tori or streamer lines.
    Most birds were killed during setting. There was considerable variance between vessels (range among trips 0.000 to 0.456 birds per 1 000 hooks), with <2% of sets accounting for more than half (52%) the birds killed. Much of the variance could be explained in terms of fishing season, time of setting, wind strength during setting, and distance from the Prince Edward Islands. Moon phase did not appear to explain much variation in bird mortality. Allowing for these factors, some vessels caught more birds than others. Although the fishery is restricted to setting lines between nautical dusk and dawn, 15% of sets took place during the day or straddled dawn/dusk. The effective use of streamer lines also was not possible for all sets due to weather conditions. Despite considerable improvements relative to the 1996-97 season, further efforts are needed to ensure that fishers adhere to permit requirements and only set lines at appropriate times and when conditions permit the effective deployment of streamer lines. Consideration should be given to closing the fishery during February to mid-March when White-chinned Petrels are caught in greatest numbers.