Seabird by-catch in the Patagonian toothfish longline fishery at the Prince Edward Islands: 1998–1999

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 1998-June 1999. Data on seabird bycatch were obtained from fishery observers aboard all 11 sanctioned fishing trips, representing a fishing effort of 5.1 million hooks. This is 19% more than the number of hooks set in 1997-98, but only 79 seabirds (150/0 of the total killed in 1997-98) were reported killed by observers. Average seabird bycatch rate by sanctioned vessels was 0.016 birds per 1000 hooks, compared with 0.289 in 1996-97 and 0.117 in 1997-98. Comparisons between years for the same vessel, using the same gear design and at the same time of year, show marked decreases in seabird bycatch rate during 1998-99.
Five bird species were reported killed: white-chinned Petrels Procellaria aequinoctialis predominated (790/0), followed by giant petrels Macronectes spp. (13%) and Grey Petrels P. cinerea (6%). A worrying development is the increase in numbers of Grey Petrels killed (only one prior to this year). Birds were caught on only 3.1% of lines set (n=1187). Bird bycatch was primarily linked to daytime sets, with most birds caught in the late afternoon or shortly after dusk. Use of an underwater setting device (a Mustad funnel) significantly reduced bird bycatch to acceptable levels (0.002 birds per 1000 hooks), but it was not tested during the period when seabird bycatch typically peaks (mid-late summer). An average of 4.5 live birds were caught per 100 hauls; although these are released alive, the much higher catch rate of Spanish, double-line gear is cause for concern.
Seabird bycatch rates during 1998-99 are the lowest reported for any toothfish fishery in the Southern Ocean. Continued application of mitigation measures (use of streamer lines, setting lines at night or in conjunction with an underwater setting device) coupled with increasing experience by both crews and observers undoubtedly contributed to the low bycatch rate. Other factors that might account for the small numbers of birds killed include a switch in fishing emphasis to waters more distant from the Prince Edward Islands, and a reduction in the amount of offal released from vessels. The former factor may be especially important during the high-risk late summer period; consideration should be given to limiting fishing within 200 km of the islands during this period. Permit holders should be congratulated for achieving such a low seabird bycatch rate, but continued vigilance is required to ensure that bycatch rates remain at this low level.