484 



Fishery Bulletin 104(3) 



fisheries in the South Atlantic (i.e., Brazil 0.126 

 birds/1000 hooks; [Neves and Olmos, 1998], Uru- 

 guay 4.7 birds/1000 hooks; [Stagi et al., 1998]), 

 but similar to those reported for the CCAMLR 

 region (1998: 0.025 birds/1000 hooks; 1999: 0.07 

 birds/1000 hooks; 2000: 0.0014 birds/1000 hooks; 

 [Robertson et al., 2001]). 



We made bycatch estimations from vessels, 

 while voluntarily using mitigation measures to re- 

 duce fishery-induced mortality on seabirds — such 

 as tossing thawed bait (less bouyant than frozen 

 bait), setting lines only at night, and splashing 

 the net buoys when birds came near the line. In a 

 nine-month period, 343 seabirds were incidentally 

 caught by vessels targeting kingclip, representing 

 an annual mortality estimate of 457 birds. Previ- 

 ous crude estimations made for day-setting were 

 considerably higher (2 birds/1000 hooks, Gandini 

 and Frere, 2001). 



The main factor affecting seabird mortality 

 was water depth, which is directly related to the 

 location of the setting because water depth in- 

 creases towards the shelf break, where white- 

 chinned petrels forage actively throughout the 

 year (Weimerskirch et al., 1999; Berrow et al., 

 2000). Sixty-five percent of the birds were caught be- 

 tween five days after or before the full moon. A full 

 moon affected albatrossess more significantly than it 

 did petrels. Albatrosses forage mainly during the day, 

 whereas white-chinned petrels forage both at night and 

 during the day (Weimerskirch et al., 1999). Our results 

 support the theory that darkness reduces seabird by- 

 catch. Therefore, improving mitigation measures (i.e., 

 using streamer lines, splashing bouys, etc.), during full 

 moon phases, may reduce bird bycatch further. Birds 

 were more susceptible to being caught in autumm and 

 winter. Our findings agree with those of White et al. 

 (2001), who mentioned that vulnerability for seabirds in 

 Patagonian shelf waters is higher between September 

 and June than during the rest of the year. 



Population impacts and recommendations 

 to reduce bycatch of seabirds 



At least 500,000 pairs (nearly 86*7? of the world popula- 

 tion) of black-browed albatrosses breed on the Malvinas 

 and Falkland Islands and forage on the highly productive 

 Patagonian shelf. Thus, the black-browed albatross catch 

 estimated in this study represents <!% of the total popu- 

 lation. Similarly, the world population of white-chinned 

 petrels is estimated at more than a millon breeding pairs 

 (Croxall et al., 1984; Woods and Woods, 1997); therefore, 

 less than 1% of the white-chinned petrel population is 

 removed by longlining each year. Although these esti- 

 mates may not seem to be critical for the affected species, 

 they may be more significant than indicated because even 

 a small increase in long-lived species may cause popu- 

 lations to decline. Moreover, the lack of information on 

 seabird bycatch by illegal, unreported, and unregulated 

 fishing, make the overall population-level impact from 



bycatch not only difficult to assess but likely much higher 

 than currently realized. Estimations of seabird bycatch 

 by illegal fleets range from 7000-15,000 albatrosses and 

 1200-2000 petrels killed during 2000 (Baird, 2001). 

 These figures are almost seven times larger than our 

 estimates for the Argentinian kingclip fleet operating 

 in the south Atlantic. 



Our data indicate that collaboration between fisher- 

 man and technicians to find devices that reduce bait 

 loss and that improve fish CPUE for practical applica- 

 tion (no additional actions to be taken during fisher- 

 ies operations) is likely critical to maintaining seabird 

 populations. We recommend offering financial benefits 

 to fishing crews that catch fewer seabirds and offering 

 appropriate fishing gear and incentives for compliance in 

 order to reduce seabird bycatch in the Atlantic Ocean. 



Acknowledgments 



We are indebted to Diego Brigatti who provided valuable 

 assistance with the vessels, to Julian Crugeiras from 

 ARGENOVA SA fishing company, and to Eric Oilman 

 and Dee Boersma for their critical comments on an 

 earlier version of this note. This study was carried out 

 with financial support from the Wildlife Conservation 

 Society, Jeniam Fundation, Fish and Wildlife Service, 

 and Universidad Nacional de la Patagonia Austral. 



Literature cited 



Baird, S. J. 



2001. Report on the International Fisher s Forum on 

 solving the incidental capture of seabirds in longline 



