Black-browed Albatrosses and longliners: intrinsic and extrinsic variability affecting the mortality along the Patagonian shelf

MARCO FAVERO; AGUSTINA GÓMEZ LAICH; ROCÍO MARIANO-JELICICH; GABRIEL BLANCO; ALEJANDRO ARIAS; MARÍA PATRICIA SILVA RODRIGUEZ; HUGO BRACHETTA; GUILLERMO CAÑETE

Montevideo, Uruguay

Congreso; Third International Albatross and Petrel Conference; 2004

Aves Uruguay, Birdlife International

Population decreases of Black-browed Albatrosses (BBA) breeding in islands of the South-western Atlantic Ocean have been partially attributed to the mortality of birds while interacting with longline fishing vessels. Reductions of about 20% of the populations in Malvinas (Falkland) Islands were reported for the period 1995 – 2000 (N Huin pers. comm). Studies on the mortality of seabirds along the Patagonian shelf and shelf break from 1999 to 2001 indicated by-catch rates of 0.04 ± 0.40 birds/1,000 hooks, with a maximum of 0.20 ± 0.30 birds/1,000 hooks (Favero et al. 2003). Around 10,000 albatrosses and petrels were killed by longliners through this three-year period. Most captures were observed near the edge of the continental shelf or on the shelf break, between 37ºS and 48ºS, where most of the fishing effort was concentrated. Most of the birds killed were BBA (more than 55% of total captures) and White-chinned Petrels (WCP, 20% of captures). BBA were mainly caught when lines were deployed under low or intermediate wind intensities. A positive relationship between by-catch rates and luminosity during the night setting was observed, with higher rates observed during full moon nights. The captures registered during the fall-winter (i.e. interbreeding season) were widely distributed to the North of the shelf break, while those observed during spring-summer were mostly concentrated in the southernmost latitudes, closer to the presumed breeding area in Malvinas. While mortalities during winter were mainly associated to the Patagonian toothfish fishery, those observed during summer were associated with longliners targeting on kingklip in the Patagonian Shelf.