Estimating mortality of black-browed albatross (Thalassarche melanophris, Temminck, 1828) and other seabirds in the Argentinean factory trawl fleet and the use of bird-scaring lines as a mitigation measure

Seabird bycatch represents one of the main threats to vulnerable seabird populations, particularly albatross and petrels, and requires urgent conservation management interventions at a global scale. We studied seabird mortality associated with demersal factory trawl vessels that target Argentine Hake Merluccius hubbsi along the Argentine Patagonian Shelf and tested the efficacy of bird-scaring lines as a seabird bycatch mitigation measure. From November 2008 to June 2010, dedicated seabird observers recorded three sources of seabird mortality: entanglements with the trawl net; collisions with the trawl cables (corpses hauled aboard); and collisions with trawl cables (birds observed killed or injured). During 141 days and 389 hauls, we recorded 17 seabird species associated with vessels, ten of which interacted with fishing gear. The most vulnerable species was the black-browed albatross ( Thalassarche melanophris ). From 41 recovered corpses, we identified black-browed albatross mortality rates of 0.013 and 0.093 birds/haul for net entanglement and cable collision (corpses hauled aboard), respectively. From counts of birds killed or injured by cable collisions, we estimate a black-browed albatross mortality rate of 0.237 birds/h. We use official fishing effort data to consider the potential scale of seabird mortality for the entire fleet and identify the main factors contributing to seabird mortality in this fishery. Bird-scaring lines eliminated seabird mortality caused by collisions with trawl cables and are recommended as a short- to medium-term measure to mitigate seabird mortality in this fishery.