Black-browed albatrosses in Chile rebound in response to reduced mortality in fisheries

Citation
Robertson G, Moreno C, Lawton K, et al (2013) Black-browed albatrosses in Chile rebound in response to reduced mortality in fisheries. In: ACAP - 1st Meeting of the Population & Status Working Group. PCSWG1 Doc 03 Rev 1, La Rochelle, France
Abstract

Black-browed albatrosses are a common victim of incidental mortality in commercial fishing operations. Chile holds globally important populations of black-browed and grey-headed albatrosses with the bulk (~85%) of black-browed albatrosses breeding at two of six known sites, the Diego Ramirez and Ildefonso archipelagos. Virtually the entire population of greyheaded albatrosses breeds at Diego Ramirez. In the nine years between 2002 and 2011 the number of black-browed albatrosses at Diego Ramirez (selected islands only) and Ildefonso (whole archipelago) increased by 52% and 18%, respectively. The increase for both islands groups combined was 23%. In the same period the population size of greyheaded albatrosses at Diego Ramirez showed no signs of change. Between 2011 and 2012 the number of black-browed albatrosses at the northern group of Ildefonso, which in 2011 held 41% of total numbers, increased by 6.8%. To explain the reason for the increases we examined trends in fishing effort for the five main longline and trawl fisheries in Chile with a history of interactions with seabirds; the extent of overlap between the fisheries and albatross foraging ranges; and albatross bycatch rates for each of the five fisheries. We conducted a modelling exercise to test the hypothesis that bycatch reduction explained the observed increases. Finally, we examined trends in chlorophyll-a distribution as a possible contributing factor in the increases. The evidence indicates the increase in black-browed albatross numbers was explained by reduced mortality in fisheries, principally the industrial longline fishery for Patagonian toothfish. This fishery commenced in 1989 and had the highest effort (up to 16 million hooks/year) and observed mortality (1,555 black-browed albatrosses in 2002) of the five fisheries examined. In 2008 albatross mortality fell to zero following fleet conversion from the traditional Spanish method to the Chilean method (also known as trotline with nets) of fishing. Developed to minimise toothfish depredation from longlines by toothed whales, baited hooks on Chilean method gear sank five-times faster than hooks on Spanish system gear (mean: 0.80 m/s c.f. 0.15 m/s), which made them inaccessible to black-browed albatrosses (and other seabird species). The population increases at Diego Ramirez and Ildefonso testifies to the recuperative powers of blackbrowed albatrosses following reduction in unnatural levels of mortality, and encourages continued efforts to implement seabird-friendly gears and practices in fisheries with detrimental impacts on seabirds.