Black-browed albatross numbers in Chile increase in response to reduced mortality in fisheries

Black-browed albatrosses (Thalassarche melanophrys) are a common victim of incidental mortality in commercial fishing operations. Chile holds globally important populations of black-browed albatrosses and grey-headed (Thalassarche chrysostoma) albatrosses with about 85% of the former species breeding at the Diego Ramirez and Ildefonso Archipelagos. In the nine years between 2002 and 2011 the number of black-browed albatrosses at these sites increased by 52% and 18%, respectively, or 23% for both sites combined. In the same period the population size of grey-headed albatrosses showed no signs of change. To explain the reason for the increases we examined trends in fishing effort for the five main longline and trawl fisheries with a history of interactions with seabirds; the extent of overlap between the fisheries and albatross foraging ranges; and albatross bycatch rates for each fishery. The circumstantial evidence and evidence from the SEABIRD population model suggest the most likely reason for the population increase was reduced mortality in the industrial longline fishery for Patagonian toothfish. In 2002 Spanish system vessels in this fishery took an estimated 1555 black-browed albatrosses. In 2006 and 2007 the fleet converted to a new method of fishing, called the Chilean system (or trotline-with-nets), which reduced seabird mortality to zero. Developed to minimise depredation of toothfish by sperm whales and killer whales, the re-designed gear configuration resulted in a fivefold increase in mean sink rates of baited hooks (from 0.15 m/s to 0.80 m/s), making them inaccessible to seabirds. The Chilean system is an example of innovation yielding both economic benefits to the fishing industry and conservation benefits to seabirds. The ability of black-browed albatrosses to respond to reduced mortality levels encourages continued efforts to implement seabird-friendly gears and practices in other fisheries with detrimental impacts on seabirds.