Effect of fishing effort on the foraging behaviour of adult and immature Black-browed Albatrosses Thalassarche melanophris

Abstract

Interactions between seabirds and fisheries, such as collisions or entanglement with fishing gear and bycatch, occur in all oceans and most fisheries. These interactions primarily occur as seabirds attempt to feed on bait, resources in nets or fisheries’ by-products such as discards and offal. The Black-browed Albatross Thalassarche melanophris is the most abundant albatross species on the Argentine Continental Shelf. This species is currently listed as ‘Least Concern’ by the International Union for Conservation of Nature (IUCN) but it is considered to be threatened in Argentina where it is known to interact significantly with diverse fisheries. Little is known about how these interactions vary with intrinsic factors such as age, a key knowledge gap. This study aimed to evaluate the effect of fishing effort by trawl and squid-jigging vessels on the foraging behaviour of adult and immature Black-browed Albatrosses wintering on the Argentine Continental Shelf. Our analysis used data from 15 satellite transmitters deployed on six adults (2011–2013) and nine immature individuals (2015). Foraging behaviour was identified using the Expectation Maximisation Binary Clustering algorithm. Generalised Linear Mixed Models (GLMMs) were fitted to determine the effect of fishing effort by different trawl and jiggingfleets (measured as the number of fishing points per hour per grid cell) on the likelihood of albatrosses engaging in foraging behaviour. In both age classes, the probability of foraging behaviour was positively correlated with trawl fishing effort. For immature albatrosses, foraging behaviour was notably affected by double beam trawlers only. For adults, it was associated with fishing effort from double beam trawlers, coastal trawlers, and high-seas ice-trawlers, although the effect was of lesser magnitude. All mentioned trawl fisheries are known to produce significant amounts of discards. Identifying these associations can help to pinpoint potential conflict areas between albatrosses and fishing activities and facilitate the planning of effective conservation measures through an ecosystem-based approach to fisheries management.