Risk assessment and relative impact of Uruguayan pelagic longliners on seabirds

Abstract

-Bycatch in longline fisheries is considered one of the main threats for the conservation of albatrosses and petrels worldwide. However, the relative impact of fisheries on all the affected populations or species still remains poorly understood. This paper applied a Productivity and Susceptibility Analysis (PSA) and the concept of "Potential Biological Removal Level" (PBR) to assess the relative impact caused by the Uruguayan pelagic longline fishery on several populations. This two-step approach allowed us to obtain an objective view of the relative impact of the Uruguayan pelagic longline fleet on most of the populations or species of albatrosses and petrels with high association with this fishery. Of fifteen species considered, fourteen were finally assessed and a ranking of risk derived. The concept of PBR was applied to the nine most at-risk species. The impact of fishing on populations could not be straightforwardly inferred from their bycatch rates. Results indicate that large albatrosses (Diomedea spp.) and Thalassarche chlororhynchos are more affected than some of the main species caught by the fishery (i.e. Thalassarche melanophrys and Procellaria aequinoctialis). Diomedea exulans from South Georgia is likely to be the population most affected by the Uruguayan fleet. This work should be seen as a case study of the fisheries operating in the southwestern Atlantic. The Uruguayan fleet within its operation area was responsible for only the 4.3% to 12.5% of the total annual effort deployed by the different fleets during 2004−2008. The combined impact of these fleets could be sufficiently high to account for many of the observed declines in the populations of D. exulans, D. dabbenena and T. chlororhynchos. However, the seabird bycatch numbers for most of the pelagic longline fleets that operate in the southwest Atlantic remain unknown. Applying mitigation measures to reduce the impact of pelagic longline fleets operating in this region should be considered a high priority.

Seabird bycatch in the Argentinean demersal longline fishery, 2001−2010

“…Although this fishery has been referred to as a contributor to continued declines (Tuck et al 2003), the low levels of incidental mortality recorded throughout the decade strongly suggest that the Argentinean demersal longline fishery poses a minor threat to this species. This species has been reported to interact with pelagic longline vessels operating in neighboring waters, such as the midwater longline fleet targeting tuna and swordfish from Uruguay (Jiménez et al 2009(Jiménez et al , 2012 and vessels operating in international waters under the administration of the International Convention for the Conservation of Atlantic Tuna (Tuck et al 2011). This is true as well for other large albatrosses (Diomedea spp.)…”

Sex‐specific effects of fisheries and climate on the demography of sexually dimorphic seabirds

“…Accordingly, we found no effect of demersal longline effort on survival in our study populations. Elsewhere, giant petrel bycatch has been recorded in trawl (Sullivan, Reid, & Bugoni, ) and pelagic longline fisheries (Tuck et al, ), but with relatively low vulnerability to bycatch compared with albatrosses (Jiménez, Domingo, Abreu, & Brazeiro, ; Sullivan et al, ; Weimerskirch et al, ). Aligned with this, there was no significant effect of trawl fishing effort on the survival of either giant petrel species, although there was a negative relationship between pelagic longline effort and female NGP survival.…”

“…Elsewhere, giant petrel bycatch has been recorded in trawl (Sullivan, Reid, & Bugoni, 2006) and pelagic longline fisheries (Tuck et al, 2011), but with relatively low vulnerability to bycatch compared with albatrosses (Jiménez, Domingo, Abreu, & Brazeiro, 2012;Sullivan et al, 2006;Weimerskirch et al, 2000). Aligned with this, there was no sig- likely to attend demersal longline vessels than males, at least during the breeding season (Otley et al, 2007), and during winter overlap more in areas with poorly managed pelagic longline fisheries than males (González-Solís et al, 2008;Phillips et al, 2009).…”

Sex‐related variation in the vulnerability of wandering albatrosses to pelagic longline fleets

“…19% of the global total (Agreement on the Conservation of Albatrosses and Petrels, ). This is also considered to be the seabird species most affected by pelagic longline fishing in the south‐west Atlantic (Jiménez et al ., , ). The small population size and very low fecundity (adults may not recruit until aged ≥ 10 years, and at most fledge one chick every 2 years; Croxall et al ., ), make this species highly vulnerable even to the low recorded bycatch rates (Bugoni et al ., ; Jiménez et al ., , ).…”