Seabirds in the Argentine Continental Shelf and Shelf-Break

Abstract

The Patagonian shelf-break represents the transition zone from the relativelyshallow waters of the continental shelf to the deep plains exceeding 2000 mdepth. Along this pronounced slope, shelf-edge and wind-driven upwellingfronts support high and persistent levels of primary and secondary productivity,attracting an important abundance and diversity of marine megafauna,including seabirds and marine mammals. Among seabirds, albatrosses, largepetrels, and shearwaters are highly migratory seabirds capable of ranging vastdistances and abundant in this region of the planet. Seabird species may usethese fronts as primary foraging areas if their prey are at a disadvantage whileexposed to thermal, haline, or nutritional stresses. Recent surveys conducted inthe northern Patagonian shelf and shelf-break areas show a spatial correlationbetween seabird abundance and species richness with confluence zones nearthe slope, and the differential use of some species and composition of seabirdassemblages in waters either north or south of the Malvinas-Brazilconfluence.The Patagonian shelf and shelf-break, and its biodiversity, is exposed to avariety of threats originated or enhanced by anthropogenic activities. In the pastfour decades, many seabird populations and other megafauna have experienceddeclines product of the widespread human perturbation and losses of originalmarine and breeding habitats. Compared to other bird species, the conservationstatus of seabirds is rapidly declining, with more than one third of the 326extant seabird species listed as threatened with extinction. Pelagic species,chiefly Procellariforms (albatrosses, petrels and shearwaters), are particularlythreatened, and their populations have declined faster than coastal species. Theexploration and exploitation of non-renewable resources, activities that areshowing an expansion over the Patagonian shelf and the shelf-break, have thepotential to alter the at-sea distribution of pelagic seabirds at micro and mesoscale.Regarding the exploitation of renewable resources, the distribution offishing effort is highly overlapped with foraging seabirds, showing impactsthat range from food supplementation through scavenging behind vessels,to resource competition and incidental mortality. Albatrosses and petrels aresusceptible to threats operating throughout their wide distribution rangesextending across national boundaries into international waters. Recent evidencehas also demonstrated that the negative effects of seabird bycatch and otherstressors affecting species on land and at sea can be exacerbated by the effectsof climate change and its concomitant changes in atmospheric circulation,water masses, and prey distribution. These environmental changes have eventhe potential of generating significant shifts in the distribution of humanactivities and the overlap with seabirds. Addressing this issue likely representsone of the major environmental conservation challenges that will require wellinformedmanagement practices and the implementation of meaningful policyresponses.