Seabirds in the Argentine Continental Shelf and Shelf-Break

The Patagonian shelf-break represents the transition zone from the relatively shallow waters of the continental shelf to the deep plains exceeding 2000 m depth. Along this pronounced slope, shelf-edge and wind-driven upwelling fronts 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, large petrels, and shearwaters are highly migratory seabirds capable of ranging vast distances and abundant in this region of the planet. Seabird species may use these fronts as primary foraging areas if their prey are at a disadvantage while exposed to thermal, haline, or nutritional stresses. Recent surveys conducted in the northern Patagonian shelf and shelf-break areas show a spatial correlation between seabird abundance and species richness with confluence zones near the slope, and the differential use of some species and composition of seabird assemblages in waters either north or south of the Malvinas-Brazil confluence. The Patagonian shelf and shelf-break, and its biodiversity, is exposed to a variety of threats originated or enhanced by anthropogenic activities. In the past four decades, many seabird populations and other megafauna have experienced declines product of the widespread human perturbation and losses of original marine and breeding habitats. Compared to other bird species, the conservation status of seabirds is rapidly declining, with more than one third of the 326 extant seabird species listed as threatened with extinction. Pelagic species, chiefly Procellariforms (albatrosses, petrels and shearwaters), are particularly threatened, and their populations have declined faster than coastal species. The exploration and exploitation of non-renewable resources, activities that are showing an expansion over the Patagonian shelf and the shelf-break, have the potential to alter the at-sea distribution of pelagic seabirds at micro and meso-scale. Regarding the exploitation of renewable resources, the distribution of fishing effort is highly overlapped with foraging seabirds, showing impacts that range from food supplementation through scavenging behind vessels, to resource competition and incidental mortality. Albatrosses and petrels are susceptible to threats operating throughout their wide distribution ranges extending across national boundaries into international waters. Recent evidence has also demonstrated that the negative effects of seabird bycatch and other stressors affecting species on land and at sea can be exacerbated by the effects of climate change and its concomitant changes in atmospheric circulation, water masses, and prey distribution. These environmental changes have even the potential of generating significant shifts in the distribution of human activities and the overlap with seabirds. Addressing this issue likely represents one of the major environmental conservation challenges that will require well-informed management practices and the implementation of meaningful policy responses.