Oceanographic Habitat of an Endangered Mediterranean Procellariiform: Implications for Marine Protected Areas

Abstract

Marine protected areas (MPAs) require ecologically meaningful designs capable of taking into account the particularities of the species under consideration, the dynamic nature of the marine environment, and the multiplicity of anthropogenic impacts. MPAs have been most often designated to protect benthic habitats and their biota. Increasingly, there is a need to account for highly mobile pelagic taxa, such as marine birds, mammals and turtles, and their oceanic habitats. For breeding seabirds foraging from a central place, particular attention should be paid to distant foraging grounds and movement corridors, which can often extend to hundreds of kilometers from breeding colonies. We assessed the habitat use by the most threatened Mediterranean seabird, the Balearic Shearwater, Puffinus mauretanicus, using vessel-based surveys during the chick-rearing period (May-June). We used a hierarchical modeling approach to identify those environmental variables that most accurately reflected the oceanographic habitat of this species by (1) delineating its foraging range using presence/ absence data and (2) identifying important foraging grounds where it concentrates in dense aggregations. The foraging range comprised the frontal systems along the eastern Iberian continental shelf waters (depth <200 m) and areas close to the breeding colonies in the Balearic Islands. Shearwaters aggregated in productive shelf areas with elevated chlorophyll a concentrations. Following the model of a core-buffer MPA, we envisioned those areas of dense aggregation (i.e., the area of influence of the Ebro River discharge and Cape La Nao regions) as the core regions deserving elevated protection and more stringent management. More diffuse protective measures would be applied within the larger buffer region, delineated by the foraging range of the species. Marine zoning measures can greatly benefit the conservation of the Balearic Shearwater and other far-ranging seabirds by extending protective measures beyond their breeding colonies during both the breeding and non-breeding seasons.

Exploiting the closest productive area: geographical segregation of foraging grounds in a critically endangered seabird

“…upwelling). Similarly, habitat use models help explain species-habitat relationships through robust mathematical descriptions and can indicate the oceanographic features primarily associated with seabirds (Louzao et al 2006a). Furthermore, habitat models can be used to predict the most likely pelagic habitats used in both time and space (Guisan & Zimmermann 2000).…”

“…5 to 300 breeding pairs (Ruiz & Martí 2004). During breeding, the foraging range of the species comprises the productive Iberian continental shelf and is influenced by oceanographic processes driving the distribution and availability of their natural prey (Louzao et al 2006a, Bellido et al 2008.…”

“…Specifically, our objectives were (1) to assess whether habitat partitioning occurs along the breeding range (northern, central and southern populations) based on SIA (δ 13 C, δ 15 N), (2) to locate population-specific potential foraging grounds along the Iberian continental shelf, and (3) to assess whether oceanographic conditions could explain observed patterns of SIs. We expected that Balearic shearwaters make foraging trips between the less productive waters around their breeding colonies and the highly productive waters on the Iberian Mediterranean continental shelf (Louzao et al 2006a). However, marine resources are patchily distributed along this continental shelf system and different mesoscale oceanographic features result in productivity hotspots in the Gulf of Lions, Cape Creus, offshore Barcelona, Ebro Delta and Cape La Nao ( Fig.…”

“…Oceanographic habitat models: We overlapped the limits of the potential foraging grounds and predictions of the habitat model of Balearic shearwaters (Louzao et al 2006a) Louzao et al 2006a). Observations of Balearic shearwaters were made during 1999, 2000, and 2002 using standardised strip-transect techniques with a 300 m strip-width transect band and snapshot counts of flying birds.…”

“…Potential foraging grounds were influenced by the main mesoscale oceanographic features enhancing ocean productivity in the western Mediterranean basin (Louzao et al 2006a), since all 3 potential foraging grounds overlapped with maximums of both chl a and SST spatial gradients. Overall, the marine Northern Current flows along the continental slope from the Ligurian Sea to the south of the Eivissa Channel, transporting nutrient-rich waters southwards (Millot 1999, Arnau et al 2004.…”