Partitioning of the Pelagos Sanctuary (north-western Mediterranean Sea) into hotspots and coldspots of cetacean distributions

Abstract

This study used Monte Carlo methods to generate simulations that considered the effort distribution to determine the locations of significant aggregations of cetacean sightings inside the northern Pelagos Sanctuary (north-western Mediterranean Sea). For three years, monitoring has been conducted from five motor vessels covering about 30,050 km. The most frequently encountered species were the striped dolphin Stenella coeruleoalba representing 64.7% of all sightings, the fin whale Balaenoptera physalus (17.0%), Cuvier's beaked whale Ziphius cavirostris (9.9%), Risso's dolphin Grampus griseus (4.3%) and the sperm whale Physeter catodon (2.2%). Sightings' positions and effort coverage were distributed over a grid of 5′ longitude and 5′ latitude. Spatial concentrations of sightings were analysed according to the distribution of effort to identify ‘hotspots’ (locations where the species occurred at a significantly greater frequency than expected), and ‘coldspots’ (locations with a significantly lower frequency than expected). Most fin whale hotspots (14) were located on the bathyal plain between 2000 and 2500 m, four hotspots were around the 1000 m isobaths, and one is located close to the seamount off Genoa. Fin whale coldspots were mainly along the coast. Striped dolphin hotspots were widely distributed over two main areas, in waters with depths between 2000 and 2500 m and at the continental slope; coldspots for this species were also mainly along the coast in the northern part of the study area. Many hotspots were found in the Genoa Canyon, and hotspots of striped dolphins, Cuvier's beaked whales, sperm whales and Risso's dolphins overlapped in this region. Some of the hotspots of Cuvier's beaked whales were identified at the seamount in the study area, where no other species was sighted frequently. Risso's dolphin hotspots were mainly near the 1000 m isobath. For sperm whales, several hotspots were identified: three associated with steep slope features (such as canyons or the continental slope), and one was in the centre of the flat area of Pelagos where the depth is 2500 m. This study highlights the ecological importance of particular locations inside the Pelagos Sanctuary—locations that should be protected from anthropogenic degradations for marine mammal conservation.

Habitat preferences of two deep-diving cetacean species in the northern Ligurian Sea

“…In the Pelagos Sanctuary, Cuvier's beaked whale exploits the upper and lower slopes along the Ligurian−Provençal coast, at depths ranging from 1000 to 2500 m (Azzellino et al 2008, Moulins et al 2008, showing preference for areas with complex topography (Moulins et al 2007, Gannier & Epinat 2008, Azzellino et al 2012. Similar habitat preferences have been found for the sperm whale, whose preferred habitat lies in the canyons in the slope area (Gannier et al 2002, Moulins et al 2008, Praca et al 2009, Azzellino et al 2012.…”

“…Previous research carried out in the Pelagos Sanctuary revealed a longitudinal segregation be tween the 2 species, with a higher presence of sperm whale in the northwestern part of the area, while Cuvier's beaked whale is more common in the Gulf of Genoa area (Gannier et al 2002, Moulins et al 2008. These opposite longitudinal gradients in the distribution of the 2 species might allow the spatial differentiation of habitat.…”

“…The first dataset was collected on board whale-watching vessels operating in the Ligurian Sea from 2004 to 2007, from different operators and from April to October each year. These whale-watching vessels had previously been used as nondedicated plat forms for carrying out cetacean research (Moulins et al 2007(Moulins et al , 2008. As a consequence, a strict protocol for data collection was al ready in place and was followed on each vessel.…”

“…Acting as a connecting corridor between continental shelf areas and the deep-sea, they play a major role in enhancing oceanographic processes and enriching the deep-sea food web (Canals et al 2006, De Leo et al 2010. As a consequence, submarine canyons are widely recognized as hotspots in cetacean distributions (Hooker et al 1999, Mussi et al 2001, Moulins et al 2008. Previous interspecific comparisons suggest that a spatial (Moulins et al 2008) or temporal (Azzellino et al 2008) segregation may facilitate the coexistence of the 2 species in canyons.…”

“…As a consequence, submarine canyons are widely recognized as hotspots in cetacean distributions (Hooker et al 1999, Mussi et al 2001, Moulins et al 2008. Previous interspecific comparisons suggest that a spatial (Moulins et al 2008) or temporal (Azzellino et al 2008) segregation may facilitate the coexistence of the 2 species in canyons. Difficulties in effectively modeling the habitat preferences of the 2 species arise from false-absence bias and from the complexity of the topography that usually characterizes their preferred habitat.…”