The habitat preferences of marine mammals west of Scotland (UK)

Abstract

This study used classification and regression trees (CART) to investigate and compare the habitat preferences of marine mammals in this area. Data were collected in early summer (June/July) in 2004 and 2005 and the distribution of marine mammal species was compared to 10 ecogeographic variables (EGVs). Of 13 species of marine mammals sighted during the study, there were sufficient sightings to examine the habitat preferences of seven. For all species a measure of 'shelf tendency' (distance to coast or water depth) was an important variable and the species could be separated into two groups, the deep-water species and the shelf species, with little overlap between them. The occurrence of both deep-water species (long-finned pilot whales and Atlantic white-sided dolphins) was also related to dynamic variables such as sea surface temperature (SST) or primary productivity. Two of the shelf species (northern minke whales and grey seals) were only linked to topographic variables and were limited to quite specific habitats. A third species (harbour porpoise) was primarily related to topographic variables, but in the shallowest waters was also related to local variation in SST. The occurrence of the final two species (common and white-beaked dolphins) was linked to SST and local primary productivity. However, while both species preferentially occurred in areas with higher productivity, the two species differed in their preference for SST, with common dolphins preferentially occurring in warmer waters and whitebeaked dolphins in colder waters.

Stable isotope analysis reveals habitat partitioning among marine mammals off the NW African coast and unique trophic niches for two globally threatened species

“…Nevertheless, the mean δ 13 C value of Tursiops truncatus was close to that of Globicephala melas, a typical deepwater species in the North Atlantic (MacLeod et al 2007) that is also known to occur over the continental shelf off Banc d'Arguin and off the Grande Plage (Maigret et al 1976, Robineau & Vely 1998 (Robineau & Vely 1998). This observation does not seem to correlate with the typical prey of the 2 species of Globicephala (Overholtz & Waring 1991).…”

“…Tursiops truncatus is found in both coastal and offshore habitats along the Mauritanian coastline (Robineau & Vely 1998). This probably explains the large intraspecific variability in the δ 13 C values and suggests the occurrence of persistent individual differences in foraging habits or even the existence of coastal versus offshore populations and/or ecotypes in the area, as has been found elsewhere (Segura et al 2006).Nevertheless, the mean δ 13 C value of Tursiops truncatus was close to that of Globicephala melas, a typical deepwater species in the North Atlantic (MacLeod et al 2007) that is also known to occur over the continental shelf off Banc d'Arguin and off the Grande Plage (Maigret et al 1976, Robineau & Vely 1998 (Robineau & Vely 1998). This observation does not seem to correlate with the typical prey of the 2 species of Globicephala (Overholtz & Waring 1991).…”

“…Nevertheless, the mean δ 13 C value of Tursiops truncatus was close to that of Globicephala melas, a typical deepwater species in the North Atlantic (MacLeod et al 2007) that is also known to occur over the continental shelf off Banc d'Arguin and off the Grande Plage (Maigret et al 1976, Robineau & Vely 1998. G. melas displayed a slightly higher δ 13 C value than Globicephala macrorhynchus, a species usually inhabiting deeper water over the upper slope in the North Atlantic (Davis et al 2002), although nothing is known about its distribution off Mauritania.…”

“…The diet of these species off NW Africa is unknown, but elsewhere P. macrocephalus preys mostly on large, oceanic squid with a high trophic level (Clarke et al 1976, Pauly et al 1998b, Ostrom et al 1993, González et al 1994, which is consistent with its high δ 15 N in the study area. By contrast, B. acutorostrata primarily consumes schooling fish (Das et al 2003, Hassani et al 1997, Pauly et al 1998b, MacLeod et al 2007). This kind of prey could explain its semblance with S. coeruleoalba with respect to δ 15 N values, although only one specimen of the latter was analysed.…”

Using climate downscaling to hypothesise impacts on apex predator marine ecosystem dynamics

“…Water temperature is a critical determinant of cetacean distribution patterns (MacLeod 2009;Kaschner et al 2011;Salvadeo et al 2011). Therefore, changes in water temperature due to climate change could alter dolphin distribution directly or via changes in their habitat or prey (Learmonth et al 2006;Harlin-Cognato et al 2007;MacLeod et al 2007;MacLeod 2009;Lambert et al 2011). However, it is difficult to predict how cetaceans will adapt to climate-related thermal changes or select favourable environments under different climate scenarios without collecting a large dataset that covers multiple species and spatial scales (Pearson & Dawson 2003;Lambert et al 2011).…”