Influence of thermal fronts on habitat selection by four rorqual whale species in the Gulf of St. Lawrence

Abstract

Understanding the factors influencing habitat selection is critical to improving management and conservation plans for large whales. Many studies have linked the distribution of cetaceans to basic environmental features such as underwater topography and sea surface temperature (SST), but the mechanisms underlying these relationships are poorly understood. Dynamic mesoscale processes like thermal fronts are prime candidates to link physiographic factors to whale distribution because they increase biological productivity and aggregate prey. However, previous studies of large whales have found little evidence of such associations, possibly because they were not at the appropriate spatio-temporal scales. We quantified the relationship between SST fronts and the distribution of blue Balaenoptera musculus, finback B. physalus, humpback Megaptera novaeangliae and minke B. acutorostrata whales in the northern Gulf of St. Lawrence. We compared the distribution of 1094 whale sightings collected from boat surveys conducted in 1996 to 2000 to the locations of frontal areas determined from 61 satellite maps. The distributions of whales and thermal fronts were highly correlated (random resampling and Mantel tests of matrix similarity). Spatial distributions differed among species, probably reflecting differences in feeding strategies. Identification of surface fronts from satellite imagery thus effectively complemented field observations of whales. These findings significantly increase our understanding of habitat quality in rorqual whales, and encourage a greater use of dynamic environmental variables in future studies of whale habitat use.KEY WORDS: Sea surface temperature · Thermal fronts · Blue whale · Finback whale · Humpback whale · Minke whale · Habitat selection · Gulf of St. Lawrence 335: 207-216, 2007 iness of krill (Murase et al. 2002) and fishes (Whitehead & Carscadden 1985). Patchiness of organisms in coastal ecosystems is often caused by the dynamic features of mesoscale oceanographic processes like fronts, eddies and upwellings (Olson & Backus 1985). These processes usually involve spatial scales of 1 to 10 km and temporal scales of 1 to 10 d (Hofmann & Powell 1998). In most cases, when these upwellings reach the surface, one of their manifestations is a thermal gradient between warm surface waters and cold upwelled waters. Such mesoscale oceanographic processes increase biological productivity and aggregate prey species (Olson & Backus 1985), thus influencing the distribution of several pelagic fish species (e.g. Fiedler & Bernard 1987, Podesta et al. 1993. Gaskin (1987) predicted that these transition zones between tidally mixed and thermally stratified areas could be an important feature of right whale habitat in the lower Bay of Fundy. This hypothesis was supported by some anecdotal evidence (Murison & Gaskin 1989) but not by quantitative results (Woodley & Gaskin 1996). Similarly, Baumgartner et al. (2003) suggested that spatial and interannual variability in right whale occurrence on the Sco...

Comparing California Current cetacean–habitat models developed using in situ and remotely sensed sea surface temperature data

“…Taxonomic names, see Table 1 Becker et al: California Current cetacean-habitat model comparison remotely sensed model predicted an almost linear increase in group size with increasing SST variation, suggesting that fin whales congregate at localized frontal regions. This result is consistent with that of Doniol-Valcroze et al (2007), who found high correlations between the distribution of fin whales and thermal fronts in the Gulf of St. Lawrence. The model built with remotely sensed data had a lower ASPE value and a better predicted/standard density ratio than the model built with in situ data, suggesting that remotely sensed data may be more effective at characterizing frontal activity due to their ability to measure heterogeneity in 2 dimensions.…”

Potential feeding and spawning habitats of Atlantic bluefin tuna in the Mediterranean Sea

“…Moreover, the absolute values of environmental variables at the position of the occurrence of the species might be not relevant, because large pelagic species, such as ABFT, albacore tuna, right or rorqual whales, seem to seek specific oceanic features showing high horizontal gradients such as fronts (see e.g. Royer et al 2004, Schick et al 2004, Stokesbury et al 2004, Zainuddin et al 2006, Doniol-Valcroze et al 2007, Rooker et al 2008, Pershing et al 2009, Lawson et al 2010. This is in line with Barry & Elith (2006) when reviewing errors and uncertainties of species distribution models, who concluded that the most robust modelling approaches are likely to be those in which care is taken to match the model with knowledge of ecology.…”

Foraging areas, migratory movements and winter destinations of blue whales from the western North Atlantic

“…Passive acoustic monitoring systems deployed in US waters also indicated the presence of blue whales both near and off the shelf edge in southern N ewfoundland and the Grand Banks (Clark 1995). Other than these limited observations, data on blue whale distribution, movement patterns, and habitat use in the western N orth Atlantic are extremely sparse, the notable exception being the SLE and northwestern GSL, where there has been sustained research effort during the summer and early fall over the past 35 years (Doniol-Valcroze et al 2007, Ramp & Sears 2013; but see Stenson et al 2003, Whitehead 2013. Stranding and whaling reports suggest that the blue whale winter range may extend as far south as the Caribbean and the Gulf of Mexico (Clark 1995, Sears & Calambokidis 2002, Reeves et al 2004.…”