Influence of thermal fronts on the distributionand behaviour of four species of rorqual whales from the Gulf of St. Lawrence, Quebec , Canada

Abstract:

A large number of ecological studies are devoted to finding quantitative relationships between animal distribution and basic environmental features. Sea surface temperature (SST) for instance has been frequently used to analyze patterns of distribution in cetaceans but results have been quite variable and at times contradictory. Some studies have recently begun to use oceanographic features that are more complex and dynamic and can provide better explanations for whale distribution. Surface thermal fronts for instance are present in the ocean at many spatial scales and can act as mechanisms that increase biological productivity and aggregate prey species like euphausiids and fish. The aim of this project was to quantify the relationship that might exist between distribution patterns of rorqual whales in the Gulf of St Lawrence and the occurrence of SST fronts. Specifically, we wanted to test the hypothesis that thermal fronts, induced by topography and tidal mixing, could create attractive areas for rorqual whales and affect their distribution and behavior. Satellite maps of surface temperature were used to locate and measure temperature discontinuities using an edge detection algorithm. For each map, Mantel tests of matrix similarity were used to compare the distribution of SST fronts with positions of blue, fin, humpback and minke whales seen on the same day from boat surveys. Results from 61 maps and 1102 whale sightings from 1996 to 2002 showed strong quantitative correlations between whale distribution patterns and the presence of persistent thermal fronts. Surface feeding behavior was also observed more often in frontal areas and there were differences between species which may reflect different feeding strategies. Identification of surface fronts from satellite imagery can therefore complement in situ observational studies to help explain and even predict habitat selection in large whales, and allow better conservation decisions.

Doniol-Valcroze, T. and R. Sears. 2003. Influence of thermal fronts on the distributionand behaviour of four species of rorqual whales from the Gulf of St. Lawrence, Quebec , Canada . Oral presentation to the 15th biennial conference on the biology of marine mammals, Greensboro , December 14-19, 2003.