Although biological data concerning the North Atlantic fin whale ( Balaenoptera physalus) have been collected since the beginning of this century, much is still unknown regarding their biology and evolution. The aim of this study was to increase our knowledge of the evolution, population structure and molecular ecology of this species using modern molecular techniques. Fin whale samples were collected in six feeding areas from the North Atlantic Ocean, the Mediterranean Sea and the Sea of Cortez (North Pacific Ocean). To facilitate the molecular analyses, two new sexing techniques were developed, and several hyper-variable microsatellite loci were isolated from humpback whale (Megaptera novaeangliae) genomic DNA. The sex as well as the genotype at six microsatellite loci was determined and the first 288 nucleotides of the mitochondrial (mt) control region sequenced in 407 samples. Population genetic and phylogeographic analyses of mtDNA and nuclear loci supported the hypothesis that North Atlantic and North Pacific fin whales constitute separate populations. However, the degree of divergence did not correlate with the rise of the Panama Isthmus and suggested the occurrence of occasional gene flow between the two oceans. The analysis of the mtDNA indicated the existence of several separate populations in the North Atlantic Ocean and Mediterranean Sea. The mtDNA analysis identified eastern and western fin whale populations, both distinct from the Mediterranean Sea fin whales. The result of the microsatellite loci analysis revealed significant levels of heterogeneity only between the most distant areas. The observed difference in the relative level of divergence at mtDNA and nuclear loci was consistent with expanding populations not yet in "drift-mutation" equilibrium, which have diverged recently. This scenario was supported by the distribution of pairwise differences among the mtDNA nucleotide sequences. The sex ratio in the samples collected from Gulf of St. Lawr

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The spatial distribution of four species of rorqual whales was studied along the north shore of the Gulf of St. Lawrence during the months of June to October from 1989 to 2000. A research effort of 6511 hours at sea yielded 849 sightings of blue whales (Balaenoptera musculus), 5291 of finback whales (Balaenoptera physalus), 3822 of humpback whales (Megaptera novaeangliae) and 6489 of minke whales (Balaenoptera acutorostrata). Spatial and behavioural data were collected at sea using inflatable boats, and Global Positioning Systems (GPS) were used to obtain accurate positions. These data were plotted and analysed using a Geographic Information System (GIS) to test the hypotheses that patterns of distribution were not random, were associated with bathymetry and reflected specific differences in habitat use. The resulting maps illustrated the clustered distribution of rorqual whales linked to sea-bottom topography, probably associated with areas of local upwelling and increased productivity. Blue and fin whales shared almost the same distribution, humpback whales were found in slightly deeper, offshore waters whereas minke whales were more abundant in shallower waters. Little attention has been given until now to local patterns of distribution in the area and such information can be useful for practical management considerations. The results emphasise the importance of scale in ecological studies of marine mammals and the need for further research using additional oceanographic parameters, in order to better understand habitat selection.

No description available.