Aerial surveys of cetaceans in the Gulf of St. Lawrence in 1995 and 1996

Aerial line-transect surveys of cetaceans were flown in the Gulf of St. Lawrence in late August and early September of 1995 and in late July and early August of 1996. Systematic north-south transects were spaced 15' of longitude apart. In 1995, the study area comprised the entire Gulf, divided into three strata for analysis; 69% was flown. In 1996, a single stratum covered only the north shore shelf; 75% of the design was flown. The survey platform was a light high-winged aircraft with bubble windows flown at 213 m (700 ft). Ten species were seen. Minke whales (Balaenoptera acutorostrata), Atlantic white-sided dolphins (Lagenorhynchus acutus), and harbour porpoises (Phocoena phocoena) yielded enough sightings to support good estimates, while fin whales (Balaenoptera physalus), humpback whales (Megaptera novaeangliae), white-beaked dolphins (Lagenorhynchus albirostris), and long-finned pilot whales (Globicephala melas) yielded few sightings and unreliable estimates. Blue whales (Balaenoptera musculus) and belugas (Delphinapterus leucas) were seen too rarely to support any analysis. The tenth species was a small delphinid, not positively identified. Minke whales were ubiquitous, but more common in the northern strata. We estimated about 1000 in the whole Gulf in 1995 and about 600 in the northernmost stratum in 1996 (these numbers, and those following, are uncorrected for visibility bias). We estimated about 12 000 Atlantic white-sided dolphins in the Gulf in 1995, but in 1996 saw hardly any, perhaps because we flew the survey earlier. Harbour porpoises (12 000 in 1995 and 21 000 in 1996) were most numerous in the northern stratum, but were also widely distributed at lower densities in the central and southern Gulf. White-beaked dolphins (2500 in 1995 and 2500 in 1996) occurred only in the Strait of Belle Isle and the extreme northeastern Gulf. We estimated a few hundred fin whales in the northern and central strata and about 100 humpbacks, mostly in the northeast. Long-finned pilot whales were only seen in the southeastern Gulf, surveyed only in 1995 (about 1500). Resume : Des inventaires aeriens le long de transects ont ete effectues au-dessus du golfe du Saint-Laurent a la fin d'aout et au debut de septembre en 1995 et a la fin de juillet et au debut d'aout en 1996. Les transects nord-sud etaient systematiquement espaces par 15 minutes de longitude. En 1995, tout le golfe a ete inventorie, divise en 3 strates pour fins d'analyse; 69% a ete survole. En 1996, une seule strate ne couvrait que la plate-forme le long de la rive nord; 75% a ete survole. Le vehicule utilise etait un petit avion leger a ailes hautes et a fenetres en bulles volant a 213,4 m (700 pieds) d'altitude. Dix especes ont ete reperees. Nous avons vu suffisamment de Petits Rorquals (Balaenoptera acutorostrata), de Dauphins a flancs blancs (Lagenorhynchus acutus) et de Marsouins communs (Phocoena phocoena) pour faire une bonne estimation des populations, mais le nombre restreint de Rorquals communs (Balaenoptera physalus), de Rorquals a bosse (Megaptera novaeangliae), de Dauphins a nez blanc (L. albirostris )e t de Globicephales noirs (Globicephala melas) observes ne permettait de faire que des estimations approximatives des populations. Les Rorquals bleus (Balaenoptera musculus) et les Belugas (Delphinapterus leucas) ont egalement ete vus trop rarement pour permettre toute analyse. La dixieme espece etait un petit delphinide qu'il a ete impossible d'identifier. Les Petits Rorquals ont ete vus partout, mais ils abondaient surtout dans la strate nord. Nous avons estime leur nombre a environ 1 000 dans tout le golfe en 1995 et a environ 600 dans la strate nord en 1996 (ces nombres et