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. Law rence 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 longit ude 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 platfo rm was a light high-winged aircraft with bubble windows flown at 213 m (700 ft). Ten species were seen. Minke whales (Balaenoptera acutorostrata), Atl antic white-sided dolphins (Lagenorhynchus acutus), and harbour porpoises ( Phocoena phocoena) yielded enough sightings to support good estimates, whil e fin whales (Balaenoptera physalus), humpback whales (Megaptera novaeangli ae), white-beaked dolphins (Lagenorhynchus albirostris), and long-finned pi lot whales (Globicephala melas) yielded few sightings and unreliable estima tes. Blue whales (Balaenoptera musculus) and belugas (Delphinapterus leucas ) were seen too rarely to support any analysis. The tenth species was a sma ll delphinid, not positively identified. Minke whales were ubiquitous, but more common in the northern strata. We estimated about 1000 in the whole Gu lf in 1995 and about 600 in the northernmost stratum in 1996 (these numbers , and those following, are uncorrected for visibility bias). We estimated a bout 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 porpois es (12 000 in 1995 and 21 000 in 1996) were most numerous in the northern s tratum, but were also widely distributed at lower densities in the central and southern Gulf. White-beaked dolphins (2500 in 1995 and 2500 in 1996) oc curred only in the Strait of Belie Isle and the extreme northeastern Gulf. We estimated a few hundred fin whales in the northern and central strata an d about 100 humpbacks, mostly in the northeast. Long-finned pilot whales we re only seen in the southeastern Gulf, surveyed only in 1995 (about 1500).