Dolphins of the St. Lawrence  

	Atlantic white-sided dolphin Dauphin à flancs blancs Lagenorhynchus acutus Other names: White-sides, lags

Description

• Small, indistinct beak

• Black back, fins and tail

• Clearly defined colouration zones on flanks; a white patch under a tan-yellow band

• Large, falcate dorsal fin

	White-beaked dolphin Dauphin à nez blanc Lagenorhynchus albirostris

Description

• Short, thick beak, normally white, sometimes grey

  

• Black fins, flanks, tail and top of head

• The rest of the body is covered in light to dark grey zones with large white bands along the flanks.

• Grey-white saddle behind dorsal fin

• Large, falcate dorsal fin

When they surface: Their blows are not visible. Rapid swimming and leaping often exposes their entire bodies. They gather in small groups to hundreds at a time.

Speed and colour for these powerful swimmers

White-beaked and white-sided dolphins rarely go unnoticed in the St. Lawrence. They swim in tight-knit groups, leaping successively out of the water. They sometimes leap in the wakes of ships. Swimming actively and energetically, they give the impression of flying over the water, displaying their colours: dark blue, black, grey, white and even yellow in the case of the white-sided dolphin. Exceptionally, two other species, uncommon in cold water, sometimes swim into the St. Lawrence: the short-beaked common dolphin (Delphinus delphis) and the striped dolphin (Stenella coeruleoalba).

Population, range and habitat

In the St. Lawrence: Both species regularly visit the Gulf from spring through autumn, mostly off the Lower North Shore. The prevalent white-sided dolphin is also commonly seen around the Gaspé Peninsula and approaches the shore in summer and fall. An estimated 12 000 of these dolphins visit the Gulf. The Gulf’s white-beaked dolphin population is estimated at 2600. The presence of these two species in the Estuary is exceptional and their visits brief.

Migration: These dolphins do not embark on seasonal migrations, although north-south movements have been observed.

Worldwide: Both species live in the cold, temperate waters of the North Atlantic. The white-beaked dolphin is the more northern of the two species, common in ice-free Arctic and sub-Arctic waters. 

Behaviour

Feeding: These cetaceans feed mainly on small pelagic fish, squid and, occasionally, benthic crustaceans. They exhibit cooperative behaviour while at the surface, as they encircle and capture their prey. They often associate with humpback and fin whales when feeding.

At the surface: Dolphins are rapid swimmers; they can reach speeds of 25 to 45 km/h. Their energetic swimming is quite spectacular. They surface to breathe every 10 to 15 seconds and execute leaps and aerial pirouettes, only to fall noisily back to the surface. White-beaked dolphins are less exuberant during these aerial acrobatics. They have been known to ride bow waves and swim in the wakes of boats. They also harass large whales, forcing them to accelerate, thus creating a wave on which they swim.

While diving: Little is known about their diving habits. However, their prey is commonly situated within 100 m of the surface.

Social behaviour: These two gregarious species live in groups of three to 50 at a time, within larger groups that number in the hundreds and sometimes even the thousands. Atlantic white-sided dolphins have been known to swim in very tight formation, almost touching. White-beaked dolphins exhibit group segregation: juveniles form distinct groups from adults accompanied by young.

Vocal behaviour: The vocal repertoire of these two species is not known. It is believed that, as with other odontocetes, they emit lower frequency and high-frequency sounds, likely for orientation and to locate prey (echolocation).

Reproduction

Little is known about the reproductive habits of these two species. Mating takes place from May through September, with a peak calving period in June and July for the white-sided dolphin. Gestation lasts 10 to 11 months.

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	Atlantic White-Sided Dolphin