. The Canadian field-naturalist. . Figure 1. Atlantic White-sided Dolphin, Lagenorhynchus acutus (Photograph taken by Per Berggren, Department of Zoology, University of Guelph, by permission). to the side of the tail stalk. The large, strongly curved dorsal fin is distinctive at sea. The "beak" is very short, and its upper surface is always gray- black. Lagenorhynchus Gray 1846, is a genus of robust, agile dolphins found in cool temperate waters of both hemispheres. Six species are currently recog- nized (Fraser 1966) although Bierman and Slijper (1947, 1948) formerly concluded, on t
. The Canadian field-naturalist. . Figure 1. Atlantic White-sided Dolphin, Lagenorhynchus acutus (Photograph taken by Per Berggren, Department of Zoology, University of Guelph, by permission). to the side of the tail stalk. The large, strongly curved dorsal fin is distinctive at sea. The "beak" is very short, and its upper surface is always gray- black. Lagenorhynchus Gray 1846, is a genus of robust, agile dolphins found in cool temperate waters of both hemispheres. Six species are currently recog- nized (Fraser 1966) although Bierman and Slijper (1947, 1948) formerly concluded, on the basis of limited material, that all Southern Ocean morpholog- ical forms were essentially conspecific. The three species of the southern hemisphere are Lagenor- hynchus cruciger (Quoy and Gaimard 1824), the Hour-glass Dolphin, which seems to be nearly cir- cumpolar in the waters adjacent to the Antarctic Convergence; Lagenorhynchus australis (Peale 1848), Peales, or the Black-chinned Dolphin, which is restricted to the coastal shelf of southern South America and the Falklands Shelf, and Lagenorhynchus obscurus (Gray 1828), the Dusky Dolphin, which occurs off temperate South America, South Africa, Kerguelen Island, New Zealand and several other sub-Antarctic Islands, but not in Australian waters. In the northern hemisphere, a sin- gle species, Lagenorhynchus obliquidens Gill 1865, the Pacific White-sided Dolphin, occurs in cool waters from Japan to Alaska, and south to southern California. Two species are found in the North Atlantic; Lagenorhynchus albirostris (Gray 1846), the White-beaked Dolphin, has the more northerly distribution of the two, regularly occurring from Davis Strait to Nova Scotia, and from western Norway to the Barents Sea. Lagenorhynchus acutus, the Atlantic White-sided Dolphin, is the second North Atlantic species. It attains a maximum adult length of about 280 cm, although among 65 animals examined by Sergeant et al. (1980) the largest male was 267 cm and
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