Status of the Atlantic White-sided Dolphin, Lagenorhynchus acutus, in Canada

Abstract

The White-sided Dolphin, Lagenorhynchus acutus, occurs in cool temperate waters (average about 7 to 12°C) on both sides of the North Atlantic Ocean, and around Iceland and the Faeroe Islands. On the eastern seaboard of North America its range extends from 37°N to perhaps 71°N. Northern limital records may be of that form of the White-beaked Dolphin (Lagenorhynchus albirostris) which has a dark rostrum. The maximum point estimate of population size for United States shelf waters in 1982 was 46 436. The area surveyed in providing this estimate ended at the southern extremity of Nova Scotia; there is no estimate of population size in eastern Canadian waters, but the total might be in the tens of thousands. The White-sided Dolphin is essentially a denizen of the Continental Shelf waters, and is most abundant in areas of steepest subsurface topographic relief. The average mean depth for sightings off the United States was 165 m. At birth, calves are about 109 to 114 cm in length, with the peak of births in June through July and the range extending from May to early August. Sexual maturity in females is attained at about six to eight years of age and standard body length of 201 to 222 cm. The equivalents for males are eight to nine years and 210 to 244 cm respectively. The gestation period appears to be about 11 months, and lactation may last 18 months. The total length of the reproductive cycle may be at least 2.5 years. Maximum age is unknown. The oldest specimen from Western Atlantic samples was a female estimated to be 27 years of age. The region of maximum abundance off the northeast United States and southeast Canada seems to be the Gulf of Maine, where the main item of food is assumed to be sand lance. Other common prey include Silver Hake (Merluccius bilinearis), herring (Clupea harengus) and Common Squid (//ex illecebrosus). Potential threats to this species include groundfish gill nets off eastern USA and Canada, salmon drift nets in the Labrador Sea, and possible spills from future offshore oil development. Nevertheless, there seem to be no direct threats to the species at present and no recommendations on status are made.Le dauphin a flancs blancs, Lagenorhynchus acutus, fréquente les eaux froides tempérées (dont la température moyenne varie de 7° a 12°C) des cétes de |'Atlantique nord, de I'Islande et des iles Féroé. Sur la cote est de l' Amérique du nord, son aire de répartition s'étend de 37° de latitude nord jusqu'a peut-étre 71° de latitude nord quoique les données sur la répartition dans les eaux septentrionales peuvent se rapporter au le dauphin a nez blanc (Lagenorhynchus albirostris) dont le rostre est aussi foncé. En 1982, l'estimation ponctuelle maximale des effectifs dans les eaux américaines de la plate-forme continentale se situait 4 46 436 individus. La zone du relevé se terminait 4 la pointe sud de la Nouvelle-Ecosse. On ne dispose pas d'estimations des effectifs dans les eaux canadiennes, mais le total peut se situer dans les dizaines de milliers d'individus. Avant tout un habitant des eaux...