Lagenorhynchus acutus

Atlantic White-sided Dolphin

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Atlantic White-sided Dolphin

 

Description

Atlantic white-sided dolphins are true vagabonds. They never stay long in one place. They live in the northeastern Atlantic Ocean, sometimes in large schools. A school usually contains adults and young. They are often joined by white-beaked dolphins. White-sided dolphins are rapid hunters, preying mostly on squid and small fish.

Geography

Atlantic white-sided dolphins are found in cold temperate to subpolar waters of the North Atlantic, from about 38°N (south of Cape Cod) in the west and the Brittany coast of France in the east, north to southern Greenland, Iceland, and southern Svalbard (Reeves et al. 1999; Cipriano 2002). The range includes the U.K. and the northern coasts of Scandinavia, although they rarely enter the Baltic Sea. They also sometimes move quite far up the Saint Lawrence River of eastern Canada, and they have been seen as far south as Strait of Gibraltar (Hashmi and Adloff 1991, 1992).

Ecosystem

Habitat and Ecology

The Atlantic white-sided dolphin is found primarily in waters of the continental shelf and slope, but it also occurs in oceanic waters across the North Atlantic. Along the continental slope of North America, it seems to associate with high sea-bed relief along the continental shelf (Palka et al. 1997). 

These dolphins often associate and feed with large baleen whales (fin and humpback whales), and are known to form mixed groups with pilot whales and a number of other dolphin species (including bottlenose and white-beaked dolphins). Atlantic white-sided dolphins feed mostly on small schooling fish (such as herring, mackerel, cod, smelt, hake, and sandlance), shrimp, and squid.

Conservation

The species is widespread and abundant (with current population estimates exceeding 100,000) and there have been no reported population declines or major threats identified.

 

Threats

Major Threats

Some hunting for this species occurred in the past, especially in Norway. Some dolphins are still taken in Greenland, the Faroe Islands, and eastern Canada (Jefferson et al. 1993; Reeves et al. 1999). Recent catches in Faroe Islands were 333 and 310 in 2004 and 2005, respectively (NAMMCO 2005). No assessment is associated with the Faroese hunting of white-sided dolphins, but there is no evidence that this aspect of the drive fishery has a long history, such as that of the pilot whale component (Reeves et al. 2003).

Incidental mortality in fishing gear has been documented off Canada, the United States, the United Kingdom and Ireland. Gaskin (1992) judged Atlantic white-sided dolphins to be less vulnerable to capture in pelagic near-surface drift nets and fixed groundfish gill nets than are many other small cetaceans. They may, however, be especially susceptible to capture in midwater trawl nets (Addink et al. 1997). Substantial numbers have been bycaught in pelagic trawl fisheries for horse mackerel and mackerel south-west of Ireland (Reeves et al. 1999). 

Morizur et al. (1999) investigated marine mammal bycatch in 11 pelagic trawl fisheries operated by four different countries in the Northeast Atlantic. One of the main marine mammal species identified in bycatches was L. acutus. Mean dolphin catch rate for all fisheries combined was 0.048+0.013 per tow (one dolphin per 20.7 tows), or 0.0185+0.0019 per hour of towing (one dolphin per 98 h of towing). All dolphin by-catches occurred during the night. White-sided dolphins were observed feeding around the net during towing; this behaviour may make them more vulnerable to capture. Operational difficulties in observing bycatch and potentially significant annual fluctuation in catch rates warrant further observer studies of these and other trawl fisheries. Substantial numbers have been by-caught in trawl fisheries south-west of Ireland (Couperus 1997a, b), and takes have also been recorded in gill-net and trawl fisheries along the US Atlantic coast (Waring et al. 2008).

Like other North Atlantic marine mammals, Atlantic white-sided dolphins are contaminated by organochlorines, other anthropogenic compounds and heavy metals (Reeves et al. 1999); although the effects of pollutants are not well understood in this species, they may affect reproduction or render them susceptible to other mortality factors.
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