Atlantic white-sided dolphins are gregarious, sociable dolphins. They are fast, acrobatic swimmers and can sometimes be seen bow riding astride the bows of vessels, although in some parts of their range the remain weary of ships. Other behaviors include breaching and lobtailing. They surface to breathe every 10 to 15 seconds.
They have a complex color pattern—their dorsal surface (top of the head, neck, back, dorsal fin and tail) is dark grey or black, the side is light grey with a narrow white patch that starts below the dorsal fin and extends along the flank. A yellowish patch is situated behind the white patch and extends to the tail (this yellow patch is a key distinguishing feature of Atlantic white-sided dolphins). They have a dark circle around the eye and narrow strip of light grey that extends from under they eye to their flipper. Their belly, throat and area above the flipper is white.
Atlantic white-sided dolphins form groups that can vary in size from just a few individuals to several hundred. Larger groups often form when several smaller groups merge to migrate, socialize or feed on a plentiful food source.
Atlantic white-sided dolphins are also known to gather in groups that include other toothed whales. For example, Atlantic white-sided dolphins often gather with humpback whales, fin whales, white-beaked dolphins, and long-finned pilot whales.
Although scientists don't know exactly how many Atlantic white-sided dolphins there are in the wild today, the species is not considered to be threatened. Yet despite their stable status, Atlantic white-sided dolphins, like many other marine mammals, are often hunted directly or killed indirectly as bycatch.
Atlantic-white sided dolphins are also sometimes referred to as jumper dolphins, Atlantic white-sided porpoises, springer dolphins or lags (short for "Lagenorhynchus").
During warmer months, Atlantic white-sided dolphins tend to move northward throughout their range. In cooler months they move southward. Additionaly, during the summer they are often found in inshore waters while while during the winter they remain offshore.