Pacific white-sided dolphin. Copyright Tom Kieckhefer

The white-sided dolphin is easy to identify with its short, distinct beak and black back with striking light-gray sides and pearl-white belly. The Atlantic white-sided dolphin (Lagenorhynchus acutus) also has a yellow or tan streak above its gray side extending towards the tail. Pacific white-sided dolphins (Lagenorhynchus obliquidens) are only found in the North Pacific where a northern form (occurring from Alaska to southern California) and a southern form (occurring from central California to Baja California) are known to exist. The two forms look very similar and cannot be distinguished at sea. The Atlantic white-sided dolphin lives only in the northern North Atlantic, in offshore waters. White-sided dolphins are often found in large groups, perhaps of several hundred to more than a thousand individuals. Pacific white-sided dolphins have been shown to use echolocation to locate prey. Both Pacific and Atlantic white-sided dolphins use whistle vocalizations to communicate among themselves. These two species of dolphin have been recorded to produce high frequency signature whistles that are unique to that individual dolphin.