Immature animals lack spots completely. They are dark gray or purplish gray on the back, becoming lighter gray on the sides and white on the belly. The cape along the back is distinctly separated from the lighter gray coloration of the sides. The flippers and the trailing edge of the flukes are darker than the rest of the body.
As they age, the Atlantic spotted dolphins develop grayish-white spots, first low on the sides, spreading upward. During this stage, the cape becomes less distinct, and dark spotting begins to develop on the belly, the spots increasing in number with increasing age. In adult animals, the belly is often extensively covered with dark blotches but never becomes completely black. The lips may be white, and the beak is characteristically tipped with white, a feature which may aid in identification at sea.
The Atlantic spotted dolphins have a spinal blaze and a light line which extends from the flipper to the eye.
Little is known of the natural history of the Atlantic spotted dolphins. The species occurs in herds of up to several hundred individuals, though groups of 50 or fewer (6-10) are more common. They are often seen jumping clear of the water and habitually ride the bow wave of moving vessels. As they do, the distinct cape or band of purplish gray on the back of younger animals and the spotting pattern of older animals may be visible.
Atlantic spotted dolphins feed primarily on squid but may also take carangid fishes, small eels, herring, or anchovies.
Atlantic spotted dolphins, particularly young animals, may be easily confused with Atlantic bottlenosed dolphins because of the similarities in color pattern and general body shape. However, the Atlantic spotted dolphins have considerable purplish gray in their background colors and the Atlantic bottlenosed dolphins are more dark gray to brownish gray. This along with considerable differences in the overall sizes of the two species should permit positive identification. In general, the key differences between spotted and bottlenosed dolphins are as follows:
ATLANTIC SPOTTED ATLANTIC BOTTLENOSED DOLPHIN DOLPHIN
To 7.5-8 feet (2.3-2.4 m). To 8-10 feet (2.4-3.1 m) inshore, to as much as 12 feet (3.7 m) offshore.