Identification
The Atlantic White-sided Dolphin (*Leucopleurus acutus*) is a masterclass in oceanic camouflage. Reaching up to 2.8 meters, it is a robust, thick-bodied dolphin with a short, distinct beak. Look for its "signature" flank: a complex tapestry of a dark grey back, a light grey side, and a brilliant white patch below the dorsal fin that transitions into a unique, long tan or yellowish-ochre streak stretching toward the tail. Unlike the similar White-beaked Dolphin, which is larger and has a pale snout, *L. acutus* always sports a dark beak and that unmistakable splash of yellow on the tail stock.
Habitat & Range
These are the cool-water specialists of the North Atlantic. You’ll find them in deep, offshore waters from the edge of the continental shelf to the frigid reaches of the Barents Sea and the Gulf of Maine. They prefer temperate to subarctic temperatures, often following the nutrient-rich Labrador Current or the edges of the Gulf Stream.
Behaviour
Highly gregarious, these dolphins travel in "super-pods" of hundreds. In the field, you’ll notice their energetic "porpoising"—leaping clear of the water at high speeds. They are famously "whale-followers," often seen bow-riding the pressure waves of Humpbacks and Fin whales. Their social structure is tight-knit; they are known to stay with sick or injured pod members, a testament to their high intelligence.
Diet
They are energetic hunters of schooling prey. Using high-frequency echolocation, they corral Atlantic herring, mackerel, and squid. They often use cooperative "rush-and-circle" tactics, driving fish toward the surface where they become easy targets.
Fascinating Fact
The tan streak on their tail isn't just a color—it’s a "biological ID card." This patch is so distinct that researchers can use the specific shape and shade of the yellow-to-white transition to identify individual dolphins from a moving boat, much like a human fingerprint!