Finless porpoises are small cetaceans of the family Phocoenidae found in nearshore waters of the continental shelves of many countries throughout the world. The only extant species is the finless porpoise (Neophocaena phocaenoides), which inhabits parts of the Pacific Ocean. The name “finless” refers to their lack of a dorsal fin, and they are sometimes referred to as “sewer rats” or “water dogs”. They grow to a length of about 2 metres (6 ft 7 in) and weight of up to 140 kilograms (310 lb).
The body shape is fusiform, with narrow flippers and a blunt head. The mouth contains 36-40 teeth in each jaw. The coloration is dark gray on the back, fading to white on the belly; there is often a dark band running along each side. Finless porpoises swim using an undulating motion of their bodies, propelling themselves forward with powerful strokes from their tail flukes. They can reach speeds of up to 8 kilometres per hour (5 mph).
They primarily eat fish, squid, and crustaceans. In Chinese waters, they have been observed preying on lanternfish attracted to light sources such as gas flares at night. Like other cetaceans, they are capable of vocalizing underwater using clicks and whistles for echolocation and communication; however, little is known about their specific vocalizations or social structure due largely to the difficulty in observing them underwater.
Finless porpoises were once widespread throughout coastal areas of Asia; however, populations have declined sharply over recent years due largely to entanglement in fishing gear, habitat loss and degradation, pollution, hunting for meat and traditional medicine (the animals’ fins are considered a delicacy), among other threats . As a result of these threats ,the International Union for Conservation of Nature has classified the finless porpoise as “vulnerable”.