Porpoises
Porpoises
Porpoises are small marine mammals classified under the family Phocoenidae. They are cetaceans, closely related to narwhals and belugas, and share a common ancestry with dolphins. Despite their dolphin-like appearance, porpoises can be distinguished by their more compact build, smaller size, and the distinct shape of their teeth. Unlike dolphins, porpoises possess flattened, spade-shaped teeth instead of conical ones and generally lack a pronounced beak.
Physical Characteristics
Porpoises range in size from the vaquita, which measures about 1.4 meters (4 feet 7 inches) and weighs approximately 54 kilograms (119 pounds), to the Dall's porpoise, which can reach up to 2.3 meters (7 feet 7 inches) in length and 220 kilograms (490 pounds) in weight. Some species exhibit sexual dimorphism, with females being larger than males. Porpoises are characterized by a curved blunt snout and their distinct spatulate teeth.
Species and Taxonomy
There are seven recognized species of porpoises within the family Phocoenidae. Among these, the harbour porpoise, Phocoena phocoena, is the most well-known. It is typically shy, avoiding boats and rarely leaping above water, and is distributed throughout much of the Northern Hemisphere. Other notable species include Burmeister's porpoise, recognized by the blunt tubercles on its dorsal fin, and the spectacled porpoise, named for its patch-like pigmentation around the eyes.
Behavior
Porpoises are known for their use of echolocation, producing ultrasonic clicks for navigation and social communication. In contrast to many dolphin species, porpoises do not form large social groups and are generally found in small groups or as solitary individuals. Calves are typically born in the spring and summer and remain dependent on their mothers until the following spring.
Habitat and Distribution
Porpoises are distributed across various oceanic regions, with each species having its own specific range. They are found in both coastal and offshore waters, with some species occupying the waters of the North Atlantic, North Pacific, and the southern oceans including the southern Indian Ocean, Atlantic, and Pacific oceans.
Conservation
Porpoises face numerous threats, including bycatch in fishing gear, competition for food due to overfishing, and pollution, particularly from heavy metals and organochlorides. The vaquita is one of the most critically endangered cetaceans in the world, with fewer than a dozen individuals remaining due to bycatch in gill nets. Conservation efforts include the establishment of protected reserves and breeding programs, such as the Baiji Dolphinarium at the Institute of Hydrobiology of the Chinese Academy of Sciences in Wuhan, China, focusing on the biological and behavioral study of porpoises to aid in their conservation.