Porpoises

Porpoises are similar in appearance to a dolphin, however, they are more closely related to narwhals and belugas than to the true dolphins. There are eight extant species of porpoise, all among the smallest of the toothed whales. Porpoises are distinguished from dolphins by their flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and lack of a pronounced beak. Porpoises use echolocation as their primary sensory system. Some species are well adapted for diving to great depths. Like all cetaceans, they have a layer of fat, or blubber, under the skin to keep them warm in cold water. These marine mammals produce ultrasonic clicks, which are used for both navigation (echolocation) and social communication. In contrast to many dolphin species, porpoises are not very gregarious and do not form large social groups. Calves are typically born in the spring and summer months and remain dependent on their mothers until the following spring. Porpoises have traditionally been hunted in many areas for their meat and blubber and are highly affected by bycatch. They also suffer from competition for food from fisheries, and marine pollution.