harbor-porpoise
A common, or Harbor, porpoise. / Credit: Jan Zoetekouw / Shutterstock.com

Porpoises and dolphins, as well as whales, are members of the scientific order Cetacea. Dolphins and porpoises are often confused. Both have sleek bodies and large flippers. However, porpoises don’t have beaks like dolphins. Also, porpoises have triangular dorsal fins, while dolphins have curved or hook-shaped fins. The exception are finless porpoises. They don’t have fins at all.

Porpoises are shorter than dolphins. They grow to 5 to 6.6 feet (1.5 to 2 meters) and weigh 110 to 265 lbs. (50 to 120 kilograms). In contrast, the bottlenose dolphin grows to around 8 feet (2.5 m) long and weighs between 440 to 660 lbs. (200 to 300 kg).

There are six species in three genera of porpoise. As their name implies, Gulf of California harbor porpoises are found around the northern part of the Gulf of California. Black porpoises, also known as Burmeister’s porpoise, live off the coasts of eastern and western South America, according to the International Union for Conservation of Nature (IUCN). The spectacled porpoise likes cold water and has been found all around the world in a zone just north of Antarctica. The common porpoise, or harbor porpoise, also likes cold water, but sticks to the east coast of North America, around southern Greenland, waters off the northern coasts of Scandinavia and off the coasts of Alaska and Japan. Dall’s porpoise sticks to the northern rim of the Pacific Ocean. Some finless porpoises can be found in the Yellow Sea between China and Korea, and around southern Japan, while others swim along the coasts of South Asia.

Some porpoises don’t just stay in the ocean. Some swim in rivers and channels, as well, and can handle both salt and fresh waters. For example, the finless porpoises live in coastal waters and rivers along the Indian Ocean and western Pacific Ocean.

Most porpoises are social animals. They live in groups called shoals that can have just a couple members to thousands, according to the Animal Diversity Web (ADW). Dall’s porpoise, for example, lives in shoals with two to 20 members, while a harbor porpoise’s shoal may have six to 100 members.

Porpoise diets vary, depending on species, but they mostly stick to fish, crustaceans, octopus and squid. They can also be big eaters. The harbor porpoise eats about 10 percent of its body weight each day, according to the National Wildlife Federation.

There isn’t a lot known about porpoises in general, and there seems to be a particular lack of knowledge when it comes to the animal’s reproductive habits. Since porpoises are mammals, they have live births. The females have a gestation period of 10 to 11 months and give birth to one young at a time. The young are called pups or calves.

Pups are weaned at seven to 24 months of age and are sexually mature around 2 to 8 years of age, depending on the species. Porpoises can live up to 23 years.

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