The Family Phocoenidae is the family of cetaceans in which porpoises are classified. This family includes seven species of porpoises, which belong to 4 different genera. Until recently, it was thought that there were 6 species of porpoises, but new analysis of the species has divided one species (the finless porpoise) into two (the Indo-Pacific finless porpoise and the narrow-ridged finless porpoise) - two species which, unlike the others, don't have dorsal fins.
In this article, you can learn more about porpoises in general - what they look like, where they are found, and how they feed and reproduce.
Porpoises are generally small cetaceans (less than 8 feet in length), with blunt rostrums and stocky bodies. They belong to the group of whales called the odontocetes - or toothed whales. All porpoises have spade-shaped teeth (rather than conical teeth like dolphins).
The color of porpoises differs depending on the species. Some, like the Dall's porpoise, are black and white, while others, like harbor porpoise and finless porpoise, are gray with less striking coloration.
All porpoises except the Dall's porpoise have tubercles (small, hard bumps) on their back, either on the leading edge of their dorsal fin, or on top of their dorsal ridge (in the case of finless porpoises). The function of these tubercles are not known, but some scientists have suggested they might have a hydrodynamic function.
Habitat and Distribution:
Porpoises are found around the world, in both cold and warm waters. Many are found closer to shore, while some, like the harbor porpoise, can also be found offshore.
The diet of some porpoise species are not well known. Of those with known diets, they feed on fish, squid, and sometimes crustaceans, such as shrimp.
All porpoises have teeth, and the capability to use echolocation to find prey and navigate. During echolocation, high-frequency sounds are emitted by the porpoise, which then bounce off of surrounding objects and are received back into the porpoise's lower jaw. They are then transmitted to the inner ear and interpreted to determine the size, shape and distance of surrounding objects, including prey.
The reproductive behavior of porpoises varies by species, and is not known for all seven species. The gestation period for known cetaceans lasts about 10-12 months. Females in some species have been observed pregnant and lactating at the same time, so it is possible that porpoises can have a calf each year. They generally grow faster than other cetaceans and become sexually mature earlier, but there is a tradeoff - this increased growth and reproduction also gives them a shorter life span than some of the larger cetaceans.
The proximity of most porpoise species to shore increases potential endangerment from human activities. The top threat to many porpoise species (the vaquita, for example) is getting caught as bycatch in fishing gear. Regulations and gear restrictions (e.g., the use of pingers) and closure areas have been put in place in the U.S. to protect harbor porpoises. Many scientists and conservationists are trying to do the same for vaquitas, as their population is only thought to number about 250 individuals.
References and Further Information:
- IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2.
. Accessed November 30, 2012.
- NOAA Fisheries: Office of Protected Resources. Dall's Porpoise (Phocoenoides dalli).
- Perrin, W.F., Wursig, B., and J.G.M. Thewissen. 2002. Encyclopedia of Marine Mammals. Academic Press. Wahlberg, M. Harbor porpoise (P. phocoena). Society for Marine Mammalogy, Accessed October 30, 2012.