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Dolphins & Porpoises

About AquaFacts: AquaFacts are a resource for students who are looking for information on the animals at the Aquarium or other Aquarium-related topics. Here, we’ve compiled some of the most frequently asked questions that we’ve received about dolphins and porpoises. The answers come from our biologists and from reputable sources that we reference at the end of this page. If you have a question about dolphins and porpoises that’s not addressed in this page or the references below, please feel free to email our librarian.

Dolphins & Porpoises

Questions & Answers

How many different kinds of dolphins are there?

There are an estimated 33 species of oceanic dolphins (Delphinidae family) and six porpoise species (Phocoenidae family).

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What are the differences between a dolphin and a porpoise?

There are slight physical differences between dolphins and porpoises. Porpoise teeth are shaped like spades and each tooth has a sharp edge. Dolphin teeth are shaped like cones and are pointed. Porpoises tend to be smaller than dolphins and usually do not have pronounced beaks. 

Whales, dolphins and porpoises are classified in the same animal group, Cetacea. “Whale” is a common name used to describe a large cetacean. It relates to relative size, much like the distinction between “boat” and “ship.” Killer whales, melon-headed whales, pilot whales, and false killer whales are all part of the dolphin family, but are called whales because of their size. In B.C. waters, dolphins produce sounds that we can hear, whereas porpoises communicate at frequencies beyond the range of human hearing.

How many species of river dolphins are there and where do they live?

There are seven living species of freshwater cetaceans four of which are dolphins: two species of Amazon river dolphins (which were previously thought to be one species, but thanks to DNA research, have proven that there are indeed 2 separate species!), Ganges, and Indus river dolphins, the Irrawaddy dolphin, the tucuxi, and the finless porpoise. Most of these species are threatened by overfishing and habitat loss. Amazon river dolphins inhabit flooded grasslands and forests during the rainy season. Ganges river dolphins live in a river whose banks house a tenth of the world’s human population. It is common for river dolphins to have small eyes, and the Ganges river dolphin and Indus river dolphins are almost blind. A seventh species, the baiji or Yangtze river dolphin, lived in the Yangtze River but was declared extinct in 2007 because researchers failed to find a single individual in a 2006 study.

How do tuna fisheries affect dolphins?

Yellow-fin tuna often school beneath large herds of pan-tropical spotted dolphins and spinner dolphins in the eastern Pacific Ocean. One theory explaining this pairing is that the dolphins and tuna are both feeding on surface-dwelling squid, mackerel and flying fish. When purse-seine-fishing nets are set beneath the dolphins to surround the tuna, dolphins and other animals also get tangled in the nets and very often die. These unintentionally caught animals are known as “bycatch”.

Public pressure for “dolphin safe” canned tuna led to new laws in 1990, helping to reduce the numbers of dolphins killed. However, tuna fishers are still allowed to set seine nets around dolphins, provided that dolphins are not observed being killed. Studies are presently being carried out to determine how dolphins are affected by being encircled by seine nets or by being chased at high speeds by fishing vessels. Only the yellow-fin tuna fishery affects dolphins. Albacore tuna do not associate with dolphins.

Why do dolphins make so many sounds?

Whistle-like sounds help dolphins keep in contact and communicate with each other as they travel and feed. Dolphins "echolocate" to find their food or to scan their surroundings. They direct "clicks" into the water and the clicks rebound off solid objects (fish, logs, boats) and echo back to the dolphins. Dolphins listen for the strength of the rebounding clicks to identify what the object is and its distance from them.

These clicks and whistles are created in the dolphin’s nasal passages just below their blowhole. The sounds are received by fat filled hollows in the lower jaw which then conducts the vibrations of the echo to the middle ear and brain for processing.

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What do dolphins eat?

Pacific white-sided dolphins feed on herring, squid, salmon, anchovies and pollock. Hector’s dolphins of New Zealand’s coastal waters feed on schooling yellow-eyed mullet and red cod from the ocean floor. Bottlenose dolphins feed on small fishes, eels, catfishes, mullet, squid and shrimp. White-beaked dolphins of the North Atlantic have been observed feeding with fin whales on capelin.

Are dolphins intelligent?

Dolphins are definitely smart but there is much debate over intelligence tests. Do they indicate relative intelligence or reflect the adaptations each species has made to its environment? Studies of numerous species of dolphins have shown evidence of high levels of intelligence, including complex social behaviour, detailed memory, self-recognition, and the ability to learn rudimentary symbol-based artificial codes. The differences between the various dolphin species reflect the variation in their habitat, behaviour and diet rather than being an indication of their relative intelligence.

How can I help dolphins in British Columbia?

If you see a whale or dolphin off the coast of British Columbia, we would love to hear about it. Report your sighting at www.wildwhales.org.



Facts & References

Key Facts

  • Average life span: 10-50 years (variable for each species)
  • Length of pregnancy (gestation period): 10-17 months
  • Calving: can occur every 1-5 years, one calf at a time
  • Size: “typical” dolphins are about two metres long and weigh approximately 100 kg

Did You Know?

  • Dall’s porpoises, harbour porpoises, Pacific white-sided dolphins and killer whales inhabit British Columbia’s marine waters. Visiting species in B.C. may include northern right whale dolphins, Risso’s dolphins, common dolphins, pilot whales and false killer whales.
  • The most endangered dolphins and porpoises are the Mexico’s vaquita, Malaysia’s Irrawaddy dolphin and New Zealand’s Maui’s dolphin
  • Pacific white-sided dolphins travel in schools of between two to as many as 1000 individuals: they associate with many species of dolphins, baleen whales, seals and sea lions
  • Killer whales, the largest dolphin species, can grow to eight m and weigh up to 9,000 kg
  • The Greek translation of porpoise is “pig fish” possibly because most porpoises have blunt snouts
  • When you see “dolphin” on a menu, it most often refers to a very large, tropical, fast-swimming fish, not a marine mammal: dolphinfish are also known as mahi mahi, dorado, pompano and rainbowfish

References

  1. Carwardine, Mark. 1995. Whales, Dolphins and Porpoises. Toronto: Stoddart.
  2. Darling, James D., et al. 1995. Whales, Dolphins and Porpoises. Washington: National Geographic Society.
  3. Gill, Peter and Linda Gibson. 1997. Whales, Dolphins and Porpoises. New York: The Reader’s Digest Association.
  4. Marino, Lori. 2002. “Convergence of complex cognitive abilities in cetaceans and primates.” Brain, Behavior and Evolution 59: 21–32.
  5. Perrin, William F., Bernd Wursig and J.G.M. Thewissen. (Editors). 2002. Encyclopedia of Marine Mammals. San Diego: Academic Press.
  6. Gill, Peter and Linda Gibson. 1997. Whales, Dolphins and Porpoises. New York: The Reader’s Digest Association.
  7. Haley, Delphine. 1986. Marine Mammals of the Eastern Pacific and Arctic Waters. 2nd Ed. Seattle: Pacific Search Press.
  8. Heise, Kathy. Personal communication, 28 June 2002.
  9. Perrin, William F., Bernd Wursig and J.G.M. Thewissen. (Editors). 2002. Encyclopedia of Marine Mammals. San Diego: Academic Press.
  10. Shane, Susan H. 1991. "Smarts." Sea Frontiers. 37 (2). 40-43.
  11. Wild Whales. Factsheets.
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