Dolphins & porpoises
Number of dolphin and porpoise species
The Greek translation of "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.
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 larger size.
Lots of things! Pacific white-sided dolphins feed on herring, squid, salmon, anchovies and pollock. Hector’s dolphins feed on schooling yellow-eyed mullet and red cod from the ocean floor of New Zealand’s coastal waters. 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.
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 both feed 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. This is called “bycatch."
Public pressure for “dolphin-safe” canned tuna led to new laws in 1990, which reduced the numbers of dolphins killed. However, tuna fishers are still allowed to set seine nets around dolphins, provided that dolphins are not killed as a result. Studies are being carried out to determine how dolphins are affected by seine nets, or by having fishing vessels chase them at high speeds. Only the yellow-fin tuna fishery affects dolphins. Albacore tuna do not associate with dolphins.
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.
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.
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 then being an indicator of their relative intelligence.
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