Dolphins, porpoises and whales

Press, 28 February 1984, Page 18

Dolphins, porpoises and whales

Whales, dolphins and porpoises are all mammals belonging to one big group — Cetacea.

They were once land mammals but the bones of their front toes, wrists and arms have fused into paddles, used for keeping balance.

Leaping and diving movements of their bodies, aided by powerful tail thrust, allow them to move at good speed through water. The large rorqual Fin whales can shoot through the ocean at more than 35km an hour, passing ships at sea.

Because of modifications to the mammalian breathing system, whales and their close relatives can also dive to great depths without getting the “bends.”

In addition, their bodies are adapted in a number of ways to withstand cold temperatures.

Cetaceans have either baleen plates or teeth for feeding.

The baleen whales are mainly large animals, ranging in length from 10m to 30m.

They live near the surface, feeding on planktonic krill — shoals of tiny, shrimp-like creatures — which they sieve from the water by means of whalebone plates with frayed, bristly edges. The toothed whales, including dolphins and porpoises, feed mostly on fish and squid, and often dive deep in search of prey. They are highly social, and use an extensive repertoire of sound signals in communicating with each other. These toothed cetaceans rapge in size from the 1.6 m Hector’s dolphin up the 20m Sperm whale, and the smaller kinds can be tamed and trained.

The distinctively-marked “Killer whale,” Orcinus orca, is actually a dolphin; the popular names for ceta-

ceans are frequently at odds with scientific classification. Common in New Zealand waters and plentiful in the seas to the south, Killer whales usually travel in herds which may number 30 or 40, and which appear to be largely family groups.

These “whales” are somewhat unusual in that besides feeding on fish and squid, they will also attack other dolphins, seals and even fairly large whales. They are not particularly large, growing to only about 9m, and folklore that describes them as cunning, ferocious and dangerous to man is not backed up by any actual records of deliberate fatal attacks on human beings. In fact, individual Killer whales in captivity seem to be charming animals, responding to human companionship and kindness, and quick to learn tricks to please their handlers. They have even been known to put up with having their teeth brushed.

Smaller dolphins, too, are fairly common off the coasts of New Zealand, and there have been two particularly famous ones that have befriended people. One was Pelorus Jack, a Risso’s dolphin, that used to meet ships in Cook Strait and accompany them across it. To the delight of hundreds of people, he kept up this practice, day and night-, over a period of 20 years from 1888 onwards.

More recently, there was a young female Bottlenose dolphin, Opo, that played with bathers and fishermen at Opononi, near Hokianga, during the summer of 1955 to 1956.

She was found dead in March of 1956, stranded in a pool, and it is thought that her echo-location system may have been damaged by people fishing with gelignite.

At a bay on the west coast of Australia there is a

family of Bottlenose dolphins which come into the shallows to meet human visitors, one of whom has written about them in “The Dolphins’ Gift,” a book by Elizabeth Gawain (Whatever Publishing, 1981).

For younger readers, a dolphin story called “Opo, the Happy Dolphin,” by Julia Graham, has been added to the Golden Book Library (Golden Press, 1979).