Of the six species classified by scientists as true porpoises, the harbour porpoise has the widest range and is the most commonly seen. Preferring cooler waters, it lives along the coasts of northern North America, Europe and northeastern Asia. Its near- shore habits, however, make the species vulnerable to shipping traffic, pollution and entanglement in fishing gear.
Much of what is known about harbour porpoises can be traced to the early work of David E Gaskin, a British biologist based at the University of Guelph, in Ontario, Canada. In 1969, Gaskin set up a field station on the Bay of Fundy in New Brunswick to conduct studies of porpoise biology and ecology. From shore and from ferries and other boats, he monitored the porpoises year after year as they moved through the island passages.
Gaskin and his students found that most of the harbour porpoises arrive in the Bay of Fundy in spring, soon after the water temperature reaches 8 degrees C. Females with newborn calves arrive in mid-July. The population peaks in August and stays until September or mid-October. In autumn and winter, the porpoises are few and far between. In rain, snow or fog, it is nearly impossible to see them.
Gaskin says the porpoises' seasonal movements seem to follow those of their main prey, herring and mackerel. Sometimes, he watched them chasing speedy mackerel near the surface - the one brief occasion when the porpoises abandon their shy manner - swimming up to 22 kmh as they dashed through the water in mad pursuit. Gaskin and his students examined the stomachs of dead porpoises to learn what they eat: cephalopods and a variety of fish (herring, mackerel, pollack, silver hake and whiting). Harbour porpoises seem to prefer schooling, nonspiny fish.
Farther south, in the Gulf of Maine, right whale researchers led by Scot Kraus from the New England Aquarium have also studied harbour porpoises. In July 1982, in the first Gulf of Maine census, they estimated that there were at least 8,000 harbour porpoises. Some 3,000 more were thought to be in Canadian waters in the Bay of Fundy. After the census, the researchers began to suspect that the Gulf of Maine/Bay of Fundy harbour porpoises formed a distinct population. Staying in the area from spring through autumn, they then moved offshore in the winter - perhaps to the edge of the continental shelf or the Grand Banks and Georges Bank.
Gaskin, Kraus and others have worried about threats to porpoises, especially the danger of their getting caught in gill nets. The porpoises suffocate when they cannot surface to breathe. At first, the number of deaths seemed low - fewer than 15 a year were reported in the Bay of Fundy in the early 1980s. But some fishermen do not make the reports that the law requires. Later research has shown that during the late 1980s, probably 600 to 1,000 a year were killed.
Furthermore, Gaskin and his associate Andrew Read have found fewer small calves and large females in recent years, a sign that the killings are having a damaging effect on the population and may be reducing its reproductive potential. Harbour porpoises have a low reproductive rate. A female can produce only two or three calves in her lifetim, which is an average of 7 to 8 years.
Gaskin and Read are working to control the use of gill nets and trying to make nets more visible to the porpoises. Stiffer American regulations are also necassary in the Gulf of Maine. Many conservationists think that gill nets should be outlawed.
Harbour porpoises have been well studied off California, around Denmark and in the Black Sea, yet their conservation needs are neglected. "They are small,: says Kraus, and today, no one catches them for food or other producs. "They have no value except to those of us who like them and enjoy seeing them in the wild."
Size: 1.4 to 1.8 m, 54 to 65 kg. females slightly larger than males
Calves at birth: 67 to 80 cm
Teeth: 19 to 28 small, spade-shaped teeth on each side of upper and lower jaws
Food: Fish (especially bottom fish, herring, mackerel, whiting and anchovies)
Habitat: Maintly coastal
Range: Temperate and subarctic North Atlantic and Pacific plus Black Sea and Sea of Azov
Status: Population unknown
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