The long goodbye

时间:2019-03-08 07:05:20166网络整理admin

By Jonathan Knight THE North Atlantic right whale is slowly disappearing. On current trends, it will be extinct in less than 200 years, say biologists in Massachusetts. The main problem is the number of whales being hit by ships. The northern right whale—so named because it was the “right” whale to hunt—was nearly wiped out by commercial hunters. After whaling ended in 1935, its numbers began to recover, but only slowly. Roughly 300 right whales now live in the North Atlantic, mostly along the North American seaboard. With so few animals, marine ecologists have found it hard to discover whether the population is still increasing. To answer the question, researchers led by Hal Caswell, a mathematical ecologist at the Woods Hole Oceanographic Institution on Cape Cod, compiled data from photographic records of right whale sightings since 1980. The researchers could easily tell the whales apart, because each bears a distinct pattern of scars and calluses. From these records, Caswell calculated the average survival rate. “There was a very strong declining trend in survival probability,” he says. In order to determine the overall rate of population growth, the researchers factored in data on the whales’ reproductive rates. In 1980, they estimate, the population was growing by 5.3 per cent a year. By 1994, however, it was declining by 2.4 per cent a year, Caswell and his colleagues report this week in Proceedings of the National Academy of Sciences (vol 96, p 3308). Modelling the dynamics of whale populations is notoriously difficult. But other biologists feel Caswell’s analysis is sound. “Unfortunately, what he has predicted may come true,” says Amy Knowlton, an expert on right whales at the New England Aquarium in Boston. Experts blame a rise in shipping for the right whale’s decline. Of 43 deaths documented since 1970, 15 were caused by collisions with ships. The problem is that right whales swim quite slowly in areas where there is a lot of shipping. Birth rates have also declined, possibly due to inbreeding or coastal pollution. Caswell hopes that new legislation in the US will halt the decline. From July, ships entering critical whale habitats off New England and the coast of Florida will be required to contact the US Coast Guard for the latest whale sightings. “The trend in survival rates could be reversed very quickly if the policy works,