In for the krill

 作者:纪窜     |      日期:2019-03-08 02:12:02
By Debora MacKenzie SKYROCKETING numbers of fur seals are wreaking havoc on Antarctic islands. At a meeting this week in Lima, Peru, countries that are signatories to the Antarctic Treaty called for the first ever review of the species it protects, with a view to controlling fur seals. By the 1960s, southern fur seals were almost hunted to extinction, but they were protected under the Antarctic Treaty from 1964. Numbers have since exploded, increasing more than sevenfold each year between 1982 and 1988. In 1964 only a few dozen fur seals visited Signy Island in the South Orkneys. Now more than 20 000 do so—mainly young, non-mating males escaping the breeding beaches of South Georgia. Similar numbers have spread throughout the Antarctic Peninsula. Dominic Hodgson of the British Antarctic Survey (BAS) in Cambridge says that more than four times as many seals visit Signy than at any time over the past 6000 years. Hodgson has studied cores of lake sediments from the island, which reveal fluctuating numbers of seal hairs preserved in the oxygen-free mud. The greatest number of hairs in the sediments from past centuries is just 22 per cent of today’s level. Signy Island has more land-based biodiversity than any spot in the Antarctic, says Hodgson. The seals, however, are trampling moss banks that have been undisturbed for 4000 years and killing rare plants and lichens with their excrement and moulted fur. “Those plants are adapted to extremes of dryness and cold,” says Hodgson. “Their enzymes could be useful for biotechnology.” John Croxall, also of the BAS, believes that the abundance of krill—tiny shrimp-like creatures that swarm in the Southern Ocean—may be responsible for the seal boom. Krill are the seals’ main food, he says, and baleen whales such as the blue whale compete with them for the crustaceans. However, whale numbers fell by 95 per cent after Antarctic whaling began in the 1920s and have never recovered. Treaty members are giving scientists until 2001 to decide whether the Antarctic’s terrestrial ecosystem should be actively managed for the first time. This is controversial: the Treaty was originally intended to preserve the natural ecosystem, but Hodgson argues that the present ecological situation in the Southern Ocean is not natural. “It’s been pillaged for 300 years,” he says. Hodgson favours building fences to keep invading seals off protected plants, although the animals are hard to contain with fences. Ultimately, he says, seal control may require the recovery of the whales, or more krill harvesting. He rules out hunting as a long-term solution, but Lyn Goldsworthy, who is representing Greenpeace in Lima,