A SHARK described just a quarter-century ago as “perhaps the most abundant large animal on the face of the Earth” has all but vanished from one of its prime hunting grounds, the Gulf of Mexico.
A new study has found that stocks of the oceanic whitetip shark (Carcharhinus longimanus) are 1 per cent of those measured by US government surveys of fish catches in the 1950s. Another once-common species, the silky shark, has lost 90 per cent of its population, and a third, the dusky shark, is down by 80 per cent.
Whitetips, which can grow up to four metres long, were once so numerous that if you fell in the water, they would find you. They were the most commonly caught sharks in the gulf and had a reputation as the first and most bloodthirsty to show up after shipwrecks. Now, says Ransom Myers of Dalhousie University in Halifax, Canada, “there are virtually none left” in the gulf. He compares the wipe-out to the disappearance of herds of buffalo from America’s Great Plains.
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Myers and colleague Julia Baum reached their conclusions by comparing the numbers of sharks caught accidentally on fish hooks in the 1950s and today (Ecology Letters, vol 7, p 135). They blame the onset of intensive fishing in the gulf in the 1950s for the whitetip population’s collapse.
A further sign of the perilous state of the surviving populations of sharks comes from the discovery that, for each of the species studied, sharks caught accidentally today are smaller than in the past. And their average size suggests that many have yet to reach sexual maturity.
The figures mirror those for other large predatory fish. A global study of fishing records last year by Myers suggested that typically 90 per cent of an area’s top oceanic predators disappear within a decade of new fisheries being opened. And a similar study by Baum, also published last year, found that three-quarters of the great white and hammerhead sharks in the north-west Atlantic had disappeared in recent years.
Myers has called for new restrictions on fishing in areas of the gulf where sharks are often caught accidentally. But the US National Marine Fisheries Service has rejected his plea, claiming his data is misleading because fishing methods have changed since the 1950s, and because whitetip and other shark species are known to migrate.