London, Jan. 17: The ocean’s most fearsome predator has become common prey: shark populations have fallen to less than a quarter of their former size in the northwest Atlantic with the hammerhead particularly badly hit.
Some species are approaching the point of no return, and the team that reports the gloomy statistics today warns that current plans for marine reserves will not be enough to stop the decline caused by overfishing.
Existing protections for other large marine predators, such as sea turtles and tuna, should be extended to sharks, it says. Sharks are vulnerable to overfishing because they take many years to mature and have relatively few young per breeding cycle.
But they have been increasingly exploited in recent years, both as a “by-catch” and as targets in their own right, either for food such as shark fin soup, or as ingredients in health and beauty products. Until today’s study, published in Science, the status of most shark species has been uncertain. Julia Baum and colleagues at Dalhousie University, Canada, analysed fishery records from the north west Atlantic, one of the few datasets of its kind.
The researchers estimate that, with the exception of makos, all the species they studied have declined by more than half in the past eight to 15 years. The most striking example was hammerhead sharks, down by 89 per cent since 1986.
“The hammerheads concentrate in exactly the same places where the fleets fish for tuna and swordfish so they are hit because they are at the wrong place at the wrong time,” said Prof. Ransom Myers, a professor of biology at Dalhousie and co-author of the report.
The sharks routinely feed on the herring and squid commonly used for bait by the long-line fishermen, he said, making catching sharks a routine part of fishing for the other species.
Thresher sharks have declined by 80 per cent. Great white sharks, the predator in the film Jaws, have dropped by 79 per cent. The study found that in at least two fishing areas, no great white has been recorded since the early 1990s.
Tiger sharks have declined by 65 per cent and blue sharks by 60 per cent. The team cannot conclude that the pattern of decline is consistent for the entire north Atlantic, but points out that it is likely as fishing levels are as intense elsewhere.
“This is a worldwide phenomenon,” said Prof. Myers. “There are only a few areas in the world where we have good data, but wherever we do, they show the same thing — the shark is in serious decline.”
Sharks could be protected by changing commercial fishing patterns. Some of the sharks migrate along set paths at specific times of the year. Prohibiting fishing during those periods could reduce the by-catch of sharks, said Prof Myers.
Also, establishing refuges where all fishing was forbidden would give sharks, along with other fish, a safe haven where they could feed and reproduce safely.
The US has forbidden harvesting of shark fins for shark fin soup, a favourite in Asia, but long-line fleets from Spain and Japan continue to harvest, said Prof. Myers.