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Predator in a fin soup
A sharp decline in shark numbers in the Mediterranean Sea sounds an alarm.
- By Juliet Eilperin, Los Angeles Times-Washington Post News Service
- Published: 00:06 July 18, 2008
- Shark fins in a fishing vessel. The demand for shark fin in the Asian markets is leading to a decline in shark populations in the Mediterranean Sea
- Image Credit: Enric Sala/The Washington Post
The Mediterranean Sea, says Francesco Ferretti, is “a very dangerous place for a shark''.
So dangerous that in the past two centuries, the shark population there has plummeted by more than 97 per cent, both in relative numbers and collective weight, according to a study by the graduate student, two colleagues at Dalhousie University in Nova Scotia and an Italian researcher.
They based their conclusion on evidence scoured from an unusually wide variety of records, including documents drawn from universities and archives, from fish markets and recreational fishing clubs and from local accounts of shark sightings.
The paper, co-authored with the late Dalhousie marine biologist Ransom A. Myers and others, is only the latest evidence that some of the oceans' most feared predators are themselves in dire danger.
Another team of scientists has shown in recent months that the peril is global, concluding that all but two of 21 species of open-ocean sharks and their cousins, the rays, are facing the risk of extinction.
Another found that the decline of sharks at the top of the food chain is disrupting marine ecosystems around the globe.
“Sharks are just one part of the ocean's web of life,'' said Margaret Bowman, who directs the non-profit Lenfest Ocean Programme, which helped fund all three studies.
“But these studies show if you pull out that one thread, the whole web suffers.''
Several factors help explain why the shark population has declined in the Mediterranean, Ferretti said in a recent interview.
Fishing vessels are targeting them to meet the Asian demand for shark-fin soup, he said, while simultaneously trying to compensate for the fact that they have depleted other fisheries.
“Some fishers have decided to switch to sharks because they cannot make up their product with bony fish,'' he said, noting that the presence of so many countries bordering the Mediterranean has contributed to the fishing pressure there.
“At these levels, these sharks can be considered functionally extinct, meaning that they cannot perform their role of top predators in the Mediterranean marine ecosystems anymore,'' he said.
Ferretti and his colleagues have published their findings in Conservation Biology.
Two other papers published earlier suggest that once these predators disappear, the species they prey on not only rise in numbers but also behave differently once they are in less danger of being eaten.
“We now understand that both on land and in the sea, large predators play important roles in regulating both the total number and the behaviour of their prey,'' wrote Boris Worm, the lead author of a recent paper in Trends in Ecology and Evolution.
“Unchecked by their predators, some of these prey species can wreak havoc on ecosystems — this is one important reason to keep predators around in sufficient numbers.''
Another team of researchers, headed by Nicholas Dulvy, a biology professor at Simon Fraser University in British Columbia, found that in the open ocean, sharks that used to be a bycatch for vessels seeking tuna and swordfish are increasingly being targeted for their meat and fins.
Bowman said she and other advocates hope fishery managers will “figure out how to control fishing to prevent further declines'' of sharks, and policymakers are responding.
On June 19, the National Oceanographic and Atmospheric Administration (NOAA) in the US, announced it would ban the removal of shark fins at sea in the Atlantic and the Gulf of Mexico by late July and cut the permitted catch of sandbar and porbeagle sharks.
Enric Cortes, a scientist at NOAA's Fisheries Service who conducts shark-population assessments along the East Coast, emphasised that scientists are still learning about the role sharks play in ecosystems.
They may dominate more isolated regions but they don't necessarily shape every marine environment they inhabit: “The jury is still out on that.''
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