Sharks and Rays Disappearing from the Ocean Deeps
BONN, Germany, May 22, 2008 (ENS) – Today, on International Biodiversity Day, the International Union for the Conservation of Nature, IUCN, released the first study to determine the global status of 21 species of oceanic pelagic sharks and rays. The research shows that nearly half of them – 10 species – are Vulnerable to extinction, and one species is Endangered.
The international study shows overfishing is the reason for the disappearance of these species and recommends key steps that governments can take to safeguard the sharks and rays.
“Fishery managers and regional, national and international officials have a real obligation to improve this situation,” says lead author Nicholas Dulvy, who is based at Simon Fraser University in Vancouver, British Columbia, Canada.
“We are losing species at a rate 10 to 100 times greater than historic extinction rates. Humans are making increasing use of ocean resources so many more aquatic species, particularly sharks, are coming under threat,” Dulvy said.
“But it doesn’t have to be like this,” he said. “With sufficient public support and resulting political will, we can turn the tide.”
Organized by the IUCN Shark Specialist Group, SSG, the study was conducted by 15 scientists from 13 different research institutes around the world, with additional contributions from scores of other SSG members.
The study was presented in Bonn at the Ninth Conference of the Parties to the Convention on Biological Diversity taking place through May 30.
Thresher sharks like this one are solitary and
prefer deep ocean waters. (Photo
courtesy Wikipedia)
The scientists found that the sharks and rays, including the Thresher shark, Alopias vulpinus; the Silky shark, Carcharhinus falciformis; and the Shortfin mako, Isurus oxyrinchus, are at risk of extinction due to targeted fishing for valuable fins and meat, as well as indirect bycatch in other fisheries.
In most cases, these catches are unregulated and unsustainable, the study finds.
The species classed as Endangered is the Giant devilray, Mobula mobular, which was previously considered Vulnerable. This huge ray feeds on plankton – microscopic animals, plants, or bacteria. It has a very low reproductive capacity – giving birth to a single huge pup at unknown intervals.
The IUCN Red List of Threatened Species states that its geographic range is probably limited to offshore deep waters of the Mediterranean, possibly adjoining North Atlantic waters, along the coast of Africa from Morocco to Senegal, and the Canary Islands, Madeira, the Azores, Portugal.
The giant ray is taken as bycatch on longlines, in swordfish pelagic driftnets, purse seines, trawls and in fixed tuna traps, to unsustainable levels. Given high bycatch mortality, its limited reproductive capacity and range, Mobula mobular is listed as Endangered. More research is needed on its exploitation, distribution, biology and ecology. In particular, the IUCN says, catch data are required, and stock assessments should be undertaken where the species is fished.
“The traditional view of oceanic sharks and rays as fast and powerful too often leads to a misperception that they are resilient to fishing pressure,” says Sonja Fordham, co-author of the paper and deputy chair of the IUCN SSC Shark Specialist Group.
“Despite mounting evidence of decline and increasing threats to these species, there are no international catch limits for oceanic sharks,” Fordham says. “Our research shows that action is urgently needed on a global level if these fisheries are to be sustainable.”
The increasing demand for shark fin soup, a delicacy prized in China and other rapidly growing Asian economies, means that often the valuable shark fins are retained and the shark carcasses are discarded. Frequently, discarded sharks and rays are not even recorded as caught, the study finds.
Sharks and rays are particularly vulnerable to overfishing because they take many years to become sexually mature and have relatively few offspring.
The group of scientists recommends that to conserve sharks and rays governments need to establish and enforce science-based catch limits for them. This effort depends on improved monitoring of fisheries taking sharks and rays and investment in shark and ray research and population assessments.
Governments should ensure an end to shark finning – removing fins and discarding bodies at sea, the scientists recommend. In addition, governments should minimize incidental catch, or bycatch, of sharks and rays, the scientists suggest.
Finally, the authors recommend that governments cooperate with other countries to conserve shared populations of sharks and rays.
The study on sharks and rays is published in the latest edition of “Aquatic Conservation: Marine and Freshwater Ecosystems.”
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