SHARKS鈥� dislike of very deep water may be threatening their very survival.
Recent expeditions to the abyssal plains of the world鈥檚 oceans, combined with records dating back 150 years, suggest that sharks and rays have not colonised any waters deeper than about 3000 metres, says a team led by Monty Priede at the University of Aberdeen, UK (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2005.3461). This may make the creatures more vulnerable to over-exploitation than had been thought, as it puts all their habitats within reach of commercial fishing fleets.
Researchers working for the International Council for the Exploration of the Sea (ICES) have just discovered that populations of the world鈥檚 deepest-living shark, the Portuguese dogfish, have already plummeted by over 80 per cent in waters around the UK, France, Ireland and Norway. 鈥淲e have just designated this fish as the world鈥檚 deepest shark 鈥� and it is already endangered,鈥� Priede says.
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鈥淭he decline of Portuguese dogfish in the north-east Atlantic, in the face of fishing, is due to its low reproductive output, unsustainable catches and the presence of its adult population well within the depth range of the commercial fishery,鈥� says Maurice Clarke, chairman of the ICES鈥檚 Elasmobranch working group, which has been studying commercial catches of the fish from when they began in 1990.
鈥淥ur state of knowledge on most species 鈥� even the fairly high-profile sharks 鈥� is still pretty rudimentary,鈥� says John Stevens of Australia鈥檚 CSIRO Marine and Atmospheric Research in Hobart, Tasmania. Stevens is taking part in projects to satellite-tag great white, blue and whale sharks off the coast of Australia. He and his colleagues are finding that protected whale sharks found off Ningaloo Reef in Western Australia migrate into Indonesian waters, where they are at risk from hunting.
Meanwhile Mahmood Shivji of the Oceanographic Center at Nova Southeastern University in Fort Lauderdale, Florida, has found that a variety of sharks known to be vulnerable to overfishing, such as bull, silky and hammerhead sharks, are being sold in markets in Hong Kong, where their fins are considered a delicacy. A DNA analysis by Shivji revealed that blue sharks alone account for 17 per cent of all the fins sold (Conservation Biology, vol 20, p 201). Last year, Shivji also showed there is a burgeoning illegal international trade in fins of the great white shark, the most widely protected shark in the world.
