As a result, almost all sharks are within reach of modern deep-sea trawlers, which can net fish to a depth of up to 2,300 meters (7,475 feet).
"Sharks are apparently confined to about 30 percent of the total ocean, and distribution of many species is fragmented around sea mounts, ocean ridges and ocean margins," said the paper, which appeared in the
Proceedings of the Royal Society B, a British journal.
"All populations are therefore within reach of human fisheries, and there is no hidden reserve of chondrichthyan biomass or biodiversity in the deep sea. Sharks may be more vulnerable to over-exploitation than previously thought," the report said.
Chondrichthyes is a category that include sharks, skates and rays.
Of the 490 species of shark, 25 are endangered or facing extinction, according to the "Red List" of threatened biodiversity compiled by the World Conservation Union (IUCN).
However, this number is set to grow, in the light of new data assessed by the IUCN's group of shark experts, the Swiss-based agency said on Monday.
Many shark species are very slow-growing, which means that a sudden drop in numbers can threaten their survival.
Shark species have been ravaged by commercial trawling. They are scooped up accidentally as "bycatch" by trawlers hunting more lucrative fish. They are also being increasingly targeted for their fins, which are used for the Chinese dish called shark-fin soup, and for their liver, which is rich in oil.
Some species of chondrichthyan fish have adapted to the extreme pressures and poor light of the deep ocean.
The shark, though, seems to be excluded from life in the abysses because of a lack of food and the relatively high buoyancy of its liver, said the paper, lead-authored by Imants Priede of Scotland's University of Aberdeen.
