* Thousands of new marine species found in 10-year census
* Benchmark to help assess climate change, BP oil spill
* Many fish, other marine species, dodge census takers
By Alister Doyle, Environment Correspondent
OSLO, Oct 4 (Reuters) - Scientists completed a 10-year census of marine life on Monday after finding thousands of exotic new species in a project that will help assess threats to the oceans ranging from climate change to BP's (BP.L) oil spill.
The $650 million international census, by 2,700 experts in 80 nations, discovered creatures such as a hairy-clawed "yeti crab", luminous fish in the sunless depths, a shrimp thought extinct in Jurassic times and a 7-metre (23 ft) long squid.
But the project (www.coml.org), which reckoned most types of creatures dodged the census and were still to be found, also documented overfishing of cod or tuna, hazards from oil and other pollution and impacts of global warming.
"The news about the oceans is both very good and very bad," said Paul Snelgrove, of Memorial University in Canada, who compiled the final report of a census that found more life than expected from the Arctic Ocean to volcanic vents on the seabed.
It raised the estimate of known marine animals and plants bigger than microbes, from worms to blue whales, to nearly 250,000 from 230,000. And it estimated that far more, or 750,000 other species, were still to be found.
Scientists said the biggest gaps were in still unexplored tracts of the Arctic, Antarctic and eastern Pacific oceans. And much of the deep ocean floor had barely been sampled.
"There is an enormous opportunity," said Jesse Ausubel, a co-founder of the census and program director at the Alfred P. Sloan Foundation. "There are three species out there to be discovered for every one we know."
The census itself found more than 6,000 potentially new species, led in numbers by crustaceans and molluscs, and made formal descriptions of more than 1,200 of them.
Among extremes, scientists found a metre-long tube worm an estimated 600 years old, tracked a sooty shearwater bird flying 64,000 km (40,000 miles) in the longest known annual migration and recorded a sailfish swimming at 110 kph (69 mph).
Among spinoffs, a 2009 review of the Gulf of Mexico found 8,332 species from fish to mammals in the area hit by BP's deep water blowout in April 2010, the worst spill in U.S. history.
"It's become one of the most valuable potential contributions of the census," Ausubel said of the Gulf survey. Checking the state of the Gulf against the public database would help understand damage -- and costs of BP's cleanup.
Two members of a five-strong commission named by U.S. President Barack Obama to investigate the spill - Terry Garcia and Donald Boesch -- had worked on the census.
In the longer term, monitoring the seas may help understand threats such as climate change and a related acidification of the oceans. Examination of the makeup of some of the creatures and plants might yield medical breakthroughs.
A related project had created a "barcode of life", inspired by the black and white lines on products in supermarkets, that allows scientists to identify species with a quick genetic test.
That has already exposed mislabelling of sushi in New York City and could have wide economic impact in tracking fraud in fish exports.
And the scientists said the census had successfully focused public attention on the beauty and variety of marine life and could help rally efforts to safeguard the seas.
Artists have been inspired by some creatures -- images of the yeti crab, found off Easter Island, has even been emblazoned on skateboards, Snelgrove said. "These critters are tremendous ambassadors for us," he added. (Editing by Ralph Boulton)
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