As part of the project, which began this week, scientists are flying by plane at low altitude - just 800 to 1,000 feet above the surface - across 20,000 nautical miles of U.S. and Russian waters, tracking the seals with infrared and digital cameras.

The survey is not required for the U.S. government to make a finding that any species of seals is endangered, but officials have expressed hope the study could provide more insight into how the loss of sea ice, attributed to global climate change, is harming the animals.

The study will cover four species - ringed, spotted, bearded and the ribbon seals - according to the National Oceanic and Atmospheric Administration.

All those seal species are characterized by their dependence on floating sea ice for resting, nursing their young, foraging for food and other important life functions.

The last time U.S. and Russian scientists collaborated on an ice seal study in the waters separating the two nations was in 1976, said Julie Speegle, a NOAA spokeswoman in Alaska.

NOAA in December 2010 proposed listing bearded and ringed seals as threatened under the Endangered Species Act, which could give the animals and their habitats stronger safeguards than they already receive under laws protecting marine mammals in general. Final decisions on those two species are expected in June, Speegle said.

The agency in 2008 rejected a petition to list ribbon seals under the Endangered Species Act. Those seals are known for their distinctive black-and-white striped fur. But last year, NOAA reversed itself and opened a new review on the species.

NOAA declined in 2010 to list the U.S. population of spotted seals, but invoked Endangered Species Act protections for those seals living in waters off Russia and China.

Lack of population information has been cited by NOAA as a reason for delays in listing decisions for some of the seals.

Obtaining accurate numbers for those animals, which dwell in a remote and frigid part of the world, has long been a challenge, Speegle said.

"It's a wide geographic area. Sometimes the weather conditions are pretty harsh," she said.

The scientists will use infrared technology to detect the heat of seals' bodies and digital imaging to distinguish between species, she said.

The survey flights started this week in remote Nome, Alaska, Speegle said. Flights will be conducted from other coastal locations as well, she said. The current survey will last into May, and a second survey is planned for next year, NOAA said.

(Editing by Alex Dobuzinskis, Steve Gorman; Desking by Peter Cooney)

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