WASHINGTON - A U.S. court has upheld a ban on American sport hunters returning home with polar bear trophies from Canada.

In a decision released Monday, the District Court for the District of Columbia ruled that the U.S. Fish and Wildlife Service was within its mandate to forbid the import of polar bear parts.

Although the American Marine Mammals Protection Act does allow importing bear trophies if they were legally obtained, the Fish and Wildlife Service maintained that loophole was rendered invalid because climate change is threatening the species' survival.

"The Court ... finds that the MMPA mandates the Service's conclusion that sport-hunted polar bear trophies are no longer eligible for import as a result of the species' depleted status," the judgment says.

"Sport hunting is not among the narrow, enumerated exceptions to the MMPA's ban on taking and importing depleted marine mammals."

The Humane Society of the United States welcomed the ruling.

"Just as we don't allow the import of tiger skins and baby seal fur, American conservation law prevents American hunters from bringing home the heads and hides of imperilled polar bears shot in other countries," said Jonathan Lovvorn, a lawyer for the society.

Sport hunters pay about $30,000 to go on a polar bear hunt in Arctic Canada, an important source of cash in small communities that don't have very many of them. As well, hunters who kill bears to feed their families can sell the hides for about $400 a metre for extra cash.

In 2010, an international conservation watchdog found the annual export of 300 bear skins a year from Canada isn't big enough to threaten overall numbers of the species.

Traffic, an international wildlife trade monitoring network, concluded that while the great white predators may be slowly declining, numbers aren't falling fast enough to require a trade ban. Traffic also pointed out the overall estimate of bear populations at between 20-25,000 hasn't changed in years.

Inuit leaders have said local hunters will continue to hunt bears and that banning trophy exports won't save any of the animals.

In a related decision released Monday, Judge Emmet Sullivan also threw out a vital section of a U.S Department of the Interior rule that declared global warming is threatening the survival of the polar bear.

Sullivan found the administration of former president George W. Bush did not complete a required environmental review when it said the bear's designation as threatened in 2008 could not be used as a backdoor way to control greenhouse gases blamed for global warming.

The Obama administration agreed a year later, saying that activities outside the bear's habitat such as emissions from a power plant could not be controlled using the Endangered Species Act.

The Center for Biological Diversity, an environmental group that filed a lawsuit over the 2008 rule, said the decision puts the fate of the polar bear back in the hands of the Obama administration and Interior Secretary Ken Salazar.

"The Obama administration has the chance to do right by the polar bear," said Kassie Siegel, an attorney for the group.

"They need to decide whether the polar bear gets all the protections that other endangered species get, or whether they want to readopt a flawed Bush administration decision that exempts greenhouse gases" and other pollutants from the Endangered Species Act.

Sullivan's decision directs the Interior Department to respond by Nov. 17 with a timetable for when it will complete the required environmental review. Sullivan left an interim 2008 designation intact while the case continues.