The US Fish and Wildlife Service (FWS) issued an emergency moratorium Friday on the hunting of brown bears on the Kenai National Wildlife Refuge in Alaska, citing a excess of bear deaths from hunting and other means.

As of 12:01 a.m. Saturday, the hunting of brown bears -- including grizzly bears -- is no longer allowed on the Kenai peninsula along Alaska's southern coast just south of Anchorage. The ban will be in effect for 30 days, after which the scene will be reassessed.

FWS officials said the number of known human-caused brown bear deaths this year had reached 66 -- more than 10 percent of 624, the best available estimation of the brown bear population on the Kenai Peninsula.

Andy Loranger, manager of the Kenai National Wildlife Refuge, said the current "level of mortality is not scientifically sustainable."

Adding to the FWS decision for an early end to brown bear sport hunting is that a high number of reproductive-age females have also been killed. At least one-third of brown bears killed on the refuge this year were adult females.

"Survivorship of adult female bears has been shown to be the primary driver of brown bear population dynamics. Losing so many adult female bears will have immediate negative impacts on this population," said John Morton, a wildlife biologist for the refuge.

Loranger added if the hunting season were not curtailed, the substantial loss of female bears "will result in a substantial reduction in the Kenai Peninsula's brown bear population. This would create a conservation concern for this population, which in turn would negatively impact hunters and many other Refuge visitors who value and enjoy viewing and photographing bears."

The breakdown of the 66 brown bears killed on the refuge this year amounts to 43 taken by hunters in the spring and fall hunting seasons, and 23 killed in defense of life or property, by motor vehicles, by wildlife control officials or by illegal hunting. Twenty-two of the dead bears were female.

The FWS said that it is likely that more bears have died at the hands of humans this year, but that the number of unreported killings is unclear.

"We do not take this closure lightly and will work with the Alaska Department of Fish & Game to develop a strategy to collaboratively manage brown bear populations that is consistent with the mandates of both agencies," said Loranger.