By Yereth Rosen
ANCHORAGE, Alaska (Reuters) - Two of three killer whales that wandered far up an Alaska river have died, apparently succumbing to stresses associated with being out of their saltwater habitat, federal officials said on Sunday.
The surviving whale was seen swimming downriver Saturday toward possible safety, officials with the National Oceanic and Atmospheric Administration's Fisheries Service said.
Biologists were concerned about the three whales because they had spent three weeks in southwest Alaska's salmon-rich Nushagak River and were lingering as far as 30 miles upstream from where the river flows into the saltwater of Bristol Bay.
It was the first time killer whales had been documented lingering far upriver in any area of Alaska, according to NOAA Fisheries officials.
The two whale deaths were confirmed late Saturday by a biologist with the U.S. Fish and Wildlife Service, NOAA said. Federal agencies had been tipped off by a local resident who reported seeing a floating carcass, and the biologist who searched the area by air found both of the dead whales, one floating and one on the riverbank, NOAA said.
When last seen swimming in the Nushagak River, all the whales had a filmy coating on their skin, a sign of stress.
Fresh water has a different chemical makeup than saltwater and prolonged exposure is dangerous for killer whales, said Julie Speegle, a NOAA spokeswoman in Juneau, Alaska.
"Saltwater is their natural habitat," she said. "They do often swim into fresh water pursuing prey, but usually they turn around and go back into the saltwater."
A team of NOAA-led biologists plan to conduct necropsies on the dead whales on Monday or Tuesday, Speegle said.
Meanwhile, biologists are still surveying the area to try to find the surviving whale and, if necessary, will consider steps to shoo it back into its saltwater habitat, she said.
(Edited by David Bailey)