At least nine fin whales have been found dead in recent weeks in southern Alaska waters, and researchers with the National Oceanic and Atmospheric Administration and University of Alaska Fairbanks are attempting to find out what killed them.

"We rarely see more than one fin whale carcass every couple of years," said Kate Wynne, a UAF professor and Alaska Sea Grant marine mammal specialist, and the recent rash of dead whale discoveries is "mysterious."

According to a release from UAF, the first of the whales was reportedly spotted on May 23 by crew members aboard the state ferry Kennicott, which travels between Bellingham, Washington, and ports in Southeast and Southcentral Alaska.

Over the next two weeks, boaters, fishermen and pilots reported other dead whales in the floating in the area, the UAF release said. Those reports, and the photos submitted with them, led Wynne and her NOAA colleagues to conclude that "at least nine fin whales died in a relatively small area," the release said.

For now, the "go-to answer" to questions about the deaths is a harmful algal bloom, said Bree Witteveen, a UAF Sea Grant marine mammal specialist working with Wynne on the investigation.

"It's definitely a suspect," she said in a telephone interview. But pinpointing cause of death for the marine mammals could be difficult, "even if we have evidence of a harmful algal bloom," she said.

"We honestly don't know," she said. "We probably won't ever get a definitive answer."

Fin whales are massive, growing to more than 70 feet long as adults and weighing 45 tons, making them the second-largest whale species, according to NOAA. They migrate every summer to Alaska waters, including the Gulf of Alaska, Prince William Sound and the Chukchi Sea, and filter the tiny fish they eat through the baleen in their mouths.

They travel and feed in tight groups, behavior that supports the idea that the whales encountered something toxic at the same time in May, the UAF release said.

The whales were reportedly discovered from Kodiak Island in the Gulf of Alaska to Unimak Pass, which is located near the eastern end of the Aleutian Islands and western tip of the Alaska Peninsula.

A couple of the dead whales wound up on beaches, Witteveen said. She and Wynne were able to get samples from one of those whales, she said, but another beached carcass was carried away by the night's tide before samples could be retrieved.

The single whale that they were able to examine had no obvious injuries and had a thick layer of blubber, a sign of good body condition, Witteveen said.

"It was a really healthy animal; there weren't any obvious signs of cause of death," she said.

The samples were sent to a lab for analysis, and Witteveen said she expects results within a couple of weeks.

Fin whales are endangered, and little is known about the details of their migration patterns or even their total numbers, Witteveen said.

The loss of nine whales is probably not significant from a population standpoint, "but it is enough to raise a concern that something unusual, something out of the ordinary is happening," she said.

The researchers are planning to fly over the eastern side of the Kodiak Archipelago, where most of the dead whales have been found, to look for additional carcasses or signs of algal blooms and to take water samples, Witteveen said.

Warmer-than-normal waters are among the factors that scientists have linked to harmful algal blooms.

Sea-surface temperatures in the Gulf of Alaska are running 0.9 to 3.6 degrees above average, said Jason Ahsenmacher of the National Weather Service in Anchorage.

Meanwhile, several dead walruses and hundreds of dead seabirds have been discovered in an Alaska Peninsula region about 300 miles southwest of Kodiak Island, federal officials report.

About 25 walrus carcasses were found near Izembek National Wildlife Refuge, an unexpected occurrence in an area where walrus tramplings are rare, said U.S. Fish and Wildlife Service spokeswoman Andrea Medeiros.

"You don't usually see large mortality events in that area," she said.

Law enforcement agents with Fish and Wildlife are investigating the walrus deaths to determine whether they might have been human-caused, Medeiros said.

In the same general area, carcasses of hundreds of seabirds and a dead whale were also found, she said. "I don't know if there's a connection or not," she said.

A dead humpback whale was found in the same area as the fin whales, but was determined to have been killed by an orca, Witteveen said.

Officials are asking members of the public to report and photograph any other dead animals that may seem unusual.