A mysterious die-off of large whales in the Gulf of Alaska is now classified as an "unusual mortality event," elevating the official response, the National Oceanic and Atmospheric Administration said Thursday.

The deaths were first discovered in late May, when carcasses of endangered fin whales were found floating near Kodiak. Since then, the toll has increased, and now totals 30 whales -- 11 fin whales, 14 humpbacks, one gray whale and four unidentified cetaceans, NOAA said Thursday.

Additional whale deaths have been reported in waters off British Columbia, where the toll is four humpbacks and one sperm whale, officials said.

Alaska researchers launched an investigation of the whale deaths soon after the first carcasses were sighted in late May. The unusual mortality event declaration -- under a program established in 1991 -- makes more resources available to expand that investigation, including money from a special fund and expertise from a special working group.

The whale deaths may be tied to a larger marine pattern, officials said at a Thursday teleconference.

They come at a time when scientists and resource managers are coping with several abnormalities in the Pacific marine environment. Thousands of starving sea lion pups have been stranded along the California coast, a situation that sparked its own unusual mortality event declaration; a harmful algal bloom of unusual size and duration has emerged in waters from Alaska to California; and large numbers of seabirds have died in the Pacific Northwest and Alaska from yet-to-be-determined causes.

They also come at a time when northeastern Pacific surface temperatures are much higher than normal, thanks to a persistent warm mass nicknamed "The Blob," and warm conditions are expected to continue, thanks to a developing El Nino weather system.

Those warm conditions, both in the water in and in the atmosphere, extend to the Gulf of Alaska, said Teri Rowles, lead marine mammal scientist for NOAA Fisheries.

"That always concerns us because that means there's probably a change in overall pathogen exposure, possibly harmful algal blooms and other factors," Rowles said in Thursday's teleconference.

A leading suspect in the Alaska whale deaths is some type of toxin produced by an algal bloom, she said.

"Biotoxins will be one of the top priorities but not the only priority that we'll be looking at to rule in or rule out whether it's playing a role in this death investigation and these mortalities, both in Canada and the U.S.," she said.

Infectious diseases are also possible culprits, as are other environmental factors, she said.

Not considered a likely suspect at this time is the recent Northern Edge military exercise conducted in and around the Gulf of Alaska. "At this time, we have no evidence linking the whale deaths to military activities," said NOAA spokeswoman Julie Speegle.

It has been very difficult to reach the dead whales to get samples, said Bree Witteveen, a Kodiak-based marine mammal specialist with the Alaska Sea Grant program. Alaska's coastline is vast, largely uninhabited and jagged in many places, making access nearly impossible, said Witteveen, who is based in Kodiak and is the on-site coordinator of the whale-death investigation.

"It's unfortunate, but we just cannot get to those carcasses more often than not," she said.

Only one dead Alaska whale has been sampled. Tests came back negative for domoic acid -- a toxin produced by algae -- but that whale was so decomposed the samples are not very reliable, Rowles said.

The researchers made a plea for more information from the public, chiefly quick reporting when dead or distressed whales are spotted. "The most critical thing for this UME, given that it is large whales, is our ability to get to the animals, document them and, if possible, perform sample collections either at sea or on the beach if they strand," Rowles said.

Researchers have had more luck in British Columbia, where necropsies were performed on two of the dead whales. Results have not come in yet, said Paul Cottrell, Pacific marine mammal coordinator for Canada's Department of Fisheries and Oceans.

Other clues can be gleaned from samples of harvested seafood, forage fish and the waters where the dead whales swam, the researchers said. That work is ongoing,

"It's going to take a bit of time to pull it all together. And each of these individual species that are examined are really important to us as we put the whole ecosystem picture together," Rowles said

Prior to Thursday, there had been 60 unusual morality event declarations issued by NOAA for marine mammal die-offs. The last such declaration for Alaska was issued in 2011 in response to a mysterious disease that was killing and sickening ice seals.