Experts puzzled as 30 whales stranded in 'unusual mortality event' in Alaska

Scientists 'very concerned' and suspect toxic algae, though Noaa concedes 'bottom line is we don't know what's causing deaths'

Thirty large whales have recently washed ashore on Alaskan coasts, prompting a federal agency to declare an "unusual mortality event" and mount an official investigation into the mystery of what could be killing so many marine mammals.

Related: 'A deaf whale is a dead whale': US navy sonars could be cause of strandings