More intense investigation into the case of deaths of 30 large whales in the Western Gulf of Alaska since May has been announced by a federal agency. Scientists so far have got no evidence that could tell the reason behind the large number of deaths.

NOAA Fisheries called the deaths of whale an unusual mortality event, which triggered a new level of investigation that brought with it an access to additional resources.

The agency said in a statement that the deaths are nearly three times the historical average which the region has observed since past several years.

Julie Speegle, a spokeswoman for NOAA Fisheries in Alaska said the present hypothesis for the death of whales is the harmful algal bloom. But she said they just have the hypothesis but there is so far no evidence that links the two.

So far the officials have been able to get samples from one of the 30 whales. Teri Rowles, NOAA Fisheries' marine mammal health and stranding response coordinator, told reporters during a teleconference on Thursday that the high number of whale deaths is among the toughest to investigate as the carcasses often are floating, rarely beached and difficult to access for examination.

She added that in Alaska bear that feed on the washed-up whale carcasses has also created a safety concern for researchers who are in high need to collect the samples.

Scientists and researchers without being able to conduct a more complete necropsy can look at such things as environmental factors, historical information and mortality among seabirds or other sea creatures to get a better idea of what actually is going on, she said. But it is very difficult in case where they have o better access to the carcasses.