An unusual mortality event (UME) is defined under the Marine Mammal Protection Act as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response".
Ten of the 20 whales that have been examined so far were killed by collisions with boats, something scientists are now at a loss to explain because there's been no corresponding spike in ship traffic.
Cindy Driscoll, veterinarian for the state Department of Natural Resources, said a badly decomposed whale carcass washed up on shore previous year; it was about 30 feet long with no skin or tail on it.
Representatives from NOAA will be releasing more information Thursday on the deaths of the whales and what steps will be taken next.
Forty-one whales died in the region previous year. The declaration, which now triggers an investigation into the cause of the whale deaths, was officially made on Thursday morning.
Scientists suspect the deaths may be occurring because fish the whales feed on have moved somewhere that exposes the humpbacks to increased shipping traffic. Only one or two humpbacks die from ship strikes between ME and Virginia in an average year.
The other whale carcass NOAA counts as being found in Maryland actually drifted past the state's coastline well offshore earlier this year and eventually landed on the Virginia coast, Driscoll said. "Humpback whales follow where the prey is and there may be aggregation in certain areas".
"Smaller vessels - they tend to be propeller strikes", Silber said.
Out of the 41 dead humpbacks, scientists have conducted necropsies on 20 of them.
"These mortalities are unusual because they are a marked increase in magnitude", said Mendy Garron, stranding coordinator for NOAA. "And then larger vessels, they appear to be in the form of blunt trauma - hemorrhaging or broken bones". Depending on how the investigation proceeds, NOAA hopes to find out if the reason behind the rise in humpback whale mortalities is related to natural or human causes.
There are more than 10,000 humpback whales in the North Atlantic Ocean. "You see the scarring on them".
She added that, in the same time frame there have been confirmed deaths along the East Coast for 11 minke whales, three right whales, one sei whale and two finback whales - quantities that are not considered unusual for those species, all of which are protected by the Marine Mammal Protection Act. Four populations are still endangered and one is threatened.