Scientists are baffled by the increase of humpback whales that washed ashore on the U.S. Atlantic coast over the past year and a half. The study is launched to probe the unusual rise in the death of one of the largest sea mammals.

The National Oceanic and Atmospheric Administration (NOAA) has launched an investigation on Thursday, April 27 to study a large number of humpback whale deaths, according to the official statement from the federal agency. For the past year, there are 41 humpback whales washed ashore death in the U.S. Pacific coasts from Maine to North Carolina.

NOAA declares the unusual number of deaths of humpback whales as a UME or unusual mortality event. The investigation will be conducted by experts with the focus to find the cause of mortality. On Thursday afternoon, NOAA also initiated a press conference to discuss the recent deaths of the humpback whales on the East Coast.

From the 41 death carcasses of the humpback whale, there are 20 that have been examined, as reported by CNN. Half of the whales' body showed the evidence of them hitting the marine vessels. The body of the death whales exhibited evidence of a blunt force trauma, which indicated a collision with marine vessels.

Those ten cases of whales colliding with vessels were documented in Virginia, New York, Delaware, Massachusetts and New Hampshire. There are so many possible causes of the humpback whale to get close to the shipping routes that made them colliding with the vessel.

"It's probably linked to prey sources," Greg Silber, Large Whale Recovery Coordinator for NOAA Fisheries Office of Protected Resources, said. "Humpback whales follow where the prey is and there may be aggregation in certain areas."

The investigation will gather the data and analyze them to find the clues. Further analysis also includes the monitoring the conditions of humpback whale's environmental and habitat, and human-caused threats. The humpback whale is listed as one of the endangered species and protected under the Marine Mammal Protection Act. Watch the report of the spike of humpback whale deaths on U.S. East Coast below: