The National Oceanic and Atmospheric Administration (NOAA) is currently probing an "unusual mortality event" on the number of humpback whale deaths. In the past 15 months, NOAA has reported 41 humpback whale deaths from North Carolina to Maine along the Atlantic coast.

NOAA has conducted a full necropsy examination on 20 humpback whales. The agency revealed that 10 of the 20 whales died due to ship collisions while the cause of death for the rest of the whales is still unknown.

"Of the 20 whales examined, 10 had evidence of blunt force trauma or pre-mortem propeller wounds indicative of vessel strike," NOAA said in an official report.

This is in connection with a recent study, published in the journal Marine Mammal Science, which revealed that nearly 15 percent of the humpback whales that come to feed in the southern Gulf of Maine every spring collide with boats and other marine vessels.

"A vessel of any size can harm a whale. In smaller vessels they tend to be propeller strikes. And in larger vessels they appear to be in the form of blunt trauma, hemorrhaging or broken bones," Gregory Silber, coordinator of recovery activities for large whales in NOAA's Office of Protected Resources, said in a statement.

READ: Ships Might Be Colliding With Whales More Often Than Previously Thought

According to the Washington Post, NOAA revealed that the recent spike in humpback whale deaths is “an anomaly for this geographic area" and is well beyond the average of 14 deaths per year. "Unusual mortality event," as per NOAA, is an unexpected event where a high amount of animals die off.

To probe for the humpback whale mass death, a team of investigative scientists from NOAA will team up with the Working Group on Marine Mammal Unusual Mortality to collect evidence and determine the reason behind the increased humpback whale deaths. The investigation will focus on other possible threats for the humpback whales such as toxins, illness and prey movement.

Humpback whales (Megaptera novaeangliae) is listed as an endangered species under the US Endangered Species Act. Aside from ship collisions, humpback whales also face threats of entanglement, harassment from whale watchers, loss of habitat and commercial whaling.