Massive numbers of humpback whales are dying along the coast of the Atlantic Ocean right now, and marine biologists can’t figure out exactly why it’s happening.

Since the beginning of 2016, there’ve been 41 shored, dead whales reported on the coast between Maine and North Carolina, which is a huge amount considering that usually around eight humpback whales per year are beached in that area. Ten of these whales are known to have died after hitting ships, but the causes of the other deaths are so far unknown.

This type of pattern is known to marine biologists as an “unusual mortality event” under the Marine Mammal Protection Act, which designates it as an occurrence that “demands immediate response.”

Deborah Fauquier of the National Oceanic and Atmospheric Administration (NOAA) Fisheries called the trend “alarming” in a news conference on Thursday. The agency is beginning an inquiry to learn more.

Whale Death Marine Biology
Workers examining a dead humpback whale that washed up on New York City beaches on April 5.

While marine biologists don’t yet know exactly what’s going on, it’s possible that whales beyond those ten also died from coming into contact with ships. If that’s the case, researchers still don’t know why that would be happening so much more frequently than usual. Typically, fewer than two humpback whales collide with ships along that upper section of the Eastern Seaboard.

Gregory Silber of NOAA Fisheries’ Office of Protected Resources suggested that the whales could be following the small fish they eat into regions with heavier boat traffic. Some scientists speculate that offshore drilling, military exercises, and other noisy activity could confuse whales so that they accidentally move into dangerous or shallow waters.

Ironically, most types of humpback whales — including all but one of the kinds living in the Atlantic — were taken off the Endangered Species list just last September.

Humpback whales experienced another “unusual mortality event” in 2006; researchers were ultimately unable to discover the main cause of those whales’ deaths. Hopefully this time they’ll be able to figure out what’s going on.

Photos via Getty Images / Spencer Platt, Getty Images / Ben Pruchnie