(CNN)The National Oceanic and Atmospheric Administration (NOAA) launched an investigation Thursday into a large number of humpback whale deaths from Maine to North Carolina.
The agency declared the deaths an unusual mortality event, the first one observed in humpback whales in nearly a decade. 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.”
The last unusual mortality event declared for humpback whales was in 2006. Two other events were declared in 2005 and 2003, said Deborah Fauquier, veterinary medical officer for NOAA Fisheries Office of Protected Resources. The cause of those UMEs was undetermined.
Forty-one whales died in the region last year. According to NOAA’s Office of Protected Resources, the 16 year average for the region from 2000-2015 is 14 whales per year. As of April 24, 2017, 15 whales have died.
Out of the 41 dead whales that died last year, 20 of them have been examined so far, said Mendy Garron, Stranding Coordinator for NOAA Fisheries Greater Atlantic Region. Of those, 10 appear to have hit marine vessels. The whales’ bodies showed evidence of blunt force trauma, Garron said.
Vessel strikes have been documented in Virginia (3), New York (3), Delaware (2), Massachusetts (1) and New Hampshire (1).
Greg Silber, Large Whale Recovery Coordinator for NOAA Fisheries Office of Protected Resources, said many factors could have caused the whales to move closer to shipping routes, but there hasn’t been a spike in ship traffic.
“It’s probably linked to prey sources,” he said. “Humpback whales follow where the prey is and there may be aggregation in certain areas.”
Now that the unusual mortality event has been declared, NOAA’s investigation will involve data collection and analysis as well as monitoring environmental and habitat conditions, including human-caused threats.
Humpback whales were recently taken off the endangered species list, but are still protected under the Marine Mammal Protection Act, Fauquier said.
Since the marine mammal UME program was created in 1991, there have been 63 formally recognized UMEs in the United States involving a variety of species.