The body of a dead humpback whale found last summer at the mouth of Delaware Bay. (Courtesy of MERR Institute)

Scientists have declared “an unusual mortality event” following a spike in the number of dead humpback whales being found along the East Coast, experts said, and there is uncertainty as to exactly what is causing the problem.

Last year 26 humpback whales were found dead on the shores of the Atlantic Ocean from North Carolina to Maine. And since Jan. 1, 16 more have turned up, including one found floating this past week in shallows of Delaware Bay; the fourth one there this year.

Officials at the National Oceanic and Atmospheric Administration (NOAA) said it is “an anomaly for this geographic area,” noting that the area typical sees an average of 14 a year.

A dead humpback whale beached on Block Island, R.I., in March 2016. (Courtesy of Mystic Aquarium)

Experts at NOAA have been investigating the spike and this week said they are looking at a variety of factors, including the whales’ wounds, water temperatures and the whales’ diets.

In Virginia, eight humpback whales have been found dead since Jan. 1, 2016, including five so far this year. Two have been found in Maryland waters over the past 16 months and another 11 in North Carolina, according to NOAA Fisheries division.

Mendy Garron, who is the stranding coordinator at the NOAA Fisheries Greater Atlantic Region, said 20 of dead humpback whales have been examined and 10 of them had been struck by ships — higher than the annual average of 1.4.

Those humpbacks had evidence of “blunt force trauma or large propeller cuts,” according to Deborah Fauquier, a veterinary medical officer at NOAA Fisheries Office of Protected Resources. She said the ship interaction was believed to be the cause of death.

None of the 20 humpbacks showed signs of an infectious disease, according to Garron.

Officials said it was not exactly clear why more humpbacks were coming into contact with ships. They also were unsure if there were climate-related changes or other human-related causes that could be affecting the whales.

“There’s probably no spike in vessel traffic in these areas, but the difficulty is these animals move around,” said Gregory Silber, marine resources manager in the department’s Office of Protected Resources. He said humpbacks go “where the prey is” so they could be going to areas that bring them closer to ships.

Humpbacks are baleen whales, feeding on tiny crustaceans, like krill, along with plankton and small fish, trapping them in the filters in their mouths.

Officials said any sized ship can hurt a whale. A smaller ship can hurt a whale with its propellers, and a larger ship can cause hemorrhaging or broken bones. Often crews of large ships do not know that their vessels have struck one, because the ships are so big, and therefore don’t report it.

Since 2000, there have been three previous “unusual mortality events” involving humpbacks along the Atlantic Coast. No definitive causes were found.

Experts said there are an estimated 10,400 humpbacks along the Atlantic Coast. They were once on the endangered species list but have since been removed. They are still considered protected animals.