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Growing number of humpback whales found dead off the East Coast

A deceased humpback whale carcass at the mouth of the Delaware Bay reported on July 5, 2016.
A deceased humpback whale carcass at the mouth of the Delaware Bay reported on July 5, 2016. Marine Education, Research and Rehabilitation Institute, Lewes, Del.

The federal government removed humpback whales in U.S. Atlantic coastal waters from the endangered species list last year after successful conservation efforts resulted in growing populations.

But now federal officials are taking a new look at the health of the whales after an increase in humpback deaths, or “strandings,” off the coast from North Carolina to Maine.

Concerns began early last year when a dead humpback whale was reported near a beach in Virginia. There were 26 coastal humpback whale deaths in 2016, and 18 deaths through June 1 this year, six of which were off the North Carolina coast, according to the National Oceanic and Atmospheric Administration. The number of deaths so far this year matches the total for 2014 and 2015 combined.

The trend has alarmed scientists at NOAA, which in late April began an effort to determine whether the rising number of deaths were natural or the result of human activities.

“The increased numbers of mortalities have triggered the declaration of an unusual mortality event, or UME, for humpback whales along the Atlantic coast,” said Mendy Garron, regional stranding coordinator for the NOAA Fisheries Greater Atlantic Region.

Known for their curious breaching behavior and the complex songs from males, humpbacks are among the largest of whales, reaching up to 62 feet long and weighing nearly 40 tons. These behemoths consume up to 2,000 pounds of plankton, krill and other small creatures per day by filtering water through their baleen plates.

The North Atlantic humpback whale population is estimated at between 10,400 and 10,752, about double what it was 20 years ago. Every winter, the humpbacks migrate from their summer feeding homes in the north to warmer southern waters. As they migrate, they remain near the surface where they are particularly vulnerable to threats such as entanglement in fishing gear, ship strikes, harassment and hunting.

The new challenge for scientists is to determine how to manage these threats to keep the whales off the endangered list.

“The numbers are increasing, but then we also get this concomitant increase in strandings,” said Bill McLellan of the Marine Mammal Stranding Program at UNC Wilmington. “Is it simply due to population increase? The new question is how to analyze if this is true.”

Ship strikes

So far, necropsies – the whale equivalent of an autopsy – have been performed on 20 of the 44 whales found dead in the last two years. Half of them showed signs of blunt trauma or propeller wounds – six times above the 16-year average for the region, although no vessel strikes have been documented off the North Carolina coast.

“A vessel of any size can harm a whale,” said Greg Silber, large whale recovery coordinator at NOAA Fisheries’ Office of Protected Resources in Silver Spring, Md. “In smaller vessels, they tend to be propeller strikes, and in larger vessels, they appear to be in the form of blunt trauma.”

The surge in boat strikes is largely unexplained. Regulations aimed at protecting whales are in place for busy vessel traffic areas, including speed restrictions within 20 nautical miles of key ports on the East Coast. Silber said that to his knowledge there has been no increase in vessel traffic that would explain the higher number of deaths.

One thought is that the krill and plankton that humpback whales eat could be moving into different areas, drawing humpback whales closer to shipping lanes as they feed. The change in prey patterns could be related to ocean currents or even changes in water temperature, but that has not been confirmed.

“Most large whales, when they’re feeding, they’re engaged in feeding and probably oblivious to large ships around them,” Silber said. “But it’s difficult to pinpoint a particular type of behavior.”

A rebounding humpback whale population may also create more opportunities for vessel strikes and other human interactions such as entanglement in fishing gear. Not only has the number of humpback whales been increasing overall, but there were a lot around North Carolina’s coast this winter, said McLellan. Most stay relatively close to shore, about 25 to 30 miles off shore.

But boat strikes cannot explain all of the humpback deaths, and scientists are trying to figure out what caused the other half of them.

“There is still a question of whether there is disease or pathogen off shore,” McLellan said. “There’s still something going on inside these animals.”

In the end, scientists may never know. There have been three previous spikes in deaths among humpback whales along the Atlantic coast in the last 15 years, the last occurring in 2006. The causes for them remain unknown.

Jeremy Frieling: 919-829-4610

Watch out for whales

Boaters should keep a close eye out for feeding whales and stay at least 100 feet away.

If you spot a stranded, distressed, floating or dead whale, report it to the Greater Atlantic Marine Mammal Stranding Hotline, 866-755-6622; the Southeast Marine Mammal Stranding Hotline, 877-433-8299, or U.S. Coast Guard on VHF Channel 16. Never approach or touch the whale.

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