BOSTON — The first calls came from surfers who were looking for early autumn waves off the New Hampshire coast and found dead harbor seals scattered in the surf and sand.
The report of about half a dozen dead carcasses at Jenness Beach in Rye wasn’t unusual on its own for late September, said Tony LaCasse of the New England Aquarium, which operates a marine animal rescue team.
But the reports kept coming.
Since early September, 94 dead seals have been discovered from Maine to northern Massachusetts. That’s almost four times the 24 deaths in the same period last year, considered a typical year.
The seals are generally less than a year old and have a healthy appearance. Researchers have theories about what’s causing the spike — perhaps a virus or disease — but they have no real answers and are awaiting test results from tissue and organ samples.
“It’s a little bit of a puzzle,” LaCasse said.
The harbor seal population in the Northeast is considered healthy, so the spate of deaths doesn’t yet signal broad trouble, according to Mendy Garron, regional marine mammal stranding coordinator for the National Marine Fisheries Service. She said the last census in 2001 showed 99,000 harbor seals, and a survey this year is expected to show the population has grown.
“While it’s kind of alarming to have these animals coming up in a short period of time, the numbers don’t necessarily indicate anything bad for the population,” she said. “If it continues, it could potentially have an impact.”
The past few decades have seen some notable seal die-offs in the Northeast, including in a rash of influenza deaths around 1979 and 1980 that LaCasse said were linked to bird flu. Scientists theorized that the seals were exposed when they sunned themselves on rocks dotted with bird droppings, he said.
In 2006, a morbillivirus killed hundreds of local seals, both harbor and gray seals, though the exact number is unknown, Garron said. The same virus killed 20,000 seals in the United Kingdom in the early 2000s, with harbor seals accounting for 44 percent of the deaths, she said.
The virus is among the suspects in the recent deaths, but it’s one of many (though researchers have ruled out human foul play). Unlike the 2006 deaths, the recent deaths are overwhelmingly occurring in one age group — seals that have just recently been weaned.
LaCasse said the death rate is typically high in that group. Many of the young seals haven’t learned to properly forage for food before they are weaned, and the dead animals start showing up around the coast in late summer and early autumn. In this case, though, the dead seals seemed to have sufficient blubber, indicating they were getting enough to eat, and pointing to another cause, LaCasse said.
The first major reports of seal carcasses came on Sept. 28 and Sept. 29, when 11 dead seals were found on the Maine, Massachusetts and New Hampshire coasts, including the animals spotted by the New Hampshire surfers.
Garron said after more reports came in during the following weeks, researchers decided to look backward to see if they missed the start of the trend and found about 11 deaths around Sept. 11. More recently, four deaths were reported Wednesday.
The geographic spread of the deaths splits them evenly between the southern Maine coast, north to Yarmouth, and a combined area of the New Hampshire coastline down to the North Shore of Massachusetts, Garron said.
Ellen Goethel, a member of the Hampton, N.H., conservation commission, discovered two dead seals during a walk about two weeks ago on a small stretch of town beach between Hampton and North Hampton.
“There were no marks, they looked healthy to me,” she said.
Goethel, a marine biologist, speculates the seals could be victims of some sort of natural, algae-based toxin in a particular area of ocean. But like everyone else, she doesn’t really know.
“We need to find out what it was; we don’t want it to happen again,” she said. “It’s a horrible thing. [The seals] are sweet. They look beautiful.”
Depending on what the cause is — and assuming researchers can even pinpoint it — there may not be much anyone can do about it. But LaCasse said people still care deeply about the charismatic seals, have given them federal protection for years and feel connected to them because they live so close. Plus, it’s possible the deaths can be traced a human activity or contaminant that can be stopped or avoided.
“Those type of results can affect what we as humans do in our coastal waters,” Garron said.