BOSTON — Whether they got lost, sick or swam astray chasing food, 77 dolphins that beached on Cape Cod in recent weeks have died, the second time in three months New England has seen a mass of marine mammal deaths.

Now, scientists are trying to figure out why.

They're also researching whether there's any connection to a die-off this fall of 162 harbor seals, whose carcasses were found between northern Massachusetts and Maine.

Scientists later determined the seal deaths were linked to an influenza virus similar to one found in birds but never before seen in seals. In a letter earlier this month, Massachusetts Sen. John Kerry and Rep. William Keating asked Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, to investigate "any common cause" between the dolphin and seal deaths.

"That is a big question," said Mendy Garron, regional marine mammal stranding coordinator for the National Marine Fisheries Service, part of NOAA. The initial indications are that there is no link, she said, but it's too early for a definitive answer. Necropsies are under way to determine the causes of death, and that can take a few weeks.

The strandings stretch along 25-mile stretch of Cape Cod from Wellfleet, approaching the tip of the cape, south around the curve of Cape Cod Bay to Dennis.

The first was reported in Wellfleet on Jan. 12. Five more reports followed the next day. On Jan. 14, 30 more animals got stuck on Wellfeet and reports remained steady, then trailed off in the past week.

As of Saturday, 63 of the dolphins have been found dead and 11 died later, included at least one that was euthanized. Another 24 were released into the ocean, though three of those have died, said A.J. Cady of the International Fund for Animal Welfare. The group is leading the rescue efforts.

The total strandings are unprecedented, and two and half times the annual average of 37 common dolphin strandings over the past 12 years, Cady said.

Wellfleet harbormaster Michael Flanagan said he's seen several pods of more than 100 animals in his 14 years on the job. "But you never really see that many strandings," he said.

The affected dolphins appear to be linked by little besides their species. Their conditions range from healthy to sick, and they aren't all a particular age or sex.

"Nobody really knows for sure yet whether it's one particular thing," Cady said.

There are several possibilities. For instance, the dolphins are social animals, and some could be following a sick fellow animal to shore, researchers theorize. Changes in water temperature are a possible factor leading them into the bay, but it's unclear how.

Some dolphins could be chasing prey into Cape Cod Bay, and essentially getting lost in the geographic features of Cape Cod's inner coastline. For instance, dolphins headed north along the inner Cape's coastline looking for open ocean can get trapped in Wellfleet, which juts out like a tiny hook. Then, the area's quickly receding tides can beach them in local marshes.

Rescuers try to guide lost animals to open water, either by keeping a boat between them and the coastline, or repelling them from land with unpleasant sounds, Cady said.

Once stranded, a dolphin's own weight can damage its organs. Hypothermia and sunburn are also a danger, and Flanagan said seagulls looking for a meal turn savage and pick at the mammal's eyes and organs.

After rescuers reach a dolphin, often through major muck, they quickly assess whether it's strong enough to be moved. If so, workers slip a stretcher underneath and carry the 8-foot-long, 300-pound animals into rescue trailers for a trip to the Cape's outer coastline for release. On the way, scientists perform tests to better assess the health of the animals.

Just a few years ago, it was commonly believed to be too risky to move the stranded animals, Cady said. But, he said, tracking devices placed on some rescued dolphins have shown them moving far from where they were released.

The effort and expense is considerable — the dolphin strandings have cost between $50,000 and $60,000, Cady said. But it's well worth the cost on several levels, he added. Their health tells us about the health of the ocean, which affects everyone, Cady said. It's also simply the humane things to do, he said.

People don't have to be prodded to assist dolphins. Flanagan said he gets "a million" volunteers every time an animal is stranded.

"People can relate to these mammals, because they go and see them at Sea World. ... They can see how intelligent they are," he said. "They're such gentle animals, you can't help but feel sorry for them when they're stranded and they're out of their element and there's nothing you can really do for them."