Two bottlenose dolphins that were rescued after becoming stranded on a Dennis beach earlier this week have died after beaching again in Yarmouth.

The International Fund for Animal Welfare examined and released the dolphins, a male and female, into open water after finding the two animals beached on Crowes Pasture Beach in Dennis around 4 p.m. Monday, spokeswoman Kerry Branon said.

The pair were found dead on a Yarmouth beach around noon Tuesday, and researchers are still trying to determine the cause of the deaths.

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“It did appear to be an older male. The teeth were worn and there was evidence of a risk for heart failure,” said Jane Hoppe, assistant stranding coordinator with the organization. “But it’s still too early to tell.”

Bottlenose dolphins are rarely seen around Cape Cod. Monday’s stranding was the first multiple bottlenose dolphin stranding event on the Cape in recorded history, Hoppe said. The dolphins usually swim offshore.

The dolphins were both about nine feet long. The male weighed more than 1,000 pounds and measured seven feet around the widest part of its body.

Branon said it took 14 people to move the animal so researchers could perform a necropsy to determine the cause of death.

When the rescue team found the dolphins Monday, they evaluated the pair’s health in an “animal ambulance,” Branon said.

Blood samples from the dolphins did not show immediate danger, Hoppe said.

“They both had good body condition,” she said. “We wanted to do what’s best for the animals, which was to give them a chance to swim.”