Experts Thursday identified a whale found dead this week on a private Martha’s Vineyard beach as a 28-foot-long male humpback.

A response team from the International Fund for Animal Welfare, which arrived Wednesday after reports about the washed up whale in Edgartown, still doesn’t know how it died.

But Jennifer Goebel, a spokeswoman with National Oceanic and Atmospheric Administration Fisheries, the federal organization responsible for coordinating marine mammal stranding efforts with independent groups, said researchers determined that the whale was “very thin,’’ and its organs were “very decomposed,’’ suggesting it had been deceased for some time.

“They have collected samples and are doing additional analysis,’’ she said. “But they are afraid they won’t be able to determine the cause of death.’’

Goebel said researchers from the animal welfare group would let the carcass float out to see, and hope that it sinks, since it is on private property. Dead whales have typically washed ashore on public beaches in the New England area.

In those instances, organizations work with officials from the respective city or town to remove the remains from a beach.

A person visiting the island came across the dead humpback in Edgartown on Monday, and sent pictures to the Globe. In the images, the whale can be seen on its back, close to the shoreline.

This is the second time since July that a dead whale has been found on a Martha’s Vineyard beach in recent months.

The remains of a whale, estimated between 50 and 60 feet long, washed up on South Beach in Edgartown July 4. The animal’s carcass was heavily decomposed, officials said at the time.

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.