NEW YORK (NYTIMES) - Marine biologists in Brazil were stunned to discover a young humpback whale last Friday (Feb 22) that had washed ashore on a remote, forested island in the Amazon River, at a time of year when it should have already migrated thousands of miles to Antarctica.

Members of conservation group Bicho D'Agua found the whale after following vultures that were circling a mangrove on the island in the Amazon, Marajo Island, the group said.

About 15m from the shore, scientists spotted the lifeless humpback - about 8m long - lodged in thick shrubs and brush.

It had been dead for at least several days, government officials in Pará, a state in northern Brazil, told local news outlets.

While tens of thousands of humpback whales are estimated to live in the Atlantic Ocean off Brazil, nearly all of them have migrated south by this time of year, the summer in the Southern Hemisphere, to feed near Antarctica.

But this humpback was found near the mouth of the Amazon River, some 6km from its expected feeding grounds, a baffling discovery that has stumped the scientists who found it.

"We imagine it was floating and the tide took it into the mangrove," Dr Renata Emin, president of Bicho D'Agua, told Brazilian news site G1.

"The question is: What was a humpback whale doing in the month of February on the northern coast of Brazil? It's unusual."

Biologists examined the carcass over the weekend during low tide, looking for signs of how the whale might have died, and took samples for a necropsy, the group said.

The whale, while about half the length of a full-grown humpback, was too large and in too remote an area to be entirely removed.

Dr Emin told G1 that the group hypothesised that the young whale got detached from its mother before it died.

Humpbacks travel great distances every year, slowly migrating to and from the poles. Those in the Northern Hemisphere migrate this time of year to tropical waters before returning north in the summer. In the Southern Hemisphere, they migrate south during this time of year and return north during their winter, in the breeding season.

Dr Emin said her group was examining the whale to try to determine its cause of death.

"We are collecting information, identifying marks on the body, to determine if it was trapped in a net or hit by a boat," she told G1, adding that a necropsy report was expected in about 10 days.

Dr Emin did not respond to an e-mail seeking comment.

During the 19th and 20th centuries, whalers killed at least 200,000 humpbacks in the Southern Hemisphere, decimating the population, according to scientists. But worldwide conservation efforts in recent decades, and treaties enacted to outlaw whaling, have saved the once endangered species. Commercial whaling was outlawed in South America and Antarctica in 1994.

The rising humpback population has also increased the odds that one will become entangled in fishing nets or be struck by a ship, believed to be leading causes of their deaths.

Every year, an estimated 300,000 whales and dolphins die after getting caught in fishing gear, according to the International Whaling Commission.

The commission, which also tracks ship strikes, has recorded more than 1,200 collisions between whales and ships since 2009.