TATOOSH ISLAND, Wash. — From a stretch of rocky shoreline on this tiny island, one can, on any given morning, watch otters floating on their backs, elephant seals hauling out of the water and a bald eagle flying past murres huddled along a cliff face. The startled birds perform a synchronized dive into the sea, their ovoid black-and-white bodies resembling miniature penguins.

It appears as if the island’s wildlife is thriving at this remote outpost, which is also a former Coast Guard station crowned by a decommissioned lighthouse. It was also once a whaling base for the Makah tribe, who maintain treaty rights to the land.

But for over four decades, with the blessing of Makah leaders, Tatoosh has been the object of intense biological scrutiny, and scientists say they are seeing disturbing declines across species — changes that could prove a bellwether for oceanic change globally.