SAN JUAN ISLAND, Wash. (AP) — As dawn broke over San Juan Island, a team of scientists stood on the deck of a barge and unspooled over a mile of fiber-optic cable into the frigid waters of the Salish Sea. Working by headlamp, they fed the line from the rocky shore down to the seafloor — home to the region’s orcas.

The bet is that the same hair-thin strands that carry internet signals can be transformed into a continuous underwater microphone to capture the clicks, calls and whistles of passing whales — information that could reveal how they respond to ship traffic, food scarcity and climate change. If the experiment works, the thousands of miles of fiber-optic cables that already crisscross the ocean floor could be turned into a vast listening network that could inform conservation efforts worldwide.

The technology, called Distributed Acoustic Sensing, or DAS, was developed to monitor pipelines and detect infrastructure problems. Now University of Washington scientists are adapting it to listen to the ocean. Unlike traditional hydrophones that listen from a single spot, DAS turns the entire cable into a sensor, allowing it to pinpoint the exact location of an animal and determine the direction it’s heading.

“We can imagine that we have thousands of hydrophones along the cable recording data continuously,” said Shima Abadi, professor at the University of Washington Bothell School of STEM and the University of Washington School of Oceanography. “We can know where the animals are and learn about their migration patterns much better than hydrophones.”

The researchers have already proven the technology works with large baleen whales. In a test off the Oregon coast, they recorded the low-frequency rumblings of fin whales and blue whales using existing telecommunications cables.

But orcas present a bigger challenge: Their clicks and calls operate at high frequencies at which the technology hasn’t yet been tested.

The stakes are high. The Southern Resident orcas that frequent the Salish Sea are endangered, with a population hovering around 75. The whales face a triple threat: underwater noise pollution, toxic contaminants and food scarcity.

“We have an endangered killer whale trying to eat an endangered salmon species,” said Scott Veirs, president of Beam Reach Marine Science and Sustainability, an organization that develops open-source acoustic systems for whale conservation.

The Chinook salmon that orcas depend on have declined dramatically. Since the Pacific Salmon Commission began tracking numbers in 1984, populations have dropped 60% due to habitat loss, overfishing, dams and climate change.

Orcas use echolocation — rapid clicks that bounce off objects — to find salmon in murky water. Ship noise can mask those clicks, making it difficult for them to hunt.

If DAS works as hoped, it could give conservationists real-time information to protect the whales. For instance, if the system detects orcas heading south toward Seattle and calculates their travel speed, scientists could alert Washington State Ferries to postpone noisy activities or to slow down until the whales pass.

“It will for sure help with dynamic management and long-term policy that will have real benefits for the whales,” Veirs said.