Survive the Sound: Hood Canal Bridge blocks migrating fish

POULSBO, Wash. -- The floating Hood Canal Bridge may transport thousands of people a day between Port Ludlow and Poulsbo, but it seriously hinders a different type of traffic -- that of migrating fish.

According to studies, up to 50 percent of young migrating fish will fail to make it to the other side of the bridge, instead getting snatched up by predators.

The Hood Canal Bridge is the longest saltwater floating bridge in the world, stretching 1.5 miles. With openings on each end, Washington Department of Transportation says about 83 percent of it rests on the water with concrete extending about 15 feet deep.

That means that when salmon and steelhead try to migrate out to sea, they are literally hitting a wall.

"I think that we need to do something as soon as possible," said Megan Moore, a research fisheries biologist with NOAA Fisheries who first discovered this death trap.

Tracking tagged steelhead throughout the Puget Sound, she said she's never seen mortality this high in one spot.

"These stationary tags that would just ping over and over again until the battery died," Moore said.

She published her study in 2013, shocking the scientific community that never knew there was a problem with the bridge. It first opened in the early 1960s.

Scientists had assumed the fish would migrate along the shores and through the openings. Instead, Moore's steelhead tagging study found 30 to 50 percent died somewhere in the middle.

"That's a big deal when we're spending fairly significant amounts of money in Hood Canal trying to restore habitat there," said Hans Daubenberger, a senior research scientist for Port Gamble S'Klallam Tribe.

In 2015, Port Gamble S'Klallam Tribe started looking at how all fish behave at the bridge and why it's so deadly, using acoustic, density and video techniques.

The videos captured predators in the act -- harbor seals targeting chinook salmon along the concrete edge. Chinook salmon is the primary prey of the endangered southern resident orcas, who are facing a lack of food.

The bridge creates a mile-long predator's buffet as fish, stunned by the obstacle, spend an average of two days trying to get around or under it.

A T-shaped structure at each edge of the floating portion of the bridge is making it harder for fish to get around. When they follow along the bridge to the edge, a 90-degree angle blocks them off, typically bouncing them in the other direction for another mile-plus trip to the other side, where they encounter the same obstacle.

Swimming under it is also difficult. Young steelhead, salmon and chum swim within three feet of the water's surface; the concrete is five times deeper than that.

Nearby, the seals, harbor porpoises and birds are plenty. So is their prey, the fish trapped at the wall.

"Last week, there were probably a million chinook at the bridge itself," Daubenberger said.

That means, up to half a million chinook likely didn't make it. But these scientists do not think harassing predators will help. There are so many predators, they said, that more will just take its place.

"I think passing the fish as fast as we can so they can get by the predation is the more feasible strategy," Moore said.

Scientists are looking at ways to do that and hope to start implementing possible solutions as soon as next year.

One of those is blocking light from the bridge from reaching the water. When light reflects off the water at night, it gives predators like seals a 24-hour window to see well enough to hunt.

Other possible solutions including changing currents and temperatures to attract fish to the edges. These endangered species are facing enough barriers without having a physical one.

"It's kind of adding a big insult to the problems we already have," Moore said.

For now, that barrier isn't budging. Neither are millions of fish.

The scientists said WSDOT is cooperating by allowing them to do their studies on the bridge. WSDOT said it is interested in learning more about potential recommendations and how much it'll cost.