A recent study of juvenile steelhead by the National Oceanic and Atmospheric Administration found an unusually high mortality on the south side of the 55-year-old bridge, but a lower death rate on the north side.
There are several theories about the bridge and its impact on juvenile fish. The conservation group Long Live the Kings is hoping a new study will end the mystery.
“In addition to the effects on steelhead and perhaps on juvenile salmon, there’s also some concerns that the bridge might be affecting water quality,” said Long Live the Kings executive director Jacques White.
Young fish headed out to sea from spawning grounds in the south are stopping at the center of the bridge. As they swim around the structure near the water’s surface, they become prey for the hungry seals that prowl the area looking for an easy meal.
Biologist say the juvenile fish may do this because they're confused by the pontoons blocking their path. The constant noise of traffic could also contribute to the problem. But they could also simply be taking advantage of the artificial reef the bridge creates, allowing them to feed on zoe plankton, and get trapped in pools in the bridge's interior. Once there, they can easily be eaten by the ever present seals.
“It’s almost like a mousetrap,” said Hans Daubenberger, a biologist for the Port Gamble S’Klallam tribe, which is helping fund the study. “There’s cheese or bait in the trap and they stay there, and the seals have learned this.”
The bridge may also be contributing to the Hood Canal's low oxygen levels, acting as a boom blocking the flow of currents in and out of the narrow body of water.
The study will cost $2.4 million. Funding provided by Long Live the Kings and the S’Klallam tribe is paying for a large chunk of the cost. The organization is looking for around $1.6 million from state and federal grants.
Rep. Derek Kilmer, of the 6th Congressional District, who toured the bridge during an unveiling of the study on Wednesday, said finding an answer that works for fish and people is important.
“There’s an understanding that this is a bridge that’s really important to transportation for those who live in the Olympic Peninsula and those who want to get onto the Olympic Peninsula,” Kilmer said.