Juvenile steelhead are having a hard time getting around the Hood Canal Bridge and scientists want to know why.

Over the next several years, the Port Gamble S’Klallam Tribe and partners will be collecting data about water circulation, noise and light pollution, physical barriers, food sources and predators.

In an intensive two-month push this spring, the tribe used a hydroacoustic sensor to map fish within a half mile of the bridge. Sound waves measure the size of fish and their location in the water column. They also measured water quality and took zooplankton samples.

“We’re looking at the ecological reef effect, which is how water and organisms flow around structures and how that affects the food web,” said Hans Daubenberger, the tribe’s fish habitat biologist.

While the tribe collected data this spring, it is just one of many partners in this multi-year study with Long Live the Kings, the Hood Canal Coordinating Council, state Department of Fish and Wildlife, National Oceanic and Atmospheric Administration (NOAA), Pacific Northwest National Laboratory (PNNL) and others.

NOAA plans to do an intensive acoustic tag study to determine whether fish are passing under the bridge. The state will study predator and prey populations. PNNL will look at circulation around the bridge, and a private company will study fish DNA found in seal scat.

Because the bridge is affecting steelhead, it could be affecting other species of salmon, Daubenberger said.

“We spend so much time and money restoring habitat in Hood Canal, but if high numbers of fish are not getting past the bridge, then it’s hard to recover the population,” he said.

The steelhead broodstock program in Hood Canal has struggled over the past 16 years, Daubenberger said, and this may be one of the reasons.

“If we can show a mechanism that causes this effect, it can help support other species,” he said. “Puget Sound steelhead are also a listed species under the federal Endangered Species Act, which affects tribal treaty rights to fish.”