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Light Pollution Identified As Potential Issue For Threatened Puget Sound Chinook Salmon

It’s been nearly 20 years since the federal government listed Puget Sound Chinook salmon as threatened under the Endangered Species Act. The fish inhabit one of the most urbanized watersheds in the region. Local governments have just updated a 10-year recovery plan. One of the new priorities they’re addressing is a possible link between fish mortality and artificial light.  

On a cold winter’s night, a team of federal researchers has just pulled in a net from the south end of Lake Washington. They’re working at five sites along the shoreline.

Credit Parker Miles Blohm / KNKX
Tabor and the researchers captured fish with nets along the shores of Gene Coulon Park in Renton, Wash on Thursday February 22, 2018. Baby Chinook are frequently spotted in the park where they swim from Cedar River and spend several months growing before heading out to Puget Sound and then the ocean.

Here in the shallows at Renton’s Gene Coulon Park is where lots of baby Chinook swim from the Cedar River and spend several months growing before they head out to Puget Sound and then the ocean.

The researchers are counting how many of the tiny fish gathered beneath lights they put up over the water, compared to spots where there was no light. After just two hours, the difference is pretty dramatic: six Chinook in a dark spot, 60 beneath the first light they check.

Credit Parker Miles Blohm / KNKX

Biologist Roger Tabor is not surprised. He says this is typical.

“Usually what we’re getting is a level like ten times in our light,” he says.   

Tabor is with the U.S. Fish and Wildlife Service. He says normally at night, Chinook are spread out on the lake bottom, resting and not doing much.

“But if you turn the lights on, they naturally attract to the lights, they start to school up and they’re up off the water column. And they’ll act more like you’d see during the daytime,” he says.

Credit Parker Miles Blohm / KNKX

Tabor’s longer-standing research is documenting how this attraction can make the Chinook more vulnerable to predators, such as larger fish and birds. He says that connection is pretty well established now. They’ve even seen great blue herons swoop in, while they were working.

“It happened a couple times, where they’ll come right into our lights,” he said, adding that it came as a big surprise the first time it happened. 

“Exactly where we have a pile of Chinook sitting underneath the lights, we’ll get a great blue heron there, who could eat, you know, a very large number of Chinook in a very short period of time,” Tabor said.   

So the researchers are now testing different types of light to see if there’s one that might be less attractive to the little Chinook.

Credit Parker Miles Blohm / KNKX
Olivia Williams sets up the tanks for the fish collected from each light source during the experiment at Gene Coulon Park.

The three lights they install test different wavelengths and shine different colors on the water: red, yellow and blue. They’ll do this field work about ten times this winter, then re-test it in lab settings in collaboration with scientists at the U.S. Geological Survey.

Another collaborator on this study is National Oceanic and Atmospheric Administration Fisheries. Lyle Britt specializes in fish vision for that agency. An emerging concern is the fairly recent widespread use of LEDs. While highly energy efficient, Britt says they may be more harmful to wildlife.

Credit Parker Miles Blohm / KNKX
Olivia Williams measures the fork length of a baby Chinook at Gene Coulon Park Thursday night.

“They’re very blue. And there’s a large amount of much more shorter wavelength light,” Britt said. “That triggers a couple of things. One is it penetrates water very very well. And it can have a much bigger impact on the marine environment.”  

He says that kind of light can also trigger day-time behaviors, such as feeding, making predators more active and increasing the risk for the endangered Chinook.  

The researchers hope to identify light sources that are less attractive to the endangered fish. And while it may be a small piece in the puzzle of recovering endangered Chinook, the hope is that in some cases, helping out might be as simple as changing a light bulb.   

Previous studies have led to lighting changes on major new infrastructure, including the 520 bridge.

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