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A Wallyhood Waters series

Every winter season, I read about Seattle’s “Big Dark,” the time when the sun starts setting before 4:30, and our nighttime is longer than our days. Despite this, I can’t recall seeing a dark, starry night in a long time. This is because Seattle is in a perpetual state of dusk due to artificial light at night (ALAN). While our wintertime lights make us feel safe and bring us holiday cheer, I recently learned that they also take a toll on our wildlife. 

University of Washington researchers have discovered that our artificial light is a major cause of sockeye salmon populations steeply declining since the 1970s. Here’s why: Baby salmon usually spend about a year in our lakes before swimming out to the Puget Sound. Normally, about 25% of juvenile salmon make it to the ocean. However, in Lake Washington and Lake Union, only 10% survive. This is because their predator, the Cutthroat Trout, eats them at dusk. Due to light pollution, our dusk lasts all night long, leaving baby salmon more vulnerable.

There are a few types of light that affect the fish: glare from lights that are right on the water’s edge and skyglow from light being reflected from the clouds and water. At times, we see a night sky in Wallingford that is twice as bright as the moon. Not only does this impact fish, but it hampers the behavior and migration patterns of birds, raccoons, and other wild neighbors. Although great energy savers, increased use of LED lights has caused ALAN to increase between 17% and 25%. Also, in December, there is a 37% increase in Seattle’s light pollution due to holiday lights.

So, how do we balance stewardship with holiday cheer? Researchers recommend this: 

1. Set your exterior lights and any holiday lights on a timer so they turn off while you’re asleep OR use motion sensor lights that only turn on when you need some extra light.
2. Use lower lumens, not in excess of 500–600 lumens per outdoor fixture.
3. Use warmer lights with a color temperature of 2700 Kelvin or lower; red lights are less harmful than green.
4. Check out these resources to learn more:

• • Salmon Friendly Lakes videos
  • ALAN toolkit for residents
  • DarkSky Conservation
  • BirdCast- Lights Out for Birds

Wishing you a happy holiday and many future starry nights.

Editor’s note: see past articles in Kerri’s series “Wallyhood Waters”:

• Our Salmon Neighbors