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Artificial light at night has an impact on fish behavior, altering their patterns of feeding, migrating, and predator avoidance.

Light at depth measurements Lake Washington
Photo taken from Magnuson boat launch before conducting water quality and light at depth measurements during Landsat-8 overpass windows on Lake Washington for the U.S. Geological Survey.

Many predators of salmon rely on sight to feed. Because of this, any changes to their visual environment strongly influences their effectiveness. With dramatic increases in artificial light at night (ALAN) over the past two decades, our already threatened Northwest salmon are at even greater risk of extinction.

Increases in artificial light at night expands the depths and times over which visual predators of young salmon can hunt, resulting in more salmon being eaten. While artificial light impacts from lights along shorelines are more visible to the human eye, “skyglow,” the diffuse light reflected from the atmosphere back to earth from sources up to several kilometers away, is an equally or more important impact. This is particularly true in open water urban habitats such as lakes and nearshore marine areas where juvenile salmon interact with predators for months before migrating to the Pacific Ocean.

This spring, our USGS Western Fisheries Science Center scientists will be surveying the amount of light at night throughout Seattle, Washington’s urban waters of Lake Washington, and the Ship Canal that connects the lake to the marine waters of Puget Sound. From this, they will be able to identify hotspots of direct lighting or skyglow. Visual foraging models will then be used to determine how potential increases or strategic reductions in lighting at these hotspots would increase or reduce predation risk. This science will help salmon recovery planners and city managers develop strategies to reduce the impacts of artificial light at night and improve our chances of recovering salmon.

Our research is part of a strong collaborative network focused on factors limiting salmon recovery in Lake Washington and the Ship Canal. Collaborators include University of Washington, U.S. Fish and Wildlife Service, Washington Department of Fish and Wildlife, National Oceanic and Atmospheric Administration, King County-WRIA 8, Seattle Department of Transportation, Seattle Public Utilities, the Muckleshoot Tribe, Long live the Kings, and others.

Artificial Light at Night, fish vision range
An illustration of how light changes visual hunting range during Day, Dusk, and Night. Fish deeper in the water column, where light levels decrease, lose visual hunting range. As daylight levels reduce into Dusk and Dawn, visual hunting ranges decrease. Artificial light at night has shifted the darker night-time environment into more of a perpetual twilight (Dusk) condition that coincides with higher predation.

To learn more about the impacts of artificial light at night impact on salmon, check out these relevant publications:

Beauchamp, D.A., C.M. Baldwin, J.L. Vogel, and C.P. Gubala. 1999. Estimating diel, depth-specific foraging with a visual encounter rate model for pelagic piscivores. Canadian Journal of Fisheries and Aquatic Sciences, 56(Supplement 1): 128-139. DOI: 10.1139/f99-217.

Hansen*, A.G., D.A. Beauchamp, and E.R. Schoen*. 2013. Visual Prey Detection Responses of Piscivorous Trout and Salmon: Effects of Light, Turbidity, and Prey Size. Transactions of the American Fisheries Society, 142(3): 854-867. DOI: 10.1080/00028487.2013.785978

Hansen*, A.G., and D.A. Beauchamp. 2015. Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems. Journal of Animal Ecology, 84(2): 532-544. DOI: 10.1111/1365-2656.12295.

Mazur, M.M., and D.A. Beauchamp. 2006. Linking piscivory to spatial–temporal distributions of pelagic prey fishes with a visual foraging model. Journal of Fish Biology, 69(1): 151-175. DOI: 10.1111/j.1095-8649.2006.01075.x

Tabor, R.A., E.K. Perkin, D.A. Beauchamp, L.L. Britt, R. Haehn, J. Green, T. Robinson, S. Stolnack, D.W. Lantz, and Z.J. Moore. 2021. Artificial lights with different spectra do not alter detrimental attraction of young Chinook salmon and sockeye salmon along lake shorelines. Lake Reservoir Management, 37(3): 313-322. DOI: 10.1080/10402381.2021.1906364

Vogel, J.L., and D.A. Beauchamp. 1999. Effects of light, prey size, and turbidity on reaction distances of lake trout (Salvelinus namaycush) to salmonid prey. Canadian Journal of Fisheries and Aquatic Sciences 56(7): 1293-1297. DOI: 10.1139/f99-071.