“Well-lighted bridges and dams can create twilight conditions that predators love, especially other fish,” says Peter Moyle, professor emeritus at UC Davis. He recounts that at one point the Red Bluff Diversion Dam was lit up at night and pikeminnow took the opportunity to prey on juvenile salmon. “Opening up the gates helped because the pikeminnow were headed upstream to spawn so didn’t really want to be there, and the juvenile salmon could move past the dam quickly at night.” The Sundial Bridge in Redding is thought to have contributed to low numbers of fall-run Chinook salmon on the Sacramento River between 2011 and 2013. The Bay Institute’s Jonathan Rosenfield agrees that the problem from lights should be mitigated whenever possible but wants to make sure the many other stressors the fish face are not forgotten. Says Rosenfield, “[These fish] are plagued by numerous problems, most of which are related to reservoir and river management.”

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Nighttime lights on bridges shining into bays and rivers can attract and confuse fish as they migrate at night, leaving them vulnerable to predation. “Well-lighted bridges and dams can create twilight conditions that predators love, especially other fish,” says Peter Moyle, professor emeritus at UC Davis. He recounts that at one point the Red Bluff Diversion Dam was lit up at night and pikeminnow took the opportunity to prey on juvenile salmon. “Opening up the gates helped because the pikeminnow were headed upstream to spawn so didn’t really want to be there, and the juvenile salmon could move past the dam quickly at night.” The Sundial Bridge in Redding is thought to have contributed to low numbers of fall-run Chinook salmon on the Sacramento River between 2011 and 2013. The Bay Institute’s Jonathan Rosenfield agrees that the problem from lights should be mitigated whenever possible but wants to make sure the many other stressors the fish face are not forgotten. Says Rosenfield, “[These fish] are plagued by numerous problems, most of which are related to reservoir and river management.”

About the author

Lisa Owens Viani is a freelance writer and editor specializing in environmental, science, land use, and design topics. She writes for several national magazines including Landscape Architecture Magazine, ICON and Architecture, and has written for Estuary for many years. She is the co-founder of the nonprofit Raptors Are The Solution, www.raptorsarethesolution.org, which educates people about the role of birds of prey in the ecosystem and how rodenticides in the food web are affecting them.