“We know from a decade of doing survival studies that migrating juvenile salmon are dropping out of the system pretty much everywhere in the Delta,” says UC Santa Cruz fisheries biologist Brendan Lehman. “Physical habitat features are potentially aggregating predators and prey in ways detrimental to salmon smolts and steelhead.” The scientists report in the December 2019 San Francisco Estuary and Watershed Science that artificial light and submerged aquatic vegetation pose the most severe and widespread risks to native fishes. Plants like Brazilian waterweed form dense underwater mats across vast reaches of the Delta. These mats have nurtured a rise in predatory bass populations and force prey fish into exposed channel centers. The artificial lighting pervasive along docks and buildings attracts prey fish while improving the success of sight-hunting predators. The scientists will spend upcoming field seasons examining how lighting and aquatic vegetation affect encounters between juvenile salmon and their predators.

 

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Manmade features in the Delta, including riprap-armored banks, water diversion pipes, pilings, and woody debris, may be sending juvenile native fishes into the jaws of finned invaders.

“We know from a decade of doing survival studies that migrating juvenile salmon are dropping out of the system pretty much everywhere in the Delta,” says UC Santa Cruz fisheries biologist Brendan Lehman. “Physical habitat features are potentially aggregating predators and prey in ways detrimental to salmon smolts and steelhead.” The scientists report in the December 2019 San Francisco Estuary and Watershed Science that artificial light and submerged aquatic vegetation pose the most severe and widespread risks to native fishes. Plants like Brazilian waterweed form dense underwater mats across vast reaches of the Delta. These mats have nurtured a rise in predatory bass populations and force prey fish into exposed channel centers. The artificial lighting pervasive along docks and buildings attracts prey fish while improving the success of sight-hunting predators. The scientists will spend upcoming field seasons examining how lighting and aquatic vegetation affect encounters between juvenile salmon and their predators.

 

About the author

Bay Area native Kathleen M. Wong is a science writer specializing in the natural history and environment of California and the West. With Ariel Rubissow Okamoto, she coauthored Natural History of San Francisco Bay (UC Press, 2011), for which she shared the 2013 Harold Gilliam Award for Excellence in Environmental Reporting. She reports on native species, climate change, and environmental conditions for Estuary, and is the science writer of the University of California Natural Reserve System.

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