New research is the first to demonstrate how toxic runoff from highways and other man-made structures is killing coho salmon in urban streams along the West Coast.
Despite these grim findings, the researchers believe there is hope, the NOAA Headquarters reported. The study found the inexpensive filtration of urban runoff through sand and soil could help protect the fish from the contaminant's fatal effects.
"Untreated urban runoff is very bad for salmon health," said Julann Spromberg, a research scientist at NOAA Fisheries' Northwest Fisheries Science Center in Seattle. "Our goal with this research is to find practical and inexpensive ways to improve water quality. The salmon are telling us if they work."
Coho salmon in California, Oregon and southwestern Washington are listed under the Endangered Species Act, but this stormwater runoff is making the battle for their conservation extremely difficult. In order to save the species from extinction, the researchers are urging the installation of filtration columns that are similar to "rain gardens" utilized in the Northwest.
"If we can incorporate clean water design strategies into future growth, as some transportation projects are already doing, wild salmon might have a chance," said Nat Scholz, manager of the Ecotoxicology Program at the NWSFC in Seattle and a coauthor of the study. "They can't take the kinds of losses we've documented in urban streams."
In the study, the researchers exposed adult coho from the Suquamish tribal hatchery to different levels of water pollution and clean water. They observed that all of the fish exposed to runoff from a busy urban highway in Seattle died within just 24 hours. After the researchers filtered this toxic water through a three-foot-high column composed of natural materials such as sand and soil, the coho thrives as well as they did in unpolluted water. Tests revealed the simple filtration system reduced toxic heavy metals by 58 percent and byproducts of gasoline combustion by as much as 94 percent.
"What impressed me most was the effectiveness of the treatment," said Jen McIntyre, co-author and researcher at the stormwater program at WSU's Puyallup Research and Extension Center. "It's remarkable that we could take runoff that killed all of the adult coho in less than 24 hours - sometimes less than four hours - and render it non-toxic, even after putting several storms worth of water through the same soil mixture."
The findings were published in a recent edition of the Journal of Applied Ecology.
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