The Unexpected Cause of Spawner Mortality Syndrome: Urban Stormwater

Coho_stormwater_NWTreatyTribes.pngOn May 8th Environmental and Technical Division staff attended the Association of Clean Water Agencies (ACWA) Stormwater Summit at Linn County Community College. While there they got to talk to DEQ staff about stormwater permits, network with peers, and attend various workshops covering stormwater issues. All the staff particularly enjoyed a talk given by John Stark, Ph.D in which he reviewed recent findings from the Washington Stormwater Center. The research focused on what types of pollutants are being found in urban stormwater and their effects on aquatic organisms, especially salmon. In a paper titled “Coho salmon spawner mortality in western US urban watersheds: bioinfiltration prevents lethal storm water impacts” Spromberg et. al. discover that urban stormwater contains many more pollutants than previously thought, and that these unidentified pollutants are responsible for killing high numbers (50-90%) of coho salmon when they come into freshwater to spawn, a phenomenon known as spawner mortality syndrome.

Prior to this study, there was no clear link between coho die offs and urban stormwater. Seeing the trend of mass casualties of pre-spawn coho along the west coast, scientists looked at various water quality parameters including dissolved oxygen, temperature, and habitat suitability, but could not figure out why the fish were dying. The only evidence they could find was that more impervious surfaces within a watershed correlated to more coho salmon dying when they came inland to spawn.

In this experiment, pre-spawn hatchery coho were exposed to four types of water: 1) clean well water was used as a control, 2) a lab-made stormwater mixture including known pollutants in observed quantities, 3) stormwater run-off collected from a highway and, 4) highway stormwater run-off that had been filtered through soil columns. The results were astonishing. The fish in the clean well water were fine, proving that the stress of moving the fish from one tank to another did not harm them. Then came the lab-made “stormwater”, which despite being full of metals and hydrocarbons (known stormwater pollutants) did not have any visible impact on the fish. However, the fish exposed to the highway run-off were all dead within twenty-four hours. Considering the artificial stormwater did not result in any fish showing symptoms of being sick, the fact that real stormwater was 100% lethal to the coho was entirely unexpected. Now for a bit of good news, the fish exposed to filtered stormwater, the same stuff that killed all the fish just filtered through some soil, all survived and didn’t even show symptoms of becoming ill.

In conclusion, there’s something, very likely several somethings, in urban stormwater that is killing coho. We don’t yet know what it is, but we do know one way to stop it. Rain gardens and underground injection control facilities (UICs) are already a part of urban development, and they are capable of filtering out enough toxins in urban stormwater that it is no longer toxic to adult coho. These green infrastructure facilities make a big difference in the quality of stormwater and should be incorporated as much as possible in urban development.   

Here’s a short video about the research.

And here is a 15 second video of fish in well water, filtered stormwater, and unfiltered stormwater.