Beginning in the late 1990s, several agencies in the greater Seattle area began conducting fall spawner surveys to evaluate the effectiveness of local salmon habitat restoration efforts. These surveys detected a surprisingly high rate of mortality among migratory coho females that were still ocean bright and had not yet spawned. In addition, adult coho from several different streams showed a similar progression of symptoms (disorientation, lethargy, loss of equilibrium, gaping, fin splaying) that eventually led to the death of the affected animals.
Pre-spawn mortality (PSM) has been observed in many lowland urban streams that have been surveyed to date, with overall rates that generally range from ~ 20% to 90% of the fall runs. By comparison, the rate of die-offs in non-urban (e.g., forested) drainages appears to be low. The precise cause of PSM is not known. However, at present, the weight of evidence suggests that the widespread coho die-offs are a consequence of non-point source water pollution. It appears that coho, which enter small urban streams following fall storm events, are acutely sensitive to non-point source stormwater runoff containing complex mixtures of pollutants that typically originate from urban and residential land use activities.
A variety of diagnostic approaches are currently being used to investigate the potential causes of coho PSM. These include water quality monitoring, biological indicators of contaminant exposure, histopathology, molecular and conventional analyses of infection and disease, and neurochemistry. In addition, the initial research effort has been recently expanded to evaluate the effects of urban stormwater on other coho life history stages, including embryos, parr, and smolts.
Adult female coho found dead before spawning. Note the large quantity of eggs in skeins.
This is a large, multi-year project involving many NWFSC scientists. Nat Scholz has been the lead investigator for the Center since 2002.
City of Seattle
US Geological Survey
US Fish & Wildlife Service
Collecting data from coho salmon that return to spawn in Longfellow Creek, West Seattle.
NOAA Coastal Storms Initiative
King Conservation District
Scholz, N.L., Myers, M.S., Incardona, J.P., Labenia, J.S., Rhodes, L.D. and Collier, T.K. (2004). Impacts of stormwater runoff on coho salmon in restored urban streams. Proceedings of the Society of Environmental Toxicology and Chemistry's 4th World Congress, Portland, OR. Oral presentation.
Scholz, N.L. and Collier, T.K. (2003). Chemical habitat quality: a major source of uncertainty in salmon recovery planning. Proceedings of the Georgia Basin/Puget Sound Research Conference 2003, Vancouver, BC, Canada. Oral presentation.
Collier, T.K., Labenia, J., Myers, M.S. and Scholz, N.L. (2003). Extreme PRIMO: Premature mortality of adult coho salmon associated with stormwater dishcharges. Pollutant Responses in Marine Organisms, 12th International Symposium, Safety Harbor, FL. Oral Presentation.
Collier, T., Labenia, J., Spromberg, J. and Scholz, N. (2003). Pre-spawn mortality in coho salmon of hatchery origin: So what? Proceedings of the Society of Environmental Toxicology and Chemistry's 24th Annual Meeting, Austin, TX. Oral presentation.
Photographs of two stream-side sheds used to rear salmon in unfiltered and filtered Longfellow creek water. Top) The shed on the right is fed unfiltered water while water entering the left shed is filtered through sand, activated charcoal, and a UV sterilizer. Bottom) A stainless steel trough in each shed distributes water to 24 individual aquaria each housing a salmon parr or, alternatively (not shown), trays for rearing embryos.
Video clips of affected fish in urban creeks
"Our Troubled Sound: Spawning coho are dying early in restored creeks", Seattle Post-Intelligencer, Feb. 6, 2003.
"Seattle's new drainage plan to provide wildlife with healthy creeks", Seattle Post-Intelligencer,
Dec. 5, 2003.