Collaboration in Civic Spheres

In Seattle streams, six to ten out of ten adult coho salmon die before spawning

by Matt Rosenberg December 27th, 2011

A final report published this month by a team of 17 Seattle, King County and U.S. government researchers in an open-access peer-reviewed science journal adds to evidence that metal filings from brake pads mixed into storm water run-off, and hydrocarbons from vehicle exhaust are what is responsible for the deaths under acute distress of anywhere from six to ten out of ten pre-spawning adult coho salmon returning each autumn to Seattle area urban streams where the salmon habitat has been restored. More research will be needed to definitively make the connection, but a host of other possible causes can safely be ruled out, the study says. The pre=spawning fatality syndrome has recurred over ten straight years and if it persists it is likely to mean the end of “sustainable natural production” of coho in Seattle area urban streams, the study says.

Warning signs of ‘99-’01 confirmed from ‘02-’09
In the research project’s first phase from 1999 to 2001, adult coho returning to spawn in restored Seattle area streams were consistently dying within a few hours after displaying symptoms of distress, and before spawning. These included swimming to the surface, gaping, losing equilibrium, and pectoral fin splaying. Female carcasses were found with nearly all of their eggs, indicating they had died before spawning. A follow-up project found the same symptoms – and pre-spawning death rates of 67 to 100 percent – in returning adult coho surveyed daily during spawning season in West Seattle’s Longfellow Creek from 2002 to 2009. Longfellow Creek was chosen for special focus partly because of its relatively high proportion of coho. The same disturbing symptoms were also found among pre-spawning adult coho returning at other Seattle-area urban creeks in selected years during that time frame, including Piper’s Creek in Seattle’s Carkeek Park (100 percent death rate in 2006) and Des Moines Creek (63 percent in 2004). In contrast, less than 1 percent of adult coho returning to non-urban Fortson Creek off the North Stillaguamish River died before spawning in the year sampled (2002).

Adult female coho carcass with eggs, Longfellow Creek, Seattle, 2005/PLoS-One Journal

Metal filings from brake pads; hydrocarbons from vehicles, motor oil
Researchers found that other fish species in urban streams such as sticklebacks, sculpins or cutthroat trout, were not affected and the abnormally high pre-spawning adult coho death rates in Seattle area urban streams were not due to their place of origin or common diseases, noninfectious lesions, insecticides, typical water quality indicators or rainfall. They did confirm that compared to counterparts in non-urban Fortson Creek, the coho had significantly elevated levels in their gill tissues of the metals cadmium, lead and nickel, which are released onto roads from the friction created between vehicle tires and brake pads. Researchers also found that compared to counterparts from Fortson Creek, and from Elliott Bay in Seattle, pre-spawning adult coho in Seattle area urban streams had significantly higher concentrations in their bile of the polycyclic aromatic hydrocarbon (PAH) indicators benzopyrene, and phenanthrene – which is cardiotoxic to fish. Sources of PAHs include vehicle exhaust and leaking crankcase oil.

More research needed
The study’s authors state, “The weight of evidence…suggests that adult Coho salmon are unusually vulnerable to the toxic effects of one or more chemical contaminants, most likely delivered to urban spawning habitats via stormwater runoff. The rapid progression of the syndrome and the specific nature of the symptoms are consistent with acute cardiorespiratory toxicity.” The authors do hedge their findings by noting that even though the concentrations of metals and chemicals found in the affected urban stream adult coho were higher than for control groups elsewhere, the levels were nonetheless still “well below” those known to cause direct fatal effects on rainbow trout and other fish in the salmon family. They cite other research findings that coho are especially susceptible to chemical toxicity when making the transition from freshwater to saltwater and hold that the opposite may be true, as well – meaning that lower concentrations could still be fatal.

The study adds that in order to more conclusively make the connection between high death rates for pre-spawning adult urban coho and transportation byproducts, otherwise healthy adult coho would have to be directly exposed to “environmentally relevant mixtures” of the cited metal and chemical contaminants in freshwater.

As for urban stream salmon habitat restoration in the Seattle area – including removal of barriers and weeds and addition of large woody debris, gravel and native vegetation – the authors say it has had myriad ecological, community and educational benefits but aiding the sustainability of coho is not among them. Over time, they add, it is possible new pollution control strategies such as vacuum sweeping of roadways, and a new Washington state law to reduce metals in brake pads could boost survival odds for pre-spawning Coho in urban streams here.

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