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THE COLUMBIA BASIN BULLETIN: Weekly Fish and Wildlife News<br>
<a href="http://www.cbbulletin.com/" eudora="autourl">
www.cbbulletin.com<br>
</a>July 29, 2011<x-tab> </x-tab>-- Issue No.
584<br><br>
<font size=4><b>Research Models Show Coho Salmon At High Risk In
Urbanizing Watersheds<br><br>
</b></font>For a decade researchers in Seattle have worked to solve the
mystery of why adult coho salmon are dying prematurely in urban streams
when they return from the ocean to mate and spawn.<br><br>
In a study published in Integrated Environmental Assessment and
Management researchers used models to estimate the potential impact of
urban land development on the salmon population in the decades
ahead.<br><br>
Stricken coho salmon show a syndrome of disorientation, equilibrium loss,
and other symptoms of acute toxicity, which usually cause death within a
few hours. In some watersheds as many as 90 percent of the returning fish
are killed, yet juvenile coho and related salmon species remain
unaffected, even in the same streams.<br><br>
"Forensic evidence currently points to toxic chemical contaminants
in urban storm water runoff as the likely cause of the recurrent fish
kills," said Julann Spromberg, from the National Marine Fisheries
Service. "However, urban runoff is a complex soup containing
mixtures of many different chemicals and we've yet to identify the
smoking gun. With the forensic story still unfolding, this study looked
at how wild coho populations might be affected by an increase in the
geographic extent and severity of the spawner mortality syndrome over
time." <br><br>
Spromberg and her colleague Nat Scholz focused their study on lowland
urban streams around Puget Sound. As with the rest of the Pacific
Northwest this area of lowland watersheds is undergoing substantial human
population growth. By 2025, the population of the Puget Sound region is
expected to rise from 4 million to 5.4 million people.<br><br>
"Currently there are many relatively healthy river systems that
provide high quality freshwater habitat for wild coho in this area"
said Spromberg. "However this may change if these watersheds acquire
the urban land use characteristics that typify the Seattle-area urban
drainages where coho spawners are currently dying in high
proportions." <br><br>
The authors constructed a virtual coho population, with conventional
rates of survival and straying based on the published literature. They
then imposed spawner mortality on different segments of the population,
based on actual rates observed from spawning surveys of urban creeks in
recent years which allowed them to estimate timelines for local
population extinction. <br><br>
The models showed that the proportion of the population affected was a
more important factor that the overall rate of mortality. One scenario
that simulated rapid urbanization forecast an increase in pre-spawn
mortality from 0 to 75 percent over 20 years.<br><br>
When rates were increased to 75 percent over 20 years, the model
predicted the extinction of a solitary coho population in 30 years.
Lastly, the modeling effort revealed how production from high quality
habitat areas within large river basins might mask local declines in coho
abundance due to spawner losses. <br><br>
"While our findings are for virtual populations, our models capture
the basic dynamics of how wild coho may respond to the mortality syndrome
at a population scale. This will help natural resource managers
anticipate future threats to coho conservation and recovery in Puget
Sound and elsewhere in the Pacific Northwest," concluded Spromberg.
"Our next steps include incorporating storm water impacts on embryo
and juvenile survival rates as well as refining the models by expanding
the range of input data to reflect different types of future land
uses." <br><br>
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