The Squaxin Island Tribe is taking a close look at Mill Creek to try to find out why coho salmon numbers have declined so significantly in what appears to be a fairly intact system.
“This is a very comprehensive study of the freshwater habitat in the creek” said Sarah Zaniewski, habitat biologist for the Squaxin Island Tribe. In addition to conducting habitat surveys throughout the lower Mill Creek watershed, the tribe also is surveying juvenile salmon populations and collecting water temperature data.
Like in most South Sound streams, Mill Creek coho production dropped off about 20 years ago. “But, while there was a certain level of recovery in most of the streams to a new lower sustainable level, production in Mill seems to have fallen off the cliff,” Zaniewski said. “No one seems to know why. There’s no obvious change in the past 20 years that could easily explain why we don’t find more adult spawners here.”
The tribal surveys will focus on the lower eight miles of the creek which flows out of Lake Issabella before entering Puget Sound. “We know juvenile salmon use the upper portion of the creek’s watershed, which includes two tributaries that flow into the lake,” Zaniewski said. “What we don’t know is why the overall watershed production is low.”
After a few unsuccessful years, this was the first year the tribe was able to collect consistent coho out-migration data for the creek. In past years, the tribe installed a weir trap. Smolt traps are devices used to safely capture, count and release out-migrating juvenile salmon.
“Those weir traps kept on getting blown out by high water, so this year we shifted to a screw trap, which is bulkier, but isn’t impacted so greatly by high flows,” Zaniewski said. “The trap will give us an idea of how many fish are leaving, and we’ll hopefully find what habitat they’re using in the survey.”
Because coho salmon spend their first year of life in freshwater they can be found year round. “Because they overwinter, coho are especially vulnerable to changes in freshwater habitat,” Zaniewski said. “That makes this kind of basic habitat research essential to preserving salmon.”
Understanding exactly what habitat is available for salmon will help the tribe restore local runs. “The best way to make sure there’s enough coho for everyone is to protect and restore the habitat they depend on,” said Andy Whitener, natural resources director for the Squaxin Island Tribe.