The Suquamish Tribe has spent the past 15 years tracking water temperatures in nearly 30 of Kitsap County’s salmon streams.
“Stream temperature monitoring gives us a good understanding of where some creeks and watersheds may be less suitable for salmonids because of high stream temperatures,” said Steve Todd, the tribe’s ecologist. A temperature gauge the size of a bottle-cap is installed in the stream and takes measurements every 30 minutes between June and September.
Some streams are warm in summer while other streams remain cool, but one observation is clear, he said: waters are warmer during particularly warm summers, a finding that will be a growing problem for salmon populations as climate change takes hold and land use development continues.
East Kitsap County streams support chum, coho and chinook salmon, and steelhead and cutthroat trout, all species sensitive to higher water temperatures.
Coho, steelhead, and cutthroat are the most vulnerable species to higher temperatures because their life histories include hanging out in streams, lakes and wetlands during summer months when waters are warm and flows drop.
These fish can’t thrive and survive in temperatures that are too high, Todd said, and food sources for salmon, such as macroinvertebrates, also need cool temperatures to survive.
About one-third of the streams studied have been regularly exceeding the Washington State water quality temperature standard to maintain a safe level for salmon, measured at 61 degrees F (16 C) or higher.
In particular, Curley Creek exceeded the state’s standard nearly 100 percent of the time during the summer months between 2003 and 2016. Other streams that tend to exceed the temperature standard on most days include Salmonberry, Carpenter, South Fork Dogfish, Chico and Kitsap creeks.
Based on the data collected by the tribe, the state identifies these warmer streams as “impaired waters” for temperature. Specific causes of warm water can then be determined, and steps can be taken to remedy the temperature problems.
Such remedies include protecting and restoring native trees and shrubs along streams and in wetlands to keep water temperatures cool during summer months. Also, as trees fall into the stream, they provide structural complexity vital to salmon habitat, including the formation of critical resting and rearing pools.
“Kitsap streams are fed by groundwater, not glaciers or snowmelt,” Todd said. “The fallen trees in streams slow the water, promoting the exchange of cooler groundwater with the stream’s surface water, providing an environment that supports salmon populations.”
While fish are able to adapt to changing conditions to a certain extent, the tribe wants to know whether land use development and/or groundwater extraction or surface water withdrawals cause stream temperatures to rise enough to a point where fish aren’t able to adapt any more. A warmer future with warmer waters just adds to these challenges, Todd said.