Coho in the Deschutes River are in trouble. In fact, every three years, no coho at all return to the river.
The results of a study recently completed by the Squaxin Island Tribe point to a deadly combination of a lack of trees making their way into the river and high concentrations of sediment. Each spring for the last three years, the tribe released 100,000 juvenile coho into the Deschutes. The releases were followed up with snorkel surveys to see where the fish go.
“What we discovered was that coho are attracted to wood in water, no matter where in the watershed they were,” Steltzner said. Because coho salmon spend an extra year in freshwater before heading out to the ocean, they are more dependent on river habitat than other salmon species.
In the lower watershed, salmon pooled in tributaries with lower water temperatures. Those watershed tributaries were even more packed when the fish could find wood to hide and feed around. In the upper watershed, which was surprisingly barren compared to lower watershed tributaries, they found coho only around woody debris in the water.
Even though the upper Deschutes River is relatively undeveloped – less than 10 percent has been paved over – it’s still possible to boost salmon productivity in the watershed.
“We think the reason the fish are doing better in the lower river tributaries is because there’s more sediment in the mainstem,” Steltzner said. Coho have been returning in low numbers for over 20 years since a landslide sent tons of sediment into the river. Before the landslide, the Deschutes River was the largest producer of coho in deep South Sound.
“The landslide wiped out coho in their main stronghold on Huckleberry Creek and they haven’t been able to re-establish themselves,” Steltzner said. New forestry rules put in place since the slide would prevent something of the same magnitude from happening again.
But, even taking into consideration the landslide, only 25 percent of the river’s sediment is human-caused. “The Deschutes is a geologically young system, there’s naturally a lot of sediment in the river,” Steltzner said.
Which brings us back to wood.
The long term impacts of forestry in the upper watershed has also caused a lack of wood in the river itself. “If there were more logs in the upper river, they’d trap some of the sediment, making it less of an issue for salmon,” Steltzner said.
So, the tribe is working with the South Puget Sound Salmon Enhancement Group to scope out a major engineered logjam project in the upper watershed. In a previous study more than a decade ago, the tribe identified one stretch up the upper Deschutes as a significant source of sediment.
“What we’re looking at is working with a private landowner, placing logs in the river, and creating habitat for salmon,” Steltzner said.
Connecting science with habitat restoration and the protection of treaty rights in a vital task for the tribe’s natural resources department.
“We have always depended on abundant salmon runs,” said Andy Whitener, natural resources director for the tribe. “Scientific studies help us determine how to restore salmon in the Deschutes and protect our treaty right to fish.”