[chihuahua]

There is similar work going on to restore fish passage underneath I-90 near Issaquah, Washington. Although in that case, the part of the streams that's currently inaccessible is less than a mile for most of them, and 2 miles for one of them. It's a major undertaking to restore a stream bed or channel underneath the interstate.

This will benefit Kokanee Salmon, a kind of salmon that spends all its life in fresh water and does not migrate to salt water like most salmon.

In Lewis Creek, they currently have access to only 1/2 mile of the creek, but in 2021 there were about 1000 of them returning (from Lake Sammamish) to spawn.

[dendrite9]

I remember in 2018 there were only 18 Kokanee counted spawning from Lake Sammamish.

"A striking ebb in the number of Kokanee salmon in Lake Sammamish, just east of Seattle, has officials worried that extinction is around the corner.

Five years ago, more than 18,000 of the unique freshwater species of sockeye returned to spawn in Lake Sammamish tributaries. This past year, only 19 were counted.

While a number of possible factors are likely to blame for the dramatic drop in the population, King County environmental affairs officer David St. John said warm lake temperatures in the summer from 2014-16 was likely the largest driver.

Lake Sammamish kokanee life cycles are measured in roughly three-year cycles. Kokanee migrate from Lake Sammamish to tributary streams where they spawn. The resulting offspring, juveniles known as fry, then move to the main lake where they remain for just under three years before returning to the streams to spawn, continuing the cycle."

[anitil]

That's really surprising that they could survive with such a small range! How are they counted during their migration?

[jimjeffers]

There are traditional methods like electrofishing and tagging. But there are also non-invasive methods such as environmental DNA where you can detect organism prevalence from DNA shed into the ecosystem. Our platform was built specifically to help share that type of science for restoration and remediation projects: https://www.ednaexplorer.org

[anitil]

That's amazing thanks for sharing it

[chihuahua]

There's an organization of volunteers who walk the streambed during spawning season and mark nests with colored tape on nearby branches. I assume while they're doing that, they also count the fish somehow? They also put a trap near the end of the stream at certain times of the year and count the fish in the trap - the fish are obviously released from the trap afterwards.

[anitil]

That's really interesting, I didn't think you'd be able to spot nests from the shore like that