FY23 Stillaguamish Smolt Outmigration Monitoring

The 2025 smolt trap monitoring project began in January. The final sampling day of the 2025 smolt trapping season was 7/3/25, and the following weeks involved dismantling and removing the trap from the river. We estimated the relative contribution, size, and outmigration timing of the two groups for the purposes of monitoring the Chinook Natural Stock Restoration program. Data was also collected on other salmonid species. The placement of the smolt trap in the lower Mainstem allowed for the majority of the entire watershed to be sampled for outmigrating smolts. The trap was deployed in early February and continued to capture fish through mid-July, crewed by a team of two technicians.

Measuring and understanding the inter-annual variation in run size of wild Chinook, listed as threatened under the ESA, is critical for managing harvest and prioritizing habitat restoration. Quantifying the number of smolts leaving the watershed is one of the few methods available that provides a direct measure of the year-to-year changes in freshwater survival and growth, free from the confounding influences of marine conditions.