2023 and 2024 Snohomish River Basin Juvenile Outmigration Monitoring

Installation of the Skykomish and Snoqualmie screw traps took place between February 1st and Feb 20th and full trapping operations commenced on both traps February 21st. The 2023 season ended on June 22rd on the Skykomish trap the sampling season on the Snoqualmie trap ended June 21st. The Snoqualmie trap did not fish during julian week 20 (May 14-19) due to high flows and debris clogging the trap. The Skykomish trap did not fish during Julian weeks 18 (May 1-5) and 20 (May 14-19) due to high flows that made trap operations unsafe.



The Snoqualmie River rotary screw trap is operated during the juvenile salmon outmigration from February through June. Sampling occurs on four to five weeknights and one or two weekdays per week. Sampling dates are stratified by Julian week (JW) in order to compare results annually. Table 1 shows the Julian weeks that were sampled in 2023 and the corresponding dates. Generally, sampling occurs from JW 7 to JW 25 with some variability in timing. In 2023, sampling occurred from February 21st to June 21st (JW 8 -JW 25). In JW 20, the trap was removed and not fished due to high flows and significant debris. The trap fished for approximately 948 hours, with 564 of those hours fished at night, representing 59% of the total trapping effort. During the sampling season 4,776 salmonids were captured. Captured unmarked Chinook Salmon included 613 sub-yearlings (0+) and one yearling (1+). The number of unmarked sub-yearling Chinook Salmon caught at the Snoqualmie River trap in 2023 just above the project average of 563 (Table 2). Captured unmarked Coho Salmon included 313 yearlings and 1,067 sub-yearlings. The number of unmarked 1+ Coho Salmon caught was well below the project average of 1,037. During the trapping and handling process a total of 10 salmonid mortalities were reported. Mortality as a percentage of the total salmonid catch was approximately 0.21%.



The Skykomish River rotary screw trap is operated during the juvenile salmon outmigration from February through June. Sampling occurs on four to five weeknights and one or two weekdays per week. Sampling dates are stratified by Julian week (JW) in order to more accurately compare results from year to year. Table 1 shows the Julian weeks that were sampled in 2023 and the corresponding dates. In 2023, trapping was conducted from February 21st to June 22nd (JW 8- JW 25). Normally, sampling occurs from JW 7 to JW 25 with some variability in timing.



In 2023, the trap was operated for 901 hours, which is above the average effort of 827 hours. Of those hours, 529 were fished at night, representing 59% of the total trapping effort. Sampling had to be cancelled on Julian weeks 18 and 20 due to safety hazards caused by large flood events. During the sampling season, a total of 85,154 salmonids were captured. Captured unmarked Chinook Salmon included 3,496 sub-yearlings (0+) and 73 yearlings (1+). The number of 0+ Chinook Salmon caught at the Skykomish River trap in 2023 was well above the project average of 1,988 (Table 2). Captured unmarked Coho Salmon included 593 sub-yearlings and 2,924 yearlings. The number of unmarked 1+ Coho Salmon caught in 2023 (2,924) was only 88% of the project average (3,341). During the trapping and handling process a total of 10 salmonid mortalities were reported. The 10 mortalities included three unmarked 0+ Chinook Salmon, one unmarked 0+ Coho Salmon, five Chum Salmon and one unmarked steelhead smolt. Mortality as a percentage of the total sub-yearling Chinook Salmon catch was 0.09%.

In May of 1999, the National Marine Fisheries Service (NMFS) listed the Puget Sound Chinook salmon as threatened under the federal Endangered Species Act (ESA). This listing included Chinook salmon from the Snohomish River Basin (Skykomish and Snoqualmie populations). The recovery of these species depends upon improving the effectiveness of habitat, harvest, and hatchery management across the basin. In order to achieve such improved effectiveness, additional information is necessary to fill important data gaps within the Snohomish system and to assess impacts of restoration efforts, including information on Chinook and Coho salmon abundance, productivity, spatial structure, and diversity (Snohomish Basin Salmonid Recovery Technical Committee, 2005) (. Information about the trends and inter-annual variability in these population parameters is critical to inform salmon recovery efforts, provides basic information on the productivity and capacity of the system, and can lead to significant improvements in harvest management modeling and run forecasting. Additionally, the monitoring of production and survival along with other physical, chemical, and biological conditions provides a means to evaluate recovery actions, habitat conditions, and potential ecological trajectories in the basin.



A key component to provide information on Snohomish salmon populations is the operation of two rotary screw traps in the Skykomish and Snoqualmie rivers. These projects involved trapping and enumerating juvenile Chinook and Coho salmon (as well as several un-targeted species) as they emigrate from the Snohomish River Basin to the Puget Sound. The goals of these trapping efforts are to estimate Chinook and Coho salmon natural production, migration patterns, and freshwater survival. The goal of this project is to track Chinook and coho production and survival information and migration timing within the Snohomish river basin, which can be used in part to evaluate salmon recovery efforts in the various portions of the watershed, to refine preseason run size forecasting by harvest managers, and used in combination with other monitoring and research efforts to better understand and identify priority restoration areas. These goals are accomplished through the direct quantification of juvenile salmon emigrations, evaluation of trap efficiency, and assessment of influential environmental attributes.