Newaukum Adult Salmon and Steelhead Spawner Abundance, 2023-2024

The Newaukum River basin has served as a critical pilot watershed for monitoring and guiding salmon and steelhead recovery projects within the Chehalis River basin since 2019. This report details findings from the 2023-2024 survey season, focusing on Chinook Salmon (Oncorhynchus tshawytscha), Coho Salmon (O. kisutch), and steelhead trout (O. mykiss).

Census, redd-based escapement surveys were conducted in 2023-2024, similar to previous years, with additional methods implemented for a second year to evaluate the feasibility of refining and improving escapement estimation techniques for Chinook Salmon. In addition to the redd-based estimates, we conducted carcass mark-recapture and trans-generational genetic mark recapture studies to estimate Chinook escapement. The additional carcass recovery efforts needed for these methods allowed us to increase our sample size for genetic run timing evaluation. For Coho Salmon and steelhead trout, a traditional redd-based escapement method, using index and supplemental surveys, was conducted. Major findings for the 2023-2024 season were:

Chinook Salmon (Oncorhynchus tshawytscha)

• Abundance: An estimated total of 698 Chinook spawners were observed using the redd-based method, with 383 classified as spring-run and 315 as fall-run based on field identification and an October 15th cutoff date to distinguish spring- from fall-run spawners.
• Genetic Analysis: Genetic testing of 96 Chinook carcasses from 2023 identified 6% as genetically spring-run, 21% as heterozygotes, and 73% as fall-run, highlighting the complexity of run-type structure and the presence of genetic hybrids. Note: Early spring Chinook carcasses are less likely to be recovered, which may affect representation in the genetic dataset.
• Run-Type Overlap: Among carcasses sampled prior to October 15th, genetic results indicated a mix of 45% fall-run, 42% hybrids, and 13% spring-run. These findings suggest that overlap in spawning timing complicates classification based solely on observation date and phenotypic traits.
• Distribution: The earliest Chinook spawning occurred in the Pigeon Springs area above the 508 Highway on the South Fork Newaukum. Minimal to no spawning occurred in the last few years before October 15th in the North Fork Newaukum.
• Life History: Most Chinook exhibited a sub-yearling ocean-entry life history, migrating to the ocean after one winter in freshwater. Age composition of returning adults was primarily Age-4 (67%) and Age-3 (21%).
• Challenges: The October 15th cutoff date for distinguishing spring and fall Chinook redds may overestimate the number of pure spring-run Chinook. Continued development of more nuanced methods, including genetic tools, is needed to improve understanding of population structure and run-type distribution. Additional research is also needed to clarify the role of hybrid individuals in the long-term dynamics of Chinook populations in the Chehalis Basin.

Coho Salmon (Oncorhynchus kisutch)

• Abundance: Estimated total of 5,217 spawners, with 3,888 natural origin (NOR) and 1,329 hatchery origin (HOR).
• Hatchery Influence: The proportion of hatchery-origin spawners (pHOS) in the Newaukum River basin declined from 53% in 2022 to 25% in 2023—a substantial reduction. Efforts to increase harvest opportunities for hatchery-origin coho could further reduce pHOS and limit hatchery influence on the natural spawning population.
• Distribution: Coho Salmon continued to utilize almost all smaller tributaries throughout the basin, emphasizing the importance of small stream restoration efforts to support their spawning and rearing habitat.
• Life History: Carcass analysis showed a nearly even sex ratio (52% male, 48% female), with an average fork length of 64.3 cm for females and 66.4 cm for males.

Steelhead Trout (Oncorhynchus mykiss)

• Abundance: Estimated total of 1,230 spawners, with 1,045 NOR and 185 HOR, based on the March 15th cutoff date.
• Distribution: Spawning occurred mainly in the upper portions of the North Fork and the mid- and upper-South Fork Newaukum River. Steelhead used smaller tributaries, but less frequently than Coho Salmon, and more often while flows were high.
• Life History: The predominant freshwater residence time was two years, with most steelhead spending only one year in the ocean before returning to spawn. No repeat spawners were observed in 2024.
• Challenges: The March 15th cutoff date for distinguishing NOR from HOR steelhead is imperfect, and better methods for determining hatchery influence are needed.

This year’s monitoring results highlight the complexity of salmonid population dynamics in the Newaukum River basin and underscore the need for adaptive habitat restoration strategies. For Chinook Salmon, the presence of heterozygotes and observed shifts in spawn timing point to the importance of protecting and restoring habitats that support both early- and late-spawning fish. Continued refinement of run-type classification methods is also needed to improve population assessments and guide effective management. Coho Salmon's significant use of smaller tributaries emphasizes the value of targeted restoration in these systems, rather than focusing solely on larger mainstem habitats. Steelhead monitoring suggests relatively stable population dynamics in the short term, but also highlights the need to protect key habitats that support diverse life histories. At the same time, data gaps remain regarding run timing and the origin of naturally spawning steelhead and Chinook, reinforcing the need for more accurate and timely monitoring approaches. Overall, ongoing, rigorous monitoring remains essential for guiding effective conservation and restoration strategies in the face of environmental change.