Newaukum River Smolt Production, 2022

This report provides the results from the 2022 juvenile salmonid monitoring study on the Newaukum River main stem near Centralia, Washington. The primary objective of this study is to describe the freshwater production (e.g., smolt abundance) of Pacific salmon (Oncorhynchus spp.) and steelhead trout (O. mykiss) in the Newaukum River. Specifically, we describe the abundance, timing, and diversity (body size, age structure, run timing) of juvenile outmigrants for wild Chinook (O. tshawytscha), coho salmon (O. kisutch), and steelhead trout. Based on the location and timing of our study, the results reflect juveniles that completed their freshwater rearing phase in habitats upstream of river kilometer 9.35 (river mile 5.8) of the main stem Newaukum River.

To meet the study objectives, a 1.5-meter (5–foot) rotary screw trap was operated near river kilometer 9.35 (river mile 5.8) of the main stem Newaukum River from March 11 to July 12, 2022.

Coho outmigrants were predominately of the yearling (or “1+”) age class (96.3%). Scale age data indicated that there was a small 2+ year-old component of the coho out-migration (2.0%) that started near the middle of March. Scale age data also indicated that there was a small subyearling (“0” age class) component of the coho out-migration (1.7%) that started in late June. The average fork length of all outmigrant coho was 119.0 mm (± 10.5 mm SD). The average fork length of subyearlings was 101.9 mm (± 10.8 mm SD), yearlings were 119.8 mm (± 10.4 mm SD), and two-year-old outmigrants were 125.8 mm (± 10.8 mm SD). Abundance of wild coho outmigrants in 2022 was estimated to be 51,031 ± 10,667 SD with a CV of 20.2%.

Steelhead outmigrants were predominately one (54.0%) and two (42.0%) years of age. A small proportion (4.0%) of steelhead were three years of age. Fork length averaged 150.2 mm (± 26.3 mm SD) for Age-1, 155.9 mm (± 20.9 mm SD) for Age-2, and 185.8 mm (± 29.1 SD) for Age-3. The average fork length for all measured steelhead was 151.9 mm (± 28.3 mm SD). We were not able to produce an estimate of abundance in 2022 due to not trapping over the entirety of the steelhead out-migration period.

Chinook salmon in coastal Washington begin their downstream migration as Age-0 fish (fry, parr, and transitional/smolt subyearlings). Typically, the majority of Chinook fry (≤ 45 mm fork length) out-migrate when flow conditions are not suitable for smolt trapping in the Chehalis Basin (e.g., January and February). Therefore, our goal was to estimate the subyearling (> 45 mm fork length) component of the Chinook out-migration that generally occurs from March – July. Fork length of Chinook subyearlings increased steadily throughout the trapping period and averaged 45.9 mm (± 4.5 mm, standard deviation SD) and 95.7 mm (± 6.0 mm SD) in the first and last sampled week of trapping, respectively. Roughly 90.5% of the total catch of wild Chinook outmigrants were > 45 mm. Abundance of wild Chinook subyearling outmigrants in 2022 was estimated to be 40,638 ± 2,750 SD with a coefficient of variation (CV) of 6.7%.