This dataset contains daily counts of juvenile chum salmon (Oncorhynchus keta) from the Skagit River, WA between 1990–2019. The analyzed dataset contains 30 years and 4,636 monitoring days in which 2,358,284 migrating chum salmon were counted. This dataset is the companion dataset for phenomix R package.

Juvenile chum salmon were intercepted in the mainstem of the Skagit River during their spring migration to the ocean. Every spring between late January and late July from 1990–2019, the Washington Department of Fish and Wildlife has operated an incline plane trap and an eight-foot diameter rotary screw trap, fished in tandem on the mainstem of the Skagit River (-122.34° E, 48.44° N). Traps were monitored and fish were counted nightly and every third day. The dataset provided is of raw daily counts and is not adjusted for capture efficiency. For purposes of estimating migration timing, this assumes that capture efficiency does not change throughout the season. Given that these data are catch counts, we advise not to use them for estimating total migration abundance without an estimate of trap efficiency.  More information on the Skagit River juvenile fish trap operation can be found in Zimmerman et al. 2015 TAFS 144:627-641.