Lower Columbia River Juvenile Chum Salmon Monitoring: Abundance Estimates for Chum, Chinook, Coho, and Steelhead

Chum salmon (Oncorhynchus keta) were historically abundant throughout the lower Columbia River. However, dramatic declines in abundance during the mid-20th century and persistently low returns over several decades led to populations in the Columbia River being listed under the Endangered Species Act (ESA) in 1999. Following ESA listing, state and federal agencies began recovery efforts and the Washington Department of Fish and Wildlife (WDFW) commenced monitoring of juvenile outmigrant abundance to evaluate the effectiveness of recovery projects. Over the years, WDFW has expanded its recovery efforts and subsequently established a robust monitoring program for chum salmon in the Columbia River Evolutionarily Significant Unit focusing on the generation of viable salmon population (VSP) parameter metrics (i.e., abundance, productivity, spatial structure, and diversity). One main component of the WDFW Columbia River chum salmon VSP monitoring program is the collection of juvenile outmigrant data.

For the past 5 to 15 years, WDFW has operated juvenile monitoring traps at five separate locations: Grays River mainstem, Crazy Johnson Creek (Grays River basin), Duncan Creek spawning channel, Hamilton Creek mainstem, and Hamilton Springs spawning channel (Hamilton Creek basin). Juvenile data were collected with either a rotary screw trap (RST) or fence-panel weir. Trap sites were generally operated from late-winter and early-spring (February to March) through late spring to mid-summer (May to August). Although a portion of the collected data have previously been analyzed (i.e., chum salmon fry abundances from Duncan Creek and Hamilton Springs spawning channels), the majority had not. Therefore, the purpose of this report was to summarize the juvenile chum salmon monitoring activities in lower Columbia River since 2002, with specific focus on the generation of annual abundance estimates of juvenile outmigrants. While the emphasis of the juvenile monitoring outlined in this report was to generate unbiased and precise outmigrant estimates for chum salmon, data were collected on all species encountered. Thus, when data were available, outmigrant estimates were generated for other species, including Chinook salmon (O. tshawytscha), coho salmon (O. kisutch), and steelhead (O. mykiss). Abundance estimates were stratified by site, year, species, origin (natural and hatchery), life-stage (fry, parr, and transitional/smolt), and age-class (sub-yearling and yearling). Across all five monitoring sites, we monitored a total of 35 outmigrant years and generated a total of 117 outmigrant abundance estimates and their associated levels of precision.