Studies of eulachon in Oregon and Washington: Designed to guide implementation of a monitoring program to track coast-wide status and trends in abundance and distribution. Project Completion Report July 2015 – June 2018.

In 2015, the Oregon Department of Fish and Wildlife and the Washington Department of Fish and Wildlife (WDFW) received a grant to expand on the research and monitoring of Eulachon in Washington and Oregon. We focused on the establishment of a system to track coast-wide status and trends in abundance and distribution of the ESA listed southern Eulachon distinct population segment (DPS). The primary objective was for WDFW to develop annual eulachon spawning stock biomass (SSB) estimates for the Columbia River population based on egg and larval production surveys. We developed survey protocols that estimated egg and larvae density (n/m3) at a transect comprised of six sampling stations crossing the Columbia River just upstream of the estuary. The transect was situated to capture of eggs and larvae produced from all Columbia River spawning areas (mainstem and tributaries) except for the Grays River. Separate sampling stations were located on the Grays River. We combined mean weekly egg and larvae densities with estimated river discharge (m3/s) to estimate the total number of eulachon eggs and larvae produced for specific time periods over five years of eulachon returns to the Columbia River. We converted the estimates of total egg and larvae production into SSB using estimated relative fecundity, sex ratio, and fish weight. We used bootstrapping on the Columbia River data to develop confidence limits for those estimates. Because the trend in the Columbia River SSB estimates should be interpreted relative to the rest of the Southern DPS, we also developed SSB estimates for two watersheds outside the Columbia Basin (the Naselle River and the Chehalis River). The SSB estimates for the Columbia River, Grays River, Naselle River, and Chehalis River were compared to Canadian DFO estimates for the Fraser River. The monitoring of the Chehalis River Eulachon also included the development of a relative abundance model using eDNA in conjunction with larvae density estimates, and the use of eDNA to assess upriver extent of spawning. This eDNA work in the Chehalis River complimented our temporal genetic analysis of the Columbia River run, in that both studies showed a potential for the larval outflow estimates to be biased slightly high due to Longfin Smelt larvae being present during the early part of the outmigration. Since these two species larvae share very similar morphology, the Longfin Smelt larvae are likely assumed to be Eulachon larvae by those counting larvae. In addition to the larval monitoring, we continued to collect samples of adult Eulachon to expand our knowledge about their length, weight, age, sex ratios, and fecundity (information needed to parameterize our SSB estimation model). Combining our SSB estimates with known Eulachon harvest, run estimates were developed for the Columbia River population. Those run estimates were allocated to broodyear tables based on year specific age composition and sex ratio data. We also worked on public outreach and education concerning Eulachon and their importance to the Pacific Northwest.

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