Pacific lamprey (Entosphenus tridentatus) populations have experienced widespread declines across the Columbia River Basin due to mainstem dam construction, habitat loss, and reduced access to historic spawning and rearing habitats (Close et al. 2002; Moser & Close 2003; Luzier et al. 2011; Pacific Lamprey Conservation Initiative [PLCI] 2024). As an anadromous species with a complex freshwater and marine life history, Pacific lamprey contribute to ecosystem function by transporting marine-derived nutrients, enhancing nutrient cycling, and serving as an important prey resource (Close et al. 2002; Dunkle et al. 2020; PLCI 2024). For Tribes of the Columbia River Basin, Pacific lamprey are a culturally significant First Food and traditional medicine that have sustained Indigenous cultures, lifeways, and subsistence practices for generations. Through Tribal advocacy in the 1990s and 2000s, Pacific lamprey conservation and monitoring programs were established, documenting significant population declines and spurring the development of basin-wide recovery plans (CRITFC 2011, 2025). Despite substantial investment in and implementation of recovery actions outlined in these plans, and growing recognition of the species' ecological and cultural significance, many Pacific lamprey populations remain depressed or extirpated throughout much of their historical range (CRITFC 2011, 2025).

Pacific lamprey translocations have become an increasingly important regional recovery tool in the Columbia River Basin and may be particularly important in systems where passage barriers have eliminated access to historic spawning and rearing habitats. The 2025 CRITFC Tribal Pacific Lamprey Restoration Plan identifies adult translocation and reintroduction as a priority, near-term action to address population declines (CRITFC 2011, 2025). By moving adult lamprey above dams or into previously occupied tributaries, translocation bypasses mainstem passage limitations and directly restores reproductive opportunity in otherwise inaccessible habitats. Evidence from basin-wide translocation efforts indicates that translocated adults can successfully spawn and produce ammocoetes, contributing to downstream juvenile production and, ultimately, returning adults in the Columbia River, thereby advancing basin-wide recovery goals (CRITFC 2011, 2025; Hess et al. 2022, 2023).

We propose to implement and evaluate adult Pacific lamprey translocation in the Upper Cowlitz River watershed, a historically occupied system within the Lower Columbia River Regional Management Unit (RMU). According to the 2025 Regional Implementation Plan for the Lower Columbia RMU, Pacific lamprey are listed as possibly extirpated from 250-1000 km² of the Upper Cowlitz watershed and no detections are documented in the Pacific Lamprey Known Observations and Distribution 2022 dataset (Poirier & Gray 2025). Adult translocations and subsequent monitoring in this watershed provides an opportunity to simultaneously evaluate the efficacy of translocations while contributing to RMU specific recovery goals.

For this project, we propose to translocate approximately 50 adult Pacific lamprey annually (2027 & 2028) in two major tributaries of the Upper Cowlitz River, the Tilton River and the Cispus River, and monitor occupancy and distribution of lamprey across the entire Upper Cowlitz system above the Mayfield Dam using environmental DNA (eDNA). Environmental DNA approaches have been shown to be effective for detecting low-density or cryptic lamprey populations, mapping distributions, and supporting occupancy-based assessments in translocation contexts (Carim et al. 2017; Ostberg et al., 2019; Young et al., 2022). We propose implementing eDNA monitoring in a fixed sampling design with sample collection occurring prior to translocation and then each year after translocation at the same locations to assess changes in distribution, colonization, and early indicators of establishment over a two-year post-translocation period.

The spatial design for this project is fixed across all study years, and eDNA samples will be collected at these fixed locations each year. Additional eDNA sample locations may be added opportunistically. Baseline eDNA samples were collected at these locations in 2026, they will be collected again in 2027 and 2028.