Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

Pacific lamprey (Entosphenus tridentatus), a fish species native to the Pacific Northwest (USA), have distinctive cultural and ecological value. In this study, we used counts of Pacific lamprey redds, adults, and adult carcasses to understand the species’ distribution, abundance and occurrence, and access across the Oregon Coast. Potential barriers (i.e., dams, culverts) were cumulatively tallied through the network of streams in each coastal basin, from the Pacific Ocean to the headwaters, and used as a model covariate to understand how they might impede access to habitats and alter distribution. Based on the best supported model, lamprey abundance was generally lower in high gradient streams that were further from the ocean. A north-south gradient was evident, with more northerly reaches and those with higher total spring precipitation in the Oregon Coast observing lower abundance overall. In addition, locations with lower winter precipitation had a lower probability of lamprey occurrence. The total number of potential barriers encountered was included as a predictor in the best model, with lamprey occurrence decreasing as encounters with potential barriers along the stream network increased. Beyond understanding distribution throughout Oregon coastal basins, one of the goals of this analysis was to identify locations where barrier removal or restoration could benefit Pacific lamprey populations by increasing the probability of passage and thus access to upstream habitats. We found that focusing restoration and/ or removal of barriers on watersheds in the Mid-South region of the Oregon Coast (i.e., Alsea, Coos, Coquille, Sixes rivers and the Umpqua to a lesser extent) could prioritize use of limited funds, increasing the probability of benefiting Pacific lamprey and potentially other native lampreys and migratory (e.g., salmon, steelhead; Oncorhynchus) species.