The return of the adult Pacific Lamprey offspring from translocations to the Columbia River

ObjectiveThe Pacific Lamprey Entosphenus tridentatus is valuable to tribal culture and to the ecosystem, but its abundance in the interior Columbia River has been highly variable and muted in recent years. Translocation programs have been adopted as a proactive strategy to restore Pacific Lamprey abundance to the interior Columbia River, including the Snake River basin, and these efforts have been largely successful in increasing larval and juvenile abundance in the recipient watersheds and further downstream. We address whether adult translocation offspring from three Columbia River Treaty Tribe programs return to Bonneville Dam in numbers that support previous model predictions; and whether Columbia River origin Pacific Lamprey contribute to adult production widely across the species range.MethodsWe used a genetic data set of unknown origin Pacific Lamprey that returned as adults to Bonneville Dam and broadly distributed locations within and outside of the Columbia River basin. We identified the natal origin of these adults via sibship or parentage to assign individuals to either a precise natal site of volitional production or a set of candidate parents from one of the translocation programs in the Columbia River.ResultWe showed that not only have Snake River translocation offspring returned as adults to Bonneville Dam in numbers that exceeded model projections, but offspring from two other tribal translocation programs in the Umatilla (northeast Oregon) and Yakima (south-central Washington) rivers were also detected in recent years. Offspring produced across all three translocation programs are estimated at approximately 1065 fish in 2021. Although Pacific Lamprey are known to lack precise natal homing, which may limit the benefits of translocations in the interior Columbia River basin, evidence from detections in this study supports a preference by interior Columbia River Pacific Lamprey to return home and migrate toward their natal basins. However, a portion of Snake River-origin Pacific Lamprey was estimated to deviate from main-stem routes into tributaries, including tribal ceded areas where tribal harvest occurs (e.g., Sherars Falls on the Deschutes River).ConclusionThese results indicate benefits from Pacific Lamprey translocation programs that will not only increase abundance to targeted areas but will also increase opportunities for tribal harvest of this culturally important species. Restoration actions employing human transportation of fish are able to increase adult numbers of a culturally important species, Pacific Lamprey, to areas where they can be harvested by Columbia River Treaty Tribes; evidenced by genetic analysis to determine natal origins of individuals through their lifetimes (10+ years).Impact statement