The case for basinwide passage and habitat restoration for Pacific Lamprey in the Willamette River basin (Oregon, USA)

Abstract

Objective: The Pacific Lamprey Entosphenus tridentatus is an anadromous fish that provides many ecosystem services and is important to Native American tribes, which harvest lamprey for cultural uses. The largest harvest of adult Pacific Lamprey in North America occurs at Willamette Falls (WF) in Oregon, USA. Lamprey have experienced conservation problems for decades, and harvest numbers at WF have plummeted approximately 33-fold from a maximum of over 500,000 during 1946 to an average of about 16,000 per year during 1969–1999. Recent harvest has dropped to less than 6,000 lamprey/year during 2000–2021. However, existing conservation plans do not provide a historical perspective on the lamprey harvest at WF and the cumulative threats in the Willamette River basin that likely caused lamprey harvest reductions. Land development, river impoundment, and water pollution coincided with significant decreases in lamprey harvest at WF. These (and other) threats have resulted in reduced habitat for larval lamprey in the basin and, thus, a reduction in the pheromones they release, which attract adults. Conservation plans do not identify specific, basinwide goals to increase the number of lamprey in general and to provide more lamprey for harvest in particular. Methods: Therefore, in this review paper, we provide a conservation perspective on three topics to increase and monitor lamprey abundance at WF. Result: We (1) provide an up-to-date history of the lamprey harvest and its regulation at WF; (2) recommend addressing the lack of basinwide, lamprey-specific passage and habitat restoration to improve the quantity and quality of lamprey spawning and rearing habitats; and (3) identify research needs for monitoring the lamprey population(s) at WF. Conclusion: We conclude that lamprey-specific passage improvements and habitat restoration throughout the Willamette River basin above WF are necessary to bolster abundance.