PORTLAND, Ore. – After a prolific 2023, adult Pacific Lamprey returns are looking disappointing this year. So far, fish counters estimate only 22,021 (as of Sept. 14) lamprey have passed through Bonneville Lock and Dam’s fish ladders during daytime hours on their way upstream to spawn. Last year’s daytime fish ladder count was 63,937, which Northwestern Division touted in a news release, as it was much higher than the 10-year average.
Last year, U.S. Army Corps of Engineers (USACE) biologists were optimistic about the high numbers but cautioned that there are other factors that influence adult returns.
“A lot of this is driven by ocean conditions and food availability in the Pacific Ocean,” said Sean Tackley, a Northwestern Division, Fish Policy and Program manager. “With that being said, USACE and our partners are disappointed to see numbers lower than the 10-year average. However, this kind of year-to-year variability is a consistent pattern we’ve seen over the years.”
For example, 2017 saw 82,564 lamprey pass through Bonneville’s fish ladders during the daytime; whereas, only 11,889 passed in 2020. It’s important to note that lamprey are very active at night and pass via special ramp-like passage structures, so daytime fish ladder counts are minimum estimates.
Additionally, biologists from four Tribes (Nez Perce, Umatilla, and Warm Springs, Yakama) and the Columbia River Inter-Tribal Fish Commission (CRITFC) collect adult lamprey at Bonneville, The Dalles, and John Day dams and transport them upriver to bypass passage barriers and restore lamprey populations in Columbia River Basin tributaries. USACE staff estimate the actual total number of lamprey passing Bonneville Dam this year is probably closer to 87,365, including 13,151 lamprey translocated by the Tribes at Bonneville.
Pacific lampreys are an ancient, eel-like fish but lack the jaws and paired fins of true fish species. Additionally, they have a round sucker-like mouth, no scales and feature small, round gill “pores” instead of gills.
Lampreys are important to Tribes in the Columbia River Basin as they served the rich, fatty fish alongside salmon at feasts and celebrations, according to CRITFC. Biologists also recognize their ecological significance and are working towards improving lamprey passage at the Columbia and Snake river dams.
For instance, Portland District, USACE has completed various lamprey adult passage projects in the past two years, including:
- Bonneville Dam, Bradford Island: In March 2024, staff added a new lamprey flume at the fish ladder entrance to a trap box where Tribal biologists can collect fish for translocation. The district also installed a new variable width weir, hydraulic structures on the ladder floor and other modifications to guide lamprey.
- The Dalles Dam: In March 2024, staff added a new lamprey flume in the east fish ladder junction pool to a trap box for the Tribes use for translocation.
• John Day: In March 2023, staff upgraded the existing lamprey collection system at the north fish ladder with a new water supply and a larger trap box.
“The exceptional performance of the new lamprey passage structures at Bonneville and The Dalles dams is worth celebrating,” said Tackley. “Those structures and the collaborative work of the Corps and Tribes will continue to be critical to our success in the basin. The 17,000-lamprey collected at Bonneville, The Dalles and John Day dams, and translocated by the Tribes is a new record. It’s also a testament to both our progress in lamprey passage structure design and the Tribes’ and CRITFC’s commitment to lamprey restoration in the basin.”
Portland District has additional projects planned for the coming years, including:
• Bonneville Dam, Washington Shore: In December 2024, staff will demolish and rebuild the uppermost segment of fish ladder near the visitor’s center to provide better hydraulic conditions for lamprey passage while continuing to support salmon.
• Bonneville Dam, Bradford Island: Modify the fish ladder’s exit section to improve lamprey passage. This includes rounding corners, cutting new lamprey orifices, and adding more lamprey refuge boxes.
• Bonneville Dam, Washington Shore: Install a new lamprey flume at the north fish ladder entrance.
• The Dalles Dam: Extend the recently constructed lamprey flume to provide volitional passage over the dam.
• John Day Dam: Extend the recently upgraded lamprey flume on the north fish ladder to provide volitional passage over the dam.
Tribes and other federal agencies are working to improve conditions for Pacific Lamprey:
• CRITFC: conducts translocations, genetic monitoring, Hood River natural recolonization, artificial propagation and contaminant accumulation research.
• The Bonneville Power Administration: funds translocation programs for Tribal partners, lamprey specific passage improvements, artificial propagation research, and other important research, monitoring and evaluation programs.
• The U.S. Fish and Wildlife Service (USFWS): works with Tribal, state and federal partners to conserve Pacific Lamprey through the Pacific Lamprey Conservation Initiative by assessing population status and threats; conducts and funds research, monitoring and restoration actions; facilitates and participates in technical, management, and policy forums; and advocates for Pacific Lamprey.
Most USACE work has focused on fixing adult lamprey passage at the dams, but agency biologists are studying downstream passage of juvenile and larval lamprey at the dams too.
“We continue to invest in critical studies by our partners at the Pacific Northwest National Laboratory that are designed to bolster our understanding of juvenile and larval Pacific lamprey passage and survival at the lower Columbia and lower Snake River dams,” Tackley added. “This foundational work will help us make future decisions about how and where – in concert with our juvenile salmon passage efforts – to address juvenile and larval lamprey passage deficiencies.”