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Research Details Impacts Of Low-Elevation Irrigation Diversion Dams On Pacific Lamprey Spawning
Posted on Friday, June 29, 2012 (PST)

Increased flows, lower temperatures and “outright removal of barriers” like irrigation diversion dams would dramatically increase the passage and, thereby, the survival of Pacific lamprey in the Umatilla River, according to a paper published in June in the North American Journal of Fisheries Management.


The article – “Low-Elevation Dams are Impediments to Adult Pacific Lamprey Spawn Migration in the Umatilla River, Oregon” - was authored by Aaron Jackson, the lamprey manager in the Department of Natural Resources for the Confederated Tribes of the Umatilla Indian Reservation, and Mary Moser from the Northwest Fisheries Science Center of the National Marine Fisheries Services in Seattle.


The paper ( notes the efforts of the Confederated Tribes to restore extirpated or severely depressed populations in the Columbia and Snake rivers through restoration programs to achieve self-sustaining and harvestable lamprey populations in their ceded lands.


Jackson and Moser conducted a study to determine whether the ubiquitous, low-elevation irrigation diversion dams in the mainstem Umatilla River were obstacles to adult lamprey spawning migration. Radiotelemetry was used to assess lamprey passage efficiency at seven dams located within the lowest reach of the Umatilla River.


During the four-year study, Jackson and Moser tracked 217 adult Pacific lampreys that were implanted with radio transmitters and released downstream from the dams. Their analysis indicated that dam design, fish size, and temperature had the greatest effects on passage efficiency.


Poor performance was recorded at the two lowest dams in the system and resulted in limited escapement to upper sites. During the study, one dam was breached, after which passage efficiency there immediately improved from 32 percent to 81 percent. In addition, water augmentation actions at Three Mile Falls Dam apparently contributed to improved passage of migratory-phase fish from 17 percent to 50 percent.


“Thus,” they wrote, “actions to improve adult lamprey access to historical spawning areas are feasible and are key to successful restoration of this species.”


In the paper, Jackson said diminishing lamprey abundance in the Columbia River drainage has resulted in fewer tribal harvest opportunities and the potential loss of a cultural mainstay. In recent years, the numbers of adult lampreys counted in the mainstem Columbia River have reached record lows. Consequently, Jackson wrote, tribal harvest is now restricted to extremely limited areas.


“Lampreys are considered a ‘first food’ of the indigenous peoples of the interior Columbia River basin, meaning that they are a primary traditional source of their nutrition and must be protected. In addition, lampreys are used for medicinal and ceremonial purposes and have legendary status among these tribes. The danger now exists that younger generations of tribal people may have no exposure to this important fishery resource.”


The study between 2005 and 2008 focused on lamprey passage in the lower river on six irrigations diversion dams – Three Mile Falls, Maxwell, Dillon, Westland, Feed, and Stanfield – and one hydroelectric diversion dam – Boyd’s (which was removed in 2007).


Three of the dams featured a notch in the structure to allow fish passage and five of the seven dams had fishways to accommodate salmon and steelhead. In 2009 an experimental lamprey passage structure was built at Three Mile Falls Dam.


The study observed the obvious – that passage success by adult Pacific lampreys at irrigation diversion dams was low.


“This was particularly obvious at Three Mile Falls and Boyd’s before any actions were taken to improve passage success,” the paper states. “Less than half of both the spawning-phase and the migratory-phase lampreys passed these structures. The cumulative effects of poor passage at multiple dams can quickly result in exceeding low escapement to spawning areas. For example of every 100 lampreys that entered the Umatilla River in 2005-2006, we estimate that only two would have been able to pass above the fourth dam.”


The greatest obstacles to lamprey movement are lack of attachment surfaces in high-flow areas, the presence of sharp corners that preclude attachment, and overhanging lops at the dam crest.


“At Maxwell, Feed, and Stanfield diversions more lampreys were able to pass, probably because these structures did not have an overhanging lip and each featured a notch in the structure. In contrast, Three Mile Falls, Dillon, and Westland dams all had either an overhanging lip or flashboards at the crest.”


Further, dams increase the amount of energy lampreys need to exert to get over dams particularly during low-level warm-water conditions.


“We detected lampreys at the base of the dams for days and even months after their initial approach,” the paper said. “In some cases, it may have been possible for these lampreys to spawn in suboptimal habitat below the dams, but in other cases, the lampreys probably died from their repeated energetic expenditures during warm water conditions in summer.”


In their conclusion, Jackson and Moser said lamprey restoration will require restoration of habitat “connectivity.”


Their results indicate that hundreds of low-level diversion dams and weirs in the western United States may serve as barriers to anadromous lamprey movement. Other low-elevation structures, such as culverts, may be equally problematic.


However, their results also indicate that passage can be restored through actions designed to provide passage alternatives for lampreys.


“In the Umatilla River, removal of the in-channel structures at Boyd’s hydroelectric dam significantly improved lamprey passage. In addition, our data indicate that improved summer flows for fish in the lower Umatilla River significantly increased lamprey passage efficiency at Three Mile Falls dam.


“Outright removal of barriers, retrofitting structures to accommodate lampreys, and/or improving in-stream flows may be necessary for the restoration of Pacific lamprey to come full circle,” Jackson and Moser concluded.


The paper cited the work of David Close, a CTUIR member who has authored three papers on Pacific lamprey, all three of which included Jackson as a contributor.


Major funding for the study came from the Bonneville Power Administration.


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