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Study Looks At Genetics, Migration, Behavior Of Pacific Lamprey In Willamette River
Posted on Friday, February 17, 2017 (PST)

Pacific Lamprey populations spawning in the Willamette River may display several genetic differences, characterized by size and spawn timing, according to a recent report.


The number one finding in the study was that Pacific lamprey in the Willamette River displayed, to some extent, genetic differentiation, according to corresponding author Benjamin Clemens, a faculty research assistant in the Department of Fisheries and Wildlife at Oregon State University at the time of the study in 2009 and 2010.


“Using neutral genetic loci, we found evidence for moderate genetic differentiation in adult Pacific Lamprey collected at Willamette Falls,” Clemens said. “This is surprising, given that previous genetic studies (that also used neutral loci) have suggested little genetic differentiation among Pacific Lamprey, and that Pacific Lamprey stocks are therefore fairly panmictic (random matings).”


During 2010, when the study’s researchers found evidence of genetic structuring of adult Pacific lamprey at Willamette Falls, one genetic grouping was smaller and migrated significantly earlier than the other, within-year genetic group. Moderate genetic differentiation of the adult lamprey also occurred between the years of the study – 2009 and 2010, Clemens added.


Another study in 2012 that used different genetic measurements found something similar, Clemens said. In that study, small Pacific lamprey from Willamette Falls had earlier passage times than large lamprey.


“We hypothesize that these data may indicate different migratory cohorts of Pacific Lamprey,” Clemens said.


“The temporal genetic differentiation we report for Pacific lamprey in the Willamette River is new, surprising, and biologically interesting,” the report says.


With the aid of radio tags and fixed and mobile receiving stations (airplanes and boats), researchers tracked lamprey movements in the Willamette River, generating detailed migration histories for the 372 tagged lamprey.


“Most ?sh (69.9 percent) remained in the mainstem Willamette River; the remaining 30.1 percent migrated into tributaries,” the study says. “Eighty-two lamprey exhibited multiple back-and-forth movements among tributaries and the mainstem, which may indicate searching behaviors. All migration distances were signi?cantly greater in 2010, when the amplitude of river discharge was greater. Our data suggest genetic structuring between and within years that may reflect different cohorts.”


According to the study, the final detection for most lamprey were in the mainstem Willamette, which suggests they may have spawned in the mainstem, died before entering tributaries, or entered tributaries undetected.


As for detections in tributaries, most lamprey were tracked in eastside tributaries, such as the Santiam and the Molalla rivers. Of the westside rivers, the Yamhill River had the most.


The study found that some lamprey entered a tributary, then exited and then re-entered the same or another tributary, sometimes multiple times, a back and forth movement not detected in previous studies.


“Genetic diversity does occur among adult Pacific Lamprey over dates within a year and among years,” Clemens said. “These kinds of information provide some tantalizing details and interesting nuances to show that lamprey are not boring automatons that always migrate in a simple, ever-upstream path. And that the genetics, body size, and behavior of a lamprey collected on a particular date may differ from those of another lamprey collected on another date.”


The study hypothesized that these back-and-forth movements may have been searching behaviors by the lamprey for holding, rearing, or spawning locations.


“Temperal genetic population structure and interannual variation in migration behavior of Pacific Lamprey Entosphenus tridentatus” was published online January 27, 2017 in the journal Hydrobiologia (


Clemens currently is a fish biologist and statewide lamprey coordinator with the Oregon Department of Fish and Wildlife. His co-authors are Lance Wyss, currently a restoration project manager for the Freshwater Trust. Rebecca McCoun is currently a Council Coordinator for the North Santiam Watershed Council. Ian Courter is a fisheries scientist for Mount Hood Environmental. Lawrence Schwabe is a hydrosystem compliance specialist with the Confederated Tribes of the Grand Ronde. Dr. Christopher Peery is currently a fish biologist with the U.S. Fish and Wildlife Service. Dr. Carl Schreck is a University Professor and Unit Leader of the U.S. Geological Survey Cooperative Fish and Wildlife Research Unit in the Dept. of Fisheries and Wildlife at OSU. Erin Spice is a research scientist and Dr. Margaret Docker is an associate professor, both in the Department of Biological Sciences at the University of Manitoba.


The study of lamprey migrating into the river was funded by the Columbia River Inter-Tribal Fish Commission through the Columbia Basin Fish Accords with the Bonneville Power Administration.


Lamprey are an ancient taxonomic group that goes back about 500 million years, the study says. Unlike salmon, there is little evidence that their migration return from the ocean includes homing in on natal spawning grounds, but instead they “may rely on other migration cues such as orienting to larval lamprey pheromones.”


In addition, there is no evidence that Pacific lamprey have a fixed life cycle, the study says. They have a long and variable (3 to 7 years) larval period in fresh water before migrating to the ocean and to their parasitic stage when they attach themselves to and feed on fish. That phase is about 3.5 years, but smaller lamprey will return earlier. On their return to fresh water, lamprey may hold in rivers anywhere from several weeks to a couple of years. They do not feed prior to spawning and so will shrink in body size.


Willamette River Pacific lamprey, often considered one of the healthiest runs of lamprey in the Columbia River basin, travel 205 kilometers (127 miles) from the Pacific Ocean, 162 km (101 miles) in the Columbia River and 43 km (27 miles) up the Willamette River to Willamette Falls where they congregate before continuing their migration beyond the falls. The passage beyond the falls occurs mostly April through late June.


“The population(s) – we don’t know whether it is best to label them as a single population per se, at least not at this time – have declined significantly in the Pacific Northwest (including the Columbia River Basin and Willamette River Basin) over the last 100+ years,” Clemens said.


In the late 1800s, one naturalist wrote about the abundance of Pacific lamprey at Willamette Falls as being several layers thick in places, giving the impression that the lamprey were a “profuse growth of kelp” in some areas of the falls, Clemens continued.


Although some scientists have described lamprey at Willamette Falls as “the last stronghold,” the abundance of the fish at the falls and all other areas of the Columbia basin has declined significantly.


Dams and lack of passage at certain dams, entrainment into water diversions and screens as larvae, habitat degradation, pollution, dredging, decreases in ocean prey sources that the lamprey parasitize, poor water quality, and many other causes have been implicated to cumulatively be affecting populations of Pacific Lamprey, Clemens said.


It is “clear that many different Tribes rely on the availability of adult Pacific Lamprey at Willamette Falls—where the lamprey congregate before ascending the falls via lamprey ramps or via the fish ladder—as a source of harvest,” Clemens continued. The fish are an important and integral component of tribal culture and ceremony.


“Although lamprey continue to not get the attention they deserve, alongside ‘game’ fishes, there is evidence to suggest that waters that support robust lamprey populations can support healthy salmon and steelhead populations, and vice versa,” Clemens concluded.



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