Pesticides, mercury and flame retardants found in larvae and
adult Pacific lamprey could be one of the causes of their decline, according to
a recent study.
Once abundant throughout the Columbia River basin, Pacific
lamprey have declined significantly in numbers and reach. While the Willamette
River is home to the largest stronghold of the fish, other sub-basins are
declining in numbers to the point where regional extinction is possible, the
“The levels of contaminants we are seeing in larval lamprey
have caused developmental problems in salmonids in other studies,” said Dr.
Elena Nilsen of the U.S. Geological Survey and principal investigator on the
study. “That is concerning to us.”
Other causes of the lamprey decline, according to the study,
are passage difficulties at dams and irrigation diversions both in the larval
and adult stages, habitat loss, a drop in the number of marine hosts available
to the parasitic lamprey and historical management actions (“intentional
The study, “Reconnaissance of contaminants in larval Pacific
lamprey (Entosphenus tridentatus) tissues and habitats in the Columbia River
Basin, Oregon and Washington, USA,” was published online this month in the
scientific journal Environmental Pollution, http://www.ncbi.nlm.nih.gov/pubmed/25795069.
A number of Northwest Tribes, and state and federal entities
contributed to the work that was headed up by the USGS and the Columbia River
Inter-Tribal Fish Commission. In addition to Nilsen, researchers were Whitney
Hapke and Dennis Markovchick, USGS, and Brian McIlraith, CRITFC.
For millennia, Pacific lamprey have been of great ecological
and cultural importance to Northwest Tribes.
“They provide high caloric value sustenance to native peoples
and may have acted as a buffer against predation of juvenile salmon and
steelhead trout by providing alternative prey to sea lions, northern pike
minnow, terns, and gulls,” the study says.
As larvae they filter fine sediments and nutrients, and, apparently,
a large quantity of contaminants in the rivers. As adults, they die soon after
spawning and provide nutrients to the river ecosystem, due to their anadromous
The study found a bioaccumulation of pesticides, flame
retardants and mercury at many of the sites where they evaluated lamprey
larvae, as well as PCBs in adult lamprey, particularly in the lower Willamette
“We can no longer ignore the role of water quality in the
health of our fish populations and our communities,” said Carlos Smith,
chairman for the Columbia River Inter-Tribal Fish Commission and tribal council
member for the Warm Springs Tribe. “These recent findings only highlight the
urgency to clean up our rivers and streams.”
Another recent study touting a new survey method to
determine the presence or absence of Pacific lamprey, said the distribution of
the fish, historically found from Baja California to British Columbia, is
contracting and that populations are declining. Few lamprey are found south of
Big Sur, it said.
After hatching, larval lamprey spend four to seven years
“living in sediment and feeding on detritus and other particulate matter.”
After this sedentary stage, the larvae go through metamorphosis “to prepare for
parasitizing fish and mammals in salt water,” the study says. They will then
spend one to three years as adults, all the time feeding on at least 15
different fish species, and several species of whales and other mammals, before
returning to fresh water to spawn. They do not feed during their one-year
This USGS and CRITFC study also shows the shrinking range of
Pacific lamprey in the Columbia River basin. In fact, the study used western
brook lamprey, a freshwater species, as a surrogate for Pacific lamprey in the
Yakima River basin because the researchers could not find Pacific lamprey in
The study sampled larvae in the Umatilla River basin, the
Deschutes River basin, Fifteenmile Creek, Mill Creek, Hood River, Yakima River
basin and the Willamette River basin. Fifteenmile Creek and Mill Creek are both
tributaries of the Columbia River and are located near The Dalles, Oregon.
The “protracted sedentary life of lamprey larvae in the
benthos and their relatively high lipid content predispose them to contaminant
exposure and uptake,” with contamination much higher than other anadromous
fish, the study says.
In larval tissue, pesticides accounted for the highest
concentration of contaminants. Fifteen Mile Creek, after an herbicide spill in
2000, had the highest concentration, while the Deschutes River basin was
relatively low in all contaminants.
Concentrations of flame retardants and pesticides in larval
tissue were several hundred times higher than researchers found in sediment
samples in all areas.
Concentrations of mercury were highest in the Yakima and
Willamette rivers. DDTs were highest in the Umatilla and Hood rivers. Other
legacy pesticides (DDT is an example) was highest in Mill Creek.
Mercury and DDT concentrations were highest in Willamette
River larvae, while PCB concentrations were higher in adults.
None of the concentrations of pollutants in the lamprey
exceeded the calculated screening values for human consumption, the study
concludes, although that is only for adults who consume lamprey four times or
less per month.