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Study: Contaminants Found In Pacific Lamprey Could Be Contributing To Population Decline
Posted on Friday, April 17, 2015 (PST)

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 study says.


“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 kills”).


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,


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 life history.


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 River.


“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 spawning migration.


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 basin.


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.

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