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Pacific lamprey

Photo of Pacific Lamprey (Jeremy Monroe, FI)

Scientific Name: Entosphenus tridentatus 

Status: Species of concern 

The Pacific lamprey is considered a Species of Concern. In April 2010, the USFWS released the Best Management Practices to Minimize Adverse Effects to Pacific lamprey.

  • Historical Status and Current Trends

    Historically, Pacific lampreys were thought to be distributed wherever salmon and steelhead occurred. However, recent data indicate that distribution of the Pacific lamprey has been reduced in many river drainages. They no longer exist above dams and other impassable barriers in west coast streams, including many larger rivers throughout coastal Washington, Oregon, and California, nor above dams in the upper Snake and Columbia Rivers. Available data also indicate that Pacific lampreys have declined in abundance throughout the Columbia River basin and southern California.

    Description and Life History

    Lampreys belong to a primitive group of fishes that are eel-like in form but lack the jaws and paired fins of true fishes. Pacific lampreys have a round sucker-like mouth, no scales, and gill openings. Identification of lampreys depends largely on the number, structure, and position of teeth found in adult lamprey. Adult Pacific lampreys are characterized by the presence of three large anterior teeth and many smaller posterior teeth on the oral disc. As ammocoetes (larvae), Pacific lampreys are difficult to distinguish from other lampreys.

    As adults in the marine environment, Pacific lampreys are parasitic and feed on a variety of marine and anadromous fish including Pacific salmon, flatfish, rockfish, and pollock, and are preyed upon by sharks, sea lions, and other marine animals. They have been caught at depths ranging from 300 to 2,600 feet, and as far off the west coast as 62 miles in ocean haul nets.

    After spending one to three years in the marine environment, Pacific lampreys cease feeding and migrate to freshwater between February and June. They are thought to overwinter and remain in freshwater habitat for approximately one year before spawning. During that time they may shrink in size up to 20 percent. Most upstream migration takes place at night. Adult size at the time of migration ranges from about 15 to 25 inches.


    Pacific lampreys spawn in habitat similar to that of salmon: gravel bottomed streams at the upstream end of riffle habitat. Spawning occurs between March and July depending upon location within their range. The degree of homing is unknown, but adult lampreys cue in on ammocoete areas which release pheromones that are thought to aid adult migration and spawning location. Both sexes construct the nests, often moving stones with their mouth. After the eggs are deposited and fertilized, the adults typically die within 3 to 36 days after spawning.

    Embryos hatch in approximately 19 days at 59° Fahrenheit (F) and the ammocoetes drift downstream to areas of low velocity and fine substrates where they burrow, grow and live as filter feeders for 3 to 7 years and feed primarily on diatoms and algae. Several generations and age classes of ammocoetes may occur in high densities. Ammocoetes move downstream as they age and during high flow events. We know little about movement and locations of ammocoetes within the substrates. Anecdotal information suggests that they may occur within the hyporheic zone (a porous substance zone in the sediment) and may move laterally through stream substrates.

    Metamorphosis to the juvenile phase (macropthalmia) occurs gradually over several months, usually beginning in summer and is complete by winter. As developmental changes occur, including the appearance of eyes and teeth, the juveniles leave the substrate to enter the water column. Moving downstream, they emigrate to the ocean between late fall and spring where they mature into adults.

    Reasons for Decline

    Pacific lampreys face a variety of threats to its various life history stages:

    • lack of passage (caused by dams, culverts, water diversions, tide gates, other barriers) both upstream & downstream.

    • dewatering and reduced flows (reservoir management, water diversions, construction projects);

    • poisoning (accidental spills, chemical treatments);

    • poor water quality;

    • dredging (channel maintenance and mining);

    • stream and floodplain degradation (channelization, loss of side channel habitat, scouring);

    • ocean conditions (loss of prey, increase in predators);

    • predation by nonnative fish species.

    Taking into account the potential for lamprey utilization of an area is essential to their conservation. This is especially critical for lamprey ammocoetes because they are unable to move out of areas of disturbance and a single dewatering event, physical disturbance, or contamination may have a significant effect on a local lamprey population.

    Conservation Measures

    Primary conservation opportunities to protect and restore Pacific lamprey populations include:

    • provide lamprey passage

    • protect ammocoete habitat

    • restore stream channel complexity


    Best Management Guidelines for Native Lampreys During In-water Work Living Document, Original Version 1.0 (May 2020)

    Lamprey Technical Workgroup. 2020. Barriers to adult Pacific Lamprey at road crossings: guidelines for evaluating and providing passage. Original Version 1.0, June 29, 2020. 31 pp. + Appendices.

    Pacific Lamprey Conservation Initiative Webpage.

    Practical Guidelines for Incorporating Adult Pacific Lamprey Passage at Fishways (June 20, 2017)

    Story Map: Pacific Lamprey. Produced by Erin Butts, GIS Specialist in the Columbia River Fish and Wildlife Conservation Office, US Fish & Wildlife Service, Vancouver, WA


    Last updated: April 2021

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