Species Fact Sheet Pacific lamprey Lampetra tridentata
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
lack of passage (caused by dams, culverts, water diversions, tide
gates, other barriers) both upstream & downstream.
dewatering and reduced flows (reservoir management, water diversions,
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
Primary conservation opportunities to protect and restore
Pacific lamprey populations include: