Pacific Lamprey (Entosphenus tridentatus )

Pacific Lamprey
A Pacific Lamprey rests on a streambed boulder.
(courtesy of Jeremy Monroe,
Fresh Waters Illustrated)
Pacific Lamprey
Adult Pacific Lamprey
(courtesy of Jeremy Monroe,
Fresh Waters Illustrated)
Pacific Lamprey
A Pacific lamprey moves over streambed gravel
(courtesy of Jeremy Monroe,
Fresh Waters Illustrated)

Pacific lamprey are a native anadromous fish species. Historically, Pacific lamprey, Entosphenus tridentatus, were widely distributed from Mexico north along the Pacific Rim to Japan. Their populations have declined in abundance and have become restricted in distribution throughout California, Oregon, Washington, and Idaho. Threats to Pacific lamprey within California may include dams, stream degradation, poor water quality, and impacts of climate change. They are culturally important to indigenous people throughout their range, and play a vital role in the ecosystem as food for mammals, fish and birds, nutrient cycling and storage, and as a prey buffer for other species (USFWS 2011).
State Listings
California state species protection status listings are governed by the California Endangered Species Act (CESA).
- No special status.

Federal Listings
Federal species protection status listings are governed by the Endangered Species Act (ESA).
- Species of Concern

In addition, the Pacific lamprey is a tribal trust species and thus is protected under tribal treaty and other rights (NRCS 2011). The U.S. Fish and Wildlife Service (USFWS) coordinates with tribes on a government-to-government basis in efforts to protect these tribal trust resources and their associated habitats.

Critical Habitat
The Endangered Species Act (ESA) requires the federal government to designate critical habitat for any species it lists under the ESA.
- No designated Critical Habitat
See below
The developing Pacific Lamprey Conservation Initiative (PLCI) is the USFWS's strategy to improve Pacific lamprey populations by coordinating conservation efforts among states, tribes, Federal agencies, and other involved parties.  The collaborative conservation effort goals are to facilitate opportunities to address threats, restore habitat, increase knowledge of Pacific lamprey, and improve their distribution and abundance (USFWS 2011).
Migration from Ocean to Freshwater Streams
Adult Pacific lampreys are thought to remain in the ocean for approximately 18–40 months before returning to fresh water as sexually immature adults, typically from late winter to early summer. Recent research suggests that two distinct life history strategies, analogous to summer and winter steelhead, may occur in some river systems: one, an “ocean maturing”life history that likely spawns several weeks after entering fresh water, and two, a “stream-maturing”life history—the more commonly recognized life history strategy of spending one year in fresh water prior to spawning (Clemens et al. 2013). The adult freshwater residence period for the stream-maturing life history can be divided into three distinct stages: (1) initial migration from the ocean to holding areas, (2) pre-spawning holding, and (3) secondary migration to spawning sites (Robinson and Bayer 2005, Clemens et al. 2010, Starcevich et al. 2013)

Spawning and Egg Development
Pacific lamprey usually spawn from March through July depending on water temperatures and local conditions such as seasonal flow regimes (Stillwater Sciences 2014). During spawning in the spring, mating pairs dig a depression in the stream bottom, forming a redd where they deposit and fertilize eggs. Redds are generally about 1.5 feet by 1.5 feet in area. Eggs incubate for 11-30 days, depending on the water temperature, prior to hatching. Hatched embryos remain in the gravel for up to one more month as gill slits develop. They emerge from redds as drifting larvae called ammocoetes .

Ammocoetes and Ocean Migration
Ammocoetes passively move downstream with the currents, eventually burrowing in slow water pockets of fine silts where they ingest algae, diatoms, and detritus by filter-feeding from their mouths. They move downstream to multiple rearing sites of increasing substrate sizes as they grow over a period of 3 to 8 years.

After several years, ammocoetes transform to macropthalmia with eyes, sharp teeth arranged in an oral disc, and a silvery color , usually during the summer and early fall. The juvenile macropthalmia migrate to the ocean from late fall to early summer, and then spend 1-4 years as adults feeding as external parasites on marine fish and mammals to which they attach with their oral disc. There is no evidence that lamprey imperil their hosts. Pacific lamprey spend only about ¼ of their lives in the ocean, where they grow to lengths ranging from about 16 – 27 inches. Adult Pacific lamprey migrate to streams and rivers during the spring, to mature and spawn, generally after about one year.
Watershed-scale habitat requirements
Stream and river reaches that have relatively stable flow conditions or flows that mimic the “natural” flow regime will better support all life history stages of Pacific lamprey. In addition, a mix of deep pools with good hiding cover (such as boulders and large wood), low velocity rearing areas with fine sand or silt, and silt-free cobble areas upstream of rearing areas, all combined with summer temperatures that rarely or never exceed 68 degrees Fahrenheit will provide good habitat conditions for all life stages.

Spawning habitat requirements
Spawning occurs in medium-sized rivers and smaller tributary streams, from March through July depending on water temperatures and local conditions such as as seasonal flow regimes (Stillwater Sciences 2014). Spawning generally takes place at daily mean water temperatures from 10–18°C (50–64°F), with peak spawning around 14–15°C (57–59°F). Egg incubation can last up to one month after deposition in colder waters. Pacific lamprey dig nests or “redds” of around 2 square feet in gravels and cobbles ranging in size from 1 to 3.5 inches in diameter. Redds are constructed in the downstream ends of pools and slow water areas (e.g. runs or glides), where water is flowing over gravel and cobble (“tail outs”) as well as low- gradient riffles. Redd depths range from 7 inches to 3.5 feet. As with salmon spawning areas, well-oxygenated water flowing through relatively clean substrates is critical to egg survival.

Ammocoete habitat requirements
Drifting lamprey ammocoetes emerging from redds are carried by currents into backwaters, alcoves, sloughs, or pocket pools. Once they reach slow water, they burrow into fine sand and/or silty depositional areas covered with a “frosting” of detritus. These habitats provide opportunities for filter-feeding, and are most common in un-channelized streams with complex channel morphology and seasonal floodplain wetlands and backwater areas. Ammocoetes are particularly vulnerable to irrigation diversions and therefore designs of diversions or water withdrawal must provide lamprey protection features such as site location and fish screens. For diversions that are not screened, ammocoetes trapped in ditches will perish when ditches are drained. Land managers aretherefore encouraged to “rescue” ammocoetes in these sites and transplant them to permanent water habitats at the close of the irrigation season.

Macrothalmia habitat requirements
Macrothalmia begin their downstream migration in late summer- early fall, when rains increase stream flow. Downstream migration is passive, in that the fish are carried by the current to mainstem rivers and eventually the sea. Resting habitat providing cover and low flows are essential as well as unimpeded flows and passage facilities enroute to the ocean.

Adult Upstream Migration Habitat
At present, there is no evidence that lamprey return or “home” to their natal stream or river. Adults do migrate to freshwater from the ocean and then take up to a year to become sexually mature. Water temperatures greater than 68 F have been found to reduce adult growth and disrupt timing of sexual maturation (Clemens et al. 2009). During this time they require deep pools with good cover for hiding from predators. While lamprey are able to “climb” up obstacles using their oral disc as a suction cup, successful passage over dams and/or through culverts is dependent on the surface of the facility being wet with velocities of less than 6 feet/second. Moreover, evidence suggests that Pacific lamprey lose their willingness to negotiate multiple challenging obstacles, such as the dams on the Columbia River. Unfortunately, design features that are helpful to upstream migrating salmon are dissimilar to those needed by Pacific lamprey. Studies to determine lamprey passage design criteria for dams of all sizes are in progress. Available research indicates that hydraulic conditions and the density of passage barriers between the ocean and spawning sites are important for successful migrations of lamprey. Upon reaching suitable habitat, spawning of mature adults occurs when water is 50F to 60 F.
Size and Weight Range
Adult size range: greater than 34 cm (13.4 inches)
Juvenile: 10-16 cm (3.9 inches to 6.3)

Ammocoetes Description
Eyes, oral disk, and teeth absent. Uniformly dark caudal fin; caudal ridge faded. Belly usually light colored. Trunk myomeres 60-72.
Supraoral plate = 3 cusps (usually), central cusp sometimes not evident on early juveniles ca. 150mm;
Lateral Circumorals = 4 (cusps 2-3-3-2); Infraoral plate = 4 - 6 cusps.

Juvenile Description
Total length is 10-16cm; Supraoral with 3 cusps; infraoral with 5-6 cusps; 4 lateral circumorals; teeth weakly developed in younger specimens.

Anadromous Adult Description
Total length is > 34 cm; Supraoral tooth plate with 3 cusps, infraoral with 5-6 cusps, 4 multicuspid lateral circumorals. Eye large, diameter about same as distance from posterior orbit to first branchial pore.
Caudal darkly pigmented throughout.