Entosphenus tridentatus

The Goose Lake population of L. tridentata, presumably derived from sea-run populations from the Klamath drainage, likely deserves recognition as a distinct subspecies (Moyle et al. 1989, Moyle 2002). Populations in Lake Cowichan and Mesachie Lake, British Columbia, formerly included in L. tridentata, are now regarded as a distinct species, L. macrostoma (Beamish 1987).

Distribution and abundance have declined greatly in much of the range (especially in Washington, Oregon, Idaho, and California), but the species remains widespread with many subpopulations around the margins of the northern Pacific Ocean, in much of the U.S. range, species is threatened by barriers on mainstem and tributary streams, streamflow management, stream and floodplain degradation, and reduced water quality. NatureServe's rank calculator version 3.1 yielded a rank of G3G4 or G4, depending on the estimated degree of decline.and estimated threat impact. Given the apparently secure status in British Columbia (a large area and significant portion of the range), and apparently low degree of threat and occurrence in many streams in Alaska (although status there is not well known), this species is ranked G4.

Pacific lampreys occur in rivers around the North Pacific Ocean from Hokkaido, Japan (Yamazaki et al. 2005), to Alaska (Cape Lisburne and Norton Sound; apparently rare north of the Alaska Peninsula) and south to southern Baja California (Luzier et al. 2011). Malibu Creek, Los Angeles County, seems to be the southernmost point of regular occurrence in California; scattered distribution south of San Luis Obispo County, with regular runs in the Santa Clara River (Moyle 2002). Adults are wide-ranging in the Pacific Ocean from Japan to Baja California. Landlocked populations occur in lakes or reservoirs in British Columbia, Oregon, California, and possibly elsewhere.

At least historically, Pacific lampreys penetrated far inland in the Fraser, Columbia (to Idaho), Klamath-Trinity, Eel, and Sacramento-San Joaquin rivers. Dams now block or inhibit upstream passage in many rivers.

This species is represented by a large number of subpopulations, but many of these are much reduced and of low viability.

Threats include artificial barriers to migration, poor water quality, predation by native and non-native species, stream and floodplain degradation, loss of estuarine habitat, decline in prey, ocean conditions, dredging, and dewatering (see Luzier et al. 2011). Primary threats are barriers on mainstem and tributary streams, streamflow management, stream and floodplain degradation, and reduced water quality (Luzier et al. 2011). The extirpated and most imperiled populations have no healthy lamprey populations nearby to aid in recovery (Luzier et al. 2011).

Hydropower development, habitat alterations, and land management practices (e.g., irrigation) are thought to be responsible for the declines in the Columbia and Snake rivers (Claire and Cochnauer). Many declines are probably the result of obstructions (i.e., dams) that prevent spawning migration of adults and cause habitat degradation of spawning and larval rearing areas (Weeks 1991). Pacific lampreys were formerly common in the Snake, Clearwater, and Salmon river drainages in Idaho, but dams have had an adverse impact on their migration up the Snake River (Wydoski and Whitney 2003). The population in Elsie Lake in British Columbia was apparently extirpated approximately seven years after dams were constructed on the lake's outlet (Beamish and Northcote 1989). The Goose Lake, California, population may be negatively affected by dams and other obstructions that prevent adults from reaching spawning areas and by stream channelization, grazing, and diversions of water for irrigation, which may cause ammocoete habitat to dry up or become unsuitable (Moyle et al. 1989 and 1995).

Severe declines in salmon abundance may also be influential in the lamprey decline because salmon are one of the primary food resources (Wydoski and Whitney 2003).

Pacific lampreys were historically used extensively for food, trade, ceremonial, and medicinal purposes by Indian tribes in Oregon and British Columbia (Scott and Crossman 1973, Weeks 1991). In the 1940s, they were commercially harvested at Willamette Falls on the Willamette River, Oregon. Harvests averaged 300,000 pounds annually and were used to produce a chemical to aid in blood coagulation. Currently, commercial harvest at Willamette Falls ranges from 3,000 to 11,000 pounds annually and is sold as bait or to biological supply houses. Commercial harvest is now prohibited in some areas in Oregon. However, Indian tribes still harvest lamprey for personal use. At Willamette Falls, native harvests are probably comparable to the present level of commercial harvest. In Oregon, native harvests now occur primarily at Bonneville Dam and to a lesser extent at Sherar Falls on the Deschutes River and Willamette Falls, on the Willamette River.

A 1990 spill of hydrochloric acid in John Day River, Oregon, resulted in the death of an estimated 10,000 ammocoetes (Weeks 1991).

Legal harvest of adults and ammocetes occurs in California and Alaska (Luzier et al. 2011), but this is not known to be a significant threat.