Warner sucker

Catostomus warnerensis

SPECIES CODE: E057 V01

STATUS:

Listed Threatened with Critical Habitat on September 27, 1985 (50 FR 39117 39123). Recovery Plan completed on April 27, 1998.

Note: All descriptions are abstracted and/or excerpted from the Federal Register (1985) and the Recovery Plan (1988).

SPECIES DESCRIPTION:

The Warner sucker is a member of the Catostomidae family. The species grows to a maximum length of about 20 inches (510mm) (USFWS 1985). Suckers recovered from an ice induced kill in Crump Lake were 17 years old (USFWS 1998). Warner sucker larvae feed on invertebrates in midwater or on the surface; as the species gets older it becomes generally benthic, feeding on diatoms, filamentous algae, and detritus. Adults forage nocturnally over a wide variety of substrates such as boulders, gravel and silt

REPRODUCTION AND DEVELOPMENT:

The species, due to habitat modification, has evolved to adapt to available habitat, i.e. lake and/or stream. They are dubbed lake morphs and stream morphs. Individuals residing in the lake are larger, presumably longer-lived, and are capable of surviving through years of isolation from stream spawning habitats due to drought or other factors. The lake habitat represents a less stable but more productive environment that the metapopulations of Warner suckers use on an opportunistic basis. However, Warner suckers inhabiting streams can migrate into the lake habitat and become lake morphs.

The Warner sucker typically ascends stream tributaries to lakes in the Warner Basin to spawn. Spawning usually occurs in April and May in streams, although variations in water temperature and stream flows may result in either earlier or later spawning. Sexual maturity occurs at an age of 3 to 4 years (Coombs et al. 1979). The species spawns in silt-free, gravel-bottomed, slow flowing sections of creeks. In years when access to stream spawning is limited by low flow or by physical in-stream blockages (such as beaver dams or diversion structures), suckers may attempt to spawn on gravel beds along the lake shorelines.

RANGE AND POPULATION LEVEL:

The Warner sucker is endemic to the streams and lakes of the Warner Basin in south-central Oregon. The species is presently known to occur in portions of Crump and Hart Lakes, the spillway canal north of Hart Lake, and portions of Snyder, Honey, Twentymile, and Twelvemile Creeks (USFWS 1985). The species was once abundant within its range.

HABITAT:

During times of high flow the species is able to inhabit all areas within its range. However, in times of low flow the lake habitat in inaccessible and the lake population declines. Generally, stream dwelling individuals inhabit stretches of slow flowing streams that can be characterized as long pools (50m (166.6ft) or longer) (USFWS 1998). Habitat use by lake resident suckers appears to be similar to that of stream resident suckers in that adult suckers are generally found in the deepest available water where food is plentiful.

PAST THREATS:

The decline of the species is attributed to human induced habitat modification and degradation including irrigation diversion, watershed degradation, and competition and predation by introduced exotic species.

Human induced habitat modification and degradation has caused increased siltation, erosion of banks and streambeds, straightening of streams leading to increased water velocities, changes in timing and levels of peak and low flows, increased water temperatures, and has caused eutrophication of ponds and lakes. Although natural processes can lead to erosion of banks and siltation of streambeds, these processes are usually in equilibrium with the natural recovery process. Siltation covers spawning beds, decreasing suitable spawning habitat. These changes have also restricted spawning migration, and peak flow changes have altered the timing of “natural” cues for spawning migration. Water level decreases have occurred to the point of complete dry-ups, as was the case with Hart Lake in 1992. Water diversions continue to decrease water levels causing periodic isolation between the lake and stream habitats.

In the early 1970’s, Oregon Department of Fish and Wildlife stocked white crappie, black crappie, and largemouth bass in Crump and Hart Lakes. Prior to this, brown bullhead and non-native rainbow trout were introduced into the Warner Valley. The adults of all five species feed on small fishes to varying degrees, and bass also prey on larger fish (Wydoski and Whitney 1979).

CURRENT THREATS:

Past threats still remain.

CONSERVATION MEASURES:

In 1991, 75 adults from Hart Lake were taken to Dexter National Fish Hatchery and Technology Center, Dexter, New Mexico, for maintenance and development of cultural techniques. However by 1995 all suckers at the Dexter National Fish Hatchery had died. In November of 1995, approximately 65 more suckers from Summer Lake Wildlife Management Area were transferred to Dexter for spawning purposes but as yet no attempts to spawn these fish have occurred.

LITERATURE CITED:

Coombs, C.I., C.E. Bond, and S.F. Drohan. 1979. Spawning and early life history of the Warner sucker (Catostomus warnerensis). Unpublished report to the U.S. Fish and Wildlife Service. 52 pp.

U.S. Fish and Wildlife Service. 1985. Determination That the Warner Sucker is a Threatened Species and Designation of Its Critical Habitat. Federal Registers (50) 188:39117-39123.

U.S. Fish and Wildlife Service. 1998. Recovery Plan for the Native Fishes of the Warner Basin and Alkali Subbasin. Portland, Oregon. 86pp.

Wydoski, R.S., and R.R. Whitney. 1979. Inland Fishes of Washington. University of Washington Press. Seattle, Washington. 220pp.