Warner Sucker

Catostomus warnerensis

Description

The Warner sucker is a moderate-sized sucker, reaching a maximum length of about 20 in (51 cm). It matures at three to four years of age at a length of 5.1-6.3 in (13-16 cm). A bright orange lateral stripe is present on adults during spawning runs. The Warner Sucker is a species that was isolated in the remaining waters of a Pleistocene lake that previously covered much of the Warner Basin floor. When glaciers retreated and the climate became drier, the lake gradually disappeared.

Behavior

Although primarily lacustrine (lake-dwelling), in spring this species spawns in the headwaters of streams that feed the lakes. It requires a silt-free, gravel stream bed for spawning. Breeding probably begins when the fish reaches sexual maturity at three years of age and continues until death, possibly to nine years of age. Typical spawning usually involves one female attended by two or more males. Larvae is deposited upstream and juveniles merge in about four weeks, and the young remain in creeks near the spawning areas for several months to two years before descending to larger bodies of water. Because of dams that obstruct passage and because some populations occur in pools close to suitable spawning areas, the know migrations are short, although some individuals are known to have migrated several miles.

The diet of the Warner sucker probably consists of algae, midge larvae and other small insects, zoo-plankton and other small crustaceans, and organic debris. This species is primarily a nocturnal feeder and is not active during the day.

Habitat

The habitat of the Warner sucker encompasses large natural lakes and associated marshes. Early residents in the area recalled when suckers were very abundant and ascended the creeks in masses to spawn. Specimen have been collected from lakes, reservoirs, irrigation and diversion canals, streams with various substrate types, and springs. The preferred non-breeding habitat seems to be slow or still water with a high concentration of organic material. Preferred breeding habitat is gravel substrates in streams or springs. Larvae find refuge in still water at the edge of streams of ditches, sometimes in very shallow water only 1-2 in (2-5 cm) deep.

Distribution

The Warner sucker is endemic to the streams and lakes of the Warner Basin in south-central Oregon. It now inhabits portions of Crump and Hart Lakes, the spillway canal north of Hart Lake, and portions of Snyder, Honey, Twentymile, and Twelvemile Creeks—all in Lake County, Oregon. Portions of Crump and Hart Lakes are included within the Hart Mountain National Wildlife Refuge. Much of the stream habitat is held by the Bureau of Land Management. Land on the valley floor is for the most part privately owned.

Between 1977 and 1991, eight surveys were conducted to locate Warner sucker populations. These surveys have shown that when adequate water is present, Warner suckers inhabit all the lakes, sloughs, and potholes in the Warner Valley. In 1992, a population estimate was conducted for the Honey Creek and Twentymile Creek drainages, resulting in estimates of 2,500 adults, 2,800 individuals, and 4,400 fry.

In 1992, drought conditions caused Hart Lake to dry up, and as many Warner suckers as could be salvaged were transported to other habitats. In 1996, the Hart Lake population had become reestablished with an estimated 500 individuals.

Threats

Dams and diversion structures, some in place since before the turn of the twentieth century, have prevented this sucker from reaching its spawning and rearing grounds in the stream headwaters. Water pollution and siltation at the few remaining spawning sites also threaten the survival of eggs and hatchlings.

Hart Lake and a portion of Crump Lake dried up in the early 1930s and again in the early 1960s, but periodic fluctuations in lake levels seem to be a natural feature of the Warner Valley. The Warner sucker survives these droughts by seeking refuge in streams that feed the lakes, but at a high cost in population mortality. Increased irrigation demands during such periods aggravate and prolong natural drought conditions, keeping both the water table and sucker population levels low.

Conservation and Recovery

In early 1991, the threat of a fifth consecutive drought year prompted the agencies responsible for managing the Warner sucker to plan a salvage operation to establish a refuge population of suckers at the Dexter National Fish Hatchery and Technology Center in New Mexico. Salvage operations consisted primarily of intensive trap netting in Hart Lake to collect suckers, then transportation of the captured fish to a temporary holding facility (a series of five small earth ponds linked by a 600-ft (183-m) ditch at Oregon Department of Fish and Wildlife's Summer Lake Wildlife Management Area. The suckers were held at Summer Lake Wildlife Management Area for five months until September 1991, when 75 adults were recaptured and transported to Dexter.

While being held at Summer Lake Wildlife Management Area, the suckers from Hart Lake spawned successfully, leaving an estimated 250+ young in the Summer Lake Wildlife Management Area holding ponds after the adults were taken to Dexter. The young suckers did well in the ponds, growing approximately 3.3 in (8.4 cm) during their first summer and reaching sexual maturity at the age of only two years. Sucker larvae were observed in the ponds during the summer of 1993, just over two years after the original wild suckers from Hart Lake were held there. Approximately 30 of the two-year-old suckers were captured and released in Hart Lake in September 1993. In June 1994, more than one hundred 4-7 in (10.2-17.8 cm) Warner suckers were observed in the Summer Lake Wildlife Management Area ponds. In 1996, nine adult fish were observed in these ponds along with about 20 larvae.

The suckers taken to Dexter were reduced from 75 to 46 individuals between September 1991 and March 1993, largely due to anchor worm infestation. In March 1993, the 46 survivors (12 males and 34 females) appeared ready to spawn, but the females did not produce any eggs. In May 1994, five males and seven females spawned, producing a total of approximately 175,000 eggs. However, for reasons that are not clear, none of the eggs were successfully fertilized. The remaining 20 fish at Dexter died in 1995. 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.

In 1991, the Bureau of Land Management installed a modified steep-pass Denil fish passage facility on the Dyke diversion on lower Twenty-mile Creek. The Dyke diversion. structure is a 4 ft (1.2 m) high irrigation diversion that was impassable to suckers and trout before the fishway was installed. It blocked all migration of fishes from the lower Twentymile Creek, Twentymile Slough and Greaser Reservoir populations from moving upstream to spawning or other habitats above the structure.

An evaluation of fish passage alternatives has been done for diversions on Honey Creek which identifies the eight dams and diversions on the lower part of the creek that are barriers to fish migration. In May 1994, a fish passage structure was tested on Honey Creek. It consisted of a removable fishway and screen. The ladder immediately provided passage for a small redband trout. These structures were removed by Oregon Department of Fish and Wildlife shortly after their installation due to design flaws that did not pass allocated water.

Critical habitat was designated for the Warner sucker at the time of listing in 1985.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121
http://pacific.fws.gov/

References

Bond. C. E. 1973. "Keys to Oregon Freshwater Fishes." Technical Bulletin 58. Oregon State University, Agricultural Experiment Station.

Bond, C. E. 1974. "Endangered Plants and Animals of Oregon, I. Fishes." Special Report 205. Oregon State University, Agricultural Experiment Station.

Coombs, C. I., C. E. Bond, and S. F. Drohan. 1979."Spawning and Early Life History of the Warner Sucker (Catostomus warnerensis )." Report to U.S. Fish and Wildlife Service, Sacramento. 52 pp.

U.S. Fish and Wildlife Service. 27 September 1985. "Determination That the Warner Sucker is a Threatened Species and Designation of Critical Habitat." Federal Register 50 (188): 39117-39123.