Description

The Warner sucker is a slender-bodied species that attains a maximum fork length of 456 millimeters (18 inches). Pigmentation of sexually mature adults can be striking. The dorsal two-thirds of the head and body are blanketed with dark pigment, which borders creamy white lower sides and belly. During spawning season, males have a brilliant red lateral band along the midline of the body. Females are lighter.

Historic Status and Current Trends

The probable historic range of the Warner sucker includes the main Warner lakes (Hart, Crump, and Pelican), ephemeral lakes, sloughs, and lower-gradient streams. Historically abundant and widely distributed in the basin, the Warner sucker still maintains sizable numbers in a few habitats. It is still known to occur in most lakes, sloughs, and potholes, except during drought years. Stream resident populations are found in Honey and Twentymile creeks, and in Deep Creek below Deep Creek Falls. In most habitats the Warner sucker is rare, although aggregations of spawning adults or young-of-the-year may be encountered.

Drought in the late 1980s and early 1990s dried most lake and slough habitats and basin-wide surveys conducted from 1993 to 1997, after the lakes had refilled, documented the recolonization of these habitats by native and non-native fish. Prior to the drought, the lake population of suckers was comprised of only large older individuals indicating a lack of successful reproduction or recruitment to lake habitats. During the same time, non-native piscivorous (fish-eating) fishes [crappie (Pomoxis sp.) and brown bullhead (Ictalurus nebulosus)], comprised approximately 87 percent of the fish fauna in the Warner lakes. Following the drought, recolonization by native fishes, including the Warner sucker, was found to occur at a much faster rate than for non-native fishes. Surveys in 1997 indicated that native fish [Warner suckers, tui chubs (Gila bicolor ssp.) and redband trout (Oncorhynchus mykiss ssp.)] comprised approximately 80 percent of the total catch. Information collected from 1993 to 1997 suggests that the drought may have had a significantly greater impact on non-native fishes as compared to the native species that evolved under fluctuating environmental conditions. However, over time it is anticipated that the number of crappie and brown bullhead will increase significantly to levels observed prior to the drying of lake habitat in 1992.

Habitat

Larvae are found in shallow backwater pools or on stream margins where there is no current, often among or near macrophytes (aquatic plants). Young-of-the-year use deep still pools, but also move into faster flowing areas near the heads of pools. Adults use stretches of stream where the gradient is low enough to allow the formation of long, >50 meters (>164 feet), pools. These pools tend to have undercut banks, large beds of aquatic macrophytes, root wads or boulders, a vertical temperature differential of at least 2º C (35.6º F), a maximum depth >1.5 meters (>5 feet), and over-hanging vegetation.

Reasons for Decline

General stream channel and watershed degradation from livestock grazing has caused hydrologic impacts to sucker habitat. In addition, numerous small, agricultural diversion dams on creeks reduce stream flows and prevent migrations of adults and young. In lake habitats, non-native brown bullhead and crappie are abundant. The crappie and brown bullhead are presumed predators on young suckers.

Conservation Measures

Completed actions include fencing of streams to restore riparian vegetation, acquisition of ephemeral lake habitat, and construction of a fishway for passage over a diversion dam on Twentymile Creek. The Bureau of Land Management and the USDA Forest Service have altered their grazing and forest management practices to improve habitat for Warner suckers. Additional conservation measures needed include improving stream habitat and watershed conditions throughout the Warner Basin, re-establishing migration corridors, screening irrigation diversions, controlling exotic fishes, and maintaining adequate water supplies for fish.

Many of these conservation actions will also benefit native redband trout and tui chubs. Continuing drought through 1992 dried "permanent" lakes, such as Hart and Crump, for the first time since the 1930s, highlighting the importance of preserving diverse habitat types.

References

Allen, C.S., A. Atkins, M.A. Stern, and A.V. Munhall. 1994. Status and recolonization rates of the Warner sucker (Catostomus warnerensis) and other fishes in the Warner Lakes in SE Oregon 1994. U.S. Bureau of Land Management, U.S. Fish and Wildlife Service and the Oregon Natural Heritage Program of The Nature Conservancy.

Allen, C.S., K.E. Hartzell, M.A. Stern, A.V. Munhall. 1995. Status of the Warner sucker (Catostomus warnerensis) and other fishes in the Warner Basin in SE Oregon. U.S. Bureau of Land Management and the Oregon Natural Heritage Program of The Nature Conservancy.

Allen, C., K. Hartzell, and M. Stern. 1996. Warner sucker progress report - 1996 findings. Unpublished report to Bureau of Land Management. 55 pp.

U.S. Fish and Wildlife Service. 1985. Determination that the Warner sucker is a threatened species and designation of its critical habitat. FR 50: 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.

White, R. K., T. L. Ramsey, M. A. Stern & A. V. Munhall. 1991. Salvage operations and investigations of the range and stream habitat characteristics of the Warner sucker, (Catostomus warnerensis), during spring and summer 1991. Oregon Natural Heritage Program, Portland. 44 pp.

Williams, J. E., M. A. Stern, A. V. Munhall & G. A. Anderson. 1990. Conservation status of threatened fishes in Warner Basin, Oregon. Great Basin Naturalist. 50:243-248.

Williams, J.E. Threatened Fishes of the World: Catostomus warnerensis, Snyder, 1908 (Catostomidae). Environmental Biology of Fishes