The Warner sucker Catostomus warnerensis is endemic to the Warner Basin of southeastern Oregon and northeastern Nevada.  The species was formerly abundant and widely distributed in the basin.  The species has declined in the last century due to stream habitat degradation and fragmentation, blockage of migratory corridors, entrainment in water diversions, and predation by non-native fishes.  This species was listed by the U.S. Fish and Wildlife Service as threatened in 1985.  In 2006, the Native Fish Investigations Project initiated a study to 1) determine population abundance and current distribution of Warner suckers in the Warner basin, 2) describe the population age structure, 3) search for evidence of sucker recruitment in the lakes, 4) PIT and radio tag adult suckers to assess movements and growth rates, and 5) determine the size (age) and timing of downstream stream migrants.

Warner Valley is an endorheic basin which extends approximately 80 km from north to south.  The valley is bounded by fault block escarpments which rise 700 m above the valley floor (valley floor elevation is 1,370 m. The pluvial Lake Warner, which formed during periods of abundant precipitation in the Pleistocene era, had a maximum depth of 100 m and an area of 1,250 sq. km.  Currently several lakes are present in the valley but only Hart, Crump, and Pelican are relatively permanent.  When adequate water is available, Warner suckers may inhabit all of the lakes, sloughs, and potholes of the Warner Valley in southeastern Oregon.  Stream resident populations have been found in the three major valley streams: Honey, Deep, and Twentymile Creeks.

The Warner sucker has two overlapping life histories that have evolved in response to environmental influences, the stream and lake residents.  The lake habitats are productive, but subject to periodic desiccation.  Lake suckers are larger than their stream counterparts.  Stream suckers can repopulate lake habitats after severe drought (for example, after droughts in 1992 and the mid-1930’s).  Stream habitats are influenced by water withdrawals and grazing.  Migration of adult lake-morph suckers to spawning tributaries is impaired by irrigation dams and downstream migration of stream-morph suckers is limited by unscreened diversions.  Numerous passage improvements are being implemented and/or are in the planning stages.

Warner suckers in the lakes are considered potadromous, because they primarily spawn in the streams and rear in the lakes.  However, when streams are inaccessible due to low stream flows or impassable barriers, lake suckers have been observed spawning on limited lake shore gravel beds.  Spawning occurs in the spring (April through early-June) and is associated with warming stream temperatures and relatively high spring runoff.  Adult suckers mature at 3-4 years and have been aged up to 17 years.

Nonnative piscivorous fishes were stocked into the lakes in the 1970’s.  Ratios of crappies and brown bullheads have increased since the early 1990’s and dominate the catch.  In 2001, 87% of the fish captured in Hart Lake and 92% of the fish captured in Crump Lake were nonnative.  These nonnative fishes are believed to limit the recruitment of suckers in the lakes.  In recent investigations, the size (age) distribution of lake suckers has been skewed toward larger, older adults.

Results from recent investigations (2006-2010) include:

Annual Reports and Publications:

Scheerer, P. D., S. E. Jacobs, and A. V. Munhall. 2006. 2006 Warner Valley fish investigations- Warner suckers. Oregon Department of Fish and Wildlife, Fish Research Project HLP0630009 and 134206M093, Annual Progress Report, Salem.