Status of Warner suckers in the Warner Basin, Oregon

Authors: Paul Scheerer, Steve Jacobs

Year: 2009 (xli)

Abstract

The Warner sucker, Catostomus warnerensis, is endemic to the Warner Valley, an endorheic subbasin of the Great Basin in southeastern Oregon and northwestern Nevada. This species was historically abundant and its historical range includes three permanent lakes, several ephemeral lakes, and three major tributary drainages. Warner sucker abundance and distribution has declined over the past century and it was federally listed as threatened in 1985 due to habitat fragmentation and threats posed by the proliferation of piscivorous non-native game fishes. In 2006 and 2008, we conducted investigations in Hart and Crump Lakes to quantify the abundance of Warner suckers, to search for evidence of recent recruitment, to estimate sucker abundance relative to nonnative fish abundance, and to track movements during the spawning season. We found the Warner sucker populations in Crump and Hart Lakes were severely depressed. The 2006 and 2008 abundance estimates for suckers in the lakes were some of the lowest on record. In addition, we found little evidence of recent recruitment of suckers to the lake populations. Sucker size distributions were dominated by large, older aged fish and the average sucker length has increased steadily since the lakes were recolonized following their desiccation in 1992. We also found that the proportion of nonnative fish in the catch has increased during this time period. Radio tracking of tagged fish documented losses of spawning fish in irrigation canals. In 2007, we conducted distributional surveys and obtained population estimates of suckers in the Warner basin tributaries. We found the distribution of stream suckers to be patchy with a few distinct areas of relatively high abundance. In 2009, we obtained a mark-recapture estimate and PIT tagged large numbers of suckers in the tributary stream where suckers were found to be most abundant in 2007.