Warner Sucker investigations in the Warner Valley, Oregon

Authors: Paul Scheerer, Patrick DeHaan, Clements Shaun

Year: 2012 (xliv)

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. From 2006 through 2012, we conducted investigations to: 1) describe the current distribution of suckers in the Warner subbasin, 2) estimate their abundance in the lakes and streams, 3) collect life history information, and 4) describe the primary factors that currently limit the sucker’s ability to maintain a functioning metapopulation, including connectivity or fragmentation of habitats and factors affecting successful recruitment in the lake and stream environments. In Crump and Hart Lakes, we found that the Warner sucker populations were severely depressed and recent abundance estimates in the lakes were some of the lowest on record. During the 2006-2010 drought, the lakes partially desiccated and we found little evidence of recruitment of suckers to the lake populations and noted a steady increase in the average size of lake suckers. In 2012, after the lakes re-filled, we documented successful sucker recruitment into the lakes and an increase in sucker abundance in Hart Lake. We found the distribution of stream suckers to be patchy with a few distinct areas of relatively high abundance. In 2007, we obtained a basin wide abundance estimate of ~6,900 fish in the tributary streams using a spatially-balanced random sampling design, but precision was low. In 2009 and 2011, we described the distribution of Warner suckers in the Twentymile Creek subbasin and in Honey Creek, respectively, and obtained mark-recapture population estimates with improved precision. We used radio tracking, PIT-tagging, larval drift nets and downstream rotary migrant traps to assess seasonal movements of suckers. We found little evidence of substantial downstream movements in the spring and summer months. However, we documented large numbers of suckers moving upstream during the spring spawning period. We completed genetic analysis of sucker populations in four tributary streams. None of the tributary populations showed reduced levels of genetic variation and the data suggests that each tributary contains a genetically independent spawning population. We assessed levels of genetic variation in a refuge population and found them to be similar to those in the natural populations.