Warner Sucker Investigations in the Warner Basin, Oregon

Authors: Paul Scheerer, Steve Jacobs, Shannon Richardson, Mark Terwilliger

Year: 2010 (xlii)

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 2006-2010, we conducted investigations in the Warner basin to describe current distribution of Warner suckers, to quantify their abundance in the lakes and streams, to search for evidence of recent recruitment into the lakes, to describe size structure in the lakes and streams, to estimate sucker abundance relative to nonnative fish abundance in the lakes, to track movements of lake and stream suckers during the spawning season, and to look for evidence of larval drift. We found the Warner sucker populations in Crump and Hart Lakes were severely depressed. Recent abundance estimates 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. Radio tracking of tagged lake fish documented losses of spawning fish in irrigation canals. 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, we described the distribution of Warner suckers in the Twentymile Creek subbasin and obtained a mark-recapture population estimate of ~4,600 suckers with high precision. We monitored movements of PIT-tagged and radio tagged suckers and operated a downstream migrant trap in the Twentymile Creek subbasin and found no evidence of downstream movement towards Crump Lake or losses into the irrigation ditches, yet noted large numbers of suckers moving upstream during the spawning period. After spawning, we sampled larval suckers using drift nets and dip nets, but found no evidence of larval drift. In addition, we collected tissue samples from suckers throughout the basin to examine levels of genetic variation within and among populations, to describe levels of genetic structuring among populations, to describe the relationship between stream and lake suckers, to infer live history characteristics, and to describe levels of genetic variation within an introduced population. Also, we completed a study verifying the feasibility of using pectoral rays as a non-lethal aging technique and collected pectoral rays from both lake and stream suckers to describe their age structure and age-at-maturity. Genetic analyses and the ageing study will be completed in 2011.