Assessing passage success of warner suckers at a newly constructed, sucker- friendly fishway in southeastern Oregon

Authors: Paul Scheerer, Troy Brandt

Year: 2016 (xlviii)

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. Recent recovery actions have focused on improving/providing passage at aging irrigation diversion dams that are common on tributaries in the drainage. In 2015-2016, we assessed passage success and hydraulics at a newly constructed sucker-friendly fishway at the Dyke Diversion on Twentymile Creek. The new fishway is 57 ft long with ten pools/cells, has 0.5 ft weir drops for redband trout passage, 1 ft square orifices for Warner sucker passage, and a simulated streambed floor (cobble). It was designed for a passage window of April-July, maximum orifice velocity of 4 ft/s, range of flows between 35-148 cfs, minimum pool depth of 4 ft, and a slope <4%. We PIT tagged adult suckers and monitored passage in 2015 and 2016 using fixed PIT-tag arrays located at the upper and lower fishway orifices, at the tail of the pool located downstream of the fishway, and at the riffle located upstream of the pool impounded by the irrigation diversion dam. Additionally, we measured hydraulic conditions in the fishway at various stream discharges. We documented sucker passage success in both years and developed recommendations to improve upon the initial design.