Bluehead and Flannelmouth sucker restoration in the Big Sandy River, Wyoming

Authors: John Walrath, Stephen Siddons, Beth Bear, Joe Gillis, Matt Joki, Jessica Lockwood, Robert Keith, Kevin Gelwicks

Year: 2024

Abstract

Two Wyoming native fish species, Bluehead Sucker, Catostomus discobolus and Flannelmouth Sucker, Catostomus latipinnis have declined dramatically throughout their native range, due to dam construction and operation, as well as predation, competition, and hybridization associated with nonnative fishes. In Wyoming, previous surveys of the Green River drainage identified hybridization with nonnative White Sucker, Catostomus commersoni and Longnose Sucker, Catostomus catostomus to be the primary threat to Flannelmouth and Bluehead sucker persistence and it also identified the Big Sandy basin as one of four primary basins in which conservation actions would have the greatest impact. For more than a decade, preparations were made for an eventual restoration of the Big Sandy River, including construction of a barrier to prevent nonnative species from re-invading the river, mechanical removal of nonnative suckers, construction of two native fish rearing facilities, and experimental captive rearing of native suckers. In 2021, a major restoration project was initiated on the Big Sandy River with the goals of eliminating nonnative fish species (particularly White and Longnose sucker and Burbot, Lota lota) and restoring native Flannelmouth and Bluehead sucker populations. The project area, located directly above Big Sandy Reservoir, consisted of 52.5 miles of main stem river, as well as ephemeral and perennial tributaries, and off-channel ponds on a mixture of private, federal, and state lands. The project entailed salvaging Flannelmouth and Bluehead sucker from the river, holding them in captivity while conducting chemical treatments, and repatriating them upon treatment completion. Native suckers were salvaged using various electrofishing units from July 6–September 15, 2021 and while conducting the first chemical treatment. In total, 5,844 Flannelmouth Sucker and 385 Bluehead Sucker were salvaged. Mortality while in transit and at holding facilities was high in the first few months due to multiple factors (e.g., warm water temperatures, handling stress, disease). Following salvage, two separate rotenone treatments were conducted on September 14–16, 2021 and September 13–15, 2022 to remove nonnative fishes from the project area. Prior to repatriation, all salvaged fishes were sorted and identified and genetic samples were taken to verify phenotypic identification by trained biologists. Genetic results indicated high confidence in phenotypic identification and repatriation occurred from fall 2022 to spring 2024. A total of 1,992 native suckers was repatriated; approximately 1,800 Flannelmouth Sucker and 200 Bluehead Sucker. Overall survival from salvage to repatriation was approximately 30% for Flannelmouth Sucker and 50% for Bluehead Sucker. Sampling conducted in 2024 did not identify any nonnative species in the treatment area with the exception of Lake Chub, Couesius plumbeus and confirmed successful reproduction of Flannelmouth Sucker after repatriation. We will continue monitoring the project area to determine long-term treatment efficacy and demographic and dynamic functions of the native suckers after repatriation. The salvage operation also documented that the lowest 20 miles of the treatment area is vitally important for juvenile native suckers, especially overhanging woody vegetation. Unfortunately, much of this area is also severely degraded (e.g., over-widened channel, eroding banks, monotonous habitat, warm summer water temperatures, etc), likely causing high occurrences of intraspecific competition. We are currently pursuing funds to complete restoration activities that will improve river function, which will also have the added benefit of alleviating intraspecific completion and help ensure the persistence of Flannelmouth and Bluehead sucker on the landscape.