Use of riparian wetlands by larval Lost River, shortnose, and Klamath largescale suckers in the Sprague River, Oregon

The Lost River sucker, shortnose sucker, and Klamath largescale sucker are three endemic sucker species that inhabit the Upper Klamath River Basin. The Lost River sucker and shortnose sucker were federally listed as endangered under the Endangered Species Act in 1988. Wetland habitat on the Sprague River, Oregon, was restored to provide ecosystem functions such as restoring habitat for fishes. This study characterized use of restored riparian wetland habitat on the Sprague River by larval suckers through catch-per-unit effort, standard length, and daily age distribution by year, location (i.e. three different wetland properties), habitat type (i.e. restored wetland versus the unrestored main stem Sprague River), and distance from the main stem Sprague River. Additionally, relative position in wetland habitat (i.e. upstream or downstream side of wetland) was also analyzed. Identification of larval catostomid species was inconclusive; therefore, all species were combined during data analysis and reporting. Mean standard length of larval suckers differed among locations, and with Julian day and year; however, it did not differ by habitat type or distance from the main stem Sprague River. Likewise, standard length did not differ between relative positions in wetlands. Linear regression of length at age indicated that sucker larvae captured on the Sprague River (both wetland and main stem) grew approximately 0.27 mm/day. This was greater than previous reported daily growth rates for larval Lost River and shortnose suckers captured in Upper Klamath Lake. Habitat type did not predict daily age or gut fullness levels; further corroborating results from standard length analysis. Habitat quality (e.g. habitat with wetland characteristics including shallow, warm, and vegetated) and accessibility may be more important than whether the habitat is located within a restored backwater or at the unrestored littoral zone of the main stem Sprague River. Greater growth rates in the Sprague River than in wetlands surrounding Upper Klamath Lake reflect the importance of riverine habitat for safeguarding the future of these endangered species.