Current Status of Two Endangered Suckers and Research Supporting Recovery Efforts

Lost River and shortnose suckers are federally endangered, large, long-lived catostomids endemic to the Upper Klamath River Basin of southern Oregon and northern California. Since 1995, the Klamath Falls Field Station of USGS has maintained a monitoring and research program that supports recovery efforts for these species. The primary focus of the program is a capture-recapture study designed to monitor the status of the adult spawning populations in Upper Klamath Lake, Oregon. Over the last decade, the number of spawning Lost River suckers has declined by 25-50%, and the number of spawning shortnose suckers has declined by 50-80%. Furthermore, three lines of evidence -- parameter estimates from capture-recapture models, age composition, and size composition -- all show that no substantial recruitment to the spawning population of either species has occurred since the 1990s. Implementation of remote detection systems for passive integrated transponder (PIT) tags has dramatically improved inferences about population dynamics and allowed us to begin evaluating factors that may be inhibiting recovery. Current studies are exploring the connections between sucker survival and (a) frequent episodes of poor water quality; (b) toxins produced by certain cyanobacteria in massive phytoplankton blooms that occur every year; and (c) predation of adult suckers by piscivorous birds. Climate change in the Klamath Basin is expected to exacerbate many of the factors thought to be responsible for the imperilment of these species, and thus serves as an umbrella for the various investigations.