Health, Condition, and Relative Survival of Juvenile Lost River and Shortnose Suckers in Two Klamath Basin Lakes

To identify potential causes of apparent lower juvenile survival of federally endangered Lost River suckers (Deltistes luxatus) and shortnose suckers (Chasmistes brevirostris) in Upper Klamath Lake (UKL), Oregon compared to populations in Clear Lake (CL), California, we measured water quality parameters, sampled benthic invertebrates, and sampled fish to determine sucker age, health, and condition and fish community composition in both lakes in 2013 and 2014. Most suckers captured both years in UKL were age-0, whereas five or six cohorts were present in CL catches. Triglyceride content and condition factors for suckers from both lakes suggested that food quantity is not limiting. Benthic invertebrates were much more abundant in UKL than CL. Total fish biomass was much greater in UKL compared to CL and included species that may prey on juvenile suckers. Dissolved oxygen (DO) and unionized ammonia concentrations, pH, and water temperature were within tolerance ranges for suckers in both lakes, but diel ranges in DO and pH were extreme in UKL. Cyanobacterial microcystin toxin was non-detectable in CL but was detected both years in UKL, where concentrations exceeded 10 ppb in the cell-bound portion of water samples for 4 weeks in 2014. Histopathogical investigations of fish health are ongoing.