Health and Condition of Endangered Juvenile Lost River and Shortnose Suckers Relative to Water Quality and Fish Assemblages in Upper Klamath Lake, Oregon, and Clear Lake Reservoir, California

Most mortality of endangered Lost River (Deltistes luxatus) and shortnose (Chasmistes brevirostris) suckers in Upper Klamath Lake, Oregon, appears to occur within the first year of life. However, juvenile suckers in Clear Lake Reservoir, California, appear to survive longer and may even recruit to the spawning populations. Our goal in this study was to develop productive lines of inquiry into the causes of mortality of juvenile suckers, especially in Upper Klamath Lake, through comparison of sucker health and environmental conditions in both lakes. The health of juvenile suckers was associated with physical, biological, and chemical characteristics in each lake from July to September 2013 and 2014.

Differences in sucker health and condition between lakes were considered the most promising clues to the causes of differential juvenile sucker morality between lakes. A low prevalence of petechial hemorrhaging of the skin (16 percent) and deformed opercula (8 percent) in Upper Klamath Lake suckers may indicate exposure to a toxin other than microcystin. Suckers grew slower in their first year of life, but had similar or greater triglyceride and glycogen levels in Upper Klamath Lake compared to Clear Lake Reservoir. These findings do not suggest a lack of prey quantity but may indicate lower prey quality in Upper Klamath Lake.