PIT Tags and Capture-Recapture: Essential Tools in Monitoring Endangered Fishes in the Upper Klamath Basin

Lost River and shortnose suckers are long-lived endemic fishes of the Upper Klamath Basin of Oregon and California. Both species are on the endangered species list and have been the targets of research and monitoring since the mid-1990s. Recovery planning and management actions rely on the results of a capture-recapture program based on reencounters of PIT-tagged fish. Precise estimates of survival and derived estimates of population rate of change are used as key indicators of population status. Since 2001, the abundance of spawning Lost River suckers has declined by 30-60 percent and the abundance of spawning shortnose suckers has declined by 60-80 percent. The primary reason for the declines is a lack of recruitment of new individuals to the spawning populations caused by high mortality in the early life stages. For populations in Clear Lake Reservoir (CA), capture-recapture analysis is not currently feasible because fish are encountered in a spawning tributary and flows are not sufficient for spawning in some years. However, detection of sucker PIT tags on piscivorous waterbird colonies at Clear Lake (primarily American white pelicans and double-crested cormorants) shows that avian predators may be a substantial source of mortality in that system.