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 federally endangered and have been the targets of research since the mid-1990s. Recovery planning and management rely on the results of a capture-recapture program based on reencounters of PIT-tagged fish during traditional sampling and from remote detection systems. Estimates of survival and population rate of change are used as key indicators of population status. Since 2001, the abundance of spawning Lost River suckers in Upper Klamath Lake (OR) has declined by 35-70 percent and the abundance of spawning shortnose suckers has declined by more than 70 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. Dynamics of the populations in Clear Lake Reservoir (CA) are less well understood but some recruitment occurs. Detection of nearly 1,000 sucker PIT tags on piscivorous waterbird colonies in the Basin shows that American white pelicans and double-crested cormorants may be a substantial source of mortality, especially for the smaller shortnose suckers in Clear Lake Reservoir.