Factors Contributing to a Lack of Recovery for Lost River and Shortnose Suckers

Lost River and shortnose suckers are long-lived endemic fishes of the Upper Klamath Basin (Oregon/California). Both species are endangered and have been targets of conservation and research since the 1990s. Recovery planning and management rely on results of a capture-recapture program based on reencounters of PIT-tagged adult fish during the spawning season. 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 has declined by over 40% and the abundance of spawning shortnose suckers has declined by more than 70%. Statistical models indicate some recent recruitment of new spawners, but substantial recruitment is not evident in the size composition of captured fish. The primary impediment to recovery appears to be high mortality in the early life stages, but other factors are being investigated. Populations in Clear Lake Reservoir are limited by reduced access to spawning habitat during drought conditions, and may also be limited by mortality from avian predators. Detection of hundreds of sucker PIT tags on waterbird colonies shows that American white pelicans and double-crested cormorants may be a substantial source of mortality for the smaller shortnose suckers.