Ecology of the Klamath Largescale Sucker, An Endemic Fish of the Upper Klamath Basin

The Klamath largescale sucker is a federal species of concern that is endemic to the Upper Klamath River Basin of southern Oregon and northern California. The species shares a complex evolutionary history with two federally endangered lake suckers, and genetic analyses indicate extensive genotypic overlap with one of them. Compared to the two endangered species, relatively little is known about the life history and ecology of the Klamath largescale sucker. We summarize data from various sources to describe (a) the past and present distribution of the species within the Klamath River Basin; (b) the timing and extent of spawning migrations and larval egress, including the effects of the removal of a dam, within tributaries to Upper Klamath Lake, Oregon; and (c) changes in the size composition of the population over the last decade. Over 5,000 individuals have been tagged with passive integrated transponders (PIT tags) since 2000 and tagged individuals are re-encountered each year in spawning tributaries. Eighty-six individuals were tracked by radio telemetry during spawning migrations in 2004, 2005, and 2006, and sucker larvae were passively sampled as they drifted downstream during the same years. Klamath largescale suckers spawn earlier and farther upstream in tributaries than the two lake suckers, and larval drift showed consistent production from river segments where spawning fish concentrate. Changes in population size composition were consistent with recruitment of new individuals to the adult population in a number of years since 2001. The removal of a dam on one of the tributaries resulted in a substantial increase in the number of individuals that migrated upstream past the dam site. Both the recent recruitment and the pronounced effects of dam removal contrast with results for the two lake suckers.