摘要：The endangered Lost River sucker (Deltistes luxatus) and shortnose sucker (Chasmistes brevirostris) are endemic to the Upper Klamath Basin, Oregon and California. The once very abundant populations have declined drastically due to a combination of habitat loss and impairment, disruption of reproduction and gene flow, intensive harvest, and loss of entire populations. Spawning populations within Upper Klamath Lake are declining and have not had significant recruitment for over a decade. In addition to habitat loss, these populations are threatened by periodic harmful water conditions resulting from massive algal blooms and entrainment of larvae and juveniles into water delivery systems or hydroelectric structures. Populations of shortnose sucker in Clear Lake appear to be relatively healthy and stable, but recruitment of Lost River sucker appears to be sparse. These populations are affected by drought and water management. Other populations are potentially introgressed with Klamath largescale sucker (Catostomus snyderi) or lack sufficient spawning opportunities to be self-sustaining and therefore function as sink populations. Although genetic and ecological similarities between the species are strong, it is important to better understand the needs of both species individually to assure effectiveness and efficiency in recovery efforts. Determination of the factors limiting juvenile survival and recruitment is vital and should be part of a broader program which includes comparison among populations to understand demography and vital rates. Efforts should also include habitat restoration, improvement of water quality conditions, and reduction of entrainment, as well as monitoring to evaluate effectiveness. Lastly, a controlled propagation program should be considered and/or implemented to conserve unique genetic stocks and provide opportunity for augmentation of wild-spawned populations.Las especies en peligro de extinción Lost River sucker (Deltistes luxatus) y shortnose sucker (Chasmistes brevirostris) son endémicas de la parte alta de la cuenca Klamath en Oregón y California. Las poblaciones que alguna vez fueron muy abundantes han disminuido drásticamente debido a una combinación de pérdida y degradación de los hábitats, interrupción de la reproducción y del flujo de genes, pesca intensiva y pérdida de poblaciones enteras. Las poblaciones que desovan dentro del Lago Upper Klamath están disminuyendo y no han tenido un reclutamiento significativo por más de una década. Además de la pérdida del hábitat, estas poblaciones se ven amenazadas por condiciones periódicas de aguas nocivas que son el resultado de la proliferación desmedida de algas y por el arrastre de larvas y jóvenes a los sistemas de suministro de agua o estructuras hidroeléctricas.
