Water and Endangered Fish in the Klamath River Basin: Do Upper Klamath Lake Surface Elevation and Water Quality Affect Adult Lost River and Shortnose Sucker Survival?

Abstract

In the western United States, water allocation decisions often incorporate the needs of endangered fish. In the Klamath River basin, an understanding of temporal variation in annual survival rates of Shortnose Suckers Chasmistes brevirostris and Lost River Suckers Deltistes luxatus and their relation to environmental drivers is critical to water management and sucker recovery. Extinction risk is high for these fish because most individuals in the populations are approaching their maximum life span and recruitment of new fish into the adult populations has never exceeded mortality losses in the past 22 years. We used a time series of mark–recapture data from the years 1999–2021 to analyze the relationship between lake level, water quality covariates, and survival of adult Shortnose Suckers and two spawning populations of Lost River Suckers in Upper Klamath Lake, Oregon. We compared competing model hypotheses in a maximum likelihood framework using Akaike's information criterion and then ran the top environmental covariates in a Bayesian framework to estimate how much of the variation in survival was explained by these covariates as compared to random variation. The complementary analyses found almost unequivocal support for our base model without environmental covariates. Estimated adult sucker survival was high across the time series and consistent with sucker life history (mean annual survival = 0.82–0.91). This suggests that adult suckers were generally robust to interannual variation in lake levels as well as consistently poor water quality within the years of our data set. Recovery time is limited, as a declining survival trend for adult suckers in recent years may be due to the onset of senescence. The successful recovery of suckers in Upper Klamath Lake may rely on shifting research from the causes of adult mortality and its relationship with lake surface elevation to the causes of poor recruitment into adult populations.

Does release size into net‐pens affect survival of captively reared juvenile endangered suckers in Upper Klamath Lake?

“…Fish and Wildlife Service 2013) and lacked other age‐classes, reaffirming that recruitment continued to be limited. Long‐term capture–recapture data have provided little evidence of recruitment from 1999 to 2021 (Krause et al 2022). The declining populations now consist of similar‐sized individuals approaching their estimated maximum age (Hewitt et al 2018; Krause et al 2022).…”

“…Long‐term capture–recapture data have provided little evidence of recruitment from 1999 to 2021 (Krause et al 2022). The declining populations now consist of similar‐sized individuals approaching their estimated maximum age (Hewitt et al 2018; Krause et al 2022). The bottleneck in recruitment appears to occur during the first year of life, as indicated by declining capture rates of age‐0 suckers to near zero in late summer and the lack of older juvenile suckers in sampling (Burdick and Martin 2017).…”