Population Characteristics and the Influence of Discharge on Bluehead Sucker and Flannelmouth Sucker
Rivers are among some of the most complex and important ecosystems in the world. Unfortunately, many fishes endemic to rivers have suffered declines in abundance and distribution suggesting that alterations to lotic environments have negatively influenced native fish populations. Of the 35 fishes native to the Colorado River basin (CRB), seven are considered either endangered, threatened, or species of special concern. As such, the conservation of fishes native to the CRB is a primary interest for natural resource management agencies. One of the major factors limiting the conservation and management of fishes endemic to the CRB is the lack of basic information on their ecology and population characteristics. We sought to describe the population dynamics and demographics of three populations of Bluehead Suckers (Catostomus discobolus) and Flannelmouth Suckers (C. latipinnis) in Utah. Additionally, we evaluated the potential influence of altered flow regimes on the recruitment and growth of Bluehead Suckers and Flannelmouth Suckers. Mortality of Bluehead Suckers and Flannelmouth Suckers from the Green, Strawberry, and White rivers was comparable to other populations. Growth of Bluehead Suckers and Flannelmouth Suckers was higher in the Green, Strawberry, and White rivers when compared to other populations in the CRB. Similarly, recruitment indices suggested that Bluehead Suckers and Flannelmouth Suckers in the Green, Strawberry, and White rivers had more stable recruitment than other populations in the CRB. Models relating growth and recruitment to hydrological indices provided little explanatory power. Notwithstanding, our results indicate that Bluehead Suckers and Flannelmouth Suckers in the Green, Strawberry, and White rivers represent fairly stable populations and provide baseline information that will be valuable for the effective management and conservation of the species.

Sampling sections and reaches for the upper Green, lower Green, Strawberry, and White rivers, Utah. Solid bars represent the beginning and end of sampling sections in the Green and White rivers. Solid circles represent sampling reaches in the Strawberry River.

Mean annual discharge for the upper Green, lower Green, Strawberry, and White rivers, Utah. The dashed line denotes median annual discharge and dotted lines represent 5th, 25th, 75th, and 95th percentiles of annual discharge.

Age-frequency distributions of Bluehead Suckers sampled from the upper Green, lower Green, Strawberry, and White rivers, Utah. Sample size, annual mortality (A), and recruitment coefficient of determination (RCD) are shown for each population. Subscript on RCDs denote the year of capture used to estimate RCD values.

Age-frequency distributions of Flannelmouth Suckers sampled from the upper Green, lower Green, Strawberry, and White rivers, Utah. Sample size, annual mortality (A), and recruitment coefficient of determination (RCD) are shown for each population. Subscript on RCDs denote the year of capture used to estimate RCD values.

Mean back-calculated length at age for Bluehead Suckers and Flannelmouth Suckers sampled from the upper Green (dash-dot line), lower Green (solid line), Strawberry (dotted line), and White (dashed line) rivers, Utah. Von Bertalanffy models and sample sizes are included for each population.
Contributor Notes
Associate Editor: J. F. Schaefer.