Movement, recruitment, and abundance relationships of Prairie Chub: An endemic Great Plains cyprinid

Abstract

The Prairie Chub Macrhybopsis australis is a poorly studied endemic cyprinid of the upper Red River basin and is listed as threatened in Texas and of greatest conservation need in Oklahoma. Hypothesized mechanisms have been proposed to explain the decline of pelagic broadcast spawning minnows including disrupted spawning cues, reduced recruitment, degraded habitat complexity, and reduced water availability and connectivity. Our study objectives were to evaluate Prairie Chub movement, identify spawn timing, and estimate abundance of Prairie Chub at locations in the upper Red River basin. We assessed Prairie Chub movement using a mark-recapture experiment with multiple tag and recapture occasions during late spring through summer (i.e., May-August) of 2019 and 2020. We tagged 5,771 Prairie Chub during summers of 2019 and 2020 and recaptured 213 fish across both summers. We conducted recapture events at approximately 2-week intervals from late May to August of 2019 and 2020. Movement by Prairie Chub was consistently greater than expected under the restricted movement paradigm. The average expected movement distance of the stationary population component was 2 m in 2019 and 3 m in 2020, whereas the expected average movement distance for the mobile population component was 42 m in 2019 and 75 m in 2020. We found no evidence of upstream bias in adult Prairie Chub movement during our study. We processed otoliths for 2,017 age-0 Prairie Chub across 7 rivers and two spawning seasons (i.e., 2019 and 2020). The likelihood of spawning and frequency of observed hatches per spawning date were higher in 2019 compared to 2020. The probability of spawning increased with increasing scaled discharge and average temperature in both 2019 and 2020. Spawning was more likely to occur earlier in the sample season though substantial spatial and temporal variation in spawning success was evident among rivers. The number of successful hatches observed per spawning day was highest in the Pease and Red rivers and lowest in the Salt Fork and South Wichita rivers for both years. We conducted 104 abundance surveys in 2019 and 2020. Our abundance estimates were consistently lower in upstream reaches, higher in downstream reaches, and more variable in mid reaches. We found Prairie Chub abundance was related to several covariates, but abundance did not vary much between years. Overall, adult Prairie Chub abundance was higher in the eastern portion of their range and increased with increasing discharge and turbidity but decreased at higher water temperatures. Adult Prairie Chub abundance had a quadratic relationship with salinity where Prairie Chub density peaked at a salinity of 10 ppt and then declined by nearly 100% when salinities reached 20 ppt. Our juvenile Prairie Chub abundance model had similar but weaker relationships with covariates compared to the adults; however, juvenile abundance was higher in 2020 compared to 2019. Our results indicate conservation of Prairie Chub and ecologically similar species would benefit from maintaining broadly connected habitats (i.e., for movement and drift). We show substantial variation in spawning patterns among rivers that has important implications for developing conservation actions. If agencies are concerned about abundance of Prairie Chub, then management agencies may want to consider the strong relationship with salinity when desalinization projects are proposed. Considering how salinity may narrow the realized niche of Prairie Chub, agencies interested in Prairie Chub persistence may want to prevent large changes in salinity concentrations in the species’ remaining habitat.