Characteristics of the natural flow regime paradigm explain occurrence of imperiled Great Plains fishes

Abstract

The natural flow regime (NFR) paradigm posits that naturally occurring temporal fluctuations in streamflow are necessary for maintaining natural ecological communities. Conservation actions guided by the paradigm have contributed to stream organism conservation on a global scale, yet NFR applications in highly altered Great Plains streams are lacking. We analyzed historical fish occurrence and flow data from sixteen gage locations across three Great Plains river basins with the goal of relating flow indices calculated for one year prior to each fish collection with the occurrence of fishes belonging to the highly imperiled pelagicbroadcast spawning (PBS) reproductive guild. We fit random forest models using flow indices, gage identification, and watershed area as predictor variables and PBS fish occurrence as the response variable for all suspected or confirmed PBS fishes in each basin. Results revealed that flow indices from all NFR characteristics were useful for predicting PBS fish occurrence, but the identity of the most important flow indices varied by species and river basin. We also found that gage location was an important predictor variable, indicating flowecology relationships are spatially contingent and suggesting the influence of other factors that vary spatially (e.g., river fragmentation and water quality). Partial dependence plots identified thresholds in flow indices such as the timing of maximum flows and fall rate that may be associated with the presence or absence of PBS fishes, and these plots can be used to identify flow index target values to benefit conservation efforts. Time series predictions for likelihood of occurrence at a single gage in the Brazos River basin revealed a positive correlation between likelihood of occurrence and non-drought years for three of four species present, supporting recent findings that drought suppresses PBS fish populations. This study provides insight into the flow requirements of some of the most imperiled stream fishes in North America and contributes to environmental flow science on a global scale by establishing a robust methodology for delineating flow-ecology relationships.

Tributary streams provide migratory fish with access to floodplain habitats in a regulated river: evidence from alligator gar, Atractosteus spatula

“…Previous research has established ecological links between flow pulses and occurrence or recruitment of smallbodied, opportunistic strategist fishes, such as the shoal chub (Macrhybopsis hyostoma), plains minnow (Hybognathus placitus), smalleye shiner (Notropis buccula), and sharpnose shiner (Notropis oxythrynchus) (Rodger et al 2016;Nguyen et al 2021). Our work broadens the understanding of flow-ecology relationships in the Brazos River by analyzing responses of a periodic life history strategist.…”

Hatchery supplementation increases potential spawning stock of Rio Grande Silvery Minnow after population bottlenecks

“…Many species are lacking programs for long‐term monitoring, which has been crucial to informing hatchery supplementation practices for RGS Minnow. Finally, the effective conservation of fishes will require restoration of natural flow regimes (Hoagstrom and Turner 2015; Nguyen et al 2021; Pennock et al 2022). Despite finding that hatchery supplementation can provide a demographic boost and has been beneficial for maintaining genetic diversity in the face of multiple population bottlenecks, use of hatchery‐reared fish for conservation can only be successful for recovery of imperiled fishes if the threats to the species' persistence are adequately resolved and the conditions promoting natural recruitment are restored.…”

SER: An R package to characterize environmental regimes

“…The utility of these historical environmental regime indices (e.g., hydrologic indicators, bioclimatic indices) has resulted in tremendous applications in ecological research and also other lines of research (e.g., De Pauw et al, 2022; Nguyen et al, 2021; Su et al, 2022; Tonkin et al, 2018; Tornés et al, 2021; Xu et al, 2022). However, there are several constraints to the currently used historical environmental regime indices: (1) The currently available indices are limited to hydroclimatic variables, such as flow, temperature, and precipitation.…”