Species conservation requires a clear understanding of habitat availability and subsequent use of those habitats. In cases where species declines have occurred and gone undetected by conservation managers, habitat alteration, fragmentation, and loss are often the largest contributors. River fragmentation often results in altered flow regimes, subsequently impacting the availability of riverine habitats. Blue sucker (Cycleptus elongatus) is associated with riffle and run habitat, which is especially impacted when river flows are altered. The goal of this research was to identify the extent of blue sucker habitat and mobility of the species in the Colorado River, Texas. To understand habitat selection and use, blue suckers (N = 49) were surgically implanted with telemetry tags. During 2015-2017, thirty-eight attempts were completed to relocate individuals. Optimized hotspot analysis identified three river reaches critical for blue suckers that accounted for 20% of the study area. Blue suckers used these locations year-round including during spawning. Habitats used by blue sucker were composed of gravel, cobble, boulder, and bedrock typically in riffle and run habitat. Mobility, as measured by home range size, increased as riffle density decreased. Larger home ranges were presumably necessary to find habitat to complete aspects of their life history. Results of this study suggest suitable habitats are limited throughout the fragmented riverscape. Conservation action in the form of habitat construction or increased stream connectivity through barrier mitigation could have positive impacts on the future of blue suckers in the lower Colorado River, Texas.

Aim To review the conservation status of Headwater catfish Ictalurus lupus (Girard,1859) in the United States, including quantifying environmental correlates with range contraction and hybridization and introgression with Channel catfish Ictalurus punctatus (Rafinesque, 1818) to inform conservation prioritization. Location Texas and New Mexico, USA. Methods We used random forest models to construct species distribution models (SDMs) based on historical (1980–1999) and contemporary (2000–2019) data and 13 classes of remotely sensed stream network data. We measured hybridization and introgression with the widely introduced Channel catfish using external morphology, mitochondrial DNA (mtDNA), and a nuclear gene (RAG2). Results Species distribution models illustrated temporal reduction in suitability for Headwater catfish among the species’ namesake headwater streams, including streams with steeper slopes, faster velocities, and higher elevations. Modelling also revealed reduced suitability of larger streams greater distances from groundwater springs, the same streams frequently occupied by non‐native Channel catfish. A general pattern of increased use of streams draining watersheds with altered or developed land uses was apparent. Assessment of introgression and hybridization with non‐native channel catfish at nine locations showed evidence of ongoing or past hybridization at six locations. Persistence of potentially non‐introgressed populations were found at three locations with smaller sample sizes. Main conclusions Modelling temporal changes in Headwater catfish distribution provided critical insight into the types and locations of streams that should be targeted for habitat preservation or restoration. Conservation and management of Headwater catfish will require priority decisions based on existing levels of introgression and the practicality of preventing further contact with Channel catfish. Maintaining Headwater catfish populations in springs that are also heavily used by humans will be critical for conservation of the species in the United States.

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Seasonal movements cued by environmental variables are a critical component of riverine fish life history. Life‐history events for species such as blue sucker Cycleptus elongatus are likely cued by discharge and temperature and may be disrupted if those life‐history events and environmental regimes are mismatched. However, this effect may be dependent upon the habitat occupied when environmental cues are received by individuals. We tracked telemetered blue sucker in the Colorado River, Texas, USA, from 2015 to 2017 and modelled the relative effects of discharge, temperature and habitat structure on seasonal movement patterns. Tagged fish varied in their propensity to move, although most returned to their original tagging locations. Decreasing temperatures and increasing discharge resulted in increased seasonal movements. Temperature and discharge had the largest effect on movement behaviour, but the magnitude of movements was largely dependent on the year. Temperatures between 12 and 19°C and discharges between 10 and 240 m3s−1 resulted in greater probabilities of spawning movements. Spawning was most probable in 2015 and reduced or halted in 2016 and 2017. Future climate scenarios suggest North America will experience increased drought, warmer temperatures and more variable weather patterns. These future scenarios could negatively impact blue sucker by disrupting environmental cues and habitat availability for seasonal life‐history events. Our results suggest temperature and discharge are critical cues for the species, but that their combined effect is largely dependent on the occupied habitat.

ObjectiveRegulation of river flow regimes by dams and diversions impacts aquatic biota and ecosystems globally. However, our understanding of the ecological consequences of flow alteration and ecological benefits of flow restoration lags behind our ability to manipulate flows, and there is a need for broader development of flow–ecology relationships. Approaches for establishing flow–ecology relationships have recently shifted away from state‐based methods that analyze snapshots of ecological conditions and towards rate‐based methods focused on mechanisms that link hydrology with dynamics of important ecological components and processes.MethodsWe used a rate‐based approach to validate environmental flow standards developed for the lower Brazos River, Texas, by analyzing the relationship between flow regime components and recruitment strength of imperiled Shoal Chub Macrhybopsis hyostoma, a fluvial specialist and pelagic‐broadcast‐spawning fish. We collected 254 age‐0 Shoal Chub (9–40 mm total length), extracted their otoliths to estimate age in days, and used a generalized additive model to regress the number of captured recruits that hatched on a calendar date against flow regime metrics, such as pulse magnitude, flow rate of change, and pulse timing in relation to environmental flow standards proposed by a science advisory committee (Brazos Basin and Bay Area Expert Science Team).ResultThe model revealed that flow magnitude, rate of change, and timing were all significant predictors that collectively explained 60% of variation in the recruitment strength index. Hindcasting for 1919–2020 showed a general reduction in recruitment strength following commencement of flow regulation in the lower Brazos River and revealed that high recruitment correlated with years in which most or all proposed flow tiers were attained, whereas low recruitment correlated with years when less than half of the targeted tiers were attained.ConclusionOur work represents an effective validation method for environmental flow recommendations and reveals specific flow regimes that benefit an imperiled fish species.

Migratory fishes with periodic life history strategies are sensitive to river regulation. Populations of these fishes may persist in highly regulated rivers by using tributaries that provide access to intermittently connected spawning and early life stage habitat in floodplains. We analyzed system hydrology and associated movement of a long-lived periodic strategist, the alligator gar (Atractosteus spatula), in the Brazos River, Texas. We hypothesized that: 1) flow regulation on the mainstem has resulted in the reduction of flood pulses, but tributaries have been less altered; and 2) alligator gar migrate into tributaries during high flows and temperatures. Our analysis revealed that flood pulses were reduced in the mainstem but not in an adjacent, less regulated tributary where floodplain-inundating pulses now outnumber those in the mainstem. Using data from tagged fish, we derived statistical models predicting greater occurrence of alligator gar in tributaries when water temperature exceeded 25° C and mainstem discharge exceeded 400 cms. These results emphasize that movement into less regulated tributaries can mitigate impacts of river regulation on mainstem river populations of alligator gar.

Despite significant efforts devoted to understanding the underlying complexity and emergence of collective movement in animal groups, the role of different external settings on this type of movement remains largely unexplored. Here, by combining time series analysis and complex network tools, we present an extensive investigation of the effects of shady environments on the behavior of a fish species (Silver Carp Hypophthalmichthys molitrix) within earthen ponds. We find that shade encourages fish residence during daylight hours, but the degree of preference for shade varies substantially among trials and ponds. Silver Carp are much slower and exhibit lower persistence in their speeds when under shade than out of it during daytime and nighttime, with fish displaying the highest persistence degree and speeds at night. Furthermore, our research shows that shade affects fish schooling behavior by reducing their polarization, number of interactions among individuals, and the stability among local neighbors; however, fish keep a higher local degree of order when under shade compared to nighttime positions.

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