Increased landscape disturbance and streamflow variability threaten fish biodiversity in the Red River catchment, USA

Abstract

Aim Stream fish distributions are hypothesized to be strongly associated with landscape characteristics at multiple scales. Variation in flow regimes and intensity of landscape disturbance are associated with stream fish distributions; however, relationships are poorly understood in many high‐diversity regions. Our objective was to identify occurrence relationships between fish distributions and streamflow and landscape characteristics in the south‐central United States. Location Our study area was the central Red River catchment in Oklahoma, Texas and Arkansas, USA. Methods We used existing fish surveys to model the occurrence of a diverse, warmwater assemblage among hydraulic response units (HRUs). We used multispecies occupancy modelling to identify variation in occurrence probability among 111 stream fishes in relation to landscape disturbance and flow regime characteristics. Results We found occurrence relationships with landscape disturbance and 11 metrics comprising all flow‐regime components. The relationships varied within both major species groups and some genera. Frequency and duration were the most common metrics underlying flow regime relationships. More common stream fishes tended to be positively associated with higher levels of landscape disturbance and flow regime metrics representing variability; conversely, narrow‐ranged fishes tended to be negatively associated. Occurrence relationships with flow metrics representing high‐flow events were predominately negative. As expected, many species were strongly associated with ecoregion with landscape disturbance and flow relationships held constant. Main conclusions Our study informs land use and water management decisions and stream fish conservation at multiple spatial scales. Collectively, the findings suggest potential homogenization of the Red River fish assemblage with increased landscape disturbance and streamflow variability. A reduction in landscape disturbance and maintenance of natural flow patterns at coarser scales may benefit endemic and narrow‐ranged fishes. Our findings also help guide finer‐scale land use and water management decisions by identifying stream network areas with a high occurrence probability of less tolerant fishes.

Evaluating the context dependency of large river nursery habitats for fishes in the lower Red River catchment

“…Accounting for detection is important when surveying for smaller‐bodied, rarer, and cryptic species within aquatic ecosystems (Albanese et al, 2011; Schloesser et al, 2012; Wedderburn, 2018) but may also help understand fish–habitat relationships of more common species (Guillera‐Arroita, 2017; Sliwinski et al, 2016). In fact, some species are quite difficult to detect but are quite common across a catchment (Mollenhauer et al, 2022). The importance of accounting for detection when sampling for small, juvenile fishes in the lower Red River catchment is evident from the low detection rates of some species with relatively high occupancy.…”

“…The Red River terminates near the “three rivers confluence” where the Red River, Old River, and the Atchafalaya River combine with the distributary outflow of the Mississippi River into the Atchafalaya basin. A mix of savanna, woodland, and grasslands comprise the Cross Timbers region where flow variability and stream drying are common (Mollenhauer et al, 2022). The mainstem Red River is a relatively wide, sand bed river that forms the Oklahoma–Texas border.…”

“…Additionally, tributaries (Pracheil et al, 2009), pools (de Ávila‐Simas et al, 2014), sandbars (Tracy‐Smith et al, 2012), side channels (Pease et al, 2006), and floodplains (King, 2004) are all considered important nursery habitats in various mainstem rivers. However, in large, braided rivers some of these channel features can be relatively rare, particularly due to human modifications (Blodgett & Stanley, 1980; Mollenhauer et al, 2022). Moreover, the spatial context for defining nursery habitats for different assemblage members is often lacking.…”

Evaluating the spatial and temporal distribution and ecology of Bighead and Silver Carp and native fishes of the lower Red River basin

“…We modeled age, discharge, and water temperature as fixed effects while year and fish were random effects. This catchment experiences relatively high annual weather fluctuations including longer periods of flood and drought (see Mollenhauer et al 2022).…”

“…For (Mollenhauer et al 2022), also lead to degradation of instream habitat over time where complex, braided channels tend to become greatly miniaturized over time and disconnected from the floodplain (Brewer et al 2016). The lower Red River has also been regulated to some degree using wing dikes and other structures to direct flow and increase channel depth (Matthews et al 2005).…”