Spatially variable response of native fish assemblages to discharge, predators and habitat characteristics in an arid-land river

Abstract

Summary 1. Fish assemblages and habitats were sampled annually at fixed sites in three tributaries of the Gila River catchment over a 21‐year span that included prolonged low‐ and high‐flow periods. Model selection was used to evaluate responses of seven native fishes with variable ecological traits (four small‐bodied cyprinids, one large‐bodied cyprinid, and two large‐bodied catostomids) to mean annual discharge and predacious non‐native fishes across the three sites. We also compared habitat use and overlap of native and non‐native fishes to identify potential for negative interactions among species. 2. Assemblage structure (species abundance and richness) and recruitment of native species was strongly and primarily affected by mean annual discharge and secondarily by location and densities of non‐native predators (mainly the centrarchid Micropterus dolomieui). 3. Densities of age‐0 catostomids and small‐bodied cyprinids were positively associated with discharge, and this pattern was strongest in the tributary with the lowest densities of non‐native predators. Absence or extreme low abundance of natives during low‐flow years was most pronounced at the sites where non‐native predators were comparatively common. Densities of adults of large‐bodied native species also varied by site, but often were positively associated with densities of non‐native predators. 4. Spatially variable responses of native fish assemblages indicated that the persistence of native fishes could be jeopardized if key habitats were lost or flow regimes unnaturally altered, particularly during low‐flow conditions when recruitment of native fishes is low and predation by non‐natives is high. Large‐bodied species may be less vulnerable to multiple years of poor conditions because adults are able to avoid predation by non‐natives and thus can rely on occasional high discharge years for successful recruitment. 5. As in other arid‐land streams, native fish assemblages of the Gila River Basin continue to decline. Our results indicate that conservation requires specific knowledge and consideration of physical influences as well as life‐history attributes of native and non‐native fishes.

Climate change poised to threaten hydrologic connectivity and endemic fishes in dryland streams

“…5 and 6). Population persistence of native fishes is compromised during prolonged climatically dry periods due to the combined loss of available habitat and heightened risk of competition with and predation by nonnative fishes (22,23). Further decreases in streamflow continuity associated with more frequent and intensive channel drying during spring (spawning) and summer low-flow months will effectively reduce the amount of available habitat for reproduction and may eliminate critical summertime refuges.…”

Factors associated with the success of native and nonnative species in an unfragmented arid-land riverscape

“…We evaluated factors associated with native fish and nonnative taxa success in the upper Gila River, New Mexico, USA. Long-term (19-26 years) monitoring of population dynamics in the Gila River basin revealed that native and nonnative success (density and richness) exhibited contrasting responses to flow regime variation, with natives increasing during high flow periods (Propst et al 2008;Stefferud et al 2011). These responses were not consistent across locations, however, as native density and richness were inversely associated with nonnative abundance at some sites while remaining relatively constant at others.…”

Introduced Flathead Catfish Consumptive Demand on Native Fishes of the Upper Gila River, New Mexico

“…However, understanding the behavior of Flathead Catfish is important in determining whether there are episodic movements into areas MANAGEMENT BRIEF 59 of high densities of native fish because large Flathead Catfish have been seen periodically in these reaches . Recognizing the drivers of variation in native fish productivity is important in identifying whether declines in native productivity are due to biological reasons (nonnative fish) or to environmental conditions, especially because both spatial and temporal variation in native fish biomass within the upper Gila River is driven by interactions among water discharge, nonnative fishes, and habitat characteristics (Stefferud et al 2011). Finally, native fish productivity was probably greater at our sample sites before 2011, given that large wildfires and drought decreased fish production in 2011, 2012, and 2013); accordingly, our estimates of both Flathead Catfish and native fish biomass at sites that only included samples during 2012-2014 (sites B, D, H and I) might be much less than at sites that also incorporated samples from nonfire, nondrought periods.…”

“…The historical fish assemblage of the upper Gila River was composed of 11 species, all of which have experienced population declines over the past decades, resulting in two extirpations as well as five state and federal endangered species listings. With declining native fish populations and minimal anthropogenic effects, nonnative fishes have been suggested as the primary threat to the survival and recovery of native fishes in the Gila River (Clarkson et al 2005;Stefferud et al 2011).…”