Assessing long‐term fish responses and short‐term solutions to flow regulation in a dryland river basin

Abstract

Water resource development and non-native species have been cited as primary drivers associated with the decline of native fishes in dryland rivers. To explore this topic, long-term trends in the fish community composition of the Bill Williams River basin were studied over a 30-year period (Arizona, USA). We sampled 31 sites throughout the basin that were included in fish surveys by Arizona Game and Fish in 1994-97 and the Bureau of Land Management in 1979-80. We found that non-native species have proliferated throughout the entire basin, with greater densities in the lower elevations. Native species have persisted throughout most of the major river segments, but have experienced significant declines in frequency of occurrence and abundance in areas also containing high abundances of non-native species. Next, we assessed the short-term response of the fish assemblage to an experimental flood event from the system's only dam (i.e. Alamo Dam). In response to the flood, we observed a short-term reduction in the abundance of non-native species in sites close to the dam, but the fish assemblage returned to its preflood composition within 8 days of the event, with the exception of small-bodied fish, which sustained lower postflood densities. Our findings demonstrate the importance of natural flow regime on the balance of native and non-native species at the basin scale within dryland rivers and highlight minimal effects on non-native fishes in response to short duration flood releases below dams.

Effects of size and sex on swimming performance and metabolism of invasive mosquitofish Gambusia holbrooki

“…In large rivers and streams, they are mostly present in vegetated habitats, where water velocity is much reduced. Natural flow regimes are beneficial to native fishes in lotic habitats, and high-flow events may play an important role in the mechanical removal of non-native fish, particularly during the reproductive periods of non-native species within the system (Propst & Gido 2004;Gido et al 2013;Pool & Olden 2015). active search for refuges), as suggested by Ward et al (2003) for several nonnative fishes.…”

“…Mosquitofish are small-bodied fish, inhabiting the water-column and surface microhabitats. Water resource development and non-native species have been demonstrated as primary drivers in the decline of native fishes in lotic habitats, and decreasing water flows in rivers and streams due to dam construction and water extraction can facilitate invasion by mosquitofishes (Murphy et al 2015;Pool & Olden 2015). The mosquitofish is highly invasive despite its poor swimming capacity, which may be compensated by behavioural adaptations (e.g.…”

Dynamic contributions of intermittent and perennial streams to fish beta diversity in dryland rivers

“…Given the widespread introduction of non‐native species to mainstem rivers throughout the Colorado River Basin (Olden & Poff, ), evidence suggests that non‐native populations continue to colonize upstream tributaries, and expand their distribution deeper into the branches of the river network (e.g. Pool & Olden, ). Consequently, native species persistence may be vulnerable for species that increasingly rely on intermittent tributary habitats to provide refuge from non‐native fishes (Bottcher, Walsworth, Thiede, Budy, & Speas, ; Cathcart et al, ).…”

“…As non‐native species proliferated and replaced native species in the Verde River, local (alpha) diversity of non‐native species declined slightly in the Little Colorado River. The dominance of intermittent streams in the Little Colorado River could hinder the persistence of certain non‐native species; a pattern supported by relatively intact native fish faunas in isolated, non‐native free, perennial tributaries of the neighbouring Bill Williams River (Pool & Olden, ), the Virgin River Basin (Cross, ) and the Gila River (Propst et al, ). Long distances between perennial tributaries may create barriers to range expansion and recolonization within the Little Colorado River network.…”

Beaver dams shift desert fish assemblages toward dominance by non‐native species (Verde River, Arizona, USA)

“…This function may be particularly important in intermittent tributary streams, especially with projected decreases in perennial surface flow due to water withdrawals and climate change (Marshall et al 2010). Beaver dams may also provide fish some protection from floods or peak flows (Kemp et al 2012), potentially speeding recolonisation of a drainage by nonnative species following the flood (Table 4, point H; Pool & Olden 2014). However, concentrating fish within small refuge habitats typically increases the intensity of biotic interactions (Magoulick & Kobza 2003): enforced habitat overlap between non-native predators and vulnerable native fishes within ponds could lead to extensive predation and other negative interactions, such that native fishes would derive no net benefit from the refuge habitat.…”