Anthropogenic land‐use change intensifies the effect of low flows on stream fishes

Abstract

1. As ecosystems experience simultaneous disturbances, it is critical to understand how multiple stressors interact to affect ecological change. Land-use change and extreme flow events are two important stressors that could interact to affect fish populations.2. We evaluated the individual and interactive effects of discharge and land-use change associated with oil and natural gas development on populations of two stream fishes over a 7-year period. We used repeated-state (i.e. abundance trends) and rate (i.e. colonization and persistence) responses to advance our understanding of flow-ecology relationships in a multiple-stressor framework.3. Overall, fish abundance, colonization and persistence declined as discharge decreased. The effect of land-use change associated with oil and natural gas development differed between species, with the abundance of Mottled Sculpin declining and Mountain Sucker increasing as land-use change increased. We found both synergistic and antagonistic interactions between discharge and land-use change.Land-use change intensified the effect of low flows for Mottled Sculpin and lead to greater variability in responses to flow for Mountain Sucker. These differences between species' responses are likely due to differences in their physiological tolerances and behavioural adaptations to disturbance. Synthesis and applications.Our research provides empirical evidence for the complex interactions that can arise between discharge and anthropogenic land-use change. Management efforts to reduce inputs of sediments and chemical contaminants associated with land-use change (e.g. silt fences, vegetative buffers) and promote quality refuge habitats (i.e. in-stream habitat restoration) could help mitigate the negative effects of low-flow extremes on stream fishes. Further development of flow-ecology relationships in a multiple-stressor framework will help guide management of stream fishes, and provide a better understanding of the mechanisms underlying responses of different species. K E Y W O R D S colonization, multiple stressors, natural flow regime, oil and natural gas development, persistence, rate responses, repeated-state responses, stream fishes 150 | Journal of Applied Ecology WALKER Et AL. L a n d -u s e c h a n g e (% ) La nd -u se ch an ge (% ) Land-use change (%) Land-use change (%) Land-use change (%) Land-use change (%) Land-use change (%) Land-use change (%)

Rapid colonisation post‐displacement contributes to native fish resilience

“…Our experimental approach provided mechanistic insight into factors that maintain persistence of native fish in this disturbed landscape. Longer‐term occupancy models found high site‐level persistence of mottled sculpin, likely due to high site‐level abundance where present, but lower occupancy across the landscape than mountain sucker (Walker et al, 2019). Greater mobility and colonisation rates for mountain sucker likely make them more resilient to disturbance events, compared with mottled sculpin, and explain the higher occupancy rates in areas with higher anthropogenic land use.…”

“…Stream sites associated with less anthropogenic land use contain a higher proportion of shrub cover, greater stream depths, gravel substrate and riffle habitats, whereas sites associated with greater anthropogenic land uses contain more fine sediments and run habitats (Girard & Walters, 2018). In 2018-2019, we randomly selected 31 sites from 68 previously monitored sites (Walker et al, 2019) to conduct an experimental displacement and examine colonisation (Figure 1). In addition, we selected four sites to assess fish movement abilities in the absence of experimental displacement.…”

“…We focussed on mottled sculpin and mountain sucker, as they are the most abundant species in the study system and contrast in their observed mobility (Aedo, 2008). Previous work examined year‐to‐year colonisation, persistence, and occupancy of mottled sculpin and mountain sucker in the Wyoming Range and found mottled sculpin had lower annual colonisation rates and occupancy rates than mountain sucker despite greater site‐level persistence (Walker et al, 2019). Low site‐level occupancy by mottled sculpin may be due to more limited movement and colonisation ability.…”

Interactive effects of land use, river regulation, and climate on a key recreational fishing species in temperate and boreal streams

“…In this study we used a country-wide dataset of long-time monitoring of stream fish by electrofishing to investigate interactive effects of land use, river regulation, and climate on brown trout populations. Stream flow alteration can intensify the effects of land use and climate change (Lange et al, 2014;Walker et al, 2020), and we expect that river regulation has stronger impacts on brown trout in catchments with larger extent of agricultural and urban areas, and in locations with a warmer and drier climate. Understanding how these interactions between catchment-scale and climate related stressors affect the health of fish populations is critical to the application and prioritising of mitigation and restoration measures (Staudt et al, 2013).…”

Ichthyofauna of Tributary Streams of the Cinzas River Basin, Paranapanema River, Brazil

“…The impacts of anthropogenic activities have resulted in severe damage to Neotropical aquatic ecosystems, significantly affecting hydrology and local biological diversity (Lobo et al 2015, Gonçalves et al 2019. The sequence in the streams' structure can be broken due to anthropic interferences, capable of generating discontinuities in diversity patterns (Walker et al 2019). The Paraná River basin is the second in terms of the drainage area of Brazil (Stevaux et al 1997) and is set in a vast region with large urban centers, industrial and agricultural, being the most intensively explored region of the country (Agostinho & Júlio Jr 1999).…”