Data for: Mimicking functional elements of the natural flow regime promotes native fish recovery in a regulated river

Environmental flows are essential to the conservation of riverine
biodiversity, and are increasingly designed to protect components of the
flow regime that support critical ecosystem functions. Yet, few studies
have quantified biological responses to individual components of
environmental flows. We used multivariate autoregressive state-space
(MARSS) models to analyze 25 years of fish assemblage data collected
before and after court-ratified environmental flows were implemented in
Putah Creek, a dammed stream in California, USA. We quantified functional
components of the flow regime that have been identified for Mediterranean
climate regions of western North America and identified changes in these
components from before to after the environmental flow regime was
implemented. Additionally, we compared these values to their predicted
natural ranges and modeled the probability of native and non-native fish
assemblages declining by > 80% (quasi-extinction risk) under
alternative management scenarios spanning the observed range of flow
conditions. We found that as individual functional flow metrics became
more similar to the ranges expected under natural, unaltered conditions,
the quasi-extinction risk for the native fish assemblage decreased. Three
functional flow metrics that shifted towards natural ranges following
environmental flow implementation, fall pulse flow magnitude, wet season
timing, and dry season duration, each corresponded with a 40% or greater
decrease in native assemblage quasi-extinction risk. However, decreased
spring recession flows and greater dry season baseflows post-flow
modification shifted these metrics further from their natural ranges,
increasing quasi-extinction risk for the native assemblage. Flow
management scenarios revealed that the non-native fish assemblage
quasi-extinction risk increased as flow metrics became more natural and
decreased under more altered flow conditions. Few functional flow metrics
were restored to their natural ranges following environmental flow
implementation, yet even the modest changes towards more natural flows
were found to suppress non-native and benefit native fish assemblages. Our
findings illustrate that mimicking functional components of the natural
flow regime is an important tool for designing environmental flows to
conserve freshwater biodiversity.