Predicting fish-related ecological functions and indigenous values across gradients of water availability: informing environmental flow planning

Freshwater ecosystems are valued by people and are one of the most threatened ecosystems on the planet. Environmental flows (e-flows) is a tool commonly used by managers to protect or repair riverine function and biodiversity. To create effective e-flow policy, water planners require information about flow-biota and/or flow-cultural relationships. Taking an eco-cultural approach to policy development is particularly important in systems where indigenous communities maintain strong links to the river. Today, ecologists are increasingly recognizing that functional or trait-based approaches provide a better insight into the risks posed by anthropogenic change compared to traditional species-based approaches. Surprisingly, the e-flow field has been slow to adopt a functional approach. This study advances the discipline of e-flows by transitioning away from flow-biota relationships that describe species-oriented patterns towards flow-eco-cultural relationships that describe functions and values. We use a multi-species Bayesian hierarchical model to link species-specific fish abundance (catch data) to ecological functions (traits) and indigenous values. The Bayesian model also allowed us to account for methodological complexities when studying fish (i.e. variable detection). We operationalise our results by predicting functions and values across gradients of water availability to reveal landscape-scale implications. Our study was undertaken in the Fitzroy River, a relatively pristine system in the Kimberley region of north-western Australia that is highly valued by local Indigenous communities, and is facing imminent water resource development. The findings of our study will feed directly into water planning to ensure sustainable development of this highly valued river.