Fish habitat modelling in large rivers: combining expert opinion and hydrodynamic modelling to inform river management

Abstract

Physical habitat models represent a widely used tool in river management, yet, there is a growing consensus—particularly for large rivers—that fundamental principles have limits, and it is evident that improved methodologies for assessment and design are needed. Here, we suggest a framework that takes steps towards resolving some of these issues, using changes of fish habitat in a large, regulated river as a case study. First, we propose using hydrodynamic modelling in combination with a fuzzy rule-based classification as a tool to delineate and quantify meso-scale fish habitat. Variability in spatial and temporal extent of mesohabitats can be modelled across a range of flows and under non-wadable conditions when standard mesohabitat surveys become largely unfeasible. Second, research effort and empirical data on habitat use and preference of fishes is typically focused on a small group of species and limited for many imperilled or elusive taxa; we suggest using expert knowledge to expand beyond one or a few species to build the biological models for a community-level assessment until empirical data becomes available. Third, sources of uncertainty that are linked to both fundamental elements of habitat models, namely the biological and hydrodynamic components, need to be quantified and reported in modelling outcomes. The steps described in our modelling framework represent key tools for river managers charged with developing environmental flows guidelines in large, regulated rivers.