Authors: Hansen, Henry;

Current trends in freshwater fish biodiversity on a global scale are showing continuous decline. Many of these degraded ecosystems are lotic systems that currently exhibit hybrid ecosystem states and can be restored to similar historical conditions prior to anthropogenic pressures. Other rivers exhibit novel ecosystem characteristics where no amount of restoration could return it to its former state. A greater understanding of fish–habitat relationships is needed comprehensively to identify realistic conservation opportunities in this context. Relatively few fish-habitat models integrate a novel ecosystems perspective thus conservation goals may misalign with biological and practical limitations throughout the river restoration process. Past literature highlights how current models often fail to 1) encompass the long time scales that operate on altered lotic systems, 2) account for hydrologic complexity, 3) incorporate diverse fish movement patterns, and 4) evaluate multiple disturbances simultaneously. Herein we propose a new perspective of altered rivers and the implications this has for fish habitat modeling. We focus on these challenges both historically, present time, and their future outlook. We provide a spatial and temporal overview of how new developments in fish-habitat models can be guided to better address novel river ecosystems.