History & Intricacies of Habitat Suitability Indices: What are We Measuring in Habitat Restoration

Year: 2022
Presenter/s: Paul DeVries
Symposium Session: 2022 - 07 Putting the Fish into Fish Habitat Restoration
Topics covered: fish-cutthroat, fish-salmon, fish-steelhead, lessons learned, modeling, and stream


The Habitat Suitability Index (HSI) concept has a long history of application in habitat assessment and instream flow studies, and is more recently being extended to quantifying expected habitat lift in response to stream restoration. Typically, the method involves quantifying the suitability of specific physical fish habitat metrics such as depth, velocity, substrate, cover, water temperature, dissolved oxygen, and other features as a probability of use curve function, comparing curves against specific metric values, and combining the results into an overall measure of ‘useable’ habitat area. While in principle the concept has intuitive appeal and appears simple to apply in practice, there are numerous aspects of HSI development and interpretation that can preclude HSI analyses from being a cost effective approach to estimating habitat lift in restoration projects, when other, simpler approaches can yield the information needed. The author draws on more than 30 years of experience developing and applying HSI curves in habitat and instream flow studies to summarize the finer points of the method, to help inform and guide restoration planners and practitioners interested in demonstrating the benefits of their projects.