Geospatial indicators and metrics for threats to fish habitat in the Fraser River Basin with Thompson-Nicola as a case study

Abstract

Managing and reporting on fish and fish habitat requires spatially extensive information on how threats to fish and fish habitat vary across the landscape and which may pose the most risk for ecosystems and species of concern. Geospatial methods are best suited to providing such information at large scales through modeling and mapping of ongoing threats from human activities and landscape disturbances, as well as projecting climate change threats across a region. We conducted a cumulative threat assessment for the Fraser River Basin stream network to estimate threats (applied here as exposure) important to managing Pacific salmon and Species at Risk in freshwater, and to characterize spatial patterns in threat levels across streams and habitat extents of focal species. We presented a methodology that builds on existing geospatial assessments in British Columbia for estimating human-mediated threats of Aquatic Invasive Species, flow alteration, in-stream habitat destruction, latitudinal fragmentation, longitudinal fragmentation, riparian disturbance, nutrients, pollution, and sedimentation, as well as climate change-based threats of flood risk, low stream flow, high stream flow, and high stream temperatures. We provided estimates and summaries of threats across streams, watersheds, and Pacific salmon and Species at Risk habitat extents. The ability to reassess threats over time for reporting on the status of threats to the state of fish and fish habitat was also evaluated based on the data inputs required. We then showcased examples of how information from threat scores, associated inputs, and salmon values (i.e., Conservation Units, modeled favourable spawning habitat) can be used collectively to help inform planning and prioritization for management and restoration. This was done for the Thompson-Nicola Ecological Drainage Unit and provided spatial information related to riparian restoration, water withdrawal allowance, and barrier mitigation. Uncertainties and limitations, as well as steps for future evaluation of the cumulative threat assessment were detailed.