Using systematic conservation planning to inform restoration of freshwater habitat and connectivity for salmon

Background/Question/Methods

Wild Pacific salmon support ecosystems, economies, and cultures. Today, many populations are at record lows and face multiple cumulative pressures. The loss and alienation of freshwater habitat is a key driver contributing to population declines. Efforts to restore salmon habitat are hindered by lack of coordination throughout watersheds, scarce resources, and understanding where to invest to get the most benefit for wild salmon. We used systematic conservation planning to inform the prioritization of restoration of salmon habitat connectivity in the Lower Fraser River, BC. To do this, a dataset of 669 fish barriers, ranging from hydro dams to road culverts was collated from multiple sources and expert elicitation was used to estimate their cost of restoration. The potential benefit of restoration was estimated in terms of the quantity of habitat upstream of each barrier for 14 populations of Pacific salmon, as well as four indicators of habitat quality. The r package Prioritizr was used to optimize barrier restoration under three different management objectives that ranged from maximizing only the quantity of habitat restored to emphasizing the quality of habitat. Optimizations were run across budgets ranging from $5 – 200 million to explore trade-offs at different budget levels and management priorities.

Results/Conclusions

We estimate ~75% of the alienated habitat in the Lower Fraser could have access restored with an investment of $200 million CAD, whereas 60% could be restored for half this amount. On a site-specific level the selection frequency of barriers within the optimization can inform where to focus restoration activities. When stream quality was considered within the optimization, priorities for barrier removal shifted away from urbanized floodplain valleys towards less developed areas. Differences in site priorities across scenarios that emphasize the quality and quantity of habitat differently can inform where additional restoration may be needed to address watershed scale threats to habitat quality in conjunction with the restoration of connectivity. The spatial shift in priorities meant that species like chum salmon (O. keta), which rely more heavily on the valley bottom, would see less restored habitat. To inform barrier removal strategies using these model scenarios, an iterative and adaptive approach will be required that includes the rights, values, and priorities of stakeholders. Continuous improvement in data quality, accuracy, and feedback from monitoring as barriers are restored is also crucial.