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Glacier Retreat and Salmon

For salmon, glacier retreat will have mixed effects

When it comes to retreating glaciers, researchers predict there will be benefits and costs for western North American salmon populations over the coming decades. Alaska Coastal Rainforest Director Allison Bidlack and University of Alaska Southeast researcher Eran Hood are authors on a recent multidisciplinary study led by Kara Pitman at Simon Fraser University.

In the southern, arid portions of Pacific salmon habitat, the retreat of glaciers from the landscape may spell trouble for fish populations as the loss of cold glacial meltwater during summer months leads to drier and warmer waters These conditions can stress or even kill for temperature-sensitive salmon, particularly during migration for spawning.

But in landscapes still dominated by large glaciers, like south-central and southeast Alaska, salmon stand to gain new habitat from glacier retreat. As glaciers retreat in low-lying valleys, they create new rivers and lakes that salmon can colonize. Already, there have been new areas of habitat expansion; in Glacier Bay, new river systems formed by tidewater glacier retreat that were colonized by pink salmon within 30 years of formation.

“We’ll definitely see more habitat open up as glaciers retreat, but it will also be countermanded by some river systems becoming too warm for salmon or not having enough flow. I think we’re going to be seeing this shift potentially in salmon populations across space and time, but it’s not all doom and gloom and it’s not all rosy either. It’s just going to be different,” said Bidlack.

85 percent of the major salmon watersheds in western North America still have some glacier coverage, but that’s changing quickly. Glaciers across the study region are projected to lose up to 80 percent of their volume by 2100. Though this accelerated loss due to climate change will undoubtedly have implications for salmon populations, the overall impact on salmon productivity depends greatly on the stream type, the stage of glacial retreat, and the species and life stage (adult or juvenile) of the salmon.

As salmon systems are already stressed in many areas due to climate change, habitat destruction, and hatchery practices that impact salmon biodiversity, forward-looking management will be critical to ensure sustainable salmon populations in a changing glacial landscape. “Managers need to be able to think about how those habitats are changing now and into the future, and how our fishing regulations should respond to that,” said Bidlack.

The research highlights the need for anticipatory planning even in areas that currently don’t support high populations of salmon. Recent approvals for mining projects in the heavily glacierized landscape across the British Columbia and Alaska border were based in part on the current lack of high-value habitat for salmon. This fails to take into account the future salmon populations that these landscapes could support as glaciers retreat.

The study also highlights the need for dynamic management techniques that are revisited and revised often as the pace of change to salmon populations and habitats increases. “We need to think about being more flexible and nimble in thinking about how our regulations can be responsive to these kinds of changes over time and over space,” said Bidlack.

“What happens when salmon start to move into new habitats? When do you decide to start surveying a new run of salmon, or open up a new area, or increase allowable catch in one area because the return rates are going up in another area?” said Bidlack.

“Salmon have evolved over millennia in rivers that were dynamic and ever-changing and are therefore well-adapted to cope with the landscape changes associated with glacier retreat,” stated the authors. But the rate of change and additional pressures they face today will require a new approach to management and conservation.

The study’s authors outline resources and actions that can support scientists and fishery managers in adaptive salmon management, including predictive modeling, river restoration techniques that employ ecosystem-scale, processed-bases solutions instead of engineering approaches, and more dynamic sustainable fishing targets.