New Streams of Thought: Glacial Retreat Creates New Habitat for Salmon

Glaciers cover 10 percent of our planet's land surface, but as our climate warms, many glaciers are shrinking. As glacial retreat proceeds northward along the Pacific coast of the continental United States, through Canada, to Alaska, it is creating new stream habitat for salmon that has not existed in millennia. When and how will this new stream rollout happen? Where will salmon be distributed in the future? These questions are the focus of a newly formed multidisciplinary working group led by Canadian and US researchers. The research collaboration is the brainchild of Kara Pitman, Jonathan Moore, and Matthew Sloat. Moore, an aquatic ecologist and conservation scientist who heads the Vancouver, British Columbia–based Simon Fraser University's Salmon Watersheds Laboratory, supervises Pitman, a PhD student. Sloat is director of science at the Wild Salmon Center, in Portland, Oregon. The new Glacial Retreat and Salmon Futures working group is part of the Salmon Science Network that Moore coleads, supported by the Gordon and Betty Moore Foundation (no relation to Jonathan Moore). After completing a master's degree in glacial studies, Pitman came to her doctoral work “excited about looking at how glacial retreat would have impacts on salmon and salmon habitat,” she says. She realized early on that a working group would need to include representatives of multiple scientific disciplines. The group's first in-person meeting, held in November 2017 in Vancouver, brought together 15 experts from the United States, Canada, and the United Kingdom to share expertise in fish biology, climate change, river ecosystems, hydrology, and glaciology. In addition, Swiss glaciologist Matthias Huss recently came on board. As the team's first step, Pitman is spearheading a research literature survey for a forthcoming review paper. A second focus digs deeply into the empirical data to better understand watershed and salmon changes on the glacier-fed Copper River in Alaska. Third, for watersheds from Oregon to Alaska, the team is using glacial-retreat and climate projection models to map out how streams and lakes emerge from under ice. “For the [roughly] 40,000 glaciers up and down the coast, [the team] will be predicting how those will march up the valleys,” says Moore. Salmon are better known for their homing instincts than for their colonization of new habitats. But salmon do not always return to their natal streams. Rates vary widely by species, but genetic studies indicate that as many as 15 percent of salmon stray to new territory for spawning. It is these errant salmon that exploit the novel streams that are opening up as glaciers retreat. In Glacier Bay, Alaska, working group member Alexander Milner, of Birmingham University, in England, has watched glacial retreat birth new streams since the late 1970s. Within just a few decades, for example, he witnessed Stonefly Creek—an icy stream initially devoid of fish—transform into a waterway that now supports thousands of pink, coho, and sockeye salmon. Milner's wider analysis of glaciers suggests that there are “tipping points of glacial cover where there is a switch in the community,” he says. The repercussions are complex. As glaciers retreat, the thermal shift increases local aquatic species diversity. At the same time, there is a loss of rare endemic species, such as cold stenothermic organisms that can only survive within narrow temperature limits. Researchers are only beginning to understand the complex ecological cascades that glacial retreat is stimulating. Climate-induced glacier loss also produces profound downstream effects on hydrology, sediment transport, and biogeochemical and contaminant fluxes. Chemicals locked up in ice for decades can be released as ice melts, releasing such legacy contaminants as black carbon, mercury, and persistent organic pollutants, including polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and dichlorodiphenyl trichloroethane (DDT), into meltwaters. To understand how the multiplicity of physical, chemical, and biological changes will play out for salmon as glaciers retreat, the Glacial Retreat and Salmon Futures group has their work cut out for them, including maintaining an openness and sense of humor about dealing with communication challenges that come with team members working across many disciplines and in many locales. Going forward, what they learn will be critical for salmon conservation. In environmental assessments for proposed projects, “we envision things as they currently are,” says Pitman. For example, a mine approved for construction in a currently heavily glaciated area may not threaten salmon now, she explains, but it might threaten salmon futures. Like the habitats emerging and exploited by life as glaciers melt away, the diverse group is spawning new streams of thought.

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