A study of potential new Pacific salmon habitat in western North America as a result of glacial retreat through the year 2100 poses benefits to salmon, but also warns of the need for forward-looking management decision making and conservation planning.
The study, published recently in the journal Nature, projects that by 2100, glacier retreat will create 3,818 miles (6,146 kilometers) of new streams accessible for colonization by Pacific salmon, of which 1,200 miles (1,930 km) have potential for spawning and juvenile rearing within 18 sub-regions.
“With climate change, the distribution (of salmon habitat) is probably going to be different than the distribution for salmon now, because of changes in temperature and precipitation which affect stream flow,” said Daniel Schindler, who conducts research on causes and consequences of ecosystem dynamics at the University of Washington’s School of Aquatic and Fishery Sciences in Seattle.
“We show that the loss of glaciers opens up salmon opportunities in the future,” said Schindler, who participated in the study. “That is particularly important for Southeast Alaska. Western Alaska doesn’t have as many glaciers to disappear and create new habitat.”
In Southeast Alaska, headwaters of many of those rivers are still under ice, and that habitat is disappearing quickly because of climate change.
“What we did was forecast how these watersheds will look in the future under warmer climate. As watersheds open up, those streams will be colonized by fish, insects, algae,” Schindler said. “We see that fish like salmon will establish within a decade of them opening up, mostly in coastal locations, but it shows ice currently prevents fish from going into those streams.”
About two-thirds of the effect that humans have on the Earth’s climate system is regarding heat stored in the water in the ocean, and that heat is released into the atmosphere, Schindler said, explaining that salmon encounter that climate change in the ocean and in fresh water because the ocean heat has an effect on the atmosphere, which affects precipitation.
The study warns that forecasting the location of emerging salmon habitat is imperative because while such climate change may present opportunities for salmon, it also creates prospects for large-scale resource extraction industries such as mining, which have potential to degrade these emerging salmon habitats.
“These findings can inform proactive management and conservation of Pacific salmon in this era of rapid climate change,” said the authors, who are from Simon Fraser University, Universite de Fribourg, Oregon State University, University of Montana, University of Alaska Southeast, National Marine Fisheries Service’s Northwest fisheries science Center, the U.S. Forest Service, and the University of Washington School of Aquatic and Fishery Sciences.
Their research was funded through the Gordon and Betty Moore Foundation, which supports scientific discovery, environmental conservation and preservation of the character of the San Francisco Bay Area.
The study identified 315 retreating glaciers at headwaters of present-day streams that would create salmon-accessible streams assuming a 10% stream gradient threshold for upstream salmon migration, plus 603 glaciers assuming a 15% stream gradient threshold.
While the number of glaciers currently covering salmon-accessible streams is proportionally low, given the 46,000 glaciers in the study area, salmon-accessible glaciers are particularly large, representing 50% of the total glacier area in the study region, regardless of which stream gradient threshold is used to define salmon accessibility.
The study notes that seven of the 18 sub-regions show negligible to no gains in salmon habitat because most contemporary glaciers in those sub-regions have already retreated above the limits of upstream salmon migration. In contract, the study projects an additional 2,622 kms (1,629 miles) of salmon accessible streams in the Gulf of Alaska sub-region, plus a gain of 1,064 km (over half a mile) for the Copper River, which is only a 2% increase within that large watershed.
Over the last century glacier retreat in Alaska’s Kenai Peninsula led to establishment of sockeye salmon populations that support a local commercial fishery.
In general, the analysis indicates that the greatest gains in salmon-accessible streams will happen in areas where large glaciers occupy low gradient terrain near the coast.
The timing of when these potential future salmon-accessible streams are exposed will depend on the modeled rate of glacier retreat across the 18 sub-regions studied. Researchers concluded that of the total stream distances that could be gained with potential complete deglaciation 23% will be gained by 2050 and 63% by 2100.
Some of those regional differences were quite pronounced.
The limited salmon-accessible stream gains projected for the Skeena River watershed and North Coast of British Columbia will all be created by 2050 the study found, while in the Gulf of Alaska sub-region—home of some of the largest remaining icefields in North America—only 20% of new stream habitat would be created by 2050.
Researchers acknowledged that while they propagated the uncertainty of items such as ice thickness and stream segment length that there are still additional uncertainties in the model used in their analysis. The unknown future pace of climate change as controlled by greenhouse gas emissions and feedbacks in the Earth atmosphere climate system will impact the rate of new habitat for Pacific salmon.
Gains in salmon habitat, even one kilometer of stream, can produce 500 to 1,500 juvenile coho salmon, researchers note. Thus with hundreds to thousands of kilometers of new habitat being created from glacier retreat, the study found, there’s a potential to produce hundreds of thousands to millions of additional juvenile salmon, depending on the species.