Postdoc in Fish Migration

Glacier retreat creating new Pacific salmon habitat in western North America: Supplementary materials for media

Skeena Sockeye_Freshwaters Illustrated.jpg

Supplementary materials

Citation

Pitman, Kara J, Moore, Jonathan W., Sloat, Matthew R., Huss, Matthias, Whited, Diane C., Beechie, Tim J., Brenner, Rich, Hood, Eran W., Milner, Alexander M., Pess, George R., Reeves, Gordan H., and Schindler, Daniel E. Glacier retreat creating new Pacific salmon habitat in western North America. 2021. Nature Communications. doi: (PDF).

Key findings

By 2100, the study we projects that 6,146 km and 9,296 km of new salmon-accessible streams will be revealed under the glaciers accessible to salmon when applying the RCP 4.5 climate scenario projection of glacier retreat for either the 10% or 15% stream gradient thresholds, respectively.

Across western North America, particular hotspots of habitat gain are in southern Alaska and parts of the transboundary region of BC/Yukon/Alaska. Other regions showed little to no gains (predominantly in southern to central British Columbia) in salmon habitat because most contemporary glaciers in these sub-regions have already retreated above the limits of upstream salmon migration.

Salmon populations or species (e.g., Chinook) that are stronger swimmers will be able to capitalize on more habitats. The stream gradient exerts a strong control on the extent of new salmon habitat. The Alsek River watershed is a great example of this, where under a 10% stream gradient threshold 530 kms of new rivers will be created by 2100. However, under a 15% stream gradient, there are two times (1,078 kms) more projected river kilometres created.

Some regions showed little to no gains (predominantly in southern to central British Columbia) in salmon habitat because most contemporary glaciers in these sub-regions have already retreated above the limits of upstream salmon migration.

Understanding future shifts in suitable habitat for Pacific salmon and other species of importance can support forward-looking management and conservation.

Broader context

This study provides the first estimate of how much salmon habitat will be created with glacier recession. This is one of many pathways by which glacier retreat, and climate change more broadly, can impact salmon. For example, river channels and temperatures will evolve for a long time following glacier retreat which will improve their quality for salmon.

Climate change poses many risks to salmon, and these local increases in salmon habitat quantity could be overshadowed by other widespread challenges that salmon face, ranging from ocean heat waves to competition.

Methods

The study projected future gains in Pacific salmon freshwater habitat by linking a model of glacier mass change under different climate change scenarios with a simple model of salmon stream habitat potential. The models were applied to ~46,000 glaciers throughout the Pacific Mountain ranges of western North America.

The study estimated the extent of new salmon-accessible stream kilometers that will be created following future glacier retreat for the years 2050 and 2100. Salmon-accessibility is constrained by a rivers stream gradient, in which they applied a more conservative 10% and less conservative 15% threshold.

Collaborative team

The paper resulted from a collaboration among scientists with expertise in salmon ecology, river geomorphology, glaciologists from Fisheries Biologists, River Geomorphologists, Glaciologists from Canada, USA, and the UK with affiliations from 14 different institutions; led by scientists from Simon Fraser University.

Links to related resources

Pitman, K.J., Moore, J.W., Sloat, M.R., Beaudreau, A.H., Bidlack, A.L., Brenner, R.E., Hood, E.W., Pess, G.R., Mantua, N.J., Milner, A.M., Radić, V. Reeves, G.H, Schindler, D.E., and D.C. Whited. 2020. Glacier retreat and Pacific salmon. BioScience 70(3): 220-236. doi: 10.1093/biosci/biaa015 (PDF).

Additional quotes

“Combing knowledge and analytical techniques from the fields of glaciology, geomorphology, and salmon biology was an exciting and big challenge. It took days for some of these models to run, but the result is are very exciting, and challenging, process that led to a really intricate model that showcases an interesting future for salmon rivers” says Dr. Pitman.

“There is a particular “hot spot” of new habitat in southern Alaska and the transboundary region of BC/Yukon/Alaska where there are large coastal glaciers, that once retreated will present emerging habitat for salmon to colonize. Glacier retreat is fundamentally transforming these landscapesIn this zone we should be thinking closely about conservation of salmons futures” says Dr. Pitman.

“Other areas, such as central and southern BC, where glaciers have already retreated beyond the reach of salmon, further loss of glaciers and snowpack will we need to manage and conserve differently. In these area projections show negligible new salmon habitat created in the future. And diminishing cold water inputs from glaciers during critical migration periods and could cause added stress to salmon” says Dr. Pitman

“This information can help inform forward-looking decision making and watershed planning so that they don’t just consider current salmon habitats, but also steward salmon futures” says Dr. Moore.

Supplementary figures and photos

Exit Glacier, in Alaska, is one of hundreds of glaciers that are melting and retreating.

Photo credit: Alexander Milner.

Download the high resolution version.

Map showing the relative increase in salmon habitat following glacier retreat projections for the year 2100, based on 10% gradient threshold. Relative being the percent increase between present day salmon habitat, and future salmon habitat. Coloured bar plots on the right show the projected increase of salmon rivers for the years 2050, 2100 and once the glaciers have completely vanished from the landscape. Black dots and bars represent error derived from models.

Figure credit: Kara Pitman.

Download the high resolution version.