New Climate Research Raises Questions for Tongass Salmon

The 17,000 miles of salmon streams in the Tongass rainforest of Southeast Alaska produce a third of the state’s salmon harvest, making it one of the planet’s most productive wild salmon hotspots. The region’s salmon output depends on a perfect mix of healthy streams, forests and estuaries, but new climate change research suggests the productivity of these salmon streams could be at risk.

“Climate change may become one of the most pressing challenges to Pacific salmon” in Southeast Alaska in this century, writes Juneau-based Nature Conservancy scientist Colin Shanley in research published today.

 “The predicted temperature change is small, but those few degrees actually mean a lot more for us here in Southeast Alaska. It can mean the difference between rain and snow in the winter,” says Shanley, the paper’s lead author. “That winter snow is really our summer reservoir. It not only puts water in the river, but it also maintains that water at the colder temperatures that fish need.”

Published in the peer-reviewed journal PLOS ONE, the paper suggests that as climate change leads to new stream flow patterns, some salmon stocks could struggle to adapt to changes that range from more frequent flooding to longer periods of low flows. Scientists expect these conditions to result in a shift in where salmon spawn and where young salmon rear before migrating to sea.

“Salmon are very resilient, and they can adapt to certain changes in the region’s streams. For instance, salmon may be able to time their upstream migration to coincide with adequate stream flows. But some changes are difficult to overcome, and these include more frequent and more intense floods, which can scour salmon eggs and developing fry from stream gravels,” Shanley says.

Science in Action

After an extensive review of the region’s stream flow gauges going back nearly four decades, Shanley developed a picture of how stream flows fluctuated historically. That data then became the basis for future projections, the first of its kind for Southeast Alaska salmon streams.

“The way that we learn about how climate change might affect the future is to dig into the past and look at changes and then we can project those changes into the future,” Shanley says. “It looks as if some amount of change is inevitable. And our study looked at how that might play out in Southeast Alaska salmon streams, using the best available information, so that we can begin to better understand management options.”

Future projections built from global climate models don’t specify exact changes for Tongass salmon streams, but they do outline a range of possible scenarios: all predict significant changes to streamflows over the course of the next century.            

Among The Nature Conservancy’s findings:

·      peak flows are likely to increase in the spring and fall;

·      mountainous river systems currently fed by snow are likely to experience the largest changes in stream flow as they transition to rain-fed systems;

·      The scouring effect of higher winter flows threatens the survival of eggs and fry and could limit the production of salmon in some streams of Southeast Alaska. 

The Nature Conservancy reports that ongoing forest and salmon stream restoration can help to prepare for the effects of climate change in the region.

“We began this research because we’re interested in learning how climate change may affect resources important to the people of Southeast Alaska. While these are early findings, the research does underscore the value of acting now to ensure Tongass streams and forests remain healthy as our climate changes,” says Norman Cohen, Southeast Alaska program director for The Nature Conservancy.

The article, “Climate Change Sensitivity Index for Pacific Salmon Habitat in Southeast Alaska,” appears in the online peer-reviewed journal PLOS ONE.

The Nature Conservancy is a leading conservation organization working around the world to conserve the lands and waters on which all life depends. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at www.nature.org