A Changing Climate in America’s Salmon Forest
Story by Mark Hieronymus

The before and after pictures of a rain-on-snow flood. The arrow in the lower image indicates where the new channel formed during intense flooding, cutting off nearly 1,800 feet of fish habitat.

If you were going to design a landscape with the express purpose of making salmon, trout and char, you probably couldn’t do better than the Tongass National Forest in southeast Alaska. While the rivers and streams that cut through the verdant landscape aren’t the longest in Alaska, the sheer number of them is mind-boggling. Southeast Alaska may only be 4% of Alaska’s total landmass, but it produces more than 25% of its salmon, and the Tongass—America’s Salmon Forest—is the heart of this fish factory.

I’ve been lucky enough to spend the last three decades fishing the freshwaters of southeast Alaska and the last 19 seasons guiding fly anglers from around the globe on the amazing waters of the Tongass. In that time, I have seen some changes; some good, others not so much. One of the things that falls into the “not so much” category is the effect of climate change on the fish and rivers where I make my living.

I have observed the subtle shift to drier summers and wetter, warmer winters. While less snow may seem like a good thing while shoveling your driveway in the middle of winter, it means less water in the summer for streams that depend on snowmelt for their flow. One of the streams I first fished in the early 2000s is a snow-fed river at the southern end of the Chilkat range. Back then, the stream was fairly large and there were few places shallow enough for an angler to safely cross. Since 2010, this stream has all but dried up, and what little flow remains is much warmer in the summer than ever before. In 2019, when I last fished this stream, I could only fish the mouth because the stream was little more than a trickle, and there was not nearly enough water in the stream for salmon to swim. The water temperature exceeded 67°F—at the upper range of what salmon can tolerate.

Another effect of the warmer, wetter winter is the increasing frequency of “rain on snow” events, where rain falls on accumulated snow, melting it into a huge amount of water causing rivers to quickly rise and often flood. These rain-on-snow-triggered floods can cause scouring, which removes the spawning gravel and other substrate from the river bottom, unearthing salmon eggs and baby fish before they’re ready and washing them away downstream. These scouring events also move spawning-size gravel out of upstream reaches, ultimately reducing and condensing the habitat suitable for spawning and rearing. As these events become more frequent and streams become less suitable for spawning, what will happen to the salmon and trout that rely on these areas? 

The mouths of many streams I fish in the Tongass meander through meadows as they head into tidewater. This is where the wild, tumbling streams “calm down” after their joyride through the steep topography of the Tongass, and these sections often are characterized by low-gradient flows with finer substrate (more small gravel and less cobble), lazy cut-bank S-bends, and slow, deep pools. These areas offer perfect fish habitat, but in the last few years several of these meadow sections have been cut through entirely by floods, changing the once-winding stream into a shotgun barrel pointed straight out to sea. The loss of complexity in these low, meadow reaches affects pink and chum salmon the most, as these slower sections low in the river often are their preferred spawning areas.

So, what is a fishing guide—or any individual, really—supposed to do about these conditions? It often feels like a foregone conclusion that the fish I have built my life around are going to be the losers in the era of climate change, but there also is reason for optimism. Just as the Tongass is the ideal “salmon forest,” it is also the ideal “carbon-storage” forest and has the potential to help slow some of the more severe impacts of climate change and keep our streams hospitable to the fish we love.

Trees use water, sunlight, and carbon dioxide, and convert these elements to energy through photosynthesis. After conversion, most of the carbon is retained in the tree, effectively storing it. When you add up all the trees in the Tongass, especially the remaining old-growth trees, they account for more than a billion tons of carbon—all stored in the forest. When we cut old-growth trees, we’re cutting the best and most efficient “air filters” and carbon storage systems we have, which contributes to accelerating the effects of climate change.

The byproducts of large-scale logging, such as roads, are yet another threat to our fish. According to the Forest Service, roads are the number-one cause of siltation in rivers, and siltation is bad for fish. Excess silt in a river can make it hard for fish to breathe, and if the silt settles out in areas where fish spawn, it can smother the eggs and kill them. Additionally, more than 1,100 bridges and culverts along roads in the Tongass fail to meet federal or State of Alaska standards for fish migration, impeding access to nearly 250 miles of fish habitat.

Looking forward, we need to find ways to conserve our old-growth forest on the Tongass, recognize the important role these ancient trees play in mitigating the impacts of a changing climate, and restore impacted areas so our important fish and wildlife can be more resilient. One way to do this is by reinstating the roadless rule on the Tongass, which protects backcountry areas from new logging and road building while still allowing for renewable energy development, community infrastructure and utility projects, transportation projects, and even mining. Active forest management for forest products and restoration should focus on previously cut stands of trees, which store less carbon and absorb less carbon dioxide than old-growth forests, making them less valuable for buffering the effects of climate change. Second-growth stands also already contain logging roads, so the costs of new road construction is minimal and the risk of increasing erosion and creating new barriers to fish migration is lessened—especially if we also work to fix the problem culverts and bridges.

When I first came to Alaska in the 1980s, I was shocked by the number of salmon I saw, and there have been some memorable runs since then. The pink salmon runs of 1999 and 2013 were astounding, and some of the coho returns in the mid-90s saw huge numbers of returning fish. However, 2013 set a benchmark when the total number of salmon of all types in southeast Alaska exceeded 120 million fish. By 2020, just last year, that number had fallen to 20 million. Something is happening to Alaska’s salmon, and climate change likely plays a bigger role than most people realize. Ocean conditions may share some of the blame, and those are probably climate-driven as well. If we want to slow the effects of climate change and make sure our fish continue returning far into the future, we should start by conserving our remaining old-growth trees on the Tongass and work to restore those places already hit the hardest.


Mark Hieronymus stays busy guiding fly anglers for salmon, steelhead, trout and char in the Tongass, America’s Salmon Forest. When he is not chasing fish as a guide, he is chasing fish at his other job as Trout Unlimited, Alaska Program’s Community Science Coordinator.

This blog originally appeared in the May 2021 issue of Fish Alaska.