A Web of Salmon
A puff of aromatic steam tickled my nose as I carefully opened the foil packet. Inside, lovely pink salmon fillets swam in their own little sea of butter. A year ago, that salmon swam in the Pacific Ocean. This past August, my arms ached as I pulled his 35-pound girth out of the Klutina River on the western edge of Wrangell-St. Elias National Park in Alaska. Now—after a frozen flight—he was feeding my family, my niece and nephews, and me. My teenage nephew—an avid fisherman—even complimented me on the catch.
I’m not much of a fisherman, but the mystique surrounding salmon fishing in Alaska was too strong for me to pass up. They are a cultural icon, an economic powerhouse to the tune of more than $1 billion a year, and a staple of many Alaskans’ subsistence lifestyles.
My first encounter with the significance of salmon came while teaching at an outdoor school in the redwoods of California. The creek that ran through our camp still hosted a few endangered Coho salmon once every four years. Using a high-energy obstacle course, we taught kids about salmon’s anadromous lifestyle—and the challenges these fish face as they hatch and develop in small streams, then travel to the ocean to fatten up for a few years, and finally return to their natal stream to spawn and die. It was all news to this Midwesterner, but what really captured my imagination was salmon’s connection to the forest: salmon become trees.
Well, broccoli becomes me, too. The food web is ubiquitous when you think about it. But with salmon, the marine-derived nitrogen they pick up from their years feasting in the ocean can be distinguished from terrestrial nitrogen, and then traced throughout the ecosystem. A study from James M. Helfiel at the University of Washington found that “isotopic analyses indicate that trees and shrubs near spawning streams derive ~22-24 percent of their foliar nitrogen (N) from spawning salmon.” Another study found that the amount of salmon-derived nitrogen in trees could be as high as 70 percent.
As a result, trees near salmon streams grow nearly three times faster than trees in areas without a salmon run. Sitka spruce trees along salmon streams grow to 50 cm thick in just 86 years (vs. the more typical 300 years). The correlation is so tight that scientists can look at variations in the nitrogen content of individual tree rings and correlate it to the number of salmon who spawned in the stream that year.
And it’s not just the trees. More than 137 species of mammals, birds, and fish rely on salmon in one way or another. That includes the big brown bear I met on the trail, as well as the killer whale who cavorted next to my tour boat. It also includes the American dipper I photographed above a creek. These sleek little songbirds feed on aquatic insects—critters who are more abundant where salmon runs enrich a stream with nutrients. Lots of nutrients.
For example, a single chum salmon (weighing an average of 19 pounds) swimming upstream to spawn brings with it 130 grams of marine-derived nitrogen, 20,000 kilojoules of energy in the form of protein and fat, and 20 grams of phosphorus.
The 35-pound king salmon I caught in the Klutina River likely contained almost twice as many nutrients as their smaller cousins. The 13.3 pounds of meat my fishing guide sliced off its body sure fed my family well. Before hooking the male “buck” that I kept for Christmas dinner, I reeled in and released three or four female “hens.” Hens that far upriver aren’t good eating. Their bodies were scraped, scarred, and pretty much falling apart since they had stopped eating and were focused purely on the task of developing and laying eggs.
There’s no reason for the salmon to preserve their bodies past reproduction; dying is part of the plan. Adult salmon fertilize the ecosystem that feeds and protects their young. Nutrients from the carcasses feed aquatic invertebrates—which will feed juvenile salmon as they grow. One study traced 30 percent of the carbon and nitrogen in young salmon back to other salmon.
Bears and other predators eat the best parts of the salmon carcasses, carry the nutrients inland, and leave the rest for scavengers. Eventually, those salmon become trees. That’s perfect, because salmon need trees even more than the trees need salmon. Trees provide cooling shade, hold the streambanks steady with their roots, and feed invertebrates with their fallen leaves. Even toppled trees provide habitat and shelter for young fish.
It’s hard for me to imagine something in Alaska that isn’t somehow connected to salmon. (Even sediment from glaciers is purported to fertilize algae that form the base of the salmon’s marine food chain!)
Fittingly, from the moment I arrived in Alaska and turned on the local radio station, salmon were in the headlines. It wasn’t all good. Salmon runs this year were late, or small, or non-existent. Sport and commercial fishing seasons were canceled or delayed. One resource manager described it as “death by a thousand cuts.” Habitat loss and climate change seem to underlie most issues.
As my family in Iowa savored the wild flavor of Alaska this Christmas, it seemed impossible to overstate the vastness of salmon’s web of connections. For one summer, for one dinner, that amazing web held me, too.
(You can read about Emily’s experience catching her king salmon on her blog.)
Emily’s book, Natural Connections: Exploring Northwoods Nature through Science and Your Senses is here! Order your copy at http://cablemuseum.org/natural-connections-book/. Listen to the podcast at www.cablemusum.org!
For 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Better Together--Celebrating a Natural Community” is now open!