Autumn has fallen on our Greenway landscape, and that means that iconic seasonal changes are upon us. Leaves are turning, rains are restarting, and salmon are once again returning to freshwater systems. Yep, that’s right, watching salmon run up our creeks and streams is an iconic part of seasonal shift in the region. Similar to the festive ado of a pumpkin patch, these impressive fish fight against the current and smell their way back to the streams where they were born, which scientists call “natal streams.” Once at their natal stream, female salmon lay almost 5,000 eggs, restarting the cycle of life.
A salmon’s sense of smell is 1,000 times more sensitive than a dog’s, and a dog’s nose is 1,000 times more sensitive than yours! This means that salmon are one million times better at smelling than you or I. What’s more impressive is that salmon don’t return home for four to six years. Imagine smelling your way home after five years away . . . do you think you could do it?
Now imagine that in addition to following the scent of home, you also have to dodge predators that are 300 times larger than you (our resident southern orcas), and your whole neighborhood has been remodeled while you were away. That is just a touch of what our local salmon contend with on their way back to spawn.
Adult orcas need to find and eat 100-300 pounds of salmon each day. And, since they’re eating such a large volume, they try to only go for the largest fish. Over the past few decades, the average weight of adult chinook (our largest native salmon species and resident orca’s favorite meal) has dropped from 100 pounds down to just 30 pounds per fish, meaning orca need to do a lot more fishing to be full. Hunting is made more challenging because the native chinook population has dropped to just 10% of historic numbers. Because salmon are smaller and less plentiful, our orca have to work harder to survive.
Another threat salmon face is changing waterways. Indigenous people traveled on and fished northwest rivers since time immemorial, and naturally-flowing streams meandered across valley bottoms. Our salmon evolved in these slow moving, dynamic systems, which tend to have cooler water, deeper pools, and areas where salmon can pull over and rest on their way upstream. When European and other settlers moved into this region, ecological randomness made it hard to build homes and cultivate crops, so they began managing rivers and lakes to make them more predictable, which changed the fluvial geomorphology (the science of how water moves through channels and shapes the earth). Settlers channelized the streams and drained floodplains, forcing water to flow efficiently out to sea. They also removed trees and logs that would have naturally fallen into waterways and created critical salmon habitat. The removal of trees on the banks was followed by the introduction of non-native plant species, which degraded ecological health of creekside habitats. The early settlers likely did not know how dramatically these changes would affect local salmon populations, which once were so plentiful. Now that we know the impacts, the Greenway Trust and many other organizations are working together to help support our dwindling salmon.
So, how exactly can we help salmon? Since most of the salmon’s life is out at sea, it is hard for us to help. However, we can influence the habitat quality in local creeks to support salmon’s early and late life stages. For almost 20 years, the Greenway Trust has worked to restore the riparian buffer—the ribbon of land that runs alongside creeks and streams—of Issaquah Creek and other salmon bearing streams. Issaquah Creek starts with headwaters and tributaries in the Issaquah Alps flowing 13 miles to empty into Lake Sammamish. The creek is host to Chinook, coho, and sockeye salmon, and has been identified as a critical spawning ground for salmonoid species. The Greenway Trust’s work focuses on replacing invasive species like Himalayan blackberry, English ivy, and Bohemian knotweed with native coniferous plants like Douglas fir and Western red cedar. These reintroductions bring with them a myriad of ecological benefits.
One benefit is providing food to baby salmon. Native plants on shore are the favorite home to native insects, and as branches reach over a stream, some insects will fall into the water and become food for juvenile salmon on their way out to sea. Those same branches that drop insects also provide shade in the summer months. This shade helps keep the water cool, a critical habitat requirement for salmon species because cooler water holds more oxygen, making it easier for these fish to breathe. By planting evergreen trees streamside, rainfall is intercepted by needles and branches slowing its descent to the ground. This interception reduces runoff and allows for more water to slowly enter the ground instead of rushing across the surface and into streams. That type of runoff can carry pollutants and debris into waterways, reducing clarity and choking native salmon as they make their way home to spawn. Finally, as trees age and grow, they also topple over, slowly re-adding fallen materials into the creek and re-establishing the pooling and meandering that it once had.
Starting in 2022, in addition to maintaining and expanding our work along the riparian buffer, the Greenway Trust is planning to start a project that will shape how the water flows in the creek by installing large woody material in the last mile of Issaquah Creek that winds through Lake Sammamish State Park. Large woody material replicates the impacts of large trees falling into the water, but their strategic placement helps guide the waters flow through channels and directs the way the water interacts with the stream bed and the surrounding banks. Our project intends to place over three hundred trees in the creek system to restart the natural processes that stopped over a century ago. This project is much more complicated than our traditional riparian planting efforts, but the impact and habitat improvement will be proportionally great. This project is only possible because of our partnership with the Northwest Hydraulics Consultants, The Watershed Company, Washington State Department of Natural Resources, and Lake Sammamish State Park.
Projects like these and others undertaken by many partner organizations are just one way of supporting local salmon populations. So this year, if you make it to local salmon bearing streams, take a second to check out the riparian environment and appreciate how interconnected our ecosystems are.
Want to learn more about salmon? Check out our virtual education program Forests and Fins; it’s all about salmon!