Threats to Coho Salmon
Nehalem Strategic Action Plan for Coho lists several habitat issues as limiting to the Coho Salmon Population, including:
• Access to estuary habitats
• Summer stream temperature
• Instream habitat diversity
• Fish migration barriers
Estuaries are where ocean water pushed in by the tides mixes with freshwater flowing out of the watershed into the sea. This creates a high energy and high productivity environment that juvenile salmon rely on for bulking up and getting ready to migrate to the open ocean.
Estuaries are also historically and presently major centers for humans who build homes, farm, and recreate in them. The infrastructure supporting these human uses sometimes interferes with the needs of salmon as dikes, tide gates, and culverts can impede access and flow into historical tidal wetlands.
These issues can be addressed through fish friendly tide gates, land management, and other strategies. Additionally, restoring tidal wetlands can benefit human communities by absorbing floodwaters and reducing the flood risk elsewhere in the estuary.
Summer stream temperatures are a major limiting factor for juvenile salmon in the Nehalem. In the summer the Nehalem River can reach upwards of 80 degrees fahrenheit. Juvenile salmon are stressed by temperatures above 64 degrees F and can be killed when they exceed 70 degrees F.
These hotter temperatures reduce the amount of oxygen in the water, making it more difficult for Salmon to breathe. For a salmon, 64 degree F water is like standing on a very tall mountain for a human and leaves them gasping for breath and unable to hunt for food. High water temperatures are caused by hot air temperatures and heating from the sun.
The heating from the sun can be managed by planting along streams and creeks. Native trees and shrubs provide shade to streams, keeping the water cooler. Cooler water in small streams then means the waters downstream of it are cooler too. This means that shading even small streams is important to providing cool water areas for juvenile salmon to rear in.
Like all animals, Coho require a place to hunt, to rest, to hide from predators, and to mate. Similar to how humans eat in a dining room and sleep in a bed, Coho use different types of habitat for different activities.
This means that more diverse habitat can meet more of their needs than a simplified habitat. They need pools to rear in, logs and undercuts to hide under, gravels to spawn in, and riffles that grow their favorite bugs to eat. All these different habitat types are created by logs and boulders in the stream. These logs and boulders interrupt the stream flow causing water to slow down, gravels to deposit, digging out pools, and more. They also can also slow water down causing it to flow over streambanks, exchanging nutrients with the floodplain, and recharging groundwater.
Without logs and boulders in a stream it becomes more uniform as gravels get carried away, bedrock is exposed, and flood flows are faster and higher.
Even the best habitat isn’t useful to a salmon if they can’t reach it to use it. Roads are an essential part of human infrastructure, getting us to work and home again, out to hiking trails, and allowing for businesses to transport goods around the region.
However, as many of our roads were built before we understood the needs of salmon, the culverts that keep the roads from flooding were built simply to move water and not fish.
High water velocity in too-small culverts can prevent salmon from migrating to spawning or rearing habitat. Culverts that are too high above a stream are like a wall to a salmon. Replacing those too small culverts with properly-sized culverts or a bridge allows humans and fish to both get where they need to go.
Living with Salmon
There are many ways that these limiting factors for salmon can be addressed.
A lot of these fixes for salmon are also opportunities to improve human lives. Planting native trees and shrubs along streams cools stream temperatures and also can help manage erosion of streambanks. Building log structures in a stream can slow water upstream of an erosion concern and also redirect the flow of water away from an eroding bank all while providing fish habitat. Small culverts get blocked by debris which causes flooding and washes out roads and driveways. Restoring wetlands, tidal or otherwise, can reduce the frequency and severity of flooding downstream while also recharging groundwater.
The NBWC focuses much of its work directly at this intersection between salmon and human needs.