A Salmon Story: Part 1 – Hydroelectric Dams and Habitat Destruction

March 16, 2020

Aside from their cultural and economic value, Pacific salmon have a strong ecological value that spreads across lakes, rivers, and deep into the Pacific Ocean. Salmon are a key part of west coast food webs and are especially significant to our endangered southern resident killer whales. There are five species of Pacific salmon: chum, sockeye, pink, Chinook, and Coho. According to Fisheries and Oceans Canada (DFO), sockeye, Chinook, and Coho populations are experiencing declines across southern B.C., with mixed results for chum and pink.

When it comes to the health of resident killer whales, Chinook are the most important to consider. Chinook salmon make up around 80% of a resident killer whale’s diet, and they need to eat about 200 pounds a day! Though there are some stable Chinook populations, there has been a 60% reduction in the abundance of Chinook in the Salish Sea since 1984.

While fisheries often take the brunt of the blame, it is important to recognize that the issues facing salmon are multifaceted. By their nature, fisheries have an impact on salmon stocks, but another major culprit is habitat destruction. Mining, deforestation, culverts, artificial lighting and hydroelectric dams are just a few examples of human activity damaging salmon habitat. All of these topics are worth discussing, but this post will focus on dams.

The Impacts of Dams

Damming of rivers quite literally puts a giant obstacle in the path of migrating salmon. Salmon reproduce in the rivers where they were born, and the journey from the ocean back to their spawning grounds is a difficult trip. With a dam in the way, it can be nearly impossible, and many salmon don’t make it home to reproduce. For example, the Columbia and Snake Rivers were once the largest producer of Chinook salmon on Earth when combined. They boasted historic returns of 10 to 16 million. Today, the Snake River sees only 1% of historic numbers, which makes it challenging for southern resident killer whales to find enough to eat.

Despite the additions of fish ladders, dams can kill more than 50% of young salmon going downstream, and up to 25% of adult salmon migrating to spawning grounds. The adult salmon that are strong enough to make it past a fish ladder must then avoid falling back down or getting swept into a turbine. The lucky few that make it that far are now stuck in the reservoir.

Ice Harbour Dam. Credit: Bob Brawdaw / The Tri-City Herald

Reservoirs – Not a Salmon Paradise

The negative impacts of dams on salmon are clear, and drastic change is needed to preserve these valuable fish. Scientists and activists are pushing for the removal of the four dams in the lower Snake River. For the Snake to achieve sustainable numbers of salmon, there must be a consistent minimum return of 2%-6% of adults to the upper river. Since 1975, returns have rarely exceeded the minimum of 2%. Studies have shown that removing these dams would likely allow Snake River salmon to reach healthy levels. If removal is too costly or difficult, even breaching the dams (allowing water to flow freely past them) would create a big improvement for Chinook populations and southern resident orca alike.Far from the cold, flowing, oxygen-rich streams and rivers salmon need, reservoirs provide stagnant waters which are warmed by the sun. Warmer waters both incubate disease and decrease oxygen levels. Salmon are a cold-water fish, and temperatures above 20°C can be lethal to both adults and juveniles. These changed conditions are ideal for predators that would not have thrived in a cold, fast-flowing river such as the smallmouth bass and northern pikeminnow. Northern pikeminnows happily gobble dozens of juvenile salmon a day. Finally, these stagnant waters elongate the time it takes young salmon to swim out to sea – making them even more vulnerable to predation and disease.

How to Help

So, what can we do to help the struggling salmon and resident killer whales? Make sure you limit your salmon consumption and buy sustainably harvested salmon whenever possible. You can also get involved with amazing organizations like the Pacific Salmon Foundation and Pacific Wild. Finally, keep educating yourself and those around you, and spread the word that our salmon need help.

Sources:

https://oceana.org/blog/crisis-nears-orcas-and-salmon-activists-urge-removal-4-costly-dams

https://www.nwcouncil.org/reports/columbia-river-history/damsimpacts

https://www.wildsalmon.org/facts-and-information/myths-and-facts-about-lower-snake-river-dam-removal.html

https://www.nrdc.org/experts/giulia-cs-good-stefani/another-crack-snake-river-dams

Christianson, C., Grace, S. & Waddell, J. 2015. The case for breaching the four lower Snake River dams to recover wild Snake River salmon. OrcaNetwork.org. Retrived from https://www.orcanetwork.org/Main/PDF/Snake%20River%20Endangered%20Salmon%20White%20Paper%2011%204%2015.pdf

https://www.seattletimes.com/seattle-news/environment/controversy-heats-up-over-removal-of-lower-snake-river-dams-as-orcas-suffer-loses/

https://whalemuseum.org/pages/frequently-asked-questions-about-the-southern-resident-endangered-orcas

Feature Photo taken by: Valérie Messier

Written By: Lili Wilson