Zombie Salmon: The Strange Life Cycle of Nature’s Smart Design

If you’re interested in strange and interesting natural phenomena, the term “zombie salmon” really stands out. It might make you think of the dead, but the truth is much more interesting and deep. Even though the name “zombie salmon” sounds strange, it is one of nature’s most amazing and smart designs.

Each of the five types of Pacific salmon goes through an amazing change on their amazing trip upstream to their freshwater spawning grounds. The fish’s bodies start to shut down as they use up all their energy, making it look like they are dying alive. Because of this strange behaviour, people call them “zombie salmon.”

The very difficult conditions these tough fish have to deal with on their upstream journey are what causes this strange and seemingly morbid event. Salmon need to get to the places where they spawn, which are usually up high in the river. They cover anywhere from a few miles to several hundred miles, using up all of their body’s energy in the process.

Courtesy of Chris Walling (Find his pics on Instagram: @steel_snorkel)

Imagine how much energy would be needed for such a hard trip. Most beings would never make it. But over time, nature has made salmon experts at moving upstream, even through the longest rivers and strongest currents. They are completely dedicated to getting to their spawning grounds and making sure that the next generation of salmon lives.

No matter how admirable this resolve is, it comes with a high cost: death and decay. Using up all of their stored energy and not eating much speeds up the process of their bodies breaking down. Salmon also have immunosuppression, which makes their immune systems weaker and more likely to get sick from bacteria, fungus, and viruses. Eventually, this kills them.

Salmon have a very rare type of reproduction called semelparity, which means they die after their first birth. This act of sacrifice shows how intelligently nature works and how adapting evolution works, showing the amazing things in the natural world.

Courtesy of Chris Walling (Find his pics on Instagram: @steel_snorkel)

When salmon’s bodies start to break down is a complicated process that can begin early in their upstream trip or, more often, a few weeks or months into it. Genetics, general health, stored energy, water temperature, river current strength, distance to the spawning grounds, and the risk of being eaten by animals like bears are some of the things that affect this.

An interesting study found that bears can change the senescence (deterioration) of native salmon populations. Fish populations where bears kill only fish that are already dying tend to senesce (rot) more slowly.

Even though zombie salmon die in the river where they breed, that’s not the end of what they do for the environment. Food for animals that eat other animals, like bears and birds, is very important for migrating fish. Their bodies keep feeding the river’s food web even after they die, which makes them an important part of keeping the environment in balance.

Migrating salmon are a great source of protein and fat for bears, giving them a big energy boost before the cold winter months. The dead fish that have spawned not only feed predators, but they also help the river’s ecosystem stay healthy.

Zombie salmon have an interesting life cycle that makes us think about how nature’s plans are very smart and connected. The trip they took, giving up things and helping the ecosystem, shows how complicated life is and how the natural world is naturally balanced.