In the words of evolutionary biologist Richard Dawkins, “natural selection is anything but random.”
How, then, have salmon evolved to be able to leap up two meters? Why can salmon smell chemicals with uncanny precision, able to detect them to one part per million? How can salmon survive without food for six months? The answer lies in their final trek, where they leave the ocean to spawn and travel upstream - directly to us!
Each fall, salmon embark on the arduous journey of spawning, utilizing their stellar olfactory senses to guide them to the pheromones (chemical signatures) of their birthplace stream. The salmon traverse hundreds of miles to return to the very creek where they spawned, usually travelling 50 kilometres every day (more than a marathon!). The journey isn’t an easy one; referred to as the Salmon Run, the salmon must fight the roaring currents and evade the abundant predators who eagerly lie in the shadows, awaiting a glimpse of a leaping salmon. When the salmon arrive at their birthplace, the females create nests in the gravel and usually release between 2000 and 10000 eggs. Immediately after, a male salmon fertilizes the eggs and the female covers the nest with gravel, concealing the eggs from predators. This process is repeated until the female lays all her eggs. Finally, the salmon die, providing nutrients for other organisms and for the future generation of salmon.
The salmon egg features an embryo and a nourishing yolk inside. As the embryo grows, it requires more oxygen and eventually breaks free of the egg, still keeping its yolk and becoming an alevin. The alevin still relies on its yolk sac for nourishment. Since the alevin aren’t strong swimmers, they hide as much as around 1 foot underneath the gravel to avoid predators. Once the alevin has consumed its yolk, it is considered to be a fry. Salmon fry are still very vulnerable, so they spend most of their time hiding, only peeking out to eat any organic matter available. When the fry is ready to go to the ocean, it gradually undergoes physical changes as it travels to the ocean to become a smolt. The smolt is now equipped with a silver layering that protects the smolt from the saltwater and hides it from predators. When the salmon enter the ocean, they are now considered to be adults. The adults leave the ocean when they are sexually mature, listening to their biological instincts and travelling back up to their birthplace.
Unfortunately, salmon populations are declining - in West Vancouver, the amount of salmon observed decreased from 260 in 2018 to 149 in 2019. Currently, less than 1% of the thousands of eggs from the female salmon are surviving to the next generation. To combat pollution and aid the emerging salmon on their journey to the ocean, volunteers all over West Vancouver are now busier than ever, moving boulders, logging temperatures, monitoring creeks, and cleaning up waste.
By living close to the ocean, we can actually see the salmon in action! One of the best places to view the salmon going upstream is the Brothers Creek Viewing Platform - over 40 salmon were seen just a few days ago! After going through Brothers Creek, the salmon travel under the highway at Taylor Way, ending up at Stevens Drive with the help of fish ladders. Fish ladders are man-made and are designed with water-filled steps to aid salmon in climbing upstream for areas where the salmon cannot jump high enough. When I visited the Brothers Creek viewing platform a week ago and witnessed firsthand the sheer determination of the salmon, I realized that the salmon is an organism like no other - withstanding the mighty current and prevailing against all odds to return home, their steely resolve is an inspiration to nature enthusiasts and anyone who is inspired by a challenge!
Comments