Lifecycle of the Salmon

Adult salmon spend their lives in the open waters of the Pacific Ocean. It is during this phase of their life that they reach full-size, continuing to feed upon zooplankton, as well as crab, shrimp, and smaller fish like herring or mackerel. Their main predators are orcas, large fish, and seals. Salmon are anadromous, meaning they return upriver to their place of birth in order to breed after spending a portion of their lives in the ocean. The amount of time spent in the ocean before migrating back to their natal stream varies between one and seven years, depending upon the species. When it becomes time to migrate, salmon will gather in large schools and begin their challenging journey upstream.

Salmon undergo a unique transformation as they begin their migration journey – they will develop secondary sex characteristics, including a change in colouration and hooked jaws with sharp teeth. Some species even develop a hump on their backs! These traits can be particularly pronounced in males. During this time, salmon can travel 50 km daily as they make their return to their natal stream, relying on pheromones—unique, chemical signatures that they can smell— to guide the way. Salmon do not stop to eat during this journey - they are solely focused on reproduction and will forego food for up to six months as they migrate! As they travel upstream, these resilient animals can leap up to two meters out of the water to clear fallen trees, man-made obstructions, and even waterfalls.

Upon returning to their natal stream, the female salmon will use her fins and tail to dig redds, where she will release thousands of eggs to be fertilized by male salmon’s sperm. Most spawners die after reproduction, completing the circle of life. Their bodies break down into nutrients that provide important sources of energy for other organisms, as well as the vegetation in and around their natal streams. The body of a single spawner can feed thousands of insect larvae, which then become a source of food for salmon fry.

Each fall, in freshwater streams and creeks, female salmon lay their eggs in gravel nests called redds. Male salmon then swim over top of the nests to fertilize the eggs. These fragile, fertilized salmon eggs are then covered by females to provide protection from predators, where they will develop over chilly fall and winter months. Even with the protection of the gravel nests, only one in ten salmon eggs will survive the winter. Come spring, the surviving eggs will hatch as alevins.

Alevins are newly hatched salmon—they emerge wiggling from their eggs, tiny and helpless against predators, with a yolk sack still attached to their bodies. This yolk sack acts as a food source for the first 30 to 50 days of life, allowing the alevin to remain hidden within the gravel nests. When this food source dries up, alevins begin the next stage of their life as fry.

Still small and vulnerable to predation, salmon fry continue to develop in the freshwater streams and creeks in which they were born—known as their natal streams. One of the very first acts of salmon fry is to swim to the surface of their stream and gulp a mouthful of air, which will go into a swim bladder that regulates their buoyancy. From there, salmon fry begin drifting downstream, venturing out to find food in the form of insects, insect larvae, fish eggs, and fish carcasses. They begin developing dark stripes along their bodies, which allow for better camouflage as they dart in and out of dusky stream beds. Almost 90 percent of salmon fry do not survive, due to predation, disease, or lack of food. Those who are able to beat the odds will imprint their natal stream’s unique scent before beginning their journey to the ocean.

Fry become smolts as they enter the estuary. Along the way, smolts gradually adjust to saltier water in preparation for their journey to the ocean. They continue to grow, feasting upon zooplankton, insects, and other small invertebrates that are prevalent throughout the estuary, while doing their best to avoid predators such as herons, seals, and larger fish. At this stage, they develop silvery scales which will help them camouflage in the bright, open waters of the ocean.