The Great Salmon Run - Aman Lalwani

The productive west coast of North America holds one of the greatest spectacles known to nature. During fall, dormant water bodies pulsate with millions of migrating Pacific salmon and the events that follow create the ‘salmon run.’ Mature Pacific salmon migrate from the Pacific Ocean to rivers to spawn and their annual arrival is of immense importance to Grizzly bears, Bald eagles, wolves, local fisherman, etc. Each year, these salmon provide a bountiful supply of fresh food to other creatures, therefore it is regarded as a keystone species.

Pacific salmon are born in freshwater and as they mature, they undergo physiological changes so that they can adapt to saltwater conditions. During these changes, they spend time in the brackish waters of river estuaries and once they are 15 to 20 centimetres long, they swim out to sea. The salmon spend around 4 years at sea, where they grow strength and mass to prepare for their strenuous migration back to freshwater systems, to spawn. Salmon are ‘anadromous,’ which means that once they mature, they migrate ‘up’ river systems to the exact places where they were born. The journey upstream is often exhausting as the fish must endeavour through strong rapids and currents, with the added pressure of negotiating waterfalls, predators and man-made obstructions.

As salmon avoid feeding during their run, they have sophisticated swimming and leaping abilities to survive long distances of travel riddled with strong currents and rapids. For example, Sockeye salmon can travel up to 1400 kilometres and climb nearly 2 kilometres before reaching their spawning points. Although these obstructions are a disadvantage for the salmon themselves, they serve as an opportunity for residents of the surrounding habitats. Skilled predators like Grizzly bears line up the higher reaches of waterfalls and rapids to catch leaping fish, Bald eagles circle the air above to swoop their next prey and secondary predators like Harbor seals, Black bears and sea lions play the roles of scavengers. Most of these predators take advantage of this bounty to survive their upcoming winter hibernations. Thus, the salmon are a keystone species and their presence fuels the lives of miscellaneous creatures that interact with them.

Once the surviving salmon reach their spawning grounds, they build nests (called ‘redds’) using their tails. Females deposit around 5000 pea-sized eggs into the redds and then males deposit their sperm over the eggs. Gravel is used to cover each redd up and then females construct around 7 additional redds until they can’t lay any more eggs. Each effort is rewarded with a set of broods after 2 to 6 months. 

The entire salmon run is a very exhaustive process as massive amounts of energy are utilised in the journey upstream. Once the fish have finished spawning, their conditions start to deteriorate and 90% of the salmon die. However, their bodies are not gone to waste as they decompose and result in nutrient transfer to the forest ecosystem, thus fertilising soils. In addition, dead salmon also serve as a food source to scavengers who then excrete nutrient-rich material into the forest ecosystem.

Overall, the salmon run is one of nature’s greatest events and a treat for any wildlife enthusiast. This process has taken millions of years of evolution to take place and many creatures directly depend on the salmon. However, human-induced activities threaten the smooth running of this event as it brings in rapid changes which can be difficult to adapt to. Sustainable development is the true solution that considers both the needs of humanity and wildlife to continue the smooth running of this event.