The Pacific Salmon's Journey
The incredible story of the Pacific salmon’s journey back home.
Dear Cub kids,
Have you ever heard the expression ‘fish story’? If you’re ever accused of telling one, you’re being accused of spinning a highly exaggerated tale. The expression arose from the tendency of fishermen to exaggerate the size of their catch!
Well, do I have a fish story for you! But though it is about a fish – the Pacific salmon – and though it is an incredible story, there is not a single word of exaggeration in it!
The Pacific salmon of the American northwest is a keystone species.
A keystone is the big stone at the apex of an arch that holds all the other stones in place. Keystone species play the same role in ecological communities by maintaining the structure and integrity of the community.
Does it seem like an exaggeration to say that a mere fish could be a keystone species? Bear with me! The story begins when salmon mothers lay their eggs in shallow gravel beds. The tiny fish larvae, called alevin, feed off their eggs’ yolk. Then the baby salmon, called fry, leave the gravel and feed on plankton, developing into juveniles called parr. The parr feed on small invertebrates and are camouflaged with a pattern of spots and vertical bars.
That’s a lot of changes, from egg to alevin to fry to parr, isn’t it? But it’s nothing compared to what’s about to happen! Unlike fish that remain in the waterbodies of their birth, the Pacific salmon has a huge adventure in store: they are ocean-bound! That’s right – salmon begin their lives as freshwater fish, but at about the age of four, they begin travelling downriver. As the time approaches for their migration to the sea, the parr undergo physiological changes that will allow them to survive the shift from freshwater to saltwater! At this point, salmon are called smolt. They spend time in the brackish river estuaries, allowing their body chemistry to adjust to the salt they will encounter in the ocean. When they are ready, they swim into the ocean, form schools, and set off to find deep-sea feeding grounds. They will spend up to four years as mature ocean salmon, swimming great distances, developing and maturing.
End of story? Not even close! Next comes one of nature’s most extreme migrations – the return of the salmon from the saltwater ocean to the freshwater rivers of their birth. Before attempting the swim upriver, the fish once again undergo enormous changes, readjusting to freshwater, developing enormous strength and agility, and readying themselves to become parents.
The salmon are in peak condition when they begin their great migration, called the ‘salmon run’. They battle hundreds of miles upstream, during which time they stop eating, navigate waterfalls and rapids by leaping out of the water, and avoid bears, eagles, otters, and fishermen. Female salmon that successfully overcome all of these challenges create ‘nests’ in the gravel far upstream. They lay their eggs, which are covered with sperm by the males. Both males and females then die.
I will leave you with one last twist. During the years that Pacific salmon spend in the ocean, their bodies grow rich in ocean nutrients including nitrogen, sulfur, carbon, and phosphorus. Many of the salmon are caught by bears during their run upriver. The bears carry the captured salmon into the forests along the riverbanks, devouring them and leaving partially eaten carcasses as well as their own salmon-y urine and faeces, rich in the ocean nutrients brought upriver by the returning fish. All of those minerals fertilise the forests, and drift downstream to enrich the estuaries, giving rise to a density and diversity of estuarine breeding birds in the summer that are a direct result of the numbers of salmon that swam upriver the previous autumn.
Such epic lives – in death, the salmon spawn anew, creating not just a new generation, but abundant plant and animal life from the nutrients that their bodies have delivered from the ocean to forest ecosystems hundreds of miles inland.
And that, my friends, is a fish story without a single word of exaggeration!
Author: Jennifer Scarlott, appeared in: Sanctuary Cub, September 2013.