Welcome back to our Featured Creature series, where we share a creature whose evolutionary traits, special role within its ecosystem, or fun facts have captured our attention.
This week we ask,
What creatures navigate oceans, climb mountains, feed forests, and motivate us to destroy renewable energy infrastructure?
Pacific Salmon, of course!
How do salmon find their way home?
Pacific salmon are famous for their migrations from the saltwater habitats they live in as mature adults to the freshwater rivers and streams where they were born and return to spawn. Salmon have two means of finding their way back to where they first hatched, often to the very same patch of gravel.
In the open ocean, they have a GPS system based on the earth’s magnetic fields sensed through their lateral line (a highly-sensitive line of nerves running down each side of their bodies). When they get near shore, they then follow smells that they imprinted from their natal river up to where they originally hatched, to spawn again and continue this cycle.
How do salmon manage to get back upstream?
Salmon make their way back home against the current of streams and rivers, even climbing mountains in the process. As they go, they feed upland forests by transporting ocean nutrients into the headwaters of their natal streams, supporting all kinds of life in the process (and not just hungry bears)!
What happens to Pacific salmon after they successfully spawn?
Spawned-out Pacific salmon all die after completing their journey. In late fall, on a salmon river, rotting corpses and dying fish appear everywhere, white with mold and stinking with decay. In doing so, they feed forests and the aquatic life that sustains the next generation of fish when they hatch in the spring. We don’t really know why they all die after spawning, unlike the Atlantic salmon, which live after the process is complete.
Bears also increase the ecological reach of these salmon by catching them in rivers and streams and carrying them deep into the forest to feast. This brings their helpful nutrients, particularly nitrogen, into dense stretches of forest where they can fertilize the ecosystem and help trees grow. In fact, it is estimated that eighty percent of the nitrogen in the trees of the Great Bear Forest in Canada comes from salmon. Learn about the interdependent links of salmon, bears, and forest health here.
Where do we find Pacific salmon?
Pacific salmon are an anadromous species, which means they live in seawater but spawn in freshwater. They hatch from eggs in gravel and spend their early years in freshwater rivers up high in the mountains and forests along the Pacific coast. Then, once they reach about 6-8 inches in length, they move down through the estuarial waters to spend several years in the open ocean, feeding and growing large, before they journey upstream to spawn and die.
What is the cultural significance of these fish?
Pacific salmon are part of a religious cycle of life for Indigenous peoples on the American and Canadian West coasts as well as across the planet. Their annual return is celebrated as part of a natural process in which Autumn brings a bountiful harvest of fish to add to other stores of food to last through a long cold winter. Salmon are objects of worship by coastal native inhabitants, human and nonhuman alike, who depend on the annual return of these salmon in the fall to help them get through a long cold winter.
We want renewable energy sources! So why are we destroying them for these salmon?
From the 18th into the 20th centuries, our human thirst for factory power had us constructing many dams on our rivers, with little attention to their harmful ecological impact. Many of our anadromous fish species – adapted to the specific conditions of their river watersheds – were lost forever when dams left them unable to complete their journeys upstream.
It is only in recent decades that a powerful movement for dam removal and habitat restoration has been gaining momentum as a means of saving these precious species. The beneficial effects of removing these barriers have been spectacular, as rivers – freed from their shackles – blossom with new life. Along with the salmon have come a revival of other runs, including steelhead, herring, eels, shad and other diadromous fish (ones that transition between freshwater and saltwater environments), as well as birds and wildlife previously not seen in these areas. Our rivers are showing us all that we had lost and all the flourishing that is possible once we get out of their way.
How are human activities impacting these salmon?
Pacific salmon are in serious trouble. A thirst for hydropower has placed them at dire risk of extinction. We are removing dams, building fish ladders on existing dams (since their proper design is crucial), making sure culverts and other means of fish passage stay open and unhindered. But salmon are cold water species, so a warming planet puts them in peril.