Life Cycle of Salmon

Life Cycle of a Salmon:

After a long journey to a mountain stream, the female salmon creates new life by cleaning and shaping the gravel of the streambed to form a string of nests called “reds”.   The stream current carries away any fine sediment.  She deposits thousands of eggs over a period of a few days.  Each time, her male partner immediately fertilizes them.  She covers the now fertile eggs with clean gravel and stays for a couple of weeks to defend her nests.  Cold, clean water is crucial for healthy growth and survival.  Water flowing through the gravel continually delivers oxygen to developing eggs and carries away waste.   When the eggs hatch, the young, or “fry”, depend on the yolk sacks for nourishment.  These tiny fish with their yolks still attached are called “sack fry”.  When they’re ready, they move up through the gravel to emerge in the stream.  Once they are one inch long, they are called fingerlings.  They will remember this particular stream and its smell, returning as adults to spawn and die, just as their parents did.  

Time spent in fresh water varies among salmon species from a few days to three years.  As the fingerlings grow, they move to the main channel where the best pools for salmon are deep and contain large wood and rocks for hiding and shade, for insects and for varying water speeds.  They’re carried downstream by the spring thaw and begin the amazing changes called smolting, necessary for survival in the ocean.  Smolting is triggered primarily by the increasing daylight hours and rising temperature waters of spring.  Individual, territorial behavior gives way to more cooperative, schooling behavior.  Gravel-colored markings change to a silvery hue, and internal changes, mostly affecting the kidneys, allow for the transition from fresh to saltwater.  Estuaries provide a mixture of fresh and saltwater habitats in which salmon smolts prepare for entering the ocean.  

Swimming out with the tide, young salmon leave their home rivers, moving around the Pacific Ocean in varying migratory patterns.  They live in the ocean anywhere from two to five years, growing and maturing.  Ocean life means escaping predators as well as avoiding fisherman.  To preserve dwindling fish runs, fishing limits are set on all taking of salmon.  Researchers have found that while living in the ocean, salmon have travelled phenomenal distances in search of food.  During this time they increase in weight, often time a hundred fold.  Temperature and food conditions can be highly variable from year to year.  A large percentage of fish do not survive the difficult ocean passage, especially during the early period.  Eventually, an instinctive trigger tells the mature salmon it’s time to return to their home stream and reproduce.

Triggered by an irresistible instinct to spawn, salmon find their way back to the river mouth and head upstream with great determination.  Faced with natural and man-made barriers, salmon frequently have to launch their full weight skyward.  While dams block their way, many have fish ladders, like artificial rivers, allowing the salmon to swim around the dams.  The homeward bound salmon no longer eat, living off stored fat, pausing only occasionally to rest.  They endure weeks of struggle against powerful currents up hundreds of miles of river.   Bruised and battered, wearing tooth marks from unsuccessful predators, they swim on to the headwaters, their health rapidly declining.  Even after spawning, the cycle is not quite complete.  Salmon carcasses have more to give…food for the forest, for predators and even for the insects that will in turn nourish their fry…a legacy for the next generation. 

What most amazes me about this process is the salmon’s ability to find its way back to the stream from which it came, and also the sheer tenacity of this fish and what great lengths it has to go to survive.  

When salmon, or any other species is deemed “endangered”, it means that species is in danger of extinction throughout all or a significant portion of its range.  Threatened means a species is likely to become endangered within the foreseeable future.  In protecting these threatened or endangered species, their habitats and ecosystems are also protected.

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