About Coho Salmon
The Coho Life Cycle
Eggs and alevin in gravel. Born in the spring in the gravel bed of a California creek, a coho salmon begins it's life as an alevin (al-uh-vin), a newly hatched fish that retains a nutritious yolk sac, living within the shelter of the loose gravel. At this life stage, the fish is highly dependent on cool water to flowing though the gravel and providing needed oxygen to develop. Once the yolk sac is depleted the alevin emerges from the gravel as a free swimming fry.
Coho parr - As the fish grows, the fry, also known as parr, for the bar like marks along the sides of their bodies, spends the summer and fall in the pools and riffles close to where she was born. Feeding voraciously on aquatic insects and hiding from predators in woody structures in its pool, the parr quickly grows large, sometimes enough to consume other small fish in the pool. Winter comes, and with it come heavy rains and high, fast-moving water levels. The parr takes shelter from the rapid currents in the deep pools, eddies, and woody structures in the creek.
Coho smolt - Once the spring flows begin to recede, the parr prepares to go out to sea by undergoing an important physiological change known as smoltification. Trading in the brown-and-gray parr coloration (effective camouflage in a shady creek) for sleek silver scales, which reduce their visibility in the open ocean. Smoltification prepared the young fish for migration into salty ocean waters and the coho imprints on the unique smell of their natal stream, which will serve to guide the fish back as a returning adult.
Adult female - The smolt heads downstream and out into the open ocean, avoiding larger predators and feeding on larger prey to grow into a full-sized adult coho salmon. They spends almost two years out at sea, until the second winter's rains increase flows from their home creek once again. These flows break down the sand bar that sometimes forms at the mouth of the coho's home river, and carry the scent of the natal creek out to the waiting adult. Sensing home, the coho's sole mission becomes the journey back to the creek where they were born, ignoring all other needs, including food.
Adult male - An arduous, exhausting swim brings the adult fish back to the stream, sometimes the very pool, where she was born. There, the female uses her tail to dig a redd in the loose gravel, where she waits to find a suitable mate with whom to spawn. Once he arrives, she lays several thousand eggs in the redd, and he quickly fertilizes them before she covers them up with more loose gravel. Her spawning complete, she has only a few days left to live, using them to defend her nest from other competitive salmon or roving hungry trout. Eventually, she is overcome by malnutrition and exhaustion, and she dies. As her body breaks down, the nutrients it releases reenter the food chain to feed the next generation of young coho salmon.
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