Coho Salmon Reproduction
At three to four years of age, Coho Salmon reach sexual maturity. Starting with mid to late summer and from September to October, coho swim up to 400 miles up fresh water streams where they were born.
Most Coho Salmon spawn in the fall months, however, spawning comes earlier in the north than it does in the south due to lower water temperatures coming earlier in the season.
Once Coho Salmon reach their natal site in their birth river, female Coho Salmon dig a nest where the river bed is gravel covered or pebble covered.
After the nest is made, female and male coho salmon breed. The female lays her eggs and the male’s sperm is spread over them, thus fertilizing them. After fertilization, the eggs are buried by the female Coho Salmon.
Following reproduction, all males and females die, giving the waters more nutrients and creating food for both plants and other creatures that use the river as a means of existence.
The eggs hatch about six to eight weeks after fertilization. This is in contrast to other salmon and charr species where eggs stay in the redd and do not hatch unit water temperature rises in the spring.
The Alevin Stage
After hatching, Coho Salmon spend another six to eight weeks in the redd. They are not mobile at this point, getting their nutrition of the you sac. It is not until the yolk sac is exhausted that they leave the redd and seek shelter and forage for food.
During the alevin stage, the Coho Salmon are at their most vulnerable. Water conditions can see their numbers reduced if they become unfavourable.
Silting up of their habitat during this time is very bad for their survival.
The Fry Stage
Once the Coho Salmon lose their yolk sac and unit early summer, they are called fry.
Some refer the the young Coho Salmon during this stage as fingerlings. They develop vertical lines on their sides, which last until they enter the smelt stage.
The Parr Stage
Coho Salmon fry spend anywhere from a year to two years living in fresh water growing and getting strong as their bodies change to be able to survive in salt water. While some Coho spend as many as two years in freshwater, most spend about one year before entering the ocean.
At this stage, they begin to get smaller fish that are often in the fry or alevin stage and are fond of insects both aquatic and terrestrial.
The Smolt Stage
Coho Salmon enter the shot stage when they migrate from freshwater to the ocean. They lose their parr marks and grow scales. They are usually about 6 inches/140 millimetres at the beginning of this stage.