Atlantic salmon lead double lives. They periodically migrate to and from freshwater and the North Atlantic Ocean.
Their lives begin in small streams or rivers when adult salmon spawn. A breeding pair of salmon engage in the spawning act in late autumn to early winter. The female salmon uses her powerful tail to create one or more hollows in the streambed gravel that will serve as nests for her eggs. These nests are known as a redds.
Once the redd is prepared,the male salmon will swim up along side the female. The pair will then shudder and shake as the female deposits her eggs into the nest and the male deposits his milt to fertilize the eggs.
The female then moves, about the length of her body and excavates the next nest. As she does the gravel and small stones drift with the current and the force of her tail. The precious eggs in the previous redd are are gently covered to conceal them from predators and to begin the incubation process. Redds are often made of several of these nests.
The eggs incubate and the salmon larva begin to develop, Then as the stream's hydrological conditions change with the coming of spring, the hatchlings stretch out in the egg and hatching takes place. The hatchlings are now known as alevins, or "sack fry". The reason for the second name is that the alevin has a yolk sack below its abdomen.
Once the alevin consumes the nutrients in the sack, the sack is assumed into its body. At this point the alevin enters its next life stage and are known as fry. Fry are also known as YOY, which stands for Young Of the Year.
Nature quickly begins to camouflage the fry to protect them from predators. They begin to take on the olive-green, brown and tan colors of their environment. Their flanks develop verticle bands known as parr marks. They're known as parr marks as this is the next life stage they are entering. After the fry over-winter in their natal stream, They become salmon parr.
Over the course of the next year, the parr will grow to the smolt stage. In general, parr attain to the smolt stage after a second year of life in their natal stream. Having reached a length of 7 to 10 inches, the vertical parr bands fade and the smolt's flanks take on a silvery cast. Their backs turn a charcoal grey color. This color combo is the necessary camouflage nature provides for their new life at sea. With the melting snowpack of their second winter, the smolt ride surface currents and leave their natal stream behind.
Arriving at the river's estuary, the smolt begin to experience brackish water. As smolt will make their way along the estuary, they are increasingly subjected to higher levels of salt in the water. Reaching the end of the estuary, their acclimation complete, the smolts make their way northward along the coast. Traveling 9 to 12 miles per day, they'll travel nearly 3,000 miles to the southwest coast of Greenland.
Feasting on the bounty of the North Atlantic, the smolts quickly begin to pack on the pounds. This improved nutrition enables them to quickly grow in weight and length. At this point, they're known as grilse, or sub-adults. As the late summer months arrive, the grilse will encounter other adult salmon that are on the return migration to their spawning run. Some grilse will tag along while others will remain at sea.
After two or three years at sea, the now adult, sea-run salmon will hear nature's call. Their instincts tell them that it is now their turn to further their kind. They will turn tail and make the arduous journey back to the river system they originated from. Navigating by various means, they'll make their way toward their home river. As they draw near, they actually smell the unique chemical composition of the stream in which they were born.
Nature once again transforms their appearance as they re-enter freshwater. This serves a dual purpose. First, it once again provides camouflage, but it also brings on the spawning behavior. It's very interesting and truly amazing that the salmon cease feeding when they re-enter freshwater. They will not eat for the entire stay in freshwater which lasts until the following spring.
Driven by hormones and the urge to spawn the salmon ascend the waterway to their natal stream. True to their scientific name Salmo Salar meaning "The Leaper" they'll vault up out of the depths to surmount waterfalls and stream barriers. Salmon certainly are amazing and awe-inspiring creatures. Their tenacity and determination are without match in the animal kingdom. Leaping over the final barrier, the salmon sense their arrival in a seemingly familiar pool. It is there that they will, like countless generations before them repeat the spawning act -- giving life to the next generation of their kind.