Salmon enter the rivers from April to August, (early or summer run fish), and as late as September to November, (late or fall run fish). The majority of early run fish arrive in May and June while the majority of late run fish arrive from mid September to the end of October. In either case, salmon are more likely to be seen entering rivers after a raise in water levels. Mature salmon spawn in the rivers of their birth in fall, usually late October or November depending on location and temperature of water. Adult salmon do not feed once they return to the rivers to spawn. As the male approaches sexual maturity prior to spawning, he develops an elongated head and a pronounced hook or "kype" of the lower jaw. Certain internal organs of both sexes will degenerate in favor of egg or sperm (milt) production. The female digs a nest or "redd" approximately 4-12 inches deep in the loose gravel with her tail. The female lays approximately 1500-1600 eggs per 2.2 lbs. of body weight which are fertilized by the milt of an adult male (or in limited cases, sexually mature or "precocious" parr). Repeat spawners can lay up to 50% more eggs.
Thousands of tiny Atlantic Salmon "alevin" hatch in the spring. The alevin, about 3/4 inch long, feed on the yolk of the egg from which it was hatched while still in the gravel. Approximately 4- 5 weeks after hatching the young fish makes its way through the gravel and begins active feeding. At this point they are approximately 3 inches long and are called "fry" or fingerlings. One year after hatching the fry change coloring and acquire distinctive markings on their flanks which now distinguishes them as "parr". The parr has 9 to 11 marks along its sides and a single red dot between each of these marks.
Parr remain in the river for 2 - 6 years, (generally 2-4 years), depending on water temperatures and the availability of food. At a length of 5-9 inches parr undergo a springtime transformation into "smolt". They change from their parr markings to a silvery coat for camouflage at sea. Their internal systems adapt for saltwater life and they migrate downriver to sea in May or June.
Salmon from both sides of the Atlantic rendezvous in the waters off southwestern Greenland. Lesser numbers migrate to other oceanic and coastal feeding areas. Salmon eat voraciously at sea and gain considerable weight as a result of this and other physiological changes. Their sea diet includes prawn, squid, caplin etc. which many salmon fly patterns imitate.
Although salmon may wander extensively at sea, after 1 to 3 years they return to their river of birth to spawn. The journey takes place over hereditary routes and timetables and can span 2,500 miles of open water. Fish that return after 1 year at sea, (1 sea winter) are known as "grilse", weigh from 2-6 lbs. and are most often male. Those returning after 2 or more years, (2 sea winter, 3 sea winter, etc.) are called "salmon" and may weigh 8-40 lbs. Some rivers are predominantly grilse rivers while others are predominantly salmon rivers. Still others have various proportions of both.
The Atlantic Salmon normally survives the stress of at least one spawning unlike the adults of other salmon species that die shortly after spawning. Some Atlantic Salmon return to sea immediately after spawning while others remain in the river over the winter. During this time, it is believed they do not feed. These fish return to the sea the next spring and are known as "kelts", "slinks" or "black" salmon. At this point they have been in fresh water from a few months to almost a year without feeding. After reconditioning at sea, some will return to fresh water to spawn at least one more time and in some cases three or four times in subsequent seasons.