I appreciate your inquiry,
Atlantic salmon are especially elusive because when they enter freshwater to spawn, they stop eating. They make a 3000 mile return trip to Greenland to feed on a very high protein diet of shrimp, etc and return within a few yards of where they hatched, to spawn the next generation. Often times I've fished stretches that have several waterfalls, and every year the fish make the journey over these obstacles, just to get back to home base.
So when they return to the river, they are very bright silver, and extremely strong and healthy. They won't eat again until late next spring when they return to the ocean. Once salmon reach 2 or 3 years of age, they will skip a trip to the river, and stay in the ocean to feed. These are called Multi-Sea-Winter fish, or MSW. These fish are enormous when they return. In the Miramichi a MSW fish could be in excess of 20 lbs. In Quebec, they can be up to 50 lbs!!!
So the game gets interesting when salmon aren't after the flies as a food source... There's several centuries of books and opinions on the subject of "why" they take the fly. There's a imprinted food impulse that generally works in the fall (shrimp-shaped flies in the fall could induce a strike). But in the summer months, the fly could be thought to provoke an aggressive response, playing up the hormones and general territorial nature that would make one a good spawner. As Lee Wulff once said;
"Why does a salmon rise to the fly? Why does a small boy cross the street just to kick a tin can?"
As tempermental and strange as these fish are, there is something overwhelming when a big fish grabs your fly and heads toward greenland. There is a wave of self-doubt and fear that never goes away. These are very worthy fish, and will test your endurance, both mental and physical. As a guide, I very much enjoy seeing this on other people's faces. It's a battle in the truest sense, and experience has taught me to fight hard, be respectful of the fish, and release it as quickly as possible.
When the fish are large, it is easiest to grab it by the tail, once it is sufficiently tired, but not exhausted. They give a might shake, and then just relax, while the hook is removed, a quick photo perhaps, and then released without injury from nets or being beached.
Attached is a picture of an Atlantic Salmon from the Restigouche river. This bad boy is probably 30-35 lbs. [edit, not a boy but a hen; extremely valuable due to her enormous clutch of eggs and reproductive capability]
