The full classification of the Atlantic salmon is Kingdom Animalia, Phylum Chordata, Class Osteichthyes, Order Salmoniformes, Family Salmonidae, Genus/Species Salmo salar. Kingdom Animalia includes all multicellular heterotrophic organisms with no cell walls (ie, animals); Phylum Chordata includes all backboned animals (vertebrates); Class Osteichthyes is the group of fish with jaws and bony skeletons; Order Salmoniformes consists of several types of salmon and fish similar to salmon, including trout; Family Salmonidae specifically refers to fish that are generally considered to be 'salmon', and the Genus Salmo pertains to the Atlantic Salmon.
There are generally two types of Atlantic salmon: the best-known migrates from its spawning location to the Atlantic Ocean and returns to lay its eggs. Another subspecies never travels to the ocean and is commonly referred to as 'landlocked' salmon. The Atlantic salmon can be easily distinguished from other Osteichthyes by their silvery colour, their characteristic of being spotted and deformed during the spawning season, small scales, a round dorsal fin, and their comparatively large size1. Landlocked salmon exist in a wider variety of colours than seagoing salmon, such as black and green, do not become as deformed, and are generally much smaller. The bodies of all salmon are thin and long, allowing them to travel upriver more easily.
During the first few years of their lives, young salmon2 remain in the inland water where they are born. Later, they develop into the stage known as 'smolt', and it is at this time that both oceanic salmon and landlocked salmon take separate paths. The former travels down-river to the Atlantic Ocean while the latter makes its way into an inland lake. After spending several more years of their life in the vast expanses of an ocean or lake, salmon become sexually mature. They undergo several physical changes and force themselves upriver back to their breeding ground. Obviously, this journey is harder for oceanic salmon than inland salmon, hence the returning oceanic have a low rate of survival and encounter a series of man-made as well as natural obstacles. This is the primary reason in the decrease of the salmon population in recent years. After spawning, Atlantic salmon usually return to the ocean and repeat the cycle again, this time as fully-grown 'kelts'.
The salmon encounters several obstacles as it attempts to make its way inland. A classic example of the mass destruction of a population of salmon was in the man-made hindrances on the Hudson River in New York. Before the Industrial Revolution, the Hudson was swarming with salmon travelling between the spawning ground and the Atlantic Ocean. However, dams and water-wheels were constructed on the river with the advent of industrial technology. Regardless of the obstacles, hordes of salmon charged upriver and were killed by the dams and rapidly spinning wheels, resulting in complete extinction of all salmon south of Massachusetts3. Nowadays, Pacific salmon are also facing the predicament that Atlantic salmon encountered two hundred years ago.
Salmon are evolutionarily successful Osteichthyes because of their inborn sense of reproductive duty and their long, sleek body shapes which enable them to swiftly catch prey as well as efficiently moving upriver. Unlike some species, all salmon have the will to reproduce and will try their utmost to achieve that goal, even if it results in death. Though this may have a negative impact on salmon populations when humans intervene, it has a notably positive impact on the species' overall ability to pass on genes, as each generation is guaranteed to have offspring.