this developmental stage, their young gills develop and they become active hunters. Next is the fry stage, where the fish grow and subsequently leave the breeding ground in search of food. During this time, they move to areas with higher prey concentration. The final freshwater stage is when they develop into parr, in which they prepare for the trek to the Atlantic Ocean.
Saltwater phases[edit source | edit]
When parr develop into smolt, they begin the trip to the ocean, which predominantly happens between March and June. Migration allows acclimation to the changing salinity. Once ready, young smolt leave, preferring an ebb tide.
Having left their natal streams, they experience a period of rapid growth during the one to four years they live in the ocean. Typically, Atlantic salmon migrate from their home streams to an area on the continental plate off West Greenland. During this time, they face predation from humans, seals, Greenland sharks, skate, cod, and halibut. Some dolphins have been noticed playing with dead salmon, but it is still unclear whether they consume them.
Once large enough, Atlantic salmon change into the grilse phase, when they become ready to return to the same freshwater tributary they departed from as smolts. After returning to their natal streams, the salmon will cease eating altogether prior to spawning. Although largely unknown, odor – the exact chemical signature of that stream – may play an important role in how salmon return to the area where they hatched. Once heavier than about 250 g, the fish no longer become prey for birds and many fish, although seals do prey upon them. Grey and common seals commonly eat Atlantic salmon. Survivability to this stage has been estimated at between 14 and 53%.
Nomenclature[edit source | edit]
The name, Salmo salar, is from the Latin salmo, meaning salmon, and salar, meaning leaper, according to M. Barton, but more likely meaning "resident of salt water". Lewis and Short's Latin Dictionary (Clarendon Press, Oxford, 1879) translates salar as a kind of trout from its use in the Idylls of the poet Ausonius (4th century CE).
Physiology[edit source | edit]
This is a fairly large salmonid, with average adult specimens measuring 71 to 76 cm (28 to 30 in) long and weighing 3.6 to 5.4 kg (7.9 to 12 lb). Record-sized specimens have been measured to a maximum of 153 cm (60 in) and a weight of 45 kg (99 lb). The colouration of young Atlantic salmon does not resemble their adult stage. While they live in fresh water, they have blue and red spots. While they mature, they take on a silver-blue sheen. When adult, the easiest way of identifying them is by the black spots predominantly above the lateral line, although the caudal fin is usually unspotted. When they reproduce, males take on a slight green or red colouration. The salmon has a fusiform body, and well-developed teeth. All fins, save the adipose, are bordered with black.
Distribution and habitat[edit source | edit]
At sea, the species is found mainly in the waters off Greenland and in migrations to and from its natal streams, along the northern eastern and western Atlantic coasts. Wild salmon disappeared from many rivers during the twentieth century due to overfishing and habitat change. By 2000 the numbers of Atlantic salmon had dropped to critically low levels.
Diet[edit source | edit]
Young salmon begin a feeding response within a few days. After the yolk sac is absorbed by the body, they begin to hunt. Juveniles start with tiny invertebrates, but as they mature, they may occasionally eat small fish. During this time, they hunt both in the substrate and in the current. Some have been known to eat salmon eggs. The most commonly eaten foods include caddisflies, blackflies, mayflies, and stoneflies.
Behaviour[edit source | edit]
Fry and parr have been said to be territorial, but evidence showing them to guard territories is inconclusive. While they may occasionally be aggressive towards each other, the social hierarchy is still unclear. Many have been found to school, especially when leaving the estuary.
Adult Atlant