|Atlantic salmon||Conservation status|
Least Concern (IUCN 2.3)
|Binomial name||Salmo salar|
Atlantic Salmon Tube Fly Fishing
Atlantic salmon, known scientifically as Salmo salar, is a species of fish in the family Salmonidae, which is found in the northern Atlantic Ocean and in rivers that flow into the north Atlantic and (due to human introduction) the north Pacific.
It is also commercially known as Bay Salmon, Black Salmon, Caplin-scull Salmon, Fiddler, Grayling, Grilse, Grilt, Kelt, Landlocked Salmon, Ouananiche, Outside Salmon, Parr, Sebago Salmon, Silver Salmon, Slink, Smolt, Spring Salmon or simply Winnish.
Most Atlantic salmon follow an anadromous fish migration pattern, in that they undergo their greatest feeding and growth in salt water, however adults return to spawn in native freshwater streams where the eggs hatch and juveniles grow through several distinct stages.
Atlantic salmon do not require salt water, however, and numerous examples of fully freshwater ("landlocked") populations of the species exist throughout the Northern Hemisphere In North America, the landlocked strains are frequently known as ouananiche.
The freshwater phases of Atlantic salmon vary between 1 to 5 years, according to river location. While the young in southern rivers, such as those to the English Channel, are only one year old when they leave, those further north such as in Scottish rivers can be over four years old. The average age correlates to temperature exceeding 7°C.
The first phase is the alevin stage. During this phase, the fish stays in the breeding ground and uses the remaining nutrients in their yolk sack. During this developmental stage, the young gills develop and they become active hunters. Once they are able to do so, they reach the fry stage. The fish grows and subsequently leaves 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.
During these times, the Atlantic salmon are very susceptible to predation. Nearly 40% are eaten by trout alone. Other predators include other fish and birds.
When parr develop into smolt, they begin the trip to the ocean, which predominantly happens between March and June. Migration usually acclimatise 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 1 to 4 years they live in the ocean. Typically, Atlantic salmon migrates from its home stream to an area on the continental plate off West Greenland. During this time in the salmon's life, they face predation from humans, 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 grilse phase where they become ready to return to precise fresh water tributary in which they were born. After returning to its natal stream the salmon will cease eating altogether prior to spawning. Although it is largely unknown how they return to the same spot, it has been suggested that odour — the exact chemical signature of that stream — plays an important rôle in this process. Once above around 250 g, the fish no longer become prey for birds and many fish, although seals do prey upon them. Seals that commonly eat Atlantic salmon are the Grey Seal and Common Seal. Survivability to this stage has been estimated at between 14 and 53%.
The colouration of young Atlantic salmon does not resemble their adult stage. While they live in freshwater they have blue and red spots. While they mature they take on a silver blue sheen. When they are adults the easiest way of identifying them is by the black spots predominantly above the lateral line, although its 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 for the adipose, are bordered with black.
Distribution and habitat
Beginning around 1990 the rates of Atlantic salmon mortality at sea more than doubled, and by 2000 the numbers of Atlantic salmon had dropped to critically low levels. In the western Atlantic fewer than 100,000 of the important multi-sea-winter salmon were returning. Rivers of the coast of Maine, plus southern New Brunswick and much of mainland Nova Scotia saw runs drop precipitously, and even disappear.
Beginning in the mid-1990s the Atlantic Salmon Federation in cooperation with partners were developing sonic tracking technology, and by 2008 the salmon have been tracked from rivers such as the Restigouche and the Miramichi as far along their migration routes as the Strait of Belle Isle, between Labrador and Newfoundland - and half way to feeding grounds in Greenland.
For whatever reasons, possibly related to improvements in ocean feeding grounds, returns in 2008 have been very positive. On the Penobscot returns had been about 940 in 2007, and by mid-July 2008 the return was 1,938. Similar stories were played out in rivers from Newfoundland to Quebec.
The problems at sea remain, and there is a concerted international effort called SALSEA, to find out more about the mortality at sea. It is organized by the North Atlantic Salmon Conservation Organization (NASCO).
Around the North Atlantic, efforts to restore salmon to their native habitats are underway and there is some slow but steady progress. Restoration and protection of the habitat itself is key to this process but issues of excessive harvest and competition with farmed and escaped salmon are also primary considerations. In the Great Lakes, Atlantic salmon have been introduced successfully, but the actual percentage of salmon reproducing naturally is very low. Most are stocked annually. Atlantic salmon were native to Lake Ontario but were extirpated by habitat loss and overfishing in the late 19th century. The state of New York has since been annually stocking its adjoining rivers and tributaries with the fish and in many cases does not allow active pursuit of the species. Wild salmon on entering rivers as adults ]have characteristically pointed fins which help scientists distinguish from farmed or escaped salmon.
After hatching, young salmon begin a feeding response within a couple 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 fishes. During this time they hunt both in the substrate, and also those in the current. Some have been known to also eat salmon eggs. The most commonly eaten foods include caddisflies, blackflies, mayflies, and stoneflies.
In adulthood, fish feed on much larger food: Arctic squid, sand eels, amphipods, Arctic shrimp, and sometimes herring. During this feeding time the fish's size increases dramatically.
Fry and parr have been said to be territorial, but evidence showing that they 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 Atlantic salmon are considered much more aggressive than other salmon and are more likely to attack other fish than others. Where they have become an invasive threat it has become a concern that they are attacking native salmon such as Chinook salmon and Coho salmon.