Salmon - Salmo Salar
About the Salmon.
There are two main types of salmon; those that are found in the Pacific Ocean and the rivers leading into it and those that are found in the Atlantic and its tributaries.
The salmon species that are found within the Atlantic Ocean are simply known as Atlantic salmon (Salmo salar), whilst the salmon found within the Pacific are more diverse and are made up of six main species.
The salmon lives a relatively short life in comparison to other species of fish, yet during its time in the sea it travels thousands of miles, changes appearance a number of times and faces many perils from predators and pollution.
Although the salmon is not the largest, most attractive or most unique fish, it is the most well known and definitely the most favoured in many kitchens throughout the world. It has also been given the name of "king of the fish" amongst anglers worldwide.
Adult Atlantic salmon spend much of their lives at sea in the Atlantic Ocean. However, when they are ready to spawn they then make an arduous trek back to their exact birthplace in order to continue the reproduction cycle themselves.
Almost all salmon are born upstream in cold freshwater rivers usually with a gravel bed.
Spawning occurs during late October to January when the female salmon lays her eggs in a nest, known as a "redd" that has been made by excavating a hole in the gravel bed through flapping her tail to loosen and move the gravel from its position on the river floor.
The eggs are then deposited into the "redd" after some coercion and stimulation from an accompanying male, who fertilises the eggs at the same time. The female then covers up the spawn by brushing the gravel back into its former position.
After resting, the female then repeats the operation in a new nearby location until she has released all of her eggs. This may take up to a week.
On average, the female salmon carries 600-800 eggs per pound of body weight.
Other species of salmon die immediately after reproducing, usually due to exhaustion. However, the Atlantic salmon is the only species that does not and often lives to carry out the process several times, returning to the ocean between spawnings to feed.
The salmon eggs, which are fairly large and round and orange in colour, are buried in their gravel nests for several months before hatching in late spring, usually in April or May.
The newly born salmon, known as alevin, are tiny and transparent. They stay in the "redds" for several weeks feeding off their yolk sac, which is attached to the underside of their body.
At this point in time, the alevins are approximately 1-inch long and have developed small gills. As soon as they have absorbed the nutrients from their yolk sac, they are ready to leave the "redd" in search of food and usually emerge from their nest in May or June.
They then begin to feed on aquatic insects such as caddis fly and stonefly and small crustaceans, which is when they start to grow and develop specific markings and colouration.
Baby salmon that reach a length of 2.5 inches (6.5cm) are called parr. The parr stay upstream in shallow waters, close to where they were born and feed mainly on insects and crustaceans. Growth during this stage is fairly slow and can take up to two years before they develop fully. Many fall prey to larger predatory fish including trout
The parr is generally slender in body, which is a torpedo shape. It develops 8-10 smudge-like blue-grey markings across its length with a red spot in between each print. The salmon has a large, powerful deeply forked caudal fin, which helps drive it through strong currents and thrashing waters and its adipose fin is also present. The head is small but the salmon parr does have a small mouth full of well-developed teeth.
As soon as the parr reaches 5 or 6 inches (12-15 cm) and has further changed its appearance and developed, it is ready to make its way downstream and into the ocean. This varies according to water temperature at the place of birth, for example, England-born salmon head downstream after approximately one year, however those born in the colder waters of Scotland may remain upstream for several more years before they leave their natal home. Generally, they begin their journey as the water temperature begins to rise in May or early June.
The scales of the salmon smolts have turned silver by this point and they have lost their distinctive parr markings. The back of the smolts can become green, brown or blue and they develop black x-shaped marks around the whole of the body. Their belly is white in colour. Their body has become slightly more elongated and their fins take on a darker shade.
The smolts leave their home and travel hundreds of miles downstream towards the river estuary and mouth of the sea. They often stay in the salty estuaries and bays until they have acclimatised to the salt water before taking the plunge into the big ocean.
Once the smolt reach the ocean, this is when they experience their greatest amount of feeding and grow the most, in preparation for their subsequent journey back to their natal stream just before spawning.
At sea the salmon gorge on crustaceans such as shrimps, squid, eels, whitebait, herring and other small fish. They also face predation from sea gulls, cormorants, cod, conger eels, sharks and halibut amongst other carnivorous sea creatures and birds.
Salmon that live and feed in the ocean for only one year before they return to spawn are known as "grisle" and during their short period at sea they can increase their weight by almost 20 times.
The salmon that choose to stay for a second winter can reach up to 40lb (18kg) in weight and are known as two sea-year salmon.
The Journey Home
This time, the Atlantic salmon has to travel upstream to make its way home, which is much more exhausting, as it requires huge amounts of energy to swim against the current and other obstacles that it may come across.
It is not known for certain how the salmon finds its way from the ocean to its precise place of birth, thousands of miles away in a small upland stream, yet some scientists say it is due to their excellent sense of smell and other senses, through which they are able to recognise the chemical structure of the water where they were born.
The salmon carries out its journey in a series of runs, resting in between. When it encounters an obstacle such as a waterfall or weir, which impedes a straight path, the salmon leaps over it and continues with its journey.
The salmon is able to leap or jump up to 12ft (3.5m) provided that it can start the run up in very deep water.
Once the salmon has reached its destination, usually by October or November, it stops feeding prior to spawning. This is why it is very difficult for anglers to catch salmon that are at this stage of their lives, because they are not hungry and rarely go for any bait that is put before them.
On their return the male and female salmon have a similar appearance. However, shortly afterwards the male's head become even more elongated and he grows a small protuberance on his lower jaw which is known as a "kype". His scales will also turn a brick red colour and generally darken in shade all over.
After the reproduction phase, which generally ends in December on January, those salmon that do not die of exhaustion or a fungal disease called saprolegnia, spend the winter resting in deep pools or holes in the river bed or they slowly make their way down to the ocean to repeat the process.
At this stage they are referred to as "Kelts" and their appearance has taken on an almost black appearance. They have also lost some of their stored body fat and weight and are much thinner in shape. After a while, before returning to the ocean they will regain their silvery appearance.
Atlantic Salmon Habitat
Salmon stocks all over the world are being depleted however, there are many conservation measures in place now to try and restock falling numbers. Salmon numbers have suffered due to pollution in rivers and estuaries, which not only affect the fish themselves but also the food that they eat. At sea, over-fishing of herring, shrimps and other sources of food has also affected the salmon population.
There are fewer rivers than before in England that contain salmon and most are located in Wales, Ireland and Scotland with a few in the southwest of England.
Atlantic salmon are also found in many countries just off the Atlantic Ocean including Norway, Iceland, Greenland, Portugal, Finland, Russia, Poland, France, Spain, Canada and the east coast of North America.
It is a well-known fact that the majority of salmon head to the Norwegian coast and to the sea just off Greenland to feed, although there are other areas of deep water where salmon are present.
The only countries that have healthy stocks of Atlantic salmon are Norway and Iceland, which is where the biggest species have also been caught.
The Salmon's Vital Statistics
- Average weight: 6lb - 10lb (2.7kg - 4.5kg)
- Average length: approximately 30 inches (76cm)
- Specimen weight: anything over 20lb (9.1kg)
- Life-span: usually 4 - 5 years, although can be up to 10
- Current UK record: 64lb (29kg) (River Tay, Perthshire Scotland)
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