Salmon: king of fish

Salmon king of fish

It seems extraordinary that a fish should travel thousands of miles across the Atlantic only to travel back again a year or two later to reach its exact place of birth to spawn. Although the salmon’s homecoming marks the climax of an incredible journey and often ends in death, the spawning ground is where and how it all begins….

Most Atlantic salmon spawn between November and January because they need cold, well-oxygenated, fast-flowing water in which to breed. You can easily identify salmon that are ready to spawn – the hen (female) is dark grey with black spots and a bulging belly. The male is brick-red with elongated jaws, the lower of which hooks upwards and is known as a kype.

Dig, dig, dig

The hen digs a shallow nest—called a redd -in gravel. She alternately flexes and straightens her body, flicking her tail to dis- lodge small stones, silt and plants. She tests the depth of the redd by pressing down with her anal fin and when it is 15-30cm (6-12in) deep, the male, who has been in constant attendance, swims alongside. They shed their eggs and milt simultaneously into the redd. (Oddly enough a large number of male parr – salmon under two years old – are sexually mature and nip in front of the adult male to fertilize the eggs themselves).

The female then covers the nest with gravel in the same way she prepared the redd. The eggs hatch in April-May, and the young transparent fish, known as alevins, shelter in the gravel and live off their yolk sac for the first few weeks.

First things first

Once the yolk sac has been absorbed, the infant salmon’s first problem is that of finding food. As young fry they eat mainly insects – larval stoneflies and caddis flies in particular. Those that do find enough food to see out the cold spring and resist the attacks of predators, such as adult brown trout and herons, still have plenty of pitfalls to overcome.

The young fish remains in the upper reaches of the river. It slowly develops a row of dark grey ‘thumbprints’ along its flanks, with a red spot between each. At this stage it is known as a parr, and looks very similar to a brown trout of the same age. After two years, occasionally longer, physical changes begin to take place – salt-excreting cells form and the scales begin to turn silver.

Seaward ho!

When the young fish is fully silver and about 20cm (8in) long it is known as a smolt. As soon as the water begins to warm up the smolt begins its long descent downstream towards the sea. It is not until it reaches the mouth of the river that the riches of the sea are exploited. Here it feasts on shrimps, whitebait, sandeels and small members of the cod family.

Some salmon stay in coastal waters, but others migrate – a few to the Norwegian coast – but most move to the west coast of Greenland. In the sea they face further threats from seals, gulls and predatory fish such as cod and conger eels.

The time spent in the sea fattens them up in preparation for the arduous journey upriver to spawn. At first they grow rapidly. The salmon’s weight can increase by as much as 20 times in less than a year. Some return to spawn after only one year at sea and are known as grilse; others stay for another two or more years, reaching up to 40 lb (18kg), before returning.

The long trek

The journey downstream as a smolt may have been exhausting – but the long haul back is even more gruelling. How the salmon finds its way from ocean to coast is an extraordinary feat of navigation. The fish finds its way back to its exact birthplace mainly by using its acute sense of smell. Having survived the pollution and nets in the estuaries, the salmon stops feeding – it has stored up enough fat to sustain it for over a year. Swimming against the flow, the fish moves upstream in a series of runs – a task made easier when the water is warm and the river level high.

Fish are jumpin’

When it cannot overcome obstacles, such as weirs and waterfalls, by swimming, the salmon jumps over them. It can leap as high as 3.5m (12ft) as long as it starts from deep enough water, but it can only jump during the daytime since itjudges where the top of the obstacle is by aiming for the light above it. This is how the salmon gets its name -the Romans called it Salmo, from the Latin verb satire, to leap.

Beginning and end

By November many have arrived at their birthplace, and from then until mid-January mating takes place. At the end of it the fish, now known as kelts, are weak and emaciated. Most males, and some females, die, either from exhaustion or from a fungal disease known as saprolegnia. Those that don’t perish rest in deep holes through the winter or drift towards the sea, ready to repeat the cycle again.

Both sides of the ‘pond’

The Atlantic salmon is found on both the North American and European Atlantic coastlines and migrates into the rivers of both continents to spawn. At one time its natural range in Europe extended from the most northerly rivers of Spain and Portugal to Norway and the River Pechora in Russia. However, today many of the rivers which formerly contained salmon no longer do so. Nowadays there are few salmon south of the coast of Brittany – most of the stocks once found in France, Germany, Holland and Poland are either extinct or so small that they are endangered. English salmon are now also scarce and there are fewer in Scottish, Welsh and Irish waters than there once were. Only the rivers of Norway and Iceland contain appreciable numbers.

What’s happened?

There are several reasons for the widespread destruction of salmon stocks. Weirs and dams on major rivers impede migration upstream; pollution, particularly in estuaries, has also diminished numbers.

In recent years the activities of the marine fishing industry have affected the food of the salmon at sea with fewer herring, sandeels and shrimps available. The angler is the least of its worries.