SALMON are famous for their ability to leap up waterfalls as they make their way upstream to spawn. One story tells of a fisherman who noticed that “great numbers of salmon failed in their efforts to surmount the [waterfall]” where he fished. Some even landed on the riverbank at the foot of the falls. He lit a fire on an exposed rock near the foot of the falls and put a frying pan on it. “After their unsuccessful effort,” it is reported, “some of the unhappy salmon would fall accidentally into the frying-pan.” Thus, this fisherman could later boast that ‘the salmon of his country were so abundant that they would leap into the frying pan of their own accord without troubling the fisherman to catch them.’
Granted, that story may be exaggerated. Nevertheless, salmon do leap up waterfalls. A report issued by the Salmon Research Agency of Ireland, however, showed that in recent years there has been “a dramatic decline in the numbers of wild fish moving upstream to spawn.” One survey showed that in one year, out of nearly 44,000 young salmon that were tagged and released, only 3 percent (approximately 1,300) returned.
What has accounted for this tragic decline in the numbers of the “King of Fishes,” the Atlantic salmon? Will they ever again be as plentiful as before? Understanding the intriguing and unusual life cycle of this magnificent fish provides us with insight into the causes of and possible solutions to the problem.
Life for a salmon begins between November and February in the gravel bed of a freshwater stream. The male fends off intruders while the female excavates several small hollows up to 12 inches [30 cm] deep. Together they lay and fertilize several thousand eggs in each hollow. The female then protects the eggs by covering them with gravel.
In March or April, a peculiar-looking fish emerges from the egg. Called an alevin, it is only about one inch [3 cm] long and has an ungainly yolk sac attached underneath. Initially the fish stays hidden under the gravel, feeding off its portable food supply. After four or five weeks, when its yolk sac has been absorbed, the fry, as it is now called, wriggles out from beneath the stones into the main stream. It is about two inches [5 cm] long and now looks like a proper fish. There are only two things on its mind. First, finding a new food source
“After a year or so,” says Michael, who has studied salmon and other fish for some time, “the salmon gets to be about three [8 cm] or four inches [10 cm] long. It is now called a parr and has a distinctive marking of dark patches along each side of its body. When its length reaches about six inches [15 cm], the dark markings give way to a uniform brilliant silver. Now some remarkable and complicated changes occur that set the salmon apart from most other fish.”
Michael continues: “Between May and June, the fish, now called a smolt, is prompted by some internal signal and joins thousands of others in an exodus downstream to the estuaries.” But surely a freshwater creature cannot survive in the sea, can it? When asked that question, Michael replies: “Usually it cannot, but complex changes occur around its gills, which enable it to filter out the salts found in seawater. When the changes are complete, the smolt, which is small enough to fit into the palm of your hand, sets off on an epic journey.”
Life at Sea
Why does such a small fish leave its familiar river? Where does it go? The young salmon needs to get to its feeding grounds in order to become fully mature. If it avoids predators, such as cormorants, seals, dolphins, and even killer whales, it will arrive there and feed on certain large zooplankton and sand eels, as well as herring, capelin, and other fish. After a year its weight will have increased 15-fold
The exact location of the feeding grounds was unknown until the 1950’s, when commercial fishermen began catching large numbers of salmon off the coast of Greenland. Another major feeding ground was later discovered around the Faeroe Islands, north of Scotland. More feeding grounds have since been discovered. There are even reports of salmon feeding under the Arctic ice! With the discovery of these feeding grounds, the troubles really began for the Atlantic salmon. Huge fisheries were built in Greenland and the Faeroe Islands. Thousands of tons of fish were caught by commercial fishermen, and suddenly the numbers returning to breed in the freshwater rivers plummeted. Realizing the seriousness of this problem, governments set various restrictions and quotas for fishermen. This has helped to protect the salmon while at sea.
The Return From the Sea
Eventually the mature salmon returns to the river where it was hatched, finds a mate, and the cycle begins again. “What is truly amazing,” explains Michael, “is that this remarkable fish unerringly navigates thousands of miles of ocean that it has never seen before! How it does this continues to baffle scientists. Some say that salmon navigate using the earth’s magnetism, ocean currents, or even the stars. It is thought that once it is back in the estuary, the salmon recognizes its home river by its ‘smell,’ or its chemical composition.”
“They adapt to freshwater life once more,” says Michael, “and enter the river. This homing instinct is so strong that even if waterfalls or rapids are in the way, these salmon, now much bigger and stronger, will stubbornly struggle to get over each hurdle.”
More difficulties confront the returning salmon when it comes across almost unscalable dams, hydroelectric water schemes, or other man-made obstacles. What happens then? “Many conservation-minded people provide an alternative route,” says Deirdre, a salmon researcher. “An easier incline is constructed that bypasses the large obstruction. We call this a fish ladder or a fish pass. It enables the salmon to leap safely into the higher waters on its journey to the spawning grounds.”
“That does not always work, however,” Deirdre continues. “I have seen some salmon ignore the bypass. They recognize only their original route and try ceaselessly to get over the new man-made obstacle. Many die of exhaustion or beat themselves to death against the obstruction.”
Salmon provide nutritious food. Since wild Atlantic salmon are on the decline, commercial salmon farms have been set up. The salmon are kept onshore in freshwater containers until they reach smolt size. Then they are transferred to cagelike structures situated offshore, where they are nurtured until mature and ready to be sold to restaurants and food shops.
Salmon raised in this way are also in trouble. Fish farmers use artificially produced food to feed them. That along with being confined in cages makes the salmon very prone to disease and parasites, such as sea lice. Some of the protective sprays used can be quite potent. “I used to swim beneath some of these fish farms,” says Ernest, a diver, “and it was very noticeable that the seabed was devoid of life around many of those areas.”
A “King” in Trouble
Many wild salmon are caught with offshore nets before ever reaching their home river. The high commercial value of wild salmon encourages some fishermen to take them illegally. The few salmon that manage to get back to the river also have to get past the legal anglers. To protect salmon stocks, various measures have been put in place, such as restricting fishing to designated stretches of river known as beats, imposing expensive levies, and declaring a limited fishing season. Even so, it is estimated that 1 of every 5 salmon will be caught as it makes its way back upriver.
In addition, wild salmon contract various diseases, and these have taken a heavy toll on the salmon population. One of these, known as ulcerative dermal necrosis, causes ulcers on the skin of the fish and eventually death. Industrial pollution and pesticides that find their way into the rivers are other potentially lethal hazards that salmon, as well as all other water creatures, have to combat.
Atlantic salmon travel from rivers as far away as the United States, Russia, and Spain to feeding grounds off the Faeroe Islands and Greenland before returning home to spawn.