Читать книгу The Salmon: The Extraordinary Story of the King of Fish - Michael Wigan - Страница 5

The night is overcast and promising. I packed a large spotlamp, reserve mini-torch and windcheater into the truck and chugged 5 miles through the blackness up a track to a high tributary of Sutherland’s River Helmsdale, in the north highlands of Scotland. My destination is an isolated spot, several miles from any road or house. I could only feel a light wind, which is good for salmon-watching because wind-ruffled water obscures the fish-action.

Painstakingly I checked a stretch of river, as I do every year, for numbers of paired salmon preparing to spawn. This section of the river has excellent pebbly expanses of small gravel in which salmon like to make their nests or ‘redds’, and year after year I have found salmon in couples side by side in the riffly bits behind large boulders, facing upriver. They are unworried by the bright light, instead focused on the act which ensures that their genetics pass down and that their own progeny will one autumn occupy that same riffle and reproduce there too.

In the spotlight you can see everything; the markings on their backs and their rich tartan bodies – which by this time of year are red and black and magenta – the heads of the cocks in luridly contrasting colours, and you see their tails gently finning in the current, steady as metronomes.

But tonight there was nothing there. The pools were empty. It was easy to see because the water was low, lower than I had seen it before in November – which is a wet month hereabouts.

Then I heard what sounded like hooves crashing through water. I thought I had winded stags, for some of the red stags come to the river’s edge at this intersection and they run from human scent. I thought a small party had crossed the river below, so I walked down the bank.

In the radiance of the powerful spot-light was a striking spectacle. A salmon on its side was arcing in a shallow pool, its body bent like a bow. The sound I had heard was the smacking of its body back against the water. I looked closer. There were two, a cock and a hen, small-sized. They had swum up the river this far to find suitable redds, prompted by the echo of their own birth in this tributary, maybe in the self-same stretch, in an earlier time. But the pair was marooned. They had got this far and the frost had driven the water level down as they waited to reproduce, while below them the riffly water was even slower. When salmon swim through low water the mucilaginous slime can be scraped from their bodies, exposing them to infections. It was hard to go down and impossible to go up. This pair had traded on rain and been let down.

Undeterred, they were spawning anyway, and she was busy laying eggs with her shuddering body ejaculating the pink globes into a groove in the pebbles. I was watching a heroic act of self-replication.

Presumably the rest of the normal number, maybe a dozen pairs in a three-hundred-yard stretch, had dropped back as water had shallowed. Indeed, that appeared to be so because in the main stem of the river there were salmon pairs all around. Some sections were a maelstrom of spawners, cramped for space, elbowing and shoving each other to get at the good clean gravels.

The air was chilling down. I clambered back into my truck and thought. This was a new event; sometimes the river was too high to see the fish pairs well, sometimes the wind shook up the surface too much to get a clear view, but in the best years you could look down on the spawners as if in an aquarium. You know if the fish have already spawned and buried their eggs in the gravel because when hit by the light they run and squiggle downstream. Un-spawned, they face the light. It is one of Nature’s great spectacles.

For the salmon is natural royalty – no other fish has excited human interest to the extent that Salmo salar does. Let’s tease out the mystique which has resulted in salmon-fixated anglers, in salmon-bewitched writers, in salmon biologists and random salmon-dreamers.

This is the fish that connects land and sea, it is our bridge with the maritime, and the sea is twenty-first-century man’s largest getaway. Anyone can find a boat and go out there, un-harassed, free to turn left or right or go straight on. The salmon is an emissary from this vast fecund zone, where the occupants are out of sight beneath the waves. This is the place where salmon accumulate their fat and gain body weight. It is where they feed to become some of the fastest swimmers anywhere. This is the place salmon acquire the condition that allows them to leap waterfalls, moving up rivers to re-visit their birthplace.

I have just seen the highest waterfall in Scotland which they can ascend in one mighty leap; it is 12 feet high and vertical. To help their passage the local fishery managers dam up the water in the pool below, raising its level by four feet, so that the homing salmon has a mere 8 feet to leap. Olympic athletes would balk.

I was told that the fish poke their heads out of the water and inspect the situation before assaying a leap that must cost them their last ounce of energy and strength. Then they use the upthrust from the deep boiling of the falling water to kick with their tails and twist their bodies, arrowing through spray over the lip of the ledge above. No wonder people marvel – a fish that flies!

What these fish are conveying to the upper reaches of natal rivers is a food-load accumulated in or near the Arctic Ocean. Many salmon from the American and Canadian north-east, nearby to an older class of European salmon, winter close to the shore of western Greenland. Here they gorge on krill and shrimp and capelin, small fish packed with nutrients that can be converted into body weight and condition.

It is known now that to find the food supply salmon use temperature bands as trackers. The presence of salmon is dictated by the food supply, and that is determined by seawater temperature. Lower temperatures mean slower growth rates, smaller egg sizes and later development, and smaller size can expose them more to predation. In the 1990s scientists found that capelin off Newfoundland spawned a whole month late owing to very low temperatures in spring, which would have had a knock-on effect for salmon. In this way a seasonal shift in the behaviour of prey can be critical for the body condition of salmon needing to bulk up for the journey home.

Salmon eat molluscs, worms and other fish at sea – even insects which land on the surface when they are near coasts and winds are offshore. It was always reckoned that salmon were opportunistic omnivores, and recently it has been found that their wide-ranging diet embraces lanternfish. These strange-looking denizens of the deep rise to the surface at night to prey on larvae and other floating titbits only to be intercepted by any foraging salmon as they come up.

Researchers were surprised to discover that this hunt was prosecuted even at considerable depths. Previously thought only to happen near the sea-surface layer, it transpires that salmon dive, and dive far. How they detect prey in the lightless deeps is unknown, but presumably they use echolocation or other senses so far unidentified. The behavioural picture gets more complex. Not only do they travel thousands of miles between feeding and breeding grounds, but they go downwards too. They touch our planet at its extremities.

Some of this adventurism helps explain their mighty grip on our imaginations.

The range of the fish is one of the factors. Not only does it span the north hemisphere from top to bottom but its potential larder is three-dimensional. Many animals can only find food to left and right, but salmon do so in all directions. Like birds in the air, they are free on all sides, yet often they end their breeding cycle in streams that a person could step over – so narrow they can barely turn their bodies round. Instead of turning, having spawned the fish still face upstream and drift down backwards with the current, often patched with fungus, half-alive, half-decaying. Using their salty environment as any rotational wild grazer uses its range, meeting appointments with feeding opportunities at different points, the fish climaxes in cramped confinement. Tackling lanternfish at depth, they reproduce in shallow stream-water often only half-submerged, usually under cover of darkness.

It is the transport of sea protein to the headwaters of rivers deep inland that completes the bridging of maritime and terrestrial. For the bodies of the deceased salmon that expired after spawning are deposited into an environment often starved of protein enrichment since the movement of glaciers down to the coast thousands of years ago. The residues of those shrimps, molluscs, fish and worms which have built our silver wanderer fall from its decaying carcase, seeping into the impoverished soils of the headwaters.

This is more strikingly so with the cousins of Atlantic salmon, the species inhabiting the Pacific and the American West. The largest of the seven species, kings or Chinooks, are physically bigger, but all Pacific species lay more eggs and are in greater abundance than Atlantics. Crucially, none of the Pacific species makes it back to sea; they all die after spawning inside the river-system. So when millions of these fish expire in the forested headwaters of British Columbia, Alaska, or the other states of the seaboard USA, it is equivalent to fertiliser dumping along riverbanks on landscape scale.

Certainly, bears and eagles, wolverines and carrion-eating birds all feast on salmon remains in the spawned-out cemeteries where their lives ended, but for these species too this is body-building prior to the onset of harsh winters, with protein originally gleaned from the sea. A neat protein transfer has hitched a ride on salmon.

People conjecture whether the original runs of Atlantic salmon into the rivers of Western Europe and Scandinavia may have equalled in mass what still occurs in the western Americas. Not only were the numbers of Atlantic salmon on a different scale to those of today, but so too were their dimensions. In 1885, near Rotterdam on the Rhine, 69,500 salmon were netted with an average weight of 18 pounds – a size approximating more to that of a Chinook than a modern-day Atlantic. We will never be sure what the volume of primeval runs into Europe were, except that they were spread over all of the western coastline and in infinitely greater numbers. But in 2010 I gleaned an idea of what the scene must have resembled at the foot of a lake called Meziadin in British Columbia in late July.

I had been fishing for steelhead, a sea-running trout, with Walter Faetz on the Bell Irving, a wilderness tributary of the major far north river-system named the Naas. Walter said he wanted to show something to my fellow angler and me. We drove an hour, drew up on a lakeside and launched a small boat. First, Walter motored up-lake awhile and we saw restless sockeye salmon packed in the outflow of a small river waiting for rain to allow them to run it. Then we chugged down the placid un-peopled lake to the outflow.

Here was a stretch of tumbling water, then a small circular lake maybe two hundred yards across, debouching through more rocks at the corner. Gaunt pines surrounded a scene of primitive energy. Vaulting into the air at the top end were vast fish appearing like polychrome Zeppelins out of the burbling water, to land again where they had lifted off. In their dying livery of magenta, crimson and mottled sick-yellow, king salmon lunged from the flowing river, lying down on it again and gradually submerging as if in slow motion.

In our small inflatable we paddled over where they lay. White fungus was growing on their fin-edges and backs and also on their heads. They were disintegrating whilst alive. Underneath the boat and to either side, they were flopping and swishing, listlessly lunging at each other, indifferent to our presence just feet away.

Across the current played out another enactment. Here was a long ridge of freshly churned gravel, and from its whiteness and lack of algal covering it was clear the gravel had been recently ploughed. Gently finning in the few feet of water above it were hundreds of bright crimson sockeye salmon – another, smaller species of salmon from the Pacific. The fish were stacked in layers, like wine bottles in an invisible rack. If I had got out and stood on that gravel-bank I would have surmounted millions of eggs promising the next generation of sockeye in this fecund river. Patiently awaiting our departure perched bald eagles looking huge in the spindly pines and gloomy light, preparing to compete with the patrolling grizzlies for the dying salmon. Compute the volume of fish-protein in that modest body of water and the mind boggles.

None of that protein richness would leave this environment; it formed part of the ecology – sea refreshing impoverished land far from the coast.

Out of interest I procured facts from the government website which records annual runs of salmon at a fish-pass just below Lake Meziadin. We drove there and saw salmon leaping in futility against the dam walls, others catching the faster water on the side where the fish-pass laddered its way up past the dam. The number of Chinooks that ran this branch of the Meziadin River was around 500, the number of sockeye around 200,000, and the coho run around 4,000. The River Meziadin is small – my fishing partner and I easily cast line across the central river-flow – yet the fish biomass on the redds in the autumn, acre for acre, must approximate to a beef feed-lot in the American Midwest.

What we witnessed was fish abundance from another epoch. It was part of a wider picture; that year, on the heels of scientific predictions of a diminished sockeye salmon run, in fact some 24 million fish showed up. Scientists sucked their thumbs. Fish are a jump ahead. It is tempting to wonder how close that scene with Pacific salmon in British Columbia paralleled in abundance what occurred in western Europe with their Atlantic cousins over 10,000 years ago, before human impact.

It may not only be the soil and avian predators that benefit from this transport of protein from the sea. In British Columbia, amply funded for fisheries research, it has been found that in their first year of life out of the egg, young steelhead a few inches long subsist largely on ‘spawner-derived’ feeding. After one year of age, 95 per cent of stomach content was proven to be from salmon eggs and carcases. This was discovered by tethering 400 dead salmon in a river and testing the stomach contents of young steelhead living downstream of them. In other words, they too were nourished on dead salmon at a critical development time. Related to salmon but not the same species, these migratory co-habitants would seemingly struggle if the big salmon runs disappeared.

Is this the case with Atlantics, our European species? Do their descendants subsist on their shredded flesh? No one knows.

The charm of the Atlantic’s salmon is that a small percentage do not die; having spawned, some survive. It is thought that around one in twenty live to spawn twice, and they are mostly females. This simple fact changes their whole definition from that of their Pacific cousins. Their softened bodies roll with the current towards the sea. Able to move pigment around their bodies, they have changed colour throughout their lives – in sandy-bottomed streams parr colour up sandy; put a cock salmon in a dark tank and cover the top and it darkens, faster towards spawning, but take him out and he pales. Now the sea-seeking fish silver up, fresh-minted; their bodies carry a latent promise of recovery, return and procreation again. Ancient Egypt’s Pharoahs would understand: they have an afterlife.

The passage to recovery is far from safe. Otters find them easy prey. Raucous gulls tug their barely sentient carcases from the shingle and devour them. Crows patrol the river edge for prey, squabbling over the rotten bodies. If any fortunate fish do manage to reach the ocean they run smack into hit-squads of patrolling sea mammals, in the form of grey and common seals. These far larger creatures can catch salmon by slashing them senseless with their flippers, and in a copy of sea-lion acts in the zoo, they flick them into the air, strip off the skins and swallow them as they fall.

The two seal species have protection in Europe, enjoying an almost complete prohibition on culling. Not consonant with the heavily managed catch quotas for all commercial fish, this status of sanctity and exclusion from management has its origin in the excesses of the whaling industry long ago. Whaling desecrated the populations of one of the world’s largest and most miraculous beasts in a hell-for-leather (sic) war on natural resources that has no historic parallels for goriness and intemperance. In the case of the American buffalo, one species was hunted down; in the case of the whales, several species were decimated. For whales are ocean mammals which have to surface and can therefore be seen. The oceans were raked and re-raked until almost none of the species with value were left. The scars from that era have entered Western psyches and will be a long time healing.

Seals are the major predators of fish close to the coast. Commercial fishermen have shown that they eat far more of the fish in the North Sea than fishermen are catching. However, for the time being the images of whiskered recumbent lumps straddling offshore rocks, doe-eyed saltwater Labradors, is forceful: they are sacrosanct. The only shots they have to put up with are from cameras. There is no public appetite for the resumption of anything that could look remotely like whaling, with any sea mammal. No one wants to risk a repeat of those haunting consequences.

As in some other stories we will come to, the reason for selective management is the secrecy of the sea. Beneath the waves, all is hidden. If the waters were peeled back from coastal north Scotland and the hundreds of thousands of large seals were made visible, attitudes might change. The fish would look miniature and vulnerable by comparison, their attackers gross and greedy. But we see what we see, and what we see, we believe.

Seals have trouble catching fast-moving salmon in open seas, but weakened by reproduction and their starvation in freshwater the post-coital ghosts drifting from river-mouths make easy pickings in late winter. Early spring salmon in colder waters move slower, and they are easier prey too.

A few salmon survive. No one knows what predestines these few fish to survive their ordeals, but they do. Maybe they are just the fortunate ones. Many species cling to existence with only small numbers of breeders. They say the fecund rabbit can breed a million descendants in its own lifetime. Adult ‘hen’ salmon produce some 800 eggs for each pound of their body weight, so a good fish of fifteen pounds would squirt from her quivering flanks into the redds some 12,000 eggs. If she beat the odds and returned to spawn twice, she might have grown and be able to produce more eggs the second time. The egg output, though, depends on seasonal and physical factors and can vary widely.

The most times any salmon returned that I have heard of was a fish that negotiated survival for eight re-runs, which was netted off Newfoundland and aged by scale-reading – a cross-cut scale being interpreted like the rings of a tree. This one must have been up near the rabbit in terms of prolific genetic legacy! Similar return rates have been recorded in some of the glorious rivers of New Brunswick. On the eastern side of the Atlantic, a fish analysed in Wales had returned to the redds five times.

It is in the northern oceans that depleted salmon rebuild their condition. If you were to catch and eat these salmon before they had reconstituted themselves, they would be oily and disagreeable, like cod or mackerel after spawning.

For a long time pundits tried to work out where salmon winter; it was akin to the mystical quest for the end of the rainbow. Somewhere a fish as long as your finger grew exponentially to become a fish as long as your arm. Where was this fabulous larder? It is known now that a proportion of British salmon winter off western Greenland, where Greenlanders in small boats net them close to the coast. These salmon stay more than one winter. They are a minority here; many larger salmon from North America fatten off Greenland too. A little further north, the salmon of the Russian Kola Peninsular and the salmon connected to rivers on Norway’s long coastline winter in the North Atlantic off Norway.

The salmon of eastern North America winter in the Labrador Sea and on the northern Grand Banks, as well as western Greenland. It can be overlooked: the distance across the Davis Strait starting from northern Newfoundland is only 600 miles. Greenland’s seas are a neighbourhood bouillabaisse. The fact of highly variable runs of east-coast salmon in North America is reckoned by scientists to be related to the environment, food supply and ocean temperature; so much is reasonably obvious. But unlike on the eastern side, where salmon-run prediction is not attempted, Canadian and American forecasts on fish runs are based on what is found in the sea off Newfoundland and Labrador when the water reaches four degrees. In the 1980s and 1990s, between Labrador and western Greenland sea temperatures were suppressed by Arctic waters pushing south. This in turn saw declining growth rates across species like capelin and cod, delayed spawning times and generally reduced salmon runs.

Not only are weather and climate unpredictable variables at sea, but living matter in the sea is infinitely complex. Any child at the seaside has noticed that if you bottle seawater the life seems to fade away. This is because the sea is a dynamic environment in a state of continuing flux. Filled with plankton, microscopic living particles of plants and animals, the sea is a bubbling broth. It has been calculated that the amount of organic material in an acre of sea equates to the vegetation on an acre of average land. Planktonic abundance fuels the vitality of seawater and is the foundation for a pyramid of creatures feeding from one predator level to the next.

Adult salmon are near the top of this pyramid. Fast swimmers, they evade other fish. Vulnerable to being cornered by seals and acrobatic sea mammals when in semi-confined areas like estuaries, they are generally too swift for capture. The rich soup of planktonic life becomes in turn the feed for krill, capelin, herring, shrimps and molluscs, which are all part of salmon’s ocean diet.

Important elements like phosphorus and nitrogen determine marine productivity. These either wash onto the shelves that are the underwater extensions of landmasses, or are pushed from below in the deep ocean by upwellings as ocean currents mix, driven by the Earth’s rotation. Areas of the ocean vary enormously in their productivity, the North Sea and the Grand Banks being shallow expanses and exceptionally fertile, as contrasted to vast parts of the mid-Pacific where the water, as you peer into it with the sun behind, is startlingly clear precisely because there is so little plankton and suspended material. It is as void as sterilised bottled drinking water. In other places millions of plant cells can occupy one cubic foot of seawater.

This partially explains what has been called the ‘explosive growth’ which salmon display after leaving their freshwater nurseries as six-inch smolts.

Marine biology and marine research have made quantum leaps in recent time. Two areas of rapidly advancing research concern life in the bathymetric deeps, where life-forms have been discovered way below depths at which it was formerly thought any life at all could exist, and secondly in the pelagic or surface skin of the ocean. Although we now know that salmon obtain food from depths of as much as 800 metres in the dimmed realms of the sperm whale, and can stay at 400–600 metres for as long as 24 hours, it is in the surface ocean layer that smolts have to survive when they leave rivers.

Their departure is called the smolt ‘run’. The small fish leave their natal river for the great unknown when prompted by rising temperature. A government fisheries department in Scotland used infra-red images at night on a tributary of the River North Esk to watch smolts assembling for the ‘run’. The technology was not perfect; rising water levels lost the images of fish, but the presence of smolt-traps further downriver showed that smolts did indeed continue running in high waters. For the bigger picture the technology served adequately. It showed that fish shoaled in small parties of three to six, they used the core of the current for propulsion, and they descended rivers pointing seaward.

Tagging with microchips has established another new finding. Smolts enter the sea in a mass to minimise predation. Having travelled downriver in small schools, they pack to go to sea, then closer to the sea becomes an assembly point. The reason is the same as why other small fish shoal – it enhances an individual’s survival chance to be one of many congregated in a dense mass.

A salmon river is occasionally blessed with egg-bearing gravels all the way up its sinuous length. The Miramichi in Canada is an example of a spawning bed over a hundred miles long. Hen fish will sweep out redds and lay their eggs in them from the narrowest streams at the top to the wide, gravelly wash-out bars near the river-mouth. To coordinate the smolt runs, however, the development of eggs into fry and parr and then into smolts in the headwaters of the river must be earlier in the season, so that when these young shoals of salmon go seawards they do not miss the camouflage of other shoals of smolts which have matured later and which are waiting nearer the river-mouth.

Accordingly, in northern Scottish rivers parr begin to go silvery, and turn into smolts or ‘smoltify’, as early as March in the headwaters and as late as May lower down. To prepare them for ocean life, away from the shady corners and dark shadows of natal streams, they develop an ocean livery. Their skin grows a layer of silver guanine crystals. These crystals arranged in verticals rows act as mirrors, camouflaging the little fish by reflecting its surroundings.

The keen perception of Dr Richard Shelton, formerly head of the government’s marine laboratory in Pitlochry in Scotland, noted that the only parts of the smolt to remain unaltered are the black edges to the fin and tail. He believes these are helpful visual aids to other smolts in keeping the pack together, whilst not giving too much definition away to predators.

To help the smolt register where it originated, and to find its own personal natal stream later as a fully grown fish, the hormone thyroxine is raised temporarily to allow the small brain to take in vital extra survival information.

The cohort of smolts journeys down the river, making the little flips and splashes familiar to springtime anglers, and reaches the sea to coincide with feeding opportunities. The oldest smolts reach the salt first and the youngest, maybe only a year old, go last, an order which is reversed when they return as adults. A critical feeding assignation is with the outburst of sand-eel larvae on the sandbanks.

The similar appearance of different smolts is deceptive. Those from the southern edge of range, France and Spain, are a fraction of the age of individuals from colder northern rivers. Whereas many southern European smolts are just over a year old, those from Arctic Norway, Greenland and Ungava Bay may be seven before they risk life at sea. From Iceland and Scotland smolts have dwelt from between two and five years in the river. The age difference reflects the length of the growing season, further north, less time.

It is an extraordinary thought that physically similar fish, at the same development stage, vary in age by so much. There are no obvious parallels in bird or mammal biology. Possibly there are comparable patterns in other fish, but none comes to mind. Salmon evolution is supreme adaptation.

What happens after the entry into seawater has recently been tracked in an internationally funded programme codenamed SALSEA-Merge. SALSEA is the most remarkable research on a fish at sea in recent time. The European Union, Canada, the USA, the Total Foundation in France, the Atlantic Salmon Trust in the UK and a variety of universities and agencies combined to fit out the RV Celtic Voyager and two other vessels with proper equipment, and then put the right people on board who knew what questions to ask and how to get answers.

The results fill in another corner of the lifestyle jigsaw.

The research boats spent three years catching around 27,000 juvenile salmon from 466 different locations in the North Sea, the Norwegian and Irish seas, and generally in the north-east Atlantic around the Faroe Islands and Iceland. Information from 284 out of Europe’s 1,700 salmon rivers from nine countries was used in genetic sampling and analysis. The biggest sample came from Scotland, followed by Norway. By targeting the most productive and the largest rivers, the SALSEA team reckons that 80 per cent of Europe’s productive salmon area was embraced by the research effort. The resulting picture then is a clear story about European salmon, including Russia and Scandinavia, up to 2011.

The novel side of the analysis was the use of genetics. Only recent science allows researchers to find out where a fish comes from. Work on Ireland’s River Moy had already shown what a sprinkling of other rivers had found too – that inside their catchments salmon stocks can be divided up into genetically discrete populations. It was true of a minority of rivers, but demonstrated the impressive complexity of salmon adaptation.

The Atlantic salmon in some form or other has been occupying European and North American rivers for 60 million years. In that immense time it has developed local strains to adapt to local conditions. Then the last Ice Age ended, with a thaw that peeled back the ice-covered land over all Britain north of London. A mere 15,000 years separates us from the frigid conditions that dominated before. In cosmic terms it is a blink in time. Salmon saw pristine territory opening up in front of them, and occupied it.

Rivers in Scotland have plenty in common with other rivers in salmon range. They are spring-fed. These springs can come from hundreds of feet below ground and each one has a differing chemical composition. Also, the springs bubble from the ground loaded with different temperature readings, dependent on their depth.

Variations between springs account for differing populations of salmon. For the scent in each stream, and the mineral contents, differs from that of its neighbour. Salmon have brilliant olfactory senses, being able to pick out the most dilute odours from home-stream chemistry even through a fog of additives and man-made complexities. The fish’s ancestors have used that water and over time adapted to it.

Sometimes that adaptation will translate into an identifiable genetic type. SALSEA went to sea armed in advance with the genetic map of many rivers. The researchers were hunting smolts, young salmon entering an alien saltwater world pregnant with feeding and with threat. What galvanised researchers to go to all this effort? The answer to that question is both simple and complex. At the simple level, it is because the salmon is important enough to justify it – it is a glittering symbol of environmental wellbeing. The complex answer backtracks in time.

In the 1960s European rivers had seen prodigious runs of salmon. The silver bonanza from the spring tides re-ran the programme of fresh shoals arriving through the year and it seemed as certain as the sun dropping in the west that from the start of spring these great leaping, wild, sparkling fish would go on and on revitalising rivers which had gone doggo for the winter.

Then a decline commenced. Fewer and fewer salmon came back in the 1980s, and then the 1990s. The canaries in the mine, or anglers, found their enticing presentations drifting across the stream undisturbed. Nothing jumped. Nothing swirled at the fly. The waters rolled to sea unruffled. The rivers missed their most dramatic occupant.

A few rivers had installed fish counters, usually consisting of electronic beams broken by an upstream-swimming fish, and these counters, logged by computer, were telling an alarming story which backed up the anglers’ perceptions of fewer silver visitors.

It was estimated that in the 1960s and 1970s the population of salmon in the eastern Atlantic was around eight to ten million fish. In America and Canada, where many rivers had been dammed, where forest clearance in river-country had silted up river-beds and traumatised ecosystems, there is another story of dwindling fish, but we will revisit that side of the tale later.

The decline from abundance was giving rise to serious worry.

In places where smolt survival was being measured, such as at Scotland’s North Esk government monitoring station, and the Bush and Burrishoole system in Ireland, young sea-going smolts had once returned as salmon in numbers approaching 15 per cent of the outgoing migration. This figure was falling and falling steadily. It fell to eight and then as low as five per cent. On the River Conon in the northern Scottish Highlands, where they can measure these things, the return rate of smolts in 2011 was four per cent. In some rivers the number will be even less.

For anadromous fish, which live at sea and breed in freshwater rivers, this figure was low – very low. It told scientists that ocean-wide changes were occurring. Somewhere out there a black hole was consuming the small silver fish that used to fatten in the larder of the north-east Atlantic, before returning to their birthplaces in the pebbly streams. In some American rivers spawning pairs were down to a handful of pairs, a chilling brush with death equal to a doomed scenario.

The most obvious subtractions from salmon runs were then looked at and addressed. Salmon netting, which was recorded as having been prosecuted in some parts of the UK and Europe since the twelfth century, was an obvious target. Here was an industrial-scale subtraction, taking fish before they could breed. Furthermore, it violated one of the tenets of modern fisheries management – that you must know what stock of fish you are taking.

Netsmen took salmon offshore as they migrated past. No one had a clear idea which rivers they were due to swim into. A salmon in the net was a salmon in the net; they all looked much the same. They fetched the same price, too. Logic demanded that random salmon capture cease. On the back of the idea that netting was ‘indiscriminate’, harvesting individuals valuable to species survival alongside those from more numerous components of the migration, appeals were launched to save salmon by buying out or leasing netting stations. Many were laid off and mothballed and bought out. In Scotland alone the catch by nets was ratcheted down from around 100,000 salmon a year in 1990 to 13,000 twenty years later.

Salmon netting still exists in a few places in 2013. Norway remains unreconstructed about salmon netting. Scotland has a handful of active netting-stations, resistant to being bought off and encouraged by rising wild salmon prices, England even fewer. The Norwegian Saami people from the far north, with precious little to sustain them, still net salmon on the Arctic coast. In a conservation milestone for salmon, Iceland terminated netting at sea as far back as 1932. Pressed by the European Union, the west-coast Irish drift nets were outlawed in 2007.

The most important salmon-netting haul in modern times was taken off Greenland. It commenced in 1959 when gill-netters working the fjords were startled to find glittering salmon in the mesh. A boom in salmon commenced, which pulled in drift-net fishers close to Greenland’s western shore from Denmark, the Faroes and Norway. The working season was August to October, with the winter iced over. Catches rocketed, peaking at 2,689 tons in 1971. All of a sudden salmon, which are a rare fish in the sea, were being caught like mother cod, which can lay millions of eggs. The International Council for the Exploration of the Sea (ICES) reckoned the Greenland operation in winter 1972 had removed a third of all the salmon locally present. As more attention was paid to what exactly was being caught the fish were traced to the east coast of America and Canada and, secondly, older female salmon from Scotland.

Something had to be done. The solution was devised by an Icelander called Orri Vigfusson, who is now a household name in salmon conservation. A partner in a herring fishing family that hit hard times when herring runs shifted, Vigfusson was familiar with the vagaries of fishing. Basically in sympathy with remote communities eking out precarious existences, Vigfusson saw that in order to endure the solution had to be fair. An international arm was needed to lend support and the quotas discussed at the negotiating table were assembled by the North Atlantic Salmon Conservation Organisation (NASCO), a multi-member body formed in 1984.

Encouraging alternative fisheries for the Greenlanders, and with striking success raising money all across salmon range, Vigfusson made his breakthrough leasing arrangement in 1993. The Greenlanders were not sold down the river – far from it. Their argument that the salmon fattened off their coast was accepted. The payment could be seen as a grazing fee. They were paid to abstain from their rightful fishery, beyond a small permitted tonnage for ‘subsistence’. No salmon could be exported.

The agreements have had to be regularly renewed and reassessed, a lack of finality seen by their critics as a weakness. There have been teething troubles. Greenlanders with limited opportunities for economic activity have exceeded quotas. Annual payments have been withdrawn, and then reinstated when malpractices have been straightened out. The way may have been tortuous, but it has succeeded.

A similar arrangement was reached with the Faroe Islanders, who had been shown how to catch salmon on baited long lines by Danish fishermen from the island of Bornholm who had perfected this art in the Baltic. By 1991 Vigfusson had clinched an agreement with the Faroese, made easier because the Icelandic government already had fisheries access arrangements to their seas with their closest neighbours. The Faroese were the only foreign fishermen allowed to catch Icelandic fish.

Vigfusson had shown how to raise money for salmon protection and how to broker international agreements on a new basis. Tirelessly he had circuited the salmon world, flying from one event to the next, rattling in buses round the bumpy roads on the Greenland coast, meeting one fishing community after another, making addresses and hosting fund-raisers, coming up with ideas for alternative employment, patiently arguing and negotiating. People had faith in his integrity and un-deflected purpose. He crossed national divides and came from a neutral country carrying no historical baggage. Salmon conservation using his model took a mighty stride.

Today there are still anecdotal tales, usually involving Spanish trawlers playing fast and loose with everyone and everything, but in the main salmon netting has being progressively removed as a major factor in European salmon decline.

Anglers knew they had to join the effort to restore the bountiful fish. Inducted in its virtues by an American salmon community almost completely stripped of their iconic east-coast visitor, and championed by the charismatic Alaskan-born angler and conservationist, Lee Wulff, who coined the memorable phrase ‘Gamefish are too valuable to be caught only once’, ‘catch and release’ was introduced to UK anglers around 2005. Since that time it has taken off. The fish is brought to the landing-net as fast as possible, revived by allowing the lungs to re-fill with oxygen, and let go when the body is properly horizontal in the water and the tail-movement quickens.

Talked of and practised by individual anglers for at least a century, especially when the salmon was late-season and coloured, catch and release took a formal position in salmon management relatively lately. Now it applies to fresh salmon in mint condition, not only coloured flabby ones.

Scotland’s Aberdeenshire Dee broke the mould and made catch and release compulsory all season in an unprecedented announcement that caused a mighty stir at the time. But it was done. Other rivers followed suit with milder variations on the theme. Some salmon were allowed to be killed ‘for the pot’ at times of year when runs were bountiful, and restrictions on numbers of fish allowed to be killed were applied to sensitive parts of the run, typically the early spring.

The result? Were there more shoals of salmon pushing the tide up the banks as they swarmed into those waiting river-mouths? Hell, there were! The decline persisted.

It was against this background of dwindling stocks that SALSEA girded its loins to find out what was happening in the part of the salmon zone that remained an almost total mystery – saltwater.

The background to this mystery was not only a fish that was doing a vanishing act, it was climate change. The north-eastern Atlantic, where many European salmon wintered, was warming. No thermometer was needed to discover this. Surf anglers on the north coast of Scotland’s desolate extremities threw their spinning lines baited for cod and hooked sea bass. Previously sea bass had not been caught further north than The Wash in south-eastern England. Exotic fish were dragged up in trawlers all the way to Iceland. Red mullet and sea bream edged up the latitude line. Coral reefs crumbled in unfamiliarly warm waters. Disc-shaped sunfish, previously only ever seen, and then rarely, off the south coast, were hauled onto boats far up the coast of Britain. From sardines to whales, fish moved northwards. Smolts were not immune; their pathways adapted too.

Oceanographers confirmed it: the North Atlantic was warming. For fisheries this presented challenges.

In 2011 there was a furious row in Europe’s fishing states when Iceland, not hitherto invited to the meetings which allocated quotas amongst traditional fishing nations, and not an EU member, discovered big shoals of mackerel swarming around its north coast, and started catching them. The Faroe Islands found and did the same. Tempers flared. The two small states became overnight pariahs. These fish ‘belonged’ to fishing nations further south. Iceland and the Faroe Islanders argued that the mackerel in their waters were in prime condition with top-notch fat content, perfect for market. For countries further south to limit their new bonanza was bizarre; the fish belonged to whoever had possession of them. The argument sputtered on. National politics had run up against fluctuating natural cycles, a test for diplomacy.

Fish follow temperature bands which are the conveyor belts for food. The mackerel do not care whether they swim off Iceland or off Ireland, they register the volume of shrimp and squid and other high-octane titbits that can be gorged upon, and follow them. Mackerel are not anadromous like salmon, with both a freshwater phase and a saltwater one, but their extreme mobility tested the capacity of nation states to live in a changing world. There were parallels with salmon politics.

The background to the search for smolts from European rivers was the same warming North Atlantic. There was a simple distance factor: the smolts from the southern extremity of salmon range in rivers in northern Spain had a longer journey to reach the winter food supply; further to swim, in hostile territory. All along the journey were the enhanced risks of predation and starvation. Conversely, as freshwater temperatures were also rising, smolts were growing faster in natal streams, and were bigger and often younger when they reached the salt. Ratcheting up the pressure, survival rates of fast-growing smolts are lower.

Celtic Voyager and two other research vessels embarked on their exploratory fishing trips in a world being re-drawn by dynamic flux.

Anxiety about the Atlantic salmon was sufficiently syncopated and international to produce the SALSEA programme. Although salmon smolts were the tools, the programme, lasting over three years from 2008, was designed to advance the understanding of ocean ecology and fish genetics. The authors even talk about hopes that they have provided invaluable data for ‘the future ecosystem-based management of the oceans’. Big aims.

To catch these very small fish in a large piece of sea they adapted a standard small trawl for smolt capture. A small-mesh net was pulled on two side ropes and kept on the surface by large floats on each side. At the ‘cod-end’, or last compartment in a narrowing cone-shaped net, was the fish ‘box’ accumulating smolts. The smolt trawl was towed in arcs at speeds of three to five knots, anything from 150 to 400 metres from the mother ship. It was 155 metres long with a mouth forty by ten metres. The main thing was – it worked.

Quantitative results varied by region. The report cites one case where 233 trawls netted 1,728 smolts and 53 adult salmon, at a rate of 3.4 fish per trawl. This trawl had hit a migration ‘pathway’.

The long-awaited paper, which included data collection from as far back as 1999, was published in January 2012. Authors Jens Christian Holst and Ken Whelan warn that owing to cost no such programme is likely to be done again. So we should heed what they discovered.

The location of smolts was closely linked to ocean currents. Differences in temperature and salt content change the density of seawater, which in turn drives global ocean circulation through the medium of currents. The young salmon use currents as escalators. They ride them for propulsion and add to this their swimming power. Recovered tagged fish showed that smolts’ swimming power was often equal to the speed of the ocean currents. They may be small but they are powerful.

Climate variability also affected where they went. Oceanic circulation round Scotland and the North Sea is anti-clockwise. It is also driven by winds, especially between March and May. As the climate alters, these winds have been strengthening and this affects marine growth and fish travelling in the upper layers, like smolts.

Smolts’ growth rate, as measured by SALSEA, is prodigious, fairly justifying the description ‘explosive’. Each day they might grow 0.6 per cent of their body length. At the southerly edge of Atlantic salmon range smolt survival is worst. Whether the young salmon were leaving the River Loire Allier in northern France and heading westwards round the Atlantic coast of Ireland to find feeding midway between Iceland and Norway in the Norwegian Sea, or leaving north-west Spain and negotiating the English Channel, southerly stocks struggled more. The impoverished Allier has only a bare-bones population of 500–1000 breeding salmon to start with, and the Spanish rivers are similar.

Norwegian and Russian young salmon, with less far to go, and feeding further north, do better.

When travelling off Norway Europe’s little silver fish meticulously follow the shelf-edge between the shallow coastal ledge and the deeps. The shelves form shallow-water skirts off the landmasses all round the North Atlantic where salmon winter. They differ from deep drop-offs, more characteristic of volcanic landmasses. The salmon’s landmasses have a glacial origin, shelving into the sea as glaciers turned to water. Why the smolts tracked the shelf-edge can be guessed at, how they followed an invisible fault-line underneath them is a mystery.

Richard Shelton was one of the scientists working on the early phases of research and he puzzled over this. How could the fish so accurately follow this shelf? Temperature, salinity and depth were tested for roles as routeing guides and none of them seemed to fit. In their lateral line, or the line running mid-body from end to end, salmon harbour the magnetic oxide of iron called magnetite. One possibility Shelton considered was that smolts were orienteering by the Earth’s magnetic field. This remains conjectural. But stick to the shelf-edge they did. This edge lies about halfway to Iceland. Knowing where they are is a first step to protecting them.

When they reached a projecting seabed north of Iceland called the Voering Plateau, our smolts ceased linear movement and dispersed in big gyres. In the Norwegian Sea and west and east of Greenland they feed and grow at what Shelton describes as, ‘rates rivalled by few other cold-blooded creatures’.

What was their pattern when moving? Trawling results suggested loose shoals of 100–700. There was no evidence of very large-scale shoaling behaviour, which was mildly surprising. So the canny scientists put closed-circuit cameras in the net-end at right angles to the direction of towing, to view better what was being caught.

The observers saw no huge fish agglomerations being gathered in the wings of the net, rather smolts ‘sneaking about’ as Shelton put it, in ones and twos. At night smolts were hard to find, and researchers reckoned that nocturnally they must dive deeper than the ten-metre-deep band they occupied by day. But why? Most fish rise in the so-called ‘water-column’ at night, as darkness affords safety from above. Behaving contrarily, diving smolts must do so for food. But what food? Or what improbable night-time threat are they escaping nearer the surface? Answers breed questions. The salmon’s mysterious behaviour has caused it to be dubbed ‘the oceanographer’s fish’.

The northwards drift of prey species sticking to their northwards-shifting temperature bands influences smolt locations. The team found that the smolts which reached western Greenland seas and settled north-west of Iceland, staying longer at sea and returning to the UK as hugely bigger multi-sea winter fish, were faring well.

The ability to track both regional and river-specific stocks of smolts at sea is new. Because the experiment’s focus was on fish from Europe’s main salmon rivers, the great majority of net captures were successfully ‘assigned’ to their river of origin. It is part of a wider knowledge-picture, where the factual fog is clearing over all migratory routes and behaviour. Microchip and tagging technology, along with a technique involving bouncing signals off satellites, have revolutionised knowledge about migrating creatures. The migratory wading bird, the woodcock, is the next in line for a tracking research programme. Across the natural world years of speculation are being replaced with firmer data.

The salmon fishing writer Richard Waddington devoted many pages of his 1947 book Salmon Fishing: A New Philosophy to a laboriously articulated theory that wintering salmon positioned themselves in the mid-Atlantic in order to intercept common eels migrating as elvers or ‘glass eels’ from the Sargasso Sea off eastern central America. Salmon swam with these easterly migrations of juvenile common eels, he surmised, being sustained and fattened by them all the way back to their growing zones in the freshwaters of UK and Europe. It was somehow a beguiling idea.

The author died long ago, but depending on circumstances in his afterlife he may now have the chance to reconsider and chide himself for those errant thought processes. Knowledge is a grand corrective.

Knowledge was meant to be a defining feature too of the revered Scottish ecology writer, the late Frank Fraser Darling. But when it came to salmon he stumbled. Fraser Darling wrote that the fish that ascend rivers early spawn at the bottom end, and the late-season runners go to the top. In fact it is the other way round, which is why today’s efforts to resuscitate the spring salmon, assuming that like breed like, take hatchery fish from the upper parts of rivers, not the bottom end. The top reaches are where the springers are.

He made another assumption which is fantasy: that east-coast salmon seldom come back from the sea more than once whereas west-coast salmon can breed four or five times. Scale-reading, which ages salmon, and should have put matters straight, had been around for over fifty years when he wrote this.

For some reason salmon seem to befuddle commentators. The director of Scotland’s Marine Laboratory, therefore the senior government person in fisheries, portentously declared in a book on salmon published in 2000 that it was now well established that ‘a large majority of the fish returning to spawn in a particular river originated from that river’. Wow, really? But that was what the Scottish Ecclesiastic Hector Boethius announced in the sixteenth century. SALSEA misroutes down this way too: ‘Reducing man’s impacts on our salmon stocks may be the key to ensuring their survival’. When can we move on, please? It may be a matter of debate whether the Atlantic salmon is the greatest of fish, but it is certainly the one that leads to most confusion.

Before SALSEA it was thought from examining pelagic trawls that smolts at sea ate blown insects to start with and moved deeper down the water column as they got bigger to find crustaceans and small fish. When the diet stepped up to embrace fish, growth accelerated. SALSEA saw that the diet of young salmon changes with ocean conditions. Researchers concluded that they ate almost anything. Capelin (found on the Canadian shelf and off west Greenland), young blue whiting, lanternfish, five-bearded rockling, sprats and sand eels all formed part of their sustenance. Smolts would consume eggs, larvae and young fish and zeroed in particularly onto a sort of bug-eyed shrimp called themisto.

Interestingly, the herring and mackerel which were moving in the same area, though themselves bigger, selected smaller food, mostly crustaceans called copepods. Smolts punch above their weight in the food chain.

Influences on salmon routeing included predator avoidance and their own growth. Uncircumscribed by physical limits, some young salmon migrate all the way not only to the Arctic ice-shelf, but under it. Presumably, beneath the ice-shelf at least one direction is guaranteed free from lethal attack, and there are no trawlers.

SALSEA leader, Norwegian scientist Jens Christian Holst, has written: ‘From the very first scent of salt these fish are continuously hunted by marine predators.’ They face different predator assemblages at different stages in their migration to the wintering grounds. Directly offshore, and whilst they are in the process of adapting their saltwater/freshwater balance for marine survival, sea trout, sea bass and cod feature. There are the salmon gourmands, seals. Further offshore those enemies are joined in the attack by saithe, pollack and more seals, and even rays and skates. North American Atlantic salmon face similar families of predators, but from local species.

Moving further out, coast-huggers like sea trout cease to be trouble. Diving seabirds such as gannets enter the fray. Minke whales and fin whales join the list of toothed adversaries. Even sharks, cephalopods (molluscs including cuttlefish) and tuna can eat smolts. Dr Holst says, ‘the list could be continued at length’! He adds that fast growth is an obvious survival aim for smolts trying to prolong their lives at sea. One sees why.

In eastern Canada a survival peculiarity has been noted linking smolts with spent kelts. In the straits of Ben Isle kelts gathered outside the rivers they had descended until the smolts joined them. Both young salmon and older ones then moved northwards in convoy to the feeding grounds. What is happening? Are smolts being taught their passage by their elders? Is there any protective function in the presence of the kelts mixed with the next generation? Another chapter in the mystery of salmon migration opens up.

SALSEA also recorded what effects human actions were having on smolt runs. Escaped smolts from freshwater rearing cages in lakes and lochs run as nurseries for the salmon farm industry, or young feral salmon, were identified by their genetic markers and found in numbers. Their groups were looser in formation than those of wild smolts. Just how many feral smolts were found is a matter tenderly circuited.

For it is a potent finding. Salmon farm escapement is a highly political and controversial matter and now science can tear back the veil on the resulting profile of ocean fish populations. The relevance for salmon survival of the presence of farm-origin fish competing with wild ones in the sea for the same food is a question which needs answering.

Scale-reading using digital technology was another tool in SALSEA’s knowledge review. Reading scales is nothing new and the Inspector of Fisheries in Scotland, Peter Malloch, based on the River Tay, developed basic scale-reading theories over a century ago. Wider spacing between rings told of richer feeding. From scales readers could say how well fish had fed and grown at sea, what smorgasbord of young fish, fish eggs and larvae had been eaten, prefaced by how these fish had fared in their freshwater phase.

Scales are like dentine in human teeth: they read like tree-rings and tell a story. The scales fall from our eyes: the biography of a fish is available in its scale history. In contrast to many fish population studies done for Europe’s Common Fisheries Policy using predictive modelling by computers to allocate catch quotas (an innately unsatisfactory methodology), scales reveal what conditions were recently like. They offer real-time information, not academic projections for the formulation of shaky assumptions.

Long-time series of salmon scale histories existed in several places. The Copenhagen-based International Council for the Exploration of the Sea (ICES) made available its archive of thousands of tagged and recaptured salmon details based on scale-reading. SALSEA took this forward. New developments in digital analysis have added to the knowledge bank to be gleaned from scale readings.

Scales read on adult salmon when they came back to rivers are correlated genetically to young smolts caught in the smolt trawls. Some of these scales had been taken from the adult fish long ago. So young North-Atlantic smolts were being traced by their scales to fairly distant ancestors. In total, 23,000 scales from seven rivers in six countries were studied. From this sample smolts were mostly two years old, some one and three years old, and a few four years old. The further north the river of origin the older the smolt age; southernmost smolts were growing faster in their home rivers and undertaking the marine migration earlier. As it happens, they were often dying earlier too.

The research revealed that smolts preferred temperature bands of 9–12°C and salinities over 35 per cent. They avoided the shelf directly off western Norway, possibly because salinity is low, and aimed for the deeper, more saline water further west on the shelf-edge. The colder the water the faster their growth rates. This is the opposite of growth and temperature effects in freshwater natal streams where colder water arrests growth.

One of the triggers for the whole SALSEA programme was the fear amongst salmon managers that certain pelagic fisheries in the salmon-wintering seas were sweeping up shoals of young smolts as a by-catch whilst fishing for other pelagic species. In particular there was concern that surface-trawling for mackerel and herring on the Norwegian Shelf was netting little smolts along with the rest and, in the worst scenario, inadvertently massacring entire populations from single river catchments. British fishery scientists had found Norwegian fishermen picking salmon smolts out of their pelagic nets and making special suppers from them. Russia has 40–50 trawlers working this sea far from anyone’s coast and therefore in international waters.

There is an internationally agreed fishery model run by the North East Atlantic Fisheries Commission, but it does not prohibit fishing on the surface. It has no smolt-protection aspect. This could be addressed. As Ken Whelan has said, the next phase is going to be political. Russia’s recent admission to the club of salmon fishing countries, where international rod angling is a serious financial sector, rejoicing in faithfully returning visitors willing to spend money in remote zones, may help this negotiation. Whoever thought that visiting the Kola Peninsular in the Russian Arctic would be a visitor destination of significance before the advent of salmon fishing? Now important Russians know the optimum meaning of a salmon, and the fish is becoming an icon there too.

Fishing states using these northern seas do conduct large-scale surveys of the ecosystem. Now that SALSEA has identified where the smolts are likely to be it becomes theoretically feasible to design pelagic or surface-trawling operations to minimise impacts on young salmon. Already in Norway’s wider fisheries regulations over too much of a particular by-catch triggers the closure of that sector until the unwanted non-target fish has moved on. The same might be possible in the herring fisheries of both Norway and Iceland to protect smolts there.

The other fisheries which may kill smolts are looking for blue whiting, capelin and horse-mackerel, termed ‘industrial’ fisheries because the lower-value fish are turned into fish-feed. It is a horrible irony that super-valuable young salmon are being enmeshed with large hauls of lower-grade fish used for conversion to fishmeal for aquaculture, quite possibly to end up in the stomachs of farmed Atlantic salmon. Valuable wild juveniles feed hordes of feedlot adults.

One improvement may be to alter the depth of pelagic fishing. If smolts occupy the surface of the sea down usually to six and at most ten metres in daylight, dropping lower at night, why not trawl lower still when the targets are herring and mackerel? When tried, this solution worked well. Whatever disciplines are adopted must produce an economic yield for the pelagic boats, and therein lies the challenge.

Ken Whelan is adamant that administrators in the EU fisheries division must be reminded that wise-use management of rare Atlantic salmon is now feasible. He talks of a future thinking in terms of protecting ‘corridors in the sea’ or ‘sections of the ocean’ for the smolt runs. Using known timings of smolt movement from the new migratory map it might be possible to abstain altogether from pelagic trawling where they are vulnerable and at the most sensitive periods. Such an aim sets the bar high.

Politics is never far from the marine resource scene. The impasse over the mackerel catch by Iceland and the Faroes, in an area not far away from the young salmon zone, is discouraging. Entering 2013 is the fourth year of the controversy and both the Icelandic and Faroese governments say they intend to continue harvesting their manna from heaven, though at lower levels. Iceland in 2012 was economically prostrate after a collapse of their banks; harvesting the valuable mackerel was an obvious recourse.

But time has shown that salmon protectionists are a powerful force too. SALSEA proves it, and it would be contrary to experience and history if the findings of this detailed study were simply to be buried and ignored. Iceland, for one, has a valuable sport fishery in salmon.

Development of the sport fishery has been transformational on Iceland’s western coast. Professionalised presentation of rod angling for migratory salmon as a lucrative tourist sector has been an economic triumph. Where not long ago visitors to Iceland rode ponies across the volcanic tundra, marvelling at the lunar bleakness and subsisting on a diet of puffins and mutton, now fishermen from all over the world tumble out of Reykjavik airport jabbering into their mobiles and pop-eyed with excitement at participating in one of the most charismatic salmon sport fisheries anywhere.

The water coursing over volcanic rock in treeless moonscapes is gin-clear, requiring peculiarly focused angler skills. There is no industrial pollution, people are rarer than puffins, the sea is a familiar element and provides the nation’s biggest income, and the newest landmass in Europe has an air of being truly virginal. Salmon-language is fully understood in this peculiar land of fumaroles and sulphur-belching hot springs. Agreements on salmon may form the basis for a new accord on other fish which colonise new territories, even mackerel.

Smolt stage is the black hole of salmon growth, and one reason why SALSEA ever happened. As fry and parr in rivers, the little salmon can be found and examined. Adult salmon are big enough to be tracked, at least some of the time. If they turn up on fishmonger’s slabs somewhere, people notice. Protection at that stage is a practical possibility. Smolts, in contrast, are needles in the haystack of the ocean.

SALSEA makes a stride in knowledge about salmon’s ocean phase. However, it did not satisfy all those awaiting its findings. Managers of salmon sport fisheries were looking for answers to their own pressing questions.

They complained that original promises on the development of the genetic map actually fell far short. Some tracking has limned in a few details, but the big picture remains largely unknown. They make the point that, interesting though genetics might be, the practical application of using the information on the average fishing river is limited. Say you discover there is a different genetic stock in one branch of the river – intriguing – but how can you manage the fishery, aside from keeping the tributaries in good health, to accommodate that information hidden in the DNA?

Most cogently, critics point to the report’s failure to nail salmon farming as the destroyer of wild fisheries through its lethal by-product of proliferating parasitic sea lice. The million-strong swarms of sea lice created by salmon-cage aquaculture adhere to smolts as they leave fresh water and kill them, thereby throttling wild salmon survival. They say the report’s equivocal and incomplete findings will leave politicians an escape route from firm and decisive action in favour of more time-consuming and inconclusive research, measures once sarcastically dubbed as designed, ‘to maintain the momentum of procrastination’.

They have a point. Some of the more arcane disputes about discrete genetic stocks in different branches of one river, and efforts to keep them pure, are undermined by the historical fact that river stocks have been intermixed long ago. All over Britain salmon have been moved from hatcheries and tipped into rivers wherever owners of fisheries wanted to beef up fish numbers, or revive them. It has been going on for over a century. It is the same in other salmon countries, too. Genetic purity is a myth, which is surprising given that genetic purity of stocks is the new mission for salmon theorists.

In Scotland re-stocking only with stocks from that river, and even from a specified part of the system, is now official ‘best practice’, to the frustration of many wizened fishery managers. The new knowledge about discrete strains is not being used in the most intelligent way.

It has always been hard for the genetics messiahs to deal with the fact that on the British west coast river where the Beatles originated, the Mersey, the water has been re-populated with salmon entirely by the vagaries of Nature, its own native stock having been wiped out. The Mersey now has Creole salmon of mixed origin coming from at least thirty different rivers. Who can object? ‘Nature hates a vacuum’ is true for salmon as for all else. Genetic straying has re-populated a major river.

The Thames is another melting-pot culture. Its tentative existence as a salmon river once again owes its brilliant success to stocks from many different places. Reflecting its diverse human mix London’s passing salmon population is polyglot too.

I saw a dramatic illustration of the basis for genetic straying whilst rafting in British Columbia late one summer. At day’s end our three rafts headed for a tributary with a nice shelving sand-bar to moor up on for the night. We crunched onto the beach and were stunned to find huge salmon lying dead on the water’s edge.

There was a biologist aboard. He looked closely at the fish and saw that their gills were clogged. They were king salmon, the big boys, and there were around forty of them stranded down the river-edge for a few hundred yards, all just above the tributary’s junction with the main river. The biologist said the fish were all within a day of spawning. So a valuable stock or ‘year-class’ of a rare and wondrous fish lay wasted about us never to breed, eradicated in the last moment of its evolutionary purpose. Why? The brown water was still silty from a landslide further upriver. A natural event had wiped out the big fish in this tributary for one breeding season.

What gave the event an added twist was the furious debate taking place in west Canada’s media that summer about threats to king salmon, their precarious status, and the need for firmer protection laws. Nature had thrown a joker onto the gaming table and we were staring at it.

But it was also where genetic straying and fish unfaithful to their natal imperative step in. Suppose, as we know is possible, that one pair of king salmon had gone up a tributary close by. They bred there. That strain of salmon thereby dodges fate and escapes elimination. In due course some of the progeny from that union relocate themselves as adults in breeding livery back in the original natal stream, and re-populate it.

Straying is Nature’s way of spreading risk. The same is true, surely, about the differing ages at which young salmon go to sea. If some ‘smoltify’ and migrate in their second spring, and some in their third, the risk of total elimination is spread. On big rivers in Scotland like the Tay, different grilse runs climb the system from early spring to the autumn. They are all fish which spent only one winter in the sea, the definition of grilse. Bookies call it hedging bets.

Peter Malloch might have had a lot to say on some of the purist preconceptions about river-stocking only with site-specific strains which have crept into modern management. It was Malloch who realised a century ago that salmon sometimes remained at sea a long time, and that not all fish were grilse as had been assumed before. He understood the salmon’s admirable diversity. The migratory fish turn homewards to reproduce, swimming south. It is presumed, but only so far tentatively claimed, that they follow the same passage, but going the opposite way, as that which they used as teenagers – another neat theoretical twist made available by modern science which this aristocrat of salmon analysis long ago would have appreciated.

Left behind in the marine larder are the others, the non-movers, growing and growing. Or not growing: some salmon a long time at sea are not especially big. Maybe they too are hedging their bets, passive actors in an evolutionary insurance policy.

A salmon’s eventual size is determined by its length; it can be fat or it can be thin, but without length it can never match the biggest. Girth is the feeding which beefs up the body length. Some of these wintering salmon spend two years in the vicinity of the Arctic, some three, some four, and some even prolong their Arctic sojourn to five years.

Turning southwards as the new year awakens, they ultimately acknowledge the ritual of reproduction, or so it is assumed. Scale-reading shows that after January sea-feeding picks up again following the short winter check. Thus, the fish achieve peak condition prior to the demanding migration south.

Today’s existence is tougher for salmon, for as the northern hemisphere has warmed, dragging the food supply northwards, the return journey south lengthens. Migrating salmon are starting further from home.

Krill may move, natal streams do not.

How long they take to swim home is unknown. Scale-reading differentiates between sea-time and freshwater-time, but we do not yet know in which sea, at what time. Could we? If scales were better able to track diet perhaps we could pin down more accurately how long the journeys take. Sand eels are on known sandbanks and capelin live in the north – the diet could position the predator.

However, there is another lateral-thinking way, a technique not yet fully developed for practical use. We need tags that could measure the angle of the sun at midday, then, as polarised sun filtered through the seawater, it would be possible to calculate latitude. Temperature and the intensity of the light are recordable now; the next step is a reader for polarised light. The tags used on smolts register temperature and depth, but so far they cannot measure the angle of the light. This tantalising technical advance may be not far off.

What is hard fact is that salmon are fast movers. When they do reach rivers they can travel incredible distances in a day’s journey, proven by the presence on them of sea lice. These are saltwater parasites which can only remain attached in freshwater for up to two days. Sea-liced salmon have been found thirty miles up rivers, and more. Fresh from the marine, Atlantic salmon are true Formula One fish, as some sparkling-eyed anglers have cause to know.

They do not, though, just arrive at the mouth of their natal river and motor into it. They savour the moment of transition, whilst making a vital physical adaptation to their water-balance mechanism. In the sea a salmon has to cope with water that is chemically stronger than its own body tissue, making it lose its body liquids. To compensate, a salmon at sea actually drinks seawater, which then passes through its stomach and intestine. Its kidneys expel small amounts of the salt in concentrated urine, conserving some of the swallowed water to make up for the liquid losses.

In his 2009 treasure-trove about the Atlantic salmon, To Sea and Back, Richard Shelton refers mischievously to the ‘uriniferous’ smell of farmed salmon: he has sound physiological reasons to do so! So many fish excreting powerful body wastes in a basin of seawater, only lightly refreshed by the average tides, might well produce some fairly rank odours and taint the aroma of the imprisoned inhabitants.

Entering the milder environment of freshwater a salmon finds its fluids more concentrated, not less, than those of its surroundings. It starts to absorb water through the permeable linings of its mouth and gills. The excess is filtered as dilute urine through the kidneys. So fresh and salt water are quite different environments. Salmon biology has the sophistication to occupy both.

Sometimes for weeks the fish pregnant with breeding preoccupations ride the tides near the river-mouth, tasting the fresh water debouching from the estuary, sampling it, experiencing the reawakening of chemical memories from long ago when they were fish only inches long. The expectant river-runners can be spied from the cliffs above estuary mouths drifting on the tide, maybe fleeing a hungry seal.

The year 2011 was dry for a while in midsummer in Scotland when I was sailing with the life-boat crew along the coast of east Sutherland. On a bright day in a calm sea we approached the River Helmsdale where the boat was to tie up. There, offshore, were leaping salmon, throwing themselves into the air. Those who see this often say they do it prior to entering the river, usually when a freshet of rain has gushed into the sea, bringing oxygen and water particles to their sensory receptors, stirring fusty recollections. Then, often waiting for the moon, they hitch a lift in like any surf-rider, selecting the highest tides.

Just as salmon unerringly follow the shelf-edge off Norway, so they unerringly seem to know what lies up rivers in the hinterland. If a river has lochs and lakes feeding it, salmon swim it earlier, for they can progress to a safe haven up ahead in the expanse of the loch. Scotland’s west coast has what are called ‘spate’ rivers, because they are shorter than eastern rivers, and salmon generally run into them during or after rain when water levels are higher. These fish know there is often no sanctuary or a loch; their only refuge is a deep pool, and it might already contain other occupants. On the River Helmsdale we know from the presence of sea lice on fish caught by anglers that many salmon run straight through the 24-mile system and forge on through the fish-pass into the chain of lochs at the top where they can safely bide their time until autumn spawning.

The river system made in heaven is perhaps the one with big headwater lochs providing a sanctuary for the salmon and an inducement to run the river to get to it, thereby presenting anglers with chances of an encounter. Even better, possibly, would be the system with a big loch in the middle, with salmon filtering into it from below and out of it from above, the loch also acting as a natural regulator of water levels.

Sometimes forgotten are landlocked salmon. They lack the mystique of the ocean rover, and they do not leap waterfalls to remind us of their grace and power. More importantly they do not have to worry about smolt losses to cetaceans, Russian trawlermen or any other conventional threat. Pike with backwards-curving teeth might be their toughest adversary. In addition they need none of the adaptive mutations for moving between saltwater and fresh.

The lines are not hard and fast. In anadromous salmon populations some parr never leave their rivers and behave as landlocked salmon, awaiting the return of gravid hen salmon for their sneaky off-chance at fertilising the next generation.

Perhaps it should not be surprising that populations of landlocked salmon comfortably survive today. In Norwegian, Swedish and Russian lakes there are landlocked salmon as well as in North American ones. These northerly receptacles of cold water never heat up too much for salmon’s tolerance. Landlocked salmon could be compared to brown trout, happy not to migrate whilst some of their siblings run the gamut of the wilds to become sea trout.

Norway’s huge Namsen River has a majestic and impassable waterfall. Whilst I was watching its awesome power and letting the physical reality of the cascading torrent sink in, the droll ghillie told me that only the week before a visitor angler playing a feisty salmon from a downstream-drifting boat above the fall had failed in his battle-concentration to notice the advancing roar of the crashing water. He went backwards over the top, attached with his fishing line to the fish of a lifetime, and was never seen again. The story was relayed with barely suppressed ghoulish relish. Did he get his kicks telling that story every week? At any rate, above the Aunfoss waterfall subsist the resident salmon which never migrate, cut off by a giant curtain of cascading water.

Landlocked salmon are not uncommon in North America. In Idaho I have seen the scarlet kokanee, which are Pacific-origin coho salmon, and I found the sight somehow disturbing. Here are these small shoals of highly coloured fish in the translucent shallow waters of rivers and lakes, looking nervous and wary. You sense they are trapped, freakish prisoners, despite their presence having been determined by ancient geology. Really, they are true and admirable survivors, but it does not feel like that. And their chromatic violence in the drab landscape adds to a sense of displacement.

In Lake Ontario the early settlers found landlocked salmon weighing up to forty pounds. So much for the sea only being able to build up weight; pike disprove that and the lake salmon underlined it. These monsters, however, are now gone. In Maine the landlubbers are called ‘sebago’, being the name of lake in which they were first identified, and in other Maine lakes there are different varieties of salmon non-migrants.

To an angler a salmon is in its natural place in a river. That is where an encounter can occur. A river is the proper mis-en-scene for connection with the fish by a wispy length of nylon on a bendy stick, and a hook maybe no bigger than a gnat. What salmon do in rivers is a subject upon which fishermen have ventured opinion in a veritable lexicon of viewpoints. Seldom has so much speculation been focused on one inhabitant of our environment. How many shelves could you fill with the books which have celebrated the mysteries and majesties of moles, rabbits or hedgehogs?

Long ago debate centred on whether salmon eat in rivers. It seemed impossible that a large creature could enter a river a year before undertaking the rigours of spawning and live off its reserves. Anyway, why did they take fishing flies if they were not eating?

Peter Malloch, as Scotland’s Inspector of Fisheries, seemed to have nailed the matter way back. He and his team eviscerated thousands of salmon. They never found anything in the stomachs, no matter how long the fish had been in the river. Even if, as happens in a few places, salmon over-winter in a river and do not spawn till late the following year, they still do not feed. It is a stupendous fast. However, it failed to stop many subsequent armchair theorists raising spectres and postulating that salmon must eat, that sundry reasons existed for their stomachs being empty, that what was evident knowledge was as full of holes as a colander. The fact, amazing as it is, remains: salmon cease feeding in freshwater. Like snakes, which can live for months, even years, without eating, salmon subsist on their stored marine reserves. If they open their mouths to seize fishing flies in rivers, fishermen may claim they have been artful enough to override behavioural rules; angler achievement is all the greater. Not quite as great, though, as the biology of their quarry.

An area for debate between anglers and salmon professionals is whether the leaping salmon is moving upriver or not. So many times ghillies and anglers talk of ‘fish running’, meaning they are ascending the ladder of the river-system. But if you watch salmon from under a river at their level, as is possible in the riverbed salmon museum on Sweden’s River Mörrum, you see that jumping salmon may move slightly forwards from where they took off but they drift downwards as they descend in the water-column, landing back on the launch pad. Salmon maintain their station more than some of their aerial antics would suggest.

Whereas anglers believe that salmon are running past them, and sometimes try to hasten upriver and get ahead of them, river counters using electronic beams show that salmon ‘run’ mostly at night. Summertime salmon almost invariably use the cloak of darkness to hide their journey. Some counters work with parallel sets of beams, interrupted beams signifying a fish swimming upriver. Counters can be calibrated so that only fish of a certain size register, excluding smaller ones and trout.

In Canada counting salmon in clear-water rivers can be unfussy: I have seen a wide placid river where the flow is channelled into a central funnel and a human counter perched on the platform end working a clicker to record every fish passing. These wilderness workers, operating in rotations, need good bug dope, a wide-awake buddy checking for bears tiptoeing down the platform, and extraordinary concentration. Happily the runs are often focused into just a few weeks, and, pressed for time, they move in the day.

More usual aids are military-type night-sights, which, focused against a light background, make salmon watchable as they swim upstream. Most of those fish leaping under the noses of anglers are not moving upriver but performing their acrobatics for other inscrutable reasons. Nineteenth-century writer William Scrope charmingly referred to them leaping because of ‘excitement’.

Again, anglers talk of fish running in spates. They actually wait until the debris and clouds of suspended particles have ebbed and abated and then they run, in the cleaner flow. It is dangerous for salmon to get muck in their gills, and as birds constantly preen their feathers for efficient propulsion so salmon look after the efficiency of their highly tuned bodies. One or two days after the flood-crest is a likely running time – and they are slower to chase a melting snow spate than a rain-driven spate.

Where anglers are spot-on is in the commonplace assumption that salmon get interested in fishing flies after they have moved position. A salmon that has dwelt in one place for a month may have watched innumerable flies swinging over it and pays them no greater attention than the man on the park bench does who subconsciously watches buses looping their circuit. The same fish having shifted station will be activated and lunge at the fly, maybe attempting to purify its new location of annoying irritants.

Tagging has shown that salmon often enter a river, stay a while, and then leave it. During a long summer salmon may climb rivers, fall back to brackish estuaries, wait for another oxygen-rich freshet to stimulate a move upstream again, and then repeat the yo-yo procedure. Although Atlantic salmon are renowned for their generally faithful return not only to the river of origin but to the section of river from where they broke out of the egg, they can mess with the rules too.

A salmon has been tracked tasting the water on Scotland’s west coast for a while, then moving to an east-coast river, and finally ascending the third river it had trialled in one year, where it spawned. This ranks as an extreme example of genetic straying. A salmon tagged on the Dee in Wales was re-captured in Denmark. I am unsure whether a salmon tagged in Europe has ever spawned in North America; reports vary, but betting against salmon’s versatility and survivor-adherence would be a mistake.

I was on Russia’s Kola Peninsular on a river called the Kharlovka in low-water/high-temperature conditions when it appeared to the anglers and the ghillies that the fish actually left the river, retreating to the refreshment and oxygen of the open sea. We could see them driving downriver. At this point the sea was only a mile or two distant. There would be a good enough reason: when wild salmon are closely confined fungal diseases spread fast. They can spread even faster amongst fish in low water and even disfigure a whole river population. Saltwater does the laundry.

Salmon fungus comes in more than one type, and can keep growing on fish that are already dead. The fungus is an external manifestation of a fast-spreading microbe. It is normal even in ordinary seasons to find pre-spawning salmon with white fungus starting on their heads and backs, and when spawning is done these mouldy discolorations accelerate to be abrupted only when the fish is cleansed by saltwater. Warm, low-water river conditions make matters worse.

Managers report that this occurred on the Tweed in Scotland late in 2011. It was not the potentially lethal condition called ulcerative dermal necrosis (UDN), in which lesions can penetrate into skeletal tissue, rather, as assessed by the river biologists, a more common fungal affliction broadly termed Saprolengia, caused by overcrowding.

The last time fungal diseases killed huge numbers of pre-spawners in Scotland was in the 1960s, when runs were prodigious. I remember walking down to look at the water in August with my grandmother, a dedicated angler who went to the river as others go to their office. White lethargic salmon with rot peeling from them cruised aimlessly in shallow water. I recall her sombre mood. Some see fungal outbreaks on a major scale as a response to over-population, and this distressing scene did indeed coincide with a heavy run of fish. Widespread fungal attack has not recurred on this river since.

Fishermen are the best monitors of a river-system. Their observations and speculations about this fish serve the species well. What salmon do in rivers will probably preoccupy anglers for as long as they persist in trying to catch the fish in what might be seen as an elaborate manner. Easiest perhaps then, sifting the options for evidence, to watch salmon in rivers.

I remember meeting a German salmon angler in Ireland long ago who had adopted a rigidly logical Teutonic approach to his fishing. Having showed me a rack of twenty-foot rigid poles, he asked what I thought he did when he went fishing. As if it was the most obvious thing in the world, he cried, ‘I climb a tree!’ When sun shone on the pool he was to be located hanging out of his tree wearing polaroids. From above, the river was like glass. For this Germanic genius it was self-evident that to cast into a river in the hope of catching a fish you did not know was there amounted to a bizarre and undignified expenditure of energy. So he looked down from aloft and spied, from his vantage points along the River Blackwater, whether any salmon were available for the catching.

He then drifted flies, of his own special construction, of course, over the noses of the targeted fish until they lost patience and snapped. Invariably, he assured me, they all eventually break, irritated to a frenzy, like a person with a spider crawling on his face. The idiosyncratic sportsman claimed to have caught numerous fish in this manner. He said snapping-time was always inside three-quarters of an hour.

Thinking on it, catching them on those rigid poles must have made it a mechanical exercise, lacking in the intimacy of galvanic contact. But there was the hunter satisfaction, I suppose, of having behaved in an impeccably rational manner.

I recall a scene one summer on the Saint-Jean River in Quebec where the water is pellucidly clear. I was walking down the river-bank when I came across an angler lying atop a small bush with his hat tilted over his eyes. Striking up a conversation it transpired he was waiting for ‘his’ fish and the right moment. I pressed him more and he showed me the fish, which I took a while to detect. Stretching far out in front was a rippled pavement of smooth, light-coloured rock. The water looked shallow, maybe three feet deep. Eventually I spotted, nestled into what was no more than a groove, a very large salmon, its back beautifully camouflaged in the ochre tones of the undulating river floor. The angler said he had tried his fish earlier in the day with the sun just rising. The fish had moved and moved again often but never opened its mouth. The next suitable moment would be as the sun disappeared over the canyon side. The angler had six hours to go. He seemed unruffled at the prospect, and sure the fish would succumb. He intended drifting his fly down from some distance above to give the big fish time to see it, and then letting it slide over his nose closer and closer, till … the chapter was written in his mind before it had even taken place.

The interesting time for salmon-watching is late summer when numbers are building for the orgy of spawning. Upstream of the river-bridge to my home is the entrance to a tributary. Salmon gather below the bridge for the shade, perhaps, but also to wait for the right moment to run the tributary and spawn there. The place where they accumulate looks the same as the rest of the river-bed, a trifle deeper maybe, stones studding the sandy bottom. They have stations, places they like to be. These are not, as is often loosely said, ‘behind’ rocks, rather to the side or below. There they rest, pointing upstream, close to the bottom, occasional bubbles emerging lazily from their mouths, like giveaway wisps of smoke from rainforest tribes.

In the protection of this shady place at a certain point in the autumn the salmon numbers stack up in a diamond formation. To start with, a few just take positions here and there, but as spawning approaches they tighten into a formation. As the days pass and no rain raises water levels, the space they are occupying shrinks and gets cramped with more fish still arriving. It is like a rail terminus with no trains leaving. The water lacks the refreshment of oxygen. I have seen the mass of salmon get edgy and impatient; they start to jostle and swirl at each other. There is a palpable build-up of nervous tension.

One time this was dramatised in a remarkable way. Above the bridge swam a pair of mergansers, paddling on the side of the river. Like a torpedo in an old war movie, a large fish suddenly charged the two sawbills. He launched himself from at least 60 feet and, missile-like, broke the surface enough to create a bow-wave. The mergansers, sensing something at the last moment, rose in a panic of clattering wings and flew fast away.

Well, salmon do not in theory attack birds, but the fact is that mergansers are major predators of salmon eggs, a difficult enemy for the progenitors because the sawbills get their necks and beaks under the water and then shovel through the redds removing the buried caviar. Salmon hide the eggs in their redds and assume they are safe until the little alevins wiggle out in warming springtime sunshine; they cannot remain on duty to stand guard. I have seen a merganser in Canada surfacing from redd-raiding with salmon eggs cascading down its chest. I believe that cock salmon recognised in the merganser pair, with their elongated predator shape and thin heads, a predator enemy. It was a bird-fish interaction I will never see twice.

Prior to rain, the petulant salmon under the bridge are all moving and all disturbed. They squirt forward and drift back, they nudge other salmon, their tails swish and they shift position. Rain falls. I wait for the right conditions to see under the bridge again, despite it being harder with higher water. One time I had counted around 150 salmon in diamond-formation then, following rain, the river-bed where they had been was denuded of every one. The breeding pack had moved on to the final stage: the upper tributaries and the redds.

I was taught by an old fishing ghillie how to read water at this point in the salmon chapter and to detect the presence of a river’s spawners from water movement. It is an art. You walk upstream from below, although from above is possible too. The spawners are in certain types of places, at least where I view them they are. They occupy the fast water beside and behind the bigger stones – they like active water with energy. To start with they are not in the fastest riffly current, which is shallow, but in the channels by big rocks. From below you see not the fish but the bulge in the water above where they lie. Their bodies are never long still, so the water has a thicker, darker look. Momentarily they move and a fin-edge shows. Then the fin of the partner fish, close by. If you walk up the bank opposite to the fish you can watch the pair of them. Only if you wade into the water do they swim off. It is not like in the fishing season; these creatures have a special matter on their minds, nothing less than their definitive act. As spawning time approaches they move into the faster riffles.

In Canadian fishing huts and fishing lodges and airports near fishing rivers, one man’s quotations often adorn the public spaces. They are the words of Roderick Haig-Brown, a judge in his day and resident on the banks of the Campbell River on Vancouver Island. In his book Return To The River he describes the drama on a spawning redd of a female Chinook salmon, a stupendously big fish for the little rivers it breeds in.

No one who has read Haig-Brown’s account will feel brave enough to attempt their own description. His spare, detailed and probing simple language turns the enactment of egg-release into a pageant of wildlife drama. He describes the hen’s convulsing flanks as she releases eggs, redd-digging with fierce sweeps of her mighty tail, the water current helping the process. Then the arrival of the cock squirting his cloudy milt over the egg pile, the competing immature Chinook rushing in to have his go at contributing to procreation, prior to the whole nest being rapidly covered with pebbles in protection from the throng of potential predators needing just such a feast of fresh protein before the onset of north Canadian winter rigour.

At last he describes her dying, being eaten alive by rot, the fungus which softens and breaks down the flesh. Our heroine mother is left disintegrating on the stones. But, critically in Nature’s cycle, her dismembering body flakes feed vital protein to young fish and her distant successors. It is noble writing, and gripping. In stately style he takes longer over some passages of this enactment than the real-life duration.

To watch salmon spawning is an elevating experience available to anyone living in salmon country anywhere. Yet we are glued to wildlife films for their perfecting, high-tech, laboratory touching-up, editing and enhancing. Nothing can give you the smell of the real-life river at spawning, the proximity, and the clarity.

Usually between sundown and midnight, working upstream, the hen turns on her side and scoops a depression in a sandy and gravelly substratum, laying eggs all the while in a steady outpouring. The eggs remain fertile for only one minute, so contenders vie to fertilise them, squirting their cloudy milt. Action is furious. The redds are then covered over with the same stone-shovelling to a depth of up to a foot.

I saw this process one time on a gravel-bar below my house late in November after most fish had spawned. The salmon were same-sized, around 35 pounds. I had recently handled some big salmon and although fish of this size are seldom seen in the River Helmsdale, that was the class of fish I was watching. She lay just in front of him, but instead of a vigorous and exhausting performance these two were in languorous mode. They were so large that no grilse, parr or other contenders were visibly around. Their backs were clear of the water, and the two giants seemed just to nudge each other on the redd. I had two of my children with me and, riding piggy-back, they could see it all from a better height only a few yards across the stream. I almost felt like going away out of politeness.

Enquiring later about the presence of such leviathans, a retired fishery bailiff told me he had long known about these very big salmon. They entered this river after angling had finished, often not till November, and stayed only long enough to spawn. He reckoned they were usually no more than a fortnight in fresh water.

The salmon eggs are clustered in the redds until they hatch, safe from most eventualities except major flooding when rolling rock could smash their soft mounds and disperse the egg collection for consumption by all and sundry. For there are few denizens of salmon headwaters for whom fresh eggs are not a welcome dietary enhancement. Unlucky clutches too near the surface can be frozen solid on gravel-bars exposed to hard frost which has driven down water levels. Redds are safe if there is stability in the river system until they hatch in the spring.

The actors in the conception drama have changed their costumes to participate. Both sexes’ noses become extended. If he were a medieval knight trying to unnerve his jousting opponent, the features the cock salmon arraigns himself in might fit the bill. He grows a lower-jaw projection in the form of a solid gristle hook which curves up, sometimes actually piercing the cartilage of his upper mouth, which itself arches, pre-spawning, to accommodate it. The knob has a name, the ‘kype’, but its purpose is uncertain. Salmon fishery managers have seen cock salmon thrash their heads at male parr trying to get near the females on the redds, but a knob this solid is hardly needed for that. As big cocks charge and chase each other the kype may be a proboscis for belabouring rivals. When the cock reassembles his hormones after spawning and drifts downriver as a kelt, the kype in sympathy shrinks too, till only the familiar small hook is left. Unless this happened he could never resume feeding.

The cock’s head attains super-gothic ferocity, being elongated for the spawning by three or four inches, and his skin blackens. At the finale he hardly looks like a fish at all.

When at our local hatchery we had schoolchildren on an afternoon out acquainting themselves with the species for the first time, I remember a fishery bailiff hauling a cock salmon from a deep holding tank and the wide-eyed, disgusting-looking monster squirming from side to side, eliciting a gasp of horror from the young onlookers who jumped backwards. They may have seen some X-rated movies, but this was something else.

Normally, after 50–110 days, the incubation extending to eight months in the colder Arctic, the salmon eggs break forth as tadpole-like creatures, carting as an underbelly appendage the vital egg sac. This bulging picnic is for consumption on the next stage of the pilgrimage, before they can start feeding from the outer world for themselves. As the little jelly-like creature, with its sharp, black, instantly functioning eyes expands, the picnic shrinks, and after six to eight weeks has been completely absorbed. From that time, life support is externally supplied – or existence ends.

Fry, as they are called, eat tiny crustaceans, insect larvae, nymphs and phytoplankton – a variety of miniature organisms that flourish in stream sunlight. They subsist on their hunting skills, which are rapidly developed. In summer heat food multiplies and in winter it shrinks till it disappears, their growth mirroring food availability. The further they range from the safety of shade and cover, the higher the risk of ending up in the stomach of a trout, heron, kingfisher, cormorant, or other assailant. In the fecund backwaters of Scotland’s Aberdeenshire River Deveron, where the water is clear and glassy, I have seen thousands of fry massed in corners. The fugitive instincts they need in later life are in evidence early and they move like lightning, even from passing shadows.

The parr stage is marked when they reach a couple of inches. Parr have snub noses, brownish backs, some black spotting, and a few red spots near the lateral line. This line is their nerve system, the strung-out headquarters where their sensory faculties are assembled. Parr have an easy signature in several dark bands running vertically up and down the body, no sign of which survives beyond this stage of their existence. The barring accounts for the term sometimes used to describe them: ‘fingerlings’.

Anglers know them as the energetic little fellows that can seize a fly, sometimes almost of their own size, equally in fast riffles or at the tail of the pool in torpid backwaters. We dislike holding them for fear our hands are too hot, so we customarily let them wiggle free from the hook, holding them near the surface to skip off as they hit water.

Just as seagulls are a sign of worms being turned by the plough, so mergansers are a sign of parr shoals. On the famed Restigouche River in New Brunswick, where some of the largest Atlantic salmon abide, flocks of mergansers number hundreds. They fly in menacing sinister squadrons up and down the fish-rich river, making a commotion when they all settle. In the Fifties it was found on the nearby Miramichi River that 86 per cent of the local mergansers ate parr to the tune of over a million each annually! It almost defies belief, but tests elsewhere replicate a gargantuan consumption rate. Mergansers can decimate a salmon population, faster when the water is low. Restigouche kingfishers target parr too and in times past the fishery owners painstakingly shot both mergansers and kingfishers as part of routine salmon protection.

It is perhaps one of the oddest adaptations of Atlantic salmon that some of these miniature parr can be sexually mature. As we have seen, they are capable of fertilising big hen salmon on the redds, nipping in as the cocks pause and ejecting their little sprays of milt over them. Looked at from an evolutionary point of view it completes a portrait of salmon’s variable ways of circumventing catastrophe. If all the cock fish in the sea were boiled in the lava outflow of an erupting volcano (to take a fantastic scenario), then the female fish reaching home would not be reproductively marooned. That little barred parr would be waiting, successful fugitive from kingfishers, to secure the future of one more generation of fine salmon.

Parr feed on the full range of titbits that the meagre headwaters of salmon rivers have to offer. Mayflies, stoneflies, other insects and insect larvae, worms and mussels – most things moving and many unmoving contribute to diet. Vulnerable to acidification and very low levels of pH, to chemical discharges from agricultural crops like silage, concentrated effluents, mining tailings, high aluminium and heavy metals, wood dust, oils and the like, parr need clear water and flowing streams. A simple-sounding requirement, but in a land-hungry world clean water is not such a common commodity. As they prepare to ‘smoltify’, their tails lengthen and the forks in them deepen, their fins grow, the scales soften, and they turn silvery. The great odyssey in the ocean is about to commence.

It is a matter of wonder that such small creatures can be destined to go so far. When birds migrate, they are of a similar size to their progenitors. When flounders and shad and lampreys shift in and out of the salt water on the tides they cover measurable distance on a manageable scale. Other mammal migrants travel in families and herds, adults protecting young. Caribou and elephants and migrating African antelope shepherd their young, fending off predators on their behalf. But these small salmon are unaccompanied minors, with a threat-filled odyssey ahead. On the trip they rub shoulders with whales, they are tossed and turned in the ocean’s systems, upwellings and currents and still they adhere to their programmed track. SALSEA identifies the routes and genetic families of some of the journeymen.

When common eels leave the Sargasso as elvers they allow the prevailing winds and currents to push them across the Atlantic towards freshwater lakes. The journey can take years, but the fish are essentially passive. It is the determinism of the young salmon that amazes. Predestined to reach a feeding ground, whether in the North Sea as grilse, or on the Greenland Shelf and north-east Atlantic as multi-sea-winter salmon, they are on a mission, bent on their assignation with copious krill and capelin and other nutritious sweetmeats. The whole challenge is formidable in the extreme.