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