The Salmon: The Extraordinary Story of the King of Fish. Michael Wigan

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      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 СКАЧАТЬ