The Salmon: The Extraordinary Story of the King of Fish

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.