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

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СКАЧАТЬ 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 СКАЧАТЬ