Mike Dilger’s wildlife spectacles
The broadcaster, naturalist and tour guide shares the most breathtaking seasonal events in Britain
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SPAWNING SALMON
Get settled by the water’s edge and marvel at fish bravely leaping homewards to reproduce
WITH FISHING TOPPING THE POLL of Britain’s most popular outdoor pastime, it is somewhat surprising that the fine art of fish-watching appears so far down the pecking order, when compared to birdwatching. But on a few key days spread across October and November, Atlantic salmon are capable of putting on a display that measures up to any performance our feathered friends are able to muster.
“Bottlenecks such as rapids and waterfalls are the best places from which to watch salmon leaping ”
The spectacle of salmon leaping up their natal river can be traced back to a previous autumn when they started their lives as pea-sized eggs laid by their mothers in gravelly riverbeds. In April or May, they hatch as ‘alevins’ before becoming fry and feeding on aquatic invertebrates. The minority that are not picked off by predators will then steadily develop into larger ‘parr’ with distinctively patterned flanks. Depending on water temperature and food availability, they might spend several years in the river system before a silvery sheen replaces the parr marks and they undergo a physiological change in preparation for saltwater.
Now called smolts, the fish will begin swimming downstream with the current as they head for the sea. Anywhere between 15 and 50 months will be spent feeding in rich deep-sea waters on a diet of crustaceans, post-larval sandeels and small fish. While food is plentiful for the maturing salmon, there are also many predators, such as sharks, seals, dolphins and humans, meaning only about 10 per cent of the smolts that initially leave the rivers will ever be able to return back to freshwater.
How they pilot back is still unclear, but it’s thought they use a combination of the Earth’s magnetic field and knowledge of ocean currents. Arriving at the coast, they probably locate their natal river by recalling a ‘chemical memory’ imprinted as smolts. Upon entering the estuaries, another transformation occurs when the breeding ‘tartan’ is developed. The females, called hens, become much darker, with a rainbow colouration along their flanks, while the males, otherwise known as cocks, develop red bellies, streaky flanks and a large hook, called a kype, that protrudes outwards and upwards from their lower jaw.
“Over 90 per cent frequently die once the eggs have been laid and fertilised”
Relying solely on the reserves put down at sea, the salmon are made up of rippling muscle and use their strength and agility to power up the river. The movement of the fish tends to be dictated by rainfall, with a higher flow rate actually making it easier to work their way past a variety of obstacles en route to their spawning grounds.
Justifiably famed for their leaping abilities, the height they are able to jump depends on the ‘run-up’ the plunge-pool at the base of any waterfall allows for. Driving up from the river bottom into the air, the aim is to jump over any watery obstruction, with a leap of over 3m not uncommon. Dropping back into the water the other side, they propel themselves forward against both the current and gravity with vigorous contractions of their tail. Many leaps seem to end in heroic failure as fish are thrown back into the ‘washing machine’ down below, but the majority usually end up passing the obstacle – particularly when water levels are higher.
The spawning process further upriver can be so exhausting that over 90 per cent frequently die once the eggs have been laid and fertilised. Although a few post-spawning salmon, called kelts, do seem capable of returning to the sea and spawning again in future years.
To see salmon leaping, bottlenecks such as rapids and waterfalls are undoubtedly the best place from which to watch, with early mornings and late afternoons being when the fish are most active, as well as after heavy rainfall. A good vantage point is ideal, and once you’ve identified where salmon are leaping you can then move closer for a better view. So why not swim against the current of popular opinion yourself, by catching what is surely one of our most underrated wildlife spectacles?
Did you know?
It takes several days for the hatched alevins to eat their yolk sac and become fry (above) – at which point they leave the gravel beds
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Join the queue
Before negotiating waterfalls, salmon will often wait in the relatively calm waters of the plunge pool below. To see the action, why not try using either an aquascope or an underwater camera? However, please do be careful on the wet, slippery banks and rocks at the water’s edge.
Fish supper
All manner of predators will eat salmon parr in rivers, such as goosander, grey heron, kingfisher and mink, but the only animal capable of taking on a mature salmon swimming upriver to spawn will be an otter. Look out for their distinct spraint piles – smelling of jasmine tea!
Cocks and hens
In the shallow spawning stretches upriver, you may be able to see the hen salmon digging a series of shallow depressions, called redds, in the gravel. Any eggs subsequently deposited will then be by fertilised by an attendant cock salmon who has successfully fought off the opposition.
NEXT MONTH
Mike highlights the fascinating spectacle of whiffling geese