LIFE FINDS A WAY

Come hell or high water, a salmon’s instinct to swim upstream to spawn is redoubtable

Salmon will make their way upstream to spawn come hell or high water

Thoughts linger on the recent spawning. Did pairs assemble and cut redds as usual? Were those redds swilled loose by subsequent floods? How many mergansers slid their grooved beaks into the egg troughs, emptying out the future generation of salmon?

In the north Highlands, November was wet. Local weathermen said there was intermittent rain for 75 days, but there were no huge spates. To the frustrated salmon observer, spawning was occurring but there was nothing to see. The water was never low and clear.

Some years, you can go out at night and spotlight pairs of salmon which remain undisturbed by the glare, gently finning alongside each other, facing the flow in a dream of procreation we can only guess at. After spawning they drop back, still facing the flow, but dispersing when the light falls on them, scurrying for the cover of the oceans. This year showed something new: flocks of ravens scavenged on spent salmon.

Chewed and half-eaten kelts are a common sight, even empty salmon skins. Usually, we attribute them to otters packing on winter fat. Ingenious ravens, gorging on the grallochs of this winter’s ramped-up cull of red deer hinds, seem to have learnt how to tug spent salmon from the backwaters onto the banks or steal from blackbacked gulls. A salmon is a protein feast.

People talk of redds being washed out. This is when floods sweep the gravel floor, dispersing the egg-packed salmon nests.

Certainly, if ice scours the bars and gravel banks, it is hard to imagine recently-scooped and therefore loose egg nests withstanding the force. Eggs are littered down the river and preyed on by fish and fowl. Extreme floods and ice scour leave disturbing question marks.

Six seasons ago the upper tributaries, instead of permanently surging with water, emptied out. There was no October or November rain. Slowly the upper catchments dried down to trickles.

The egg-packed female salmon fell back with the water. One or two tried to tough it out upstream, but then got caught out and marooned in draining backwaters and side pools. I found one or two desperately spanking the half-frozen water to try and flip themselves into the remnant stream.

Spawning that year took place in the main river, which churned with spawners unused to being cramped, instinct-driven to go higher up, yet unable to.

It’s a curious thought but a river needs severe weather. It suits fish to have fresh gravel deposits. The stones are looser and not embedded. A pavement of smooth, large stones is no use for spawners. They need mobile substrate, which they can sweep with their tails.

One effect of the permanent high water in autumn and fish pioneering t he higher tributaries is to alter the official concept of ‘impassable falls’. It is a fact that given enough water cascading down, salmon can climb obstacles which normally look insurmountable.

What is impassable most years becomes a fluid escalator. Above lies new gravel, which can be colonised by breeders. Only the presence later of salmon and sea trout carcases high on the moors attests to the energy of the spawning instinct and the urge to go up and up to the food-rich mountain streams.

When electro-fishing the tributaries in the following summer, you would expect to find the salmon and sea trout fries, which were actually born in the main river stem, to be absent. Precisely this occurred. Older parr were there, but not the nursery fish.

A year later, though, the next generation of questing parr, now stronger, had forged upstream to new territory. Every age class was present. Nature abhors a vacuum.

Most of salmon freshwater life is a mystery. We are free to hypothesise. Just sometimes we catch a glimpse of what the real drivers are. All our curiosity is not then in vain.

‘It’s a curious thought but a river needs severe weather’