Friday 30 November 2012

Where are they?

The answer to the question rests on some basic understandings.  The behaviour of salmon in rivers is directly linked to the fact that they are genetically hard-wired to complete their life-mission to reproduce.  From the time the salmon enters fresh water, everything it does is focused on the successful completion of that objective, which above all requires it to survive.  The greatest risk is exhaustion leading to death.  Consequently the salmon’s survival rests on the preservation of the extraordinary but finite stock of energy stored in its cells (primarily the flank walls), which is being heavily depleted by the internal creation of eggs or milt. About 80% of the mass of a mature salmon is muscle: by the end of the spawning cycle 25-30% of its body weight will have gone, which equates to 40% of its muscle mass.  Energy conservation is especially pronounced in hen fish, but less so in cocks, owing to the effects of testosterone on their behaviour (I’ll write about this in a future post).  This is why a higher proportion of hens than cocks survive spawning.

Obstacle - Canadian scale

In British rivers comparatively little of that muscle loss is attributable to the effort of swimming upstream.  First, because the salmon’s basic design is so efficient, its power so great and its reserves of stored convertible muscle energy so huge.  On the eastern seaboard of Canada it ascends rivers 3-5 times longer than any in Britain, and surmounts correspondingly bigger obstacles.  The longest salmon run on the West coast is over 1,000 Km.

Given the right water level and temperature, salmon can tackle most rivers in Britain with ease.  In the absence of major obstacles they can cruise at 3 mph for long periods.  Second, salmon are highly efficient swimmers, always following the line of least resistance whilst running upstream in order to conserve energy.  In a strong current this will be close to the bottom where the effect of flow friction is greatest and the water is moving much more slowly than in the upper layers.  I have unpleasant boyhood memories of standing waist deep without the benefit of waders in the freezing River Brathay in Cumbria on an A level geography field trip measuring current profiles.  At last the knowledge gained has proved useful to enhance standing waist deep in a freezing cold Scottish river.
Salmon will stop and rest for a host of different reasons, and for varying periods.  In thinking about resting it is essential to bear in mind that they do not come into the estuary, then at the first sniff of fresh water engage third gear and drive upstream at 3 mph all the way to the spawning redd.  Studies of GPS and RF tagged salmon have shown some remarkably erratic behaviour and movement both up and down rivers.  For example, by the early autumn there are fish spread along the entire 100 mile length of the Tweed system from Berwick to Moffat.  Some of them have progressed little more than 10 miles in the 6 months since they entered the river, whilst others have run 75 miles in 3 days.    One GPS-tagged fish went up and down the Tyne 3 times before running the full length of the North Tyne to spawn (no Geordie jokes please).  In common with so much else to do with salmon behaviour, no one knows why.  But it is during their rests, however long or short, that salmon and fly are most likely to coincide.
For this blog generalisation will suffice.  I think there are 3 broad types of rest.
·         Long term residential – I shall stay here until the urge moves me upstream, which may not be for months.  I will park in a comfortable spot, switch off and go into suspended animation to conserve my energy and grow my eggs in peace.  We’ve all seen fish like this – often large hens – and no matter hard we try, we rarely if ever catch one.  Certainly I never have.
·         Mid term waiting – I want to move on, but there’s not enough water.  These fish seem to switch off, but wake up periodically, become active and sometimes get caught.  Their active periods seem to be in common with other fish in the same pool, often at similar times of day.  We don’t know what causes these periodic flurries of activity.
·         Short halt – I want to gather my breath; or check out what lies ahead; or prepare myself to tackle an obstacle.  The places where these fish halt are easily identifiable in the head, middle and tail of a pool.   The running fish are alert, active and thus eminently catchable, because I have caught far more of this category than all the others combined.  In part this may be helped by the tendency of salmon to accumulate in these short halt lies in substantial numbers.  On the Findhorn I once saw a dozen running fish in a lie no more than a metre square taking a short halt before going up some shallow fast water.

11 pounder taken from short halt lie
River Findhorn September 2011
    The picture shows an 11 pounder taken with a Cascade conehead tube and fast sink tip in the Garden Pool of the Tomatin House water of the Findhorn.  It was taken from the short halt lie identifiable from the 'standing wave' in the mid stream just to the left of my head.  The water there is about 5-6' deep.  The obstacle of shallow water is about 50 metres upstream out of shot to the right.  Such 'standing waves' form when the river is up where collections of boulders drive the flow up to the surface.

In all cases what the salmon wants is a lie that is safe; provides a good supply of oxygen (which requires a steady flow of water through the gills); and conserves their energy by allowing them to hold their position with the minimum of effort.  The dominant factor is surviving to breed, which overrides everything else.
The salmon’s notions of safe are conditioned by the accumulated survival experience of the whole species, not the individual.  After several hundred thousand generations there is a lot of survival-based evolution hard-wired into salmon DNA.  They don’t like shallow water, because as parr they were vulnerable to herons and other avian predators.  Comfort starts at depths of around 75 cm/30 in, so don’t bother with fishing anything much shallower than that.  They don’t like too much free space below or behind them, because that is direction from which otters and mink attack, so reckon on them being at or near the bottom.  Pike and cannibal trout lurk in shady spots in slow water, so don’t bother to fish there.  Putting all those bits together gives us a pretty good idea where a salmon may lie, and as importantly, where it won’t.  There’s no point wasting your precious week casting to water a salmon considers dangerous.  It also tells us, for any given lie, how deep we have to fish the fly to get it close enough to an energy-conserving salmon to have a chance of stimulating it to take.  I’ve never caught a fish with a floating tip in water over 1.8 m/ 6 ft deep, but have been successful over the same lies with sink tips and/or weighted tubes.  Of course that statement excludes fluked running fish snatching at flies on or near the surface (see Brass Monkeys post); and over-sexed cock fish (a future post).
And that leads us on to the questions of why does the salmon take a fly; and how can we increase the chance of that happening?


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