Friday 21 June 2013

Seven Deadly Sins - Common Novice Error 3

Anthropomorphosis - or failing to make the effort to understand salmon

From the outset, let's be clear on one thing: we don't know what salmon think.  I certainly don't know, because none of the fish I've caught have given interviews, written their memoirs or done anything else to help our understanding.  Faced with this void of information we slip unconsciously into the sin of Anthropomorphism  or setting natural behaviour in a human context.  It started with the ancient Greeks, who in the absence of science attributed human forms, behaviours and thoughts to natural phenomena and animals.  Several clever early authors took profitable advantage of this by writing best-selling stories of half-human gods, god-like humans and their travels and travails.  But myth and history aside, this sin is still alive and well on the riverbank, and leads us into all manner of mistaken assumptions on how the salmon behaves that reduce the number of fish we might otherwise catch.

It's not my purpose to make you an expert on salmon behaviour, nor do I make any such claim for myself: I am not a fish biologist.  Consistent with the theme of this blog, the aim of this mid-season low-water article (sorry, but I'd rather be fishing than writing) is not to provide doctrine for adherence, but rather to provide some materials to equip and stimulate you to think more deeply and draw your own conclusions in the avoidance of sin.  I apologise in advance for this post's length, detail and lack of pictures.

A framework for thought

If we do not know what the salmon thinks we can fill some of the void through a simple logical process comprising two stages.  Underlying both is a critical assumption: modern man is the only animal on this planet gifted with free will and knowledge of his own mortality; and the conscience and sense of humour to compensate for that wilfulness and knowledge.

With that human exception, the behaviours of animals are determined by 3 universal forces that are directly aligned to securing the imperative of the survival of their species, known collectively as the '3 Fs' - food, fear and reproduction.  Their actions in responding to those forces are mostly reflexive (otherwise known as System 1 or 'front brain' processes) rather than reason-based.  The individual salmon has limited need for near-term recollection because its reflexes draw on the accumulated experience of a million previous generations printed in the genetic material within its cells (a form of ROM - or 'read-only' memory if you like).  Its default mode is therefore risk averse unless one of the Fs makes an overpowering demand for action.  As an example, while spring fish are generally tentative and quite hesitant runners, those that run closer to spawning time are more driven and determined by hormonal demands.  Only humans actively seek risk (reindeer don't ride motorbikes) and we must not allow that peculiarity to influence our perceptions of fish behaviour because theirs is a frightening world full of hazards and horrid death, even if some threats are long-extinct in the UK, such as bears.

In their turn survival and the 3 Fs have driven the salmon's evolution into the fish we observe today.  The salmon is a very old species (at least 3 million years and probably older) and therefore both highly refined and proven to be very adaptable (salmon survived the Ice Ages).  By looking closely at the salmon's physical characteristics and capabilities we can form a better idea of how its reflexive actions are triggered and hence gain a more informed view of its behaviour.   Most of those characteristics are multi-purpose, mutually reinforcing and complementary - sight, smell, sensitivity to vibration, speed etc - so it would be unwise to draw absolute deductions.  They are also directly linked to genetic programming, so stimuli linked to known information may trigger a full or partial response, whereas the unfamiliar may be disregarded.  The best example I can offer of this phenomenon is the roe deer's reaction to tobacco smoke: the roe has lived with us for long enough (about half a million years) for man's scent to be a powerful flight trigger, but a hundred years of random exposure to cigarette smoke has not yet embedded a hazard signal to be handed on to future generations.  Bearing in mind that we've only been fishing with rod and line for a couple of hundred years, it's therefore likely that most of our activities just don't register on the salmon's threat scale.  Some may even induce curiosity, whilst other seemingly innocuous things will make it run a mile.

In the interests of brevity (and the lack of fishing will make this a longer than normal post) I shall concentrate on the characteristics relevant to the salmon's behaviour in fresh water.  I shall also not be discussing migration, which will be the subject of another post in the close season. 


Evolution has given the salmon one of the most sensitive noses on the planet, with the capacity to discern at the level of parts per billion.  Put in a familiar context, that equates to detecting and identifying one pub measure of whisky in 25 tons of water.  This amazing nose is connected to the brain via high capacity channels (clearly visible when you section the head), which tells us that a lot of brain capacity is devoted to processing smell information.  While this capability contributes to the final stages of migratory navigation we now know that it is not its predominant purpose (when Norwegian researchers blocked the noses of a sample of salmon, 95% found their way back successfully - see Journal of Fish Biology).  Instead, the salmon's nose provides:

  • An acute, 24 hour, long-range early warning system, because fish-eating predators discharge trigger scent chemicals, especially in their excrement.  The salmon can detect both upstream threats in the river (across the range from herons, via otters to bears) and the general area of operations of estuarine threats such as seals and dolphins.  Fish that are physically ruptured by attack also discharge signal chemicals. Lying on or near the flow line will give a salmon the best information more rapidly than in a backwater.  A dollop of heron poop entering a pool will be quickly detected by every fish.  Although its effect on their behaviour is unknown, we may surmise that it will raise their alert levels.
  • A means of detecting other salmon upstream and deriving important information from their urinary excretions, including their sex, stress levels and their genetic-family groupings.  They are more likely to be alert and run confidently if the information coming downstream indicates a secure and friendly environment above.   Conversely the lonely springer is afforded no such comfort.  My earlier 'Morning Glory' post recorded the effect of testosterone stimuli on cock behaviours.
  • Familial information that is very important to a social schooling fish.  They were born together, migrated to sea together, hunted sand eels together, and the survivors will return together.  Although smolt to salmon survival rates are statistically quite low (around 3.5% - University of Maine 1988 included UK data) this is an average across the population as a whole: some family groups will do better, others worse.  Lying and running with your siblings or relatives reduces stress and increases confidence.  It is therefore possible that fish in a pool will seek out and congregate with any 'relatives' from the same family group or spawning tributary (with small DNA variations) that they detect.  If you take 2 fish from the same lie in quick succession, do they appear similar in most respects?  The research confirms this ability to discern relationships in fine detail, and suggests that it is significant in the final pre-spawning period.  Conversely, mixtures of diverse family groupings may induce competition and friction, especially if a pool is densely populated (either with a lot of fish, or as a confined space in low water).  Eventually the survival imperative will suppress the frictional wastage of energy, give or take the occasional cock fish outburst.
  • A means for the exploration of curiosity in relation to the unknown or unfamiliar (worm fishing?).  While there is good evidence that salmon have high aversion to smells that jam or otherwise disrupt their sensory system, I have found none to suggest that minor traces such as human scent on a fly have any effect whatsoever.  Owing to the brevity of our relationship with the salmon, we're firmly in the 'unknown' category.
  • Scope for delay and confusion, because the sensitivity covers a very broad spectrum of smells that the salmon must differentiate and classify.  Inevitably any sample of river water will include plenty of scents the salmon has never previously encountered, including tributaries other than the one in which it was born and raised.  It may also include contaminants (simple biological materials more than man-made, but think about road-drain and cow pasture run-offs as a complex and confusing scents) that make the differentiation even more difficult.  In such circumstances the salmon will be cautious and circumspect, taking its time to achieve a clearer idea of what lies ahead.  In other words, it's a fully alert fish in a holding lie, and therefore eminently catchable.

Sound and Vibration

I have deliberately not used the term 'hearing', because as water-borne animals salmon do not 'hear' in the same way as we do in air.  For them vibration, range and direction appear more important than our focus on volume and pitch.  They have auditory sensors in their heads but no external ears because they don't need them: not only does sound travel 4.4 times faster in water than air, but also the energy density is about 800 times greater.  This allows direct transfer of pressure and vibration to the auditory sensors without an intermediate stage.  Because the sound is contained within the body of water the attenuation losses are much lower than air, and so transmission distances are much greater.  However, the downside is that water can be a very noisy environment.  The effects include mechanical interactions such as rapids, falls and waves (and consequent air expulsion); falling rain and surface wind; flow harmonics; animal generated sound (prawns and mackerel are noisy, but whales and dolphins must be deafening); and of course our activities as well (for example, at Tomatin, the vibration of every car passing over the expansion joint on the A9 viaduct is faithfully transmitted into Dalnahoyn pool via the concrete and steel pier foundations).  This gives some insight into why salmon generally don't like to lie in bubbly turbulent water (a sort of Radio GaGa effect of continuous noise).

In addition salmon have acutely sensitive vibration detection arrays in their lateral lines on each flank that deliver vital functions, not all of which are fully understood.  It would take a substantial book to cover the known capabilities, so what follows is massively condensed, with due apologies to the knowledgeable and scientifically minded readers.  However, for most of us the long towed array sonars used in anti-submarine warfare provide a handy analogy.
  • The large number of nerve sensors gives exceptional sensitivity to pressure and vibration over extended ranges.  This is the main component of a 360 degree, 24 hour early warning and situational awareness system that provides information on enemies, friends and food. 
  • It sensitivity and importance does, however, make extended stays in high vibration turbulent environments uncomfortable physically and mentally (the effect of teenage Radio GaGa on their parents), not least because the salmon will feel vulnerable.
  • The length of the lateral line gives a directional capability.  The signal is maximised when it's at 90 degrees to the body and the direction of arrival is easily sensed.  A 24 inch lateral line gives a 12 lbs salmon good discrimination of direction.
  • When the salmon is moving incoming signals can be oriented to the direction of travel owing to the connections with the lateral line's navigational and spatial awareness functions.  It therefore works well even when the salmon is moving quickly.


In the interests of reduced time and volume, if you haven't previously read them, please study my earlier posts, Windows on the World and Here's Looking at You, which cover how the salmon's vision works in the underwater environment.

Water is a poor visual medium and rapidly becomes much worse as soon as the river rises or the angle of elevation of the sun falls below 5-6 degrees.  As a result the salmon is inherently short sighted because it doesn't need to see a long way, even if it could.  Nor does its eyesight give discrimination of fine detail: kestrel levels of capability are superfluous in its world.  Unlike Jack, all the salmon needs to catch a sprat is shape, movement and contrast.  The salmon's colour integration and discrimination is currently unknown, whilst its UV capacity is subject to further research.  On the plus side, the salmon's eyesight is a near 360x360 sphere, and provides its only means for detecting above water threats such as avian predators.

In effect eyesight is the inner ring of a suite of complementary sensors that contribute to the salmon's spatial and situational awareness.  It is highly geared to reflexive action - feeding on fast moving prey species; fleeing from peripherally detected threats (especially above and below and behind); sexual attraction and competition; and of course swimming at speed between obstacles in fast moving water.

However, from the angler's perspective it's the limitations of the salmon's eyesight that are most important, because they contribute to creating the preconditions for a catch.  Unfortunately, when we arrive at a pool, we scan it with superb eyes that are capable of instantaneously focusing on objects from 20 cm to 20 km, adjusting for changing light levels and resolving light and dark objects in the same field (think about the limitations of your camera in that regard).  We confidently predict running lines based on above surface visual clues and fish accordingly.   Because we don't use the other senses we completely disregard the smell and vibration that dominate the salmon's decision making and thereby fail to appreciate how it might act.  We are indeed sinful anthropomorphists!

The salmon's world - an integrated multi-sensor view

So let's don a salmon's character and start again.  As a reminder, the key behavioural determinants are:
  • I must survive to breed: I will not take chances or vicarious risks (except when my silly male hormones get the better of me).
  • I shall position myself so that I am best protected against predators, can move or hold position with minimum effort and do not handicap the operation of my sensors (excess noise, bubbles and turbulence).
  • I'm a social fish and a team player: I'm more confident in company.
  • I will heed what my sensor systems tell me: this may take time to process and I think better when I'm sitting still.  After all, my brain is only the size of a broad bean.
  • Once I have reasonable confidence I shall go forward to have a look at the next obstacle: if in doubt, I'll wait (unless it's getting late in the year).  If the obstacle is very complicated I'll do it in daylight provided there's enough water to make me feel secure, even if that means a long wait.  If it's simple but shallow I'll wait until the ospreys have gone to bed.
Let's now put that into a narrative for a fish proceeding up a pool, starting immediately after entry and the 'phew, made it' moment.
  • Move clear of the noise and vibrations of the fast water behind so I can hear and feel what's around me.  How close is the next obstacle ahead?  Any threat indicators?  Do I need to stop to think?
  • Get into the main flow to maximise scent information and stop: what's ahead?  Any threat smells?  Happy salmon? Mother in law?  Confusing smells?  Bushmills or Tomatin?
  • Move forward a bit until I can sense the next obstacle quite clearly: big or small?  complex or simple?  New smells?  Bit of confusion here as I'm picking up two different stream taints (ever wondered why 'junction' pools are so productive? Salmon indecision is the angler's friend).
  • Move forward a bit more: problem, I'm running out of water depth and flow as this isn't the main stream line.  Drop back and try again further left.
  • Move forward again, now closer to the obstacle.  My sensors tell me that it's relatively simple (no roar), but from what my eyes tell me I'm not happy with the water depth in these light conditions.  I'll drop back and wait.
If you can  only see 10 feet and you're building your spatial and situational awareness with long wavelength sensors it all takes time and thought, and often plenty of stops.  Try walking to the pub wearing welding goggles as an experiment (take them off before you get there, otherwise the bar tab will be heroic).  So look at the water again and ask yourself, "given what I now know about how a salmon behaves, where are the obstacles and the running line between them, and where is it likely to stop to gather information, process it and make a decision?" 

Free at last from the sin and purgatory of anthropomorphosis you may even catch more fish. It may all be a fluke, just like dice, but a little mercury and some wax polish can help.  Tight lines.

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