Thursday 28 March 2013

Inside the Box

Having discussed at some length what the salmon see, it’s now time to step into the practical realities of what flies are in my boxes and what if anything they catch.

All of this analysis comes with lots of statistical health warnings.  Each fish is a sample of one, relevant only to the instant of its catching and the prevailing conditions.  We don’t record the flies that fail to catch anything.  We can’t really compare one fly with another, because we can only catch one fish at a time, and replays are unknown.  We catch most fish when they’re taking most freely, in which the fly pattern may play only a minor part.  We are creatures of habit, superstition and belief, in that we are more likely to fish with a pattern that has worked for us previously.  In that respect, fly choice is a self-fulfilling prophecy and self-reinforcing truth: if the local wisdom is to use a Cascade, unsurprisingly most fish will be caught on a Cascade, even if it may be a bad choice in imperfect conditions. 

Breaking the Duck 2005
Small and stale, but utterly welcome
When I first started fishing at Tomatin, my first 3 years were plagued with very low water (2002, 2003 & 2005).  As a complete novice I obeyed the local wisdom and used a small Stoat’s Tail, finally catching my first fish with that pattern in the pre-dinner darkness on the Saturday night in 2005.  It may have been small and stale, but it was so welcome I almost kissed it! 
In 2006 the water remained generally low, but I caught more fish.  In retrospect, the Stoat’s Tail was probably as good as anything else in such barren conditions, but today I’d probably be using a #14-16 Blue Charm or Hairy Mary. 
In 2007 we had decent water, so with Hugh Falkus’ words ringing in my ears, I put on something bigger and brighter - #8 Ally Shrimp – and caught 7 salmon that week.  This converted most of the Stoat disciples to Ally Shrimp users and contributed to changing the local wisdom, even though the little Stoat would have been a much better choice in the lower water of 2008 and the drought of 2009.

Looking at the bigger picture, this chart shows the flies that have taken 50 fish since 2005.  Looking at it, you might conclude that the Cascade Conehead Tube and the Ally Shrimp double are the best flies by far as they have accounted for such a high proportion of my salmon.  Actually, the fact is that I caught a lot of fish because in the conditions that dictated those fly choices, the salmon were abnormally easy to catch.  In 2007 my average was 1.2 fish per day: in the exceptional conditions of 2011 that rose to 1.8.  In contrast, in the lean years of low water, when conditions dictated small Stoats or Blue Charms, my average was only 0.2 fish per day.  Taken in isolation, this data doesn't tell you much until you set it in the context of what other rods were doing at the same time.  That analysis exposes the following deductions:
  • In low water Blue Charms and small Ally Shrimps (#12-14, about 5 of the 15) performed above the group average, which was largely based on other patterns.  There did not appear to be much to choose between them.  However, when using an Ally in low, clear water I tend to cut the tail down to reduce the overall dressed length to approximate nymph dimensions.
  • At mid-height (up to about +12") Cascade and Ally Shrimp doubles (#6-10) were close to the group average, primarily because a large proportion of rods were using those patterns.  Statisticians call this regression to the mean, which shows that all other things being equal, my performance is about the same as the other rods'.
  • In heavy water (+12" - +24"), the Cascade Conehead tube performed far above the group average, which was predominantly based on large doubles, including Cascades.  The easily identifiable factors in the out-performance were correct depth of presentation and size in relation to the flow speed of the water.  This is because similarly sized and weighted Ally Coneheads worked nearly as well, and very large doubles on fast sink tips less well but above the average in the same periods.
As a result of these deductions and a healthy dose of Yorkshire scepticism, I do not carry a wide variety of flies.  Indeed, I have just 3 boxes in total, and carry only 2 of them on the river.  The contents will come as no surprise.

The first is marked 'LOW'

This is the main area: note the chopped-off shrimps at bottom left.  You can also spot the dishevelled but successful flies.

This is the lid

I bought the Bombers last September as an insurance experiment against very low water, which didn't materialise, so they've never got wet.  You can easily spot the Collie Dogs and Thunder & Lightnings that have caught fish, but to be frank, I've lost more fish on Collies than I've landed.  I like the T&L because its sparse dressing allows it to sink well for its size.

I have a box marked 'HIGH', which I don't show because it's only contains a a few large Shrimps and Cascades, and anyway, if the water's up, I tend to choose a tube.

And finally, a little Snowbee spring clip tube box with 9 tubes.  It's a delight of good design: palm-sized at 3" x 2"; nice high-density hook-holding foam in the lid; cunning spring clips to hold the tubes fast; and a snip at £20.  Its only drawback is that the spaces on the right are shorter and only hold small tubes - most of which I've never used!  The Yellow & Black was wandering loose at the time of the photo, and is not a permanent resident.  My small collection of 2 Sunray Shadows live in a small plastic bag at the bottom of a pocket.

It's not a lot, but my father always said that most flies are dressed to catch fishermen not fish.  If I had any more I would have a decision problem and should have to invoke the Falkus 'hat' selection method.  This way I avoid pain in both fingers and wallet, even if I'm not John Norris' best friend.

Tuesday 19 March 2013

Here's Looking at You

Following the ‘Windows on the World’, ‘Deep Thinking’ and ‘Fast Food’ posts I was asked “what do salmon actually see?”  The short answer is that I don’t know, but nor does anyone else, because salmon do not respond well to questions.  However, we can draw some inferences from the construction of the salmon’s eye and the effects of water on light, which together may be relevant to our choice of fly.

Clever Blue Eyes

Let down by my cones!
Deceived by a small fly in crystal clear water
on the only sunny day in August 2012
The salmon's vision is an example of smart evolution that contains some interesting features. 
  • To correct the spherical aberrations that would otherwise arise from its 160+ degree hemispherical field of view from each eye, the fluid in salmon's lens has differential refractive indices. It does not have to move the head to get a better view of objects in the periphery.  Your fly is in focus from the moment it first appears within visible range.
  • The eye and vision automatically stabilises to compensate for movement of the tail, which maintains a consistent view of its prey and your fly during manoeuvre.
  • The retina contains a mixture of 'cones' (acuity & precision in good light - helpful for parr eating nymphs) and 'rods' (sensitivity & low light performance based on contrast - essential for hunting prey in dark oceans and running at night).  The balance between them is adjusted by pigmentation to suit the circumstances.  This change is slow compared to the human eye because the the salmon's eye has no iris to control the amount of light entering the eye.  It therefore finds abrupt increases in light levels disorientating and disturbing (see 'Morning Glory').
  • The salmon's capability extends across the visible spectrum and possibly beyond. This may include some sensitivity to UV  and near-IR light (even sticklebacks have proven UV detection related to their mating colouration).  
  • Salmon have the optical capacity to detect red, green and blue light, but their capability for integrating this into full colour vision is unknown (a computer printer uses only 3 colours of ink to generate full colour images in your brain).  Just because it's red to our eye doesn't mean it's red to the salmon's, and what looks good to us may not to her.  Nevertheless, fly colour may be significant when brighter water and light conditions permit differentiation.

Two observations flow from those characteristics.
  • In bright and clear water conditions when the 'cones' are dominant, a small dull-coloured fly will be less easily identified as 'false' than a large one owing to its closer approximation of the prey nymph's appearance.
  • In dull light and darker water when the 'rods' are dominant, contrast and movement rather than colour will give the strongest visual cues.

Water and Light

The phenomena of refraction and reflection determine how much of the ambient light enters the water, and the ways in which the fish sees its environment as I described in ‘Windows on the World’.  Once the light has entered the water its subsequent behaviour is influenced by its wavelength and the amount of things like salts, vegetable and other biological matter, mud and debris suspended in the water.  A fair amount of the red-orange portion of the spectrum is absorbed in the first 2.5m/8’ travelled.  That’s not the same as depth, because at mid-afternoon in September the light is entering the water at an angle of 30 degrees, so 2.5 metres travelled equates to a depth of only 1.2m/4’.  Suspended peaty matter increases the red absorption and scatter, which explains why the upper levels of Scottish rivers have that classic burgundy colouration.  Similarly, much of the ultra-violet component and some of the blue and yellow wavelengths are absorbed quite early.
This means that the appearance of your fly will change a great deal depending on the time of day (the elevation of the sun), the depth at which it is presented and its distance from the fish.  Consequently, the apparent colour of your fly may be very different.  The diagram shows a fly 2m down and the same distance from a fish.  In peaty water, only 40% of the core red-orange arrives at that depth to reflect from your fly, and by the time it reaches the salmon, that figure falls to 24%.  That’s a rather dim image, even before you add effects of clouds, rain and the low elevation of the sun at Tomatin’s latitude of 57 degrees North.

Using a picture of nice bright Cascade Conehead and the wonders of Adobe Photoshop we can reduce the relevant bits of the red-orange spectrum to replicate the effect.  The scenario is 3 pm at Tomatin in mid-September, with the water at +12” and rising, cloudy with sunny intervals: in other words, perfect fishing conditions.  The photographs have been size-corrected to allow for the salmon's viewing range and tinted to match the water's colour.  The background is based on Window 1 to avoid the complications of reflection in Window 2 or the shadowing in Window 3.

Our view in air, white light
Surface, 1m range
Surface, 2m range
Depth & range 1m

Depth & range 2m
Depth & range 2m

Although the last 2 images look very faint to the human eye, they recreate the low-contrast conditions for which the salmon's 'rod' vision is optimised - the high-speed pursuit of grey sprats in the grey-green waters of the sub-Arctic. They do, however, suggest that at 2m depth the brightness and colour of your fly's dressing becomes less important than its size, definition, and above all, its movement. You will see that the black materials in the mid-body of the Cascade stand out more strongly than you might expect. This underlines the wisdom of the Tweed ghillies' preference for large black/yellow tubes for deep early season fishing, as evidenced in the pictures below.

Black & Yellow Tube
Black predominant

Yellow & Black Tube
You can see that the black portion of the tube is much more clearly defined and stands out better in the murk than the ostensibly brighter yellow.

Two metres is very deep fishing on most medium-sized rivers, not least because the salmon could be another metre of more below that level.  That is sinking line or T-14 territory, and there are only small parts of 3 pools on the Tomatin House water with that depth.
There are, however, 2 other conditions in which the evidence of these images may be relevant:
  • When presenting a fly around 1m depth in coloured water with poor light conditions between 10am and 3pm, when a mixture of dark body definition and flash might be useful.
  • When fishing at any depth in normal water in the rapidly declining underwater light levels that occur after 3pm.  By 4.30 pm your fly fished at 1m depth has the same dull appearance as it would at 2m at 2.30 pm because the underwater light level has almost halved over the intervening two hours.  Two out of the 3 late taking pre-dinner fish in my sample took black flies.

The water-light relationship suggests, if it's deep, dirty or dull, try a bigger darker fly.

Monday 4 March 2013

Reading Railway Maps

It’s confession time.

Do we spend any time thinking about how we are going to fish the pool in front of us?

Or, do we just start at the top and make our way down pace by pace, trusting to Lady Luck?

And, do we always fish this pool the same way?

There are plenty more questions where those came from, but three are enough to make the point that we tend to apply more enthusiasm and energy than thought to the challenge of catching salmon.  I certainly did in my early years.  Yet even a short pause for thought leading to a simple plan can make a big difference.
Every pool is different and changes every day: water level, colour and temperature; air temperature and pressure; light, cloud and atmospheric conditions; and of course the location of the fish.  If we tried to bring all of those factors into our thinking we would rapidly descend into indecision because there’s too much to grasp and we don’t know what’s most important.  So we have to simplify.
First, what do we think the fish are doing?  Are they running, holding or settled?  If so, where?  (Have a look at last November’s post – 'Where are they').  Start by eliminating all the places they won’t be – those less than 30”/75cm deep; too insecure; too turbulent; too bright; or short of easy oxygen.  You’ve now reduced the problem by half.  Then work out the most likely running line that salmon will follow from one end of the pool to the other: the short halt lies will be on or very close to this line, and the holding areas not far away.  At the end of this process we have a mental railway map of the pool, comprising a main ‘running’ line from end to end; some ‘stations’ along it where fish congregate at the short halt; and some adjacent ‘sidings’ for slower-time holding areas.  Like all railways, the map is very narrow: 90% of all the hen fish I have ever caught took within a couple of metres of the running line.  (We’ll leave the more distributed resident fish snoozing on their ‘branch lines’ in peace for now).
Second, how deep is the water along the railway and how fast is the flow? (See the ‘Deep Thinking’ post).  The answers determine your initial choices of leader and fly size, but you should be ready to change both as you progress down the pool.
Third, where is the main flow and what is the current profile across the river?  Are there any obstacles or disruptions to the flow that will affect the movement of our line and the correct presentation of the fly? 
This example shows a common current pattern, with the strongest flow in the middle and a relatively quiet margin under the far bank.  A standard cross-cast (1) that reaches the assumed lie under the far bank causes the fly to land and anchor in slack water, whilst the line rapidly bows (2), which causes the fly to travel downstream (3) at high speed.  This will not sort itself out until the fly has reached the centreline, so half the cast was wasted.
The usual remedy is ‘mending’ the line – throwing a loop upstream with a ‘semi-cast’ to take out the bow.  Getting this right takes effort and practice.  If you are using a sink tip and weighted fly its efficacy is reduced because the far end is firmly stuck in the water.  In this case the cast (1) is followed by a mend (2) M2, which stops the problem getting worse, but you still waste the first third of the swing and all of the extra effort involved in getting to the far bank.  The simple message is don’t bother.  

Not only are there probably no fish there anyway, but mathematically you improve your chances by a massive 50% by working a more modest 60% of the water with your fly behaving properly.  An oblique cast to just beyond the centreline (1) produces a sustained line shape (2) that creates the ideal direction of fly travel (3).  Most importantly, the fly is effective immediately because you can take any slack in the leader with a small movement of the rod tip.

Of course there’s a place for square casting, especially in slower water, and mending the line is an essential skill.  But restraining your enthusiasm for hitting the far bank and opting for the oblique approach is a useful first step towards getting the fly in the right place.

Let’s now bring all this together in a practical example.  The picture is a ‘railway’ map of the Garden Pool at Tomatin for a water level of +12”/30cm.  The banks are green; the shallows grey; the main line red; the stations yellow (1-6); and the fast flow in blue (direction bottom right to top left).  These 6 are not the only lies in Garden, but they are the most heavily populated, and the more fish there are in a lie, the better your chance of a positive response.

At this water height and speed you want a larger fly (either a #6/8 double or a 1” tube) and a 5’ green or brown sink tip (it’s around 6’ deep at point 3).  Certainly you will need the brown tip to cut quickly down through the turbulent water at lies 1 &2, remembering that the more oblique your cast the slower the sink rate owing to the ‘lift’ of the water on the line.

To get the best fly presentation at lies 1 & 2 start well upstream and cast obliquely down at around 30 degrees to the flow.  This will keep the lateral speed under control; give the salmon more time; and increase the fly’s exposure to any fish actually running the main line.  If you are going to pull off a fluke it always pays to increase your chances.  (By now you should have spotted that this pool was the basis for the preceding current profile sketches.)

As you move downstream move progressively closer to the near bank (there’s no prizes for standing on a fish at 2); increase the casting angle to allow for the reducing flow speed; and continue to resist the temptation of the far bank.  Lies 3, 4 & 5 are typical mid-stream boulder features.  Although they are not visible in low water, at +12” and above they create a ‘standing wave’ (i.e. one that stays in much the same place in the current), as shown in the next diagram.

A wedge of static and slow moving water forms around the obstacle and forces the flow upwards, creating waves at the surface.  The shape of the wedge varies with the size, number and distribution of the rocks and the profile of the bottom.  Note that the deflecting effect of the current means that the standing wave is usually downstream of the lie.  Also that the wedge will form some distance upstream of the front edge of the obstacle. Your target therefore comprises the area upstream from the standing wave, possibly for as much as 12-15’/4-5m, depending on the depth and speed of the water.  The width of the standing wave in the stream will give you a clear indication of the lateral extent of the lie.  The salmon will be somewhere close to the bottom of the wedge that allows them to hold position with minimum effort – in front, between, beside or behind the rocks.  Remember that they are unlikely to venture far beyond its boundary to take, so you have to get the fly into the wedge, moving laterally at about 45 degrees above and ahead of the fish.

By the time you approach lie 5 you will need to change the leader and fly as the water is slower and shallower.  It is a large lie in length and breadth that only holds fish when the river us up 12" or more to provide adequate depth.  Lie 6, which also only comes into play at that level, is the exception that requires you to disobey, just for once, my ‘forget the far bank’ rule.  This is the heroic 35 yard pinpoint cast for which you have been saving your energy for the past hour.  Here the running line is close to the far bank.  Just short of the overhanging trees are two rocks set 4’ apart, where the fish stop for a breather after running the long shallow fast water from Colonel’s.  In your enthusiasm to get there, please don’t succumb to the temptation of standing on the fish in the back end of lie 5 that the next rod would like to catch.  But when you put the fly in the right place, at the right angle, moving the right way…………

On her way back
Garden Lie 6, 1430 pm, 12 September 2011
...then sometimes the magic happens.