Deep Thinking

Carrying on from last week’s ‘Windows on the World’ post, the sketch represents the assumed ‘taking zone’ for an alert active hen salmon in a non-residential lie.  Viewed from above it comprises a fan shape, probably extending out to some 60 degrees left and right.  However, its actual size in 3 dimensions will be determined by the nature of the lie, the degree of shelter that it provides and the strength of the current beyond its immediate confines.   In most cases an energy-conserving hen fish is unlikely to expend much effort in moving to inspect a fly, no matter how attractive, if it’s outside this zone.  Her embedded survival will probably prevail over a passing urge, and that is the basis of my working assumption of a 6’/2 metre radius of action.

 

Obviously there are no firm rules: lies come in every shape and size from a shallow depression in the bottom to submerged boulder fields, while their viability and nature changes with the water level.  In every case the key to success is to present the fly in a realistic fashion in the taking zone within and around those spaces.

That is not straightforward because we have to achieve it in 3 dimensions, in flowing water.  It is not a simple matter of just advancing downstream one pace per cast in the belief that we will thereby cover the whole volume of water and all the taking zones within it.  That steady advance addresses part of the longitudinal (up & down the river) and lateral (left/right) dimensions, but by no means all, because the swing of our fly does not describe a smooth regular arc across the river.  Differing flow speeds in the breadth of the river affect the movement of the line and can have disproportionate impacts on the fly’s direction and speed of travel.  Unless you do something to correct this problem, your fly will miss some lies completely.  To make matters worse, even if it enters the zone it may not be moving properly and the fish will totally disregard it.  I’ll be looking at these problems and their solutions over the next couple of posts.

However, as its title implies, this week’s post is concerned with the third dimension of depth.  This is fundamental but simple.  If you do not present the fly at the right depth you will miss every taking zone in a pool completely, no matter how well you cast, mend the line or control the horizontal movement of the fly.  Fortunately you can solve the depth problem with a mixture of technology and observation to establish the depth of the water in which the salmon are lying.
 

If you combine the hen’s 6’/2m range with the 45 degree angle of attack you arrive at an answer of 4’ 6”/1.4m.  This gives you a rough estimate of the maximum depth at which you can reasonably hope to catch a hen salmon with a fly fished near the surface in slow or medium speed water.  The good news is that many good fishing pools on Scottish rivers are not very deep; and give or take the boulders their bottoms are quite level leading to uniform depths in the head and middle sections. 




Of course rivers have pools that are narrow, on bends or astride some geological fault which makes them significantly deeper, but at Tomatin 4 of the best pools are relatively shallow with an average low-water depth around 3’ 6”/1.1m.  This means that you can catch fish with a floating line and simple leader until the river has risen by 10”/25cm.

Tomatin House Pool at +12", perfect for floating line, with most of the water within casting range up to 4' deep.  The lies in this shot are not adjacent to the obvious rock in the middle, but rather 10' short and left at 8 o'clock from it; and directly in front of your feet.

However, at +10" and higher the fish are very awake, alert and vulnerable to the attractions of a fly.  It probably offers your best chance to catch salmon, but you won’t catch many if the fly is above their taking zone.  You have to get deeper, which requires a sink tip or a weighted fly.  I prefer to add weight to the leader before adding weight to the fly because it makes casting and turnover easier.

This simple chart shows the depth (in feet) you can expect to fish an unweighted fly with each grade of sink tip, using the colour codes of the popular Airflo Polyleader range, and the Rio T-14 depth-charge device (which needs a skagit line to cast it).  However, there are other things to bear in mind when making your choice for reaching the necessary depth:

 

• The ‘lift’ on the line and tip increases with the water speed, so in faster water add an extra unit of weight – leader or fly.
• The depth to which the tip sinks is time-dependent.  If the lies you wish to get at are in the early part of the swing; the surface of the water is especially rough; or you are fishing a narrow river or section, go heavier still to get down quickly (but don’t dawdle at the ‘dangle’ or else you will snag the bottom).
• Be ready to change either the tip or the fly as the depth and flow speed reduce further down the pool.
• Large doubles sink faster than small.
• Look at the fluff to metal ratio – fluffy flies generate lift and ride higher in the water.
• With smaller and lighter tubes the size of hook you use will have an effect on their fishing depth.
• There’s a bewildering range of tube flies in the tackle shops and in many anglers’ boxes.  To avoid indecision I ration myself to a little box of 9 tubes, subdivided into light (plastic), medium (copper) and heavy (brass).
• I like coneheads: people say that the extra weight at the front balances the hook at the back, but whatever the physics, they work for me.
• When fishing near the surface I always use a fluorocarbon leader or tippet because it is heavier than water, nylon and copolymer.  Good reliable fluorocarbon is expensive – don’t be tempted by cheap tippets when you’re spending a lot of money to hook a salmon.  In my experience, Riverge is strong and reliable, while Seaguar, optimised for salt water work, is especially abrasion resistant, which is handy in rocky rivers.
• Depending on the colour of the water, you don't need much tippet on the end of a polyleader: 3'/1m suits most occasions.

Tomatin Garden Pool at +2' and 6' deep on the far side, flowing medium to fast.  Floating line, green slow sink polyleader,  and 1" Conehead Cascade, with an 11 lbs hen fish firmly on.

The longer 10’/3m sink tips obviously go deeper, but their extra weight loads the rod more heavily and demands more effort to extract from the water at the start of the next cast.  Conversely that extra weight will turn over a heavier tube better than a short tip, provided that the sum of the two is within the capacity of your rod and line combination.  With a big hefty 15’ #10/11 this shouldn’t be a problem, but at 14’ #8/9 you will feel the difference (future posts will look at rod and line choices).

 

You can also get lines with interchangeable tips: I have one of the original  Loop Multi-Tip lines, which casts well, especially with the medium sink tip.  On the other hand, in full floating configuration its handles a 5’ sinking polyleader with ease.  However, if you are buying a new line today, I wouldn’t recommend an interchangeable tip.  They are a great deal more expensive than the ‘parent’ line plus a selection of polyleaders, so you are paying a premium for an optimised balance that exceeds most people’s casting capabilities.

 

Finally, there are full sinking lines and their shooting head cousins.  The Upper Findhorn is not a big river or very deep, so in 10 years I don’t recall a situation where a full sinking line would have been the answer to my prayers.  On a big river, especially early in the season, a full sinking shooting head would give you the combination of distance, balance and depth to meet the range and depth challenges better than a floating line – polyleader combination, but those conditions are beyond the remit of this blog.  Anyway, I worry about loading myself with yet more reasons for indecision!

 

Having addressed the critical issue of depth, in the next post I shall look at the factors that influence the management and presentation of the fly in the horizontal plane.