Tuesday 27 November 2012

Hot and Cold Running Water

Water level, temperature and fly size

In my last post I wrote about the effect of this year's very cold water on the Findhorn on salmon behaviour.  This article takes the discussion another step forward by comparing 2012 against the experience of the 10 previous years, before going on to examine some of the issues of fly size in differing water conditions.

The red marks plot the full dressed length of the fly (i.e. from the eye to the end of the feathers and tinsel) against the water level when each fish was caught, at normal water temperatures.  The data encompasses 30 salmon from 2002-11, and shows clear correlation between the height and hence speed of water flow and the size of fly.  Of course, this does not actually prove anything, because I did not test the hypothesis by trying to catch salmon in fast brown water with small flies, or in low water with big tubes.  I was just following Falkus' advice.

1 inch Cascade Conehead
Actual size
The red marks do make a few points.  Most obviously they show that however hard you try, catching salmon in low water is difficult, mainly because the fish are switched off.  In contrast, the cluster along the 0.4 metre line shows how much easier life becomes when the water is up and the fish are awake, running and active.  There are nearly 4 times as many fish in those 2 clusters than in the low water string.  It also indicates that at that level, the combinations of 1 inch tubes and coneheads in brown water and 8/10 Shrimp and Cascade doubles in clearing water are highly effective.

Cascade Size 6
Actual size
In contrast the blue ellipse covers the 3 fish I took in the exceptionally cold conditions of 2012.  The flies were about 2 sizes larger (e.g. size 6-8 double) than those successfuly employed at normal temperatures (typically 10-12 double) given the same water level.  Whilst it does not prove Hugh Falkus' contention of colder water - bigger fly, it suggests that it is probably correct.

Size 16 Blue Charm
3 x magnified
When you get down to the tail end of the graph you are into the realm of almost random events with very small flies.  The extreme case was a 11 lbs hen fish caught on a brilliant sunny morning on a tiny size 16 Blue Charm delivered by a Vision 12' #7 grilse rod on a long fine leader.  The others were taken on a mixture of small Stoats, Shrimps and Blue Charms in the 12-14 range. 

The sample is so small that there is no evidence that pattern X is better than Y, or that one colour is uniquely superior to any other.  On the other hand, those fish were the product of many hours' application and thousands of casts, so we can reliably infer that all the other pattern/size combinations I tried were inferior, because they didn't catch anything.  If undecided, revert to the Falkus hat selection method, but do match the size to the water speed.

But fly size and pattern are only two parts of the equation for catching salmon; depth and presentation follow, and are the subject of my next post.

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