SALMON FLY SIZE
One of the most confusing aspects for a novice taking up fly fishing for salmon is what fly to fish. If catching salmon depended on selecting the unique pattern, colour, style and size of fly, for any set of prevailing conditions very few salmon would ever get caught. Taking into account all the local, regional and personal variations in salmon fly design there is such a bewilderingly large assortment to choose from that the possibility of selecting "the" fly on any particular day would be more difficult than selecting the six winning numbers in the National Lottery three weeks running. Salmon are difficult enough to tempt at the best of times and because of this it is wrong for writers to discuss fly selection as though "their" choice was effected from privileged divine information. Because of all the different flies available for a novice to choose from I believe it is best to stick with only a few patterns in a selection of sizes to accommodate different conditions.
There are many particulars which must be taken into account before deciding on which fly to use, i.e. like water height and clarity etc. However the most important aspect in my mind is the water temperature. Water temeperature plays a significant factor in the taking behaviour of adult salmon. It has long been established from the fishing records of highly experienced and very successful anglers that when the water is cold, below 40 F ( Fahrenheit), salmon are much more likely to take a large fly, i.e. one longer than 3 inches (75 mm) fished deep with a sinking line, rather than a small fly, i.e. one of 1.25 inches (33 mm), or less, fished close to the surface with a floater. Since the salmon's metabolism is directly affected by the surrounding water temperature it stands to reason that when the water is cold the fish will be lethargic and sluggish in its movements, and as a result, will not want to move far to intercept a fly. Many agony aunts who write in a number of the daily tabloids will tell you that when it comes to sex, size is not important, when related to salmon fishing however fly size is very important. This is why presenting our flies slowly and deep when the water temperature is below the mid 40's F (Fahrenheit) we stand a far better chance of tempting fish. When the water is cold I always feel that my best chance of success is to present the fly at nose level to the fish. When fishing during the early spring months of February through to the end of March if my fly brushes bottom occasionally I happy in the knowledge that it is being presented correctly for the water temperatures.
As the water warms up the fish become more active and as of consequence become more alert and start to focus their attention upwards, towards the surface. Although there are recorded instances of fish taking flies with a four, five or six inch wing like a Collie Dog, when fished fast across a pool, when the water is in the high 60's F (Fahrenheit), and conversely taking a small 0.5 inch (12.5 mm ) Stoats Tail type flies when in the lower 40's F (Fahrenheit) these successes are not commonplace, particularly when comparing the numbers taken by the "accepted", established approach for the given set of water temperatures . Well kept fishing diaries of earlier generations of salmon anglers, show us that as the water temperature increases the fly size should be reduced. Many of these records also show us that salmon prefer the water to be perceptibly colder than the air. If the water and air temperatures are very similar they show an obvious reluctance to move to a fly, or any lure for that matter, regardless of the depth at which they are fished. Once the air temperature rises a few degrees above that of the water, i.e. usually about 5 degrees F (Fahrenheit) salmon start to take an interest in what is being presented. On occasions salmon will rise to a small fly fished only a few inches below the surface when the water temperature is hovering around the lower to mid 40 F (Fahrenheit). I have found that this behaviour is most likely to occur during the autumn rather than the spring. During the spring it generally takes a few mild days of decent weather to bring about any positive changes in air temperatures, however during the autumn, especially during the months of October and November and to a lesser extent September overnight ground frosts can drastically lower water temperatures. It is also this drop in water temperature which brings about a behavioural change, making them sexually aggressive. Quite often at this time of the year it is necessary to employ more than one set of tactics throughout the day. Sometimes it is necessary to start off fishing with a sinking line and large fly, but come the middle of the afternoon, if the sun makes an appearance and the water and air temperatures rise it well may be necessary to change over to a small fly fished with a floating line. One indication of when to change from a floater to a sinker, regardless of the time of year is when you start to see parr or trout rise to a hatch of flies. By regularly monitoring the water and air temperatures throughout the day and changing over to a floater as soon as the air rises above the water by 5 degrees F (Fahrenheit) I have frequently taken fish when other anglers who have adhered to a large deeply fished fly have finished the day, or week with a blank.
By correlating and tabulating the fly size to water temperatures from my own fishing diary as well as the overall fly sizes addressed in the writings of many past and present distinguished angling authorities I have created a graph to show the size of fly that has proved the most effective in tempting fish for a wide range of given water temperatures. In order to give a true representation of fly size for the water temperature's listed, I have given the fly sizes in millimetres rather than hook sizes. This is for two reasons. The first of these is that the overall hook size seems to vary depending on hook style and manufacturer. Very often when a fly / water temperature table is given, the hook size is quoted. This as far as I am concerned is wrong and will only lead to unnecessary confusion for a novice when he / she is trying to decide the size of fly to use. The second reason for not quoting hook size is that very often the size of the hook is irrelevant when compared to the overall size of the fly, as the fly in question may have the dressing well past the bends of the hooks. If we look at the modern type flies like the Pot Bellied Pigs Allys Shrimp etc with the "feelers" and tail hairs extending well beyond the bend of the hook you will see what I mean. In order to try and alleviate this problem I have given the overall fly size rather than merely quoting hook size.
The table although helpful should only be used as a guide, as it only shows the size of fly for “normal” water conditions, (clarity and height) with the air temperature assumed 5 F (Fahrenheit) higher than that of the water. If the air temperature is lower than that of the water, or if a smaller differential exists between the air and water, the size of fly will have to increase in relation to the difference. Correspondingly if the difference between the two is greater than 5 degrees ( Fahrenheit) the size of fly will have to be reduced. Further to this if the river is in spate and running dirty, or flowing below summer level the temperature sizes will not apply. We must also remember that the fly size shown is very much part of a much more complex equation which includes many changeable variables. As the season progresses the water temperature will rise due to higher air temperatures, as of consequence the volume of water flowing will be reduced as well. This therefore means that the pools will now be narrower, shallower and slower. Air temperature, water temperature, clarity and height are unequivocally and intrinsically linked in determining fly size. Since the graph is a resultant from a number of anglers fishing many different rivers at different times of the year, with different water flows and clarities the sizes given for any given set of water temperatures will needless to say vary a little from one river system to another. The table however is still a good reference base which the novice can confidently use when choosing the size of fly to use.
Even although the table is a generalisation of fly size it can still be put to good advantage. Suppose the river we are fishing is in spate, with an extra 18 inches on the gauge and running murky. First of all take the water temperature as you would normal do to determine the size of fly for normal conditions (the river running with normal height and clarity). Having done this we now select a fly for a much lower water temperature. Example, during the warmer months of the season from about mid May through to the end of October I have found that a substantial increase in water height, more than 12 inches, a fly for a water temperature 6 degree's lower is about right, i.e. about 2 degrees for every inch rise. If the water on the other hand is also running turbid a further increase in fly size will be needed. When running "thick" choose a fly for a water temperature an additional 6 degrees lower, 4 degrees when "cloudy" and 2 degrees when running the colour of strong un-milked tea. This means if the water temperature was 56 F (Fahrenheit) and the table suggested a 25 mm fly for normal conditions come a 12-inch (30.5 cm) dirty spate our fly would have to be increased to 58 mm. By adopting this approach you will discover that the size of fly will either increase or decrease by a little over a factor of two, i.e. double or half in size. Some writers will tell you to go up one hook size, i.e. about the equivalent of only 2 degree's on the graph when the water is high and coloured and to come down by the same amount when the water is low and clear. I must stress that from what I have found increasing or decreasing my fly by the equivalent of only 2 degrees, or one hook size, when the river is running high and coloured, or lower than normal this approach is not very productive. If the water is below normal height, warm and running clear, I have found halving the size of my fly much more likely to produce fish. As is always the case though when salmon fishing one must always be vigilant and take note of any changes in water height and temperatures that might occur throughout the day. This is especially so with spate rivers as some have a tendency to rise and fall very fast, or when fishing rivers during the spring, which suffer from snow, smelt. When the water level starts falling, or if the water temperature increases reduce your size of fly. Conversely if the water height increases, or the water temperature takes a downward turn increase your fly size accordingly. When the water temperature is very cold 34 F (Fahrenheit) and the river is flowing with some extra height it is virtually impossible to fish effectively with a fly rod since we would need a fly well in excess of 150 mm. At this time it might well pay instead of increasing the size of our fly to put on one of the same size, but with a superior visibility factor. This is assuming we are fishing with a fly 102 mm long. Since I don't like fishing with flies any larger than this I will, if a larger lure is called for opt for the spinning rod.
When the river is very low and warm there is no doubt "small" is best. I have occasionally taken salmon on size 14 bronze wee double trout hooks, i.e. about 10 mm in total length, when out fishing for trout.
There is no doubt that the size of flies can vary somewhat from one river system to another for similar conditions ,however in some rivers they can also vary within beats. Generally on most rivers the further upstream you go the smaller the fly you should use. However the reverse seems to be the case on the Beauly. This is because the water temperature on the upper beats is colder than on the lower river below Kilmorack Dam, as a result fly sizes one or two sizes larger are needed by anglers fishing above the Aigas Dam. The distance between both dams being no more than 3 miles. On the whole however experience has shown me through the years that the further upstream on a river one fishes the smaller the fly one needs to use in order to interest fish.
For most situations, whether fishing a large or small fly we strive to present them as slowly as possible. We must therefore consequently present the fish with the size of fly that looks as if it is capable of hold station within the flow in which it is being fished. Most creatures will only venture into flows in which they are capable of controlling their progress. Creatures entering a flow, which is over powerful for them, will get washed away downstream where they may be killed, or injured by being slammed against a rock or something. As a result of this I feel it is important to fish the "appropriate" size of fly for the flow being fished. This often means it might be necessary to change fly sizes two, or three times when fishing down a pool. There is no fixed number of changes, the number of times you will have to change flies depends on the variances of the flows within the pool in question. In the fast streamy water at the head of a pool I would opt for a slightly larger fly than the water temperature suggests and then as I near the belly of the pool I will change to a smaller one. If you do not want to change flies as you progress down the pool another method I sometimes employ is to fish with the same size of fly from head to tail, but at different speeds. By following this practise though I have had to educate myself to become aware of the subtle nuances of current flow, which will affect my flies, traverse across the pool.