Copyright 2014 James Marsh
How Do We Know What Flies To Use?
I received a call from a guy that ask me what flies he should use on a certain trout stream he was planning to fish.
When I answered his question, he asked me when I had last fished the stream. I told him it had been several
months. He then asked me if I had any reports from others fishing it within the last day or two. I didn't and I
answered him accordingly. He then asked how I knew what flies one should be using if I hadn't fished it recently or
at least received reports from other anglers who had fished it recently. I tried to explain our recommendations
were based on data from actual samples of larvae and other food from the stream: the weather at the time as
well as weather history for the past several days, water temperature at the time as well as the average for the
past several days; and current stream flow data. We never base anything on anyone's fishing reports as far as
what fly or fishing method they used. We are always interested in what they observed otherwise.
In case you don't understand the importance of larvae samples, it simply tells one for a fact what food is available
in a given section of water. That, alone with a good understanding of the type of water and its chemistry, as
relates to how well a particular insect does in that type of water, will give a good idea as to the quantity of
a particular insect. It takes more than one sampling because if it is an aquatic insect, it may be an egg at the time.
This is very general explanation as to how this is done. Although I could write a book about it, it isn't really
complicated. It is something you can't learn everything about without a great deal of study and effort.
We have a huge data base that took us 14 years of hard work, 180 to 250 days per year, to put together. We
also use data from a few aquatic entomologist familiar with fly fishing for trout in several streams we haven't
personally taken larvae samples from. There are actually only a few people that fit that category. There is a good
reason why. There's no money to be made in aquatic entomology from a fly fishing standpoint.
Trout will always focus on the most plentiful and available food for them to eat at any given time. It is nature's way
for them to survive, that is, using the least amount of energy to acquire the most food.
Let me put this in more common sense terms. Lets say Joe Blow fishes "X" fly for an hour on a certain trout
stream and fails to catch a single trout. He then changes the fly to a "Y" fly and catches three trout the next hour.
Most anglers will exclaim the trout wouldn't hit the "X" fly but they will hit the "Y" fly. That is completely worthless
information that has no real basis for anything. First of all, the time of day he fished the "Y" fly was different from
the time he fished the "X" fly. Unless, he is completely stupid, he wouldn't have fished the exact same water (beat
one section of the stream to death), rather he would have fished a completely different area of the stream.
Thirdly, if he had of continued to fish the "X" fly, he may well have caught six trout the second hour of fishing.
Using such trial and error information for a fly fishing strategy would be worth about as much as having gone to
one particular location in the state of Colorado selected randomly (just for example) on the mid-term election day
of October 4th and asking 6 random people on the street who was going to win the Senate Race. That
information is worth about the same as Joe Blow's fishing report.
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