The importing of British flies for use on our
streams made a problem we were not prepared to face: the entomology
of streams in the British Isles is vastly different from that of ours
but we treated the matter as if they were similar. Many of the
English patterns didn't work on our streams simply because our
trout did not recognize them as familiar food. And to worsen the
situation we began to assign the names of British patterns to our own
aquatic insects which we felt bore resemblance. Thus, in this
cart-before-the-horse procedure, our March Brown (the natural) was so
named because someone thought it looked somewhat like the English
March Brown pattern. Never mind that our March Brown is Stenonema
vicarium while the Brits' is Rhithrogena haarupi. Close
but no cigar. Slowly, we began to abandon the English patterns in
favor of new flies representing our own aquatic insects.
In England Dr. Francis Ward began researching
the trout's perspective of insects floating on the surface, taking into
account the physical laws governing the refraction of light - the
bending of light rays entering the water. In 1931 Colonel E.W.
Harding expanded Dr. Ward's studies in a landmark book titled
The Flyfisher and the Trout's Point of View. Heretofore,
most anglers assumed that if they could plainly see a mayfly
floating on the surface of clear water, a trout lying beneath the
surface could see the insect with equal clarity. Col. Harding
proved this assumption to be fundamentally in error, but with a
few strings attached.
Harding indicated that a trout had an uninhibited
view of objects beneath the surface, provided the water remained
clear. But looking upward, its view of anything in the element of
air, i.e., on or about the surface, was dependent upon the extent to
which the refraction of light would permit. Its vision to the outside
world was said to be defined by the shape of a cone with its apex
at the trout's eyes and a circular window at the surface on the other
end. Since the angle of the cone is a fixed 97 degrees the area of
the window enlarges or shrinks according to the trout's distance
from the surface.
Outside the area of the trout's window it sees
the underside of the surface film as a silvery mirror, reflecting
the bottom of the stream in shallow water. Only when a floating
insect drifts into the trout's window can it be clearly seen by the
trout. Outside the window the imprint of the insect bearing upon
the elastic film is plainly seen on the underside of the mirror.
Ward and Harding called this imprint the "light-pattern" and it is
generally regarded as the initial stimulus of the rise.
It was learned that the light-pattern may
vary broadly among the various floating insects and a few - such
as grasshoppers, beetles and inchworms - have light-patterns
distinctly their own. those of mayfly duns differ markedly
from those of spent spinners and the sprawling legs of
caddisflies produce a different imprint than the on-the-toes image
made by mayfly duns.
The findings of Ward and Harding brought
about significant setback to the "exact imitation" school, from which
it never recovered. If a trout in moving water gets an undistorted view
of a floating insect only in the brief instant it passes through
the center of the window, when why bother with unnecessary detail?
That was the attitude of most successful fly tyers and it generally
holds to this day.
~ Chauncy Lively
More next time. Chauncy's article appears
in the Spring Issue of the RIVERWATCH, the quarterly publication
of the Anglers of the AuSable, Grayling Michigan.
FAOL is proud to be a member of this fine organization,
dedicated to the protection of the AuSable River, its watershed
and environs. Dues are $25 per
year. For membership contact:
The Anglers of the AuSable
403 Black Bear Drive
Grayling, Michigan 49738
and visit their
website!
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