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ON SOME high-mountain lakes the food base
can be maddeningly simple. The trout swim
slowly and open-mouthed, like certain whales,
straining minute, suspended food organisms
known as zooplankton from the water. If
zooplankton can grow something as large
as a whale, why should a trout eat anything
else? In many lakes the fish spend all summer
and fall ingesting animals far smaller than a
size-28 hook. Even if a fly fisherman could
imitate individual organisms, it would be
useless because the trout are not taking them
one by one. The only "good" fly would have a
hundred incredibly tiny hooks dangling in the
water, imitating a cloud of suspended zooplankton.
The zooplankton in high-mountain lakes is
a predictable collection, including Copepods
such as Cyclops and Diaptomus,
Rotifers such as Rotatoria, and
Cladocera (or Water Fleas) such
as Daphnia. Most of these minute
animals feed on algae, which means that
populations will be at a peak when microscopic
plants bloom in midsummer. That is when trout
are most likely to feed on zooplankton exclusively.
The trout follow the zooplankton. Some of these
plank-tonic animals have eyespots and, reacting
to sunlight, they migrate daily. They reach
maximum abundance near the surface early in
the morning, but with growing illumination
the animals begin sinking, reaching depths
of fifty feet or more, depending on the clarity
of the water, and stay deep until late afternoon.
Then they begin a slow drift upward to the surface
again.
THE NEED to understand zooplankton has little
to do with imitation and everything to do with
tracking the trout in lakes. If you find a
shapeless, pastelike mass in the stomach of
a fish, you have caught a plankton-eating
trout. In clear lakes you should be able to
spot these fish cruising slowly at a specific
depth, but seeing them is different than
hooking them. I logged a relevant experience
fishing for plankton-feeders in 1996:
August 7th through the 12th:
Joel Hart is one of those fly fishermen who
doesn't hike anywhere just to hike. He's in
shape, and he'll walk miles to find an elk
or deer during hunting season, but when he
goes into the mountains to fish, he wants a
sure thing. Four or five times a year he'll
come with me to a favorite high lake of mine;
and two or three times a year we'll go to a
favorite high lake of his.
But he refuses to take me to Cave Lake. "Never,"
he says, "Throw me in a briar patch. Anything,
but not Cave Lake."
Joel is a stillwater specialist, one of the
finest, and, like me, he loves a tough situation.
Unlike me, he lacks a masochistic streak. He
doesn't mind getting beaten by the trout, but
he doesn't see why he should hike eight or nine
miles uphill to do it.
He never should have told me about the goldens
in Cave Lake big cruising plankton-feeders. He
shouldn't have telephoned me late one night,
saying over and over, "I could see them, but I
couldn't catch them."
STILLWATER SPECIALISTS in the United Kingdom
learned how to catch plankton-feeding rainbows
in their reservoirs, but at first they were
baffled by the strange new trout in their country.
Soon after Blagdon Reservoir was flooded in 1902,
fishermen found that rainbows "disappeared" in
midsummer. The normal surface- and shallow-water
tactics didn't work for larger fish, especially
during midday, on rich, algae-clouded Blagdon,
or later on similarly fertile reservoirs such
as Chew, Datchet, and Grafham. Anglers worked
streamer patterns ("lures" in their terminology)
on a full-sinking line. They anchored a boat in
deep water and by methodically testing different
depths they picked up trout on minnow imitations.
Peter Lapsley, in Trout from Stillwaters,
explains the technique:
The solution is to cast as long a line as possible,
to let out line after the cast until we are sure
that the lure is at the right depth and only then
start our retrieve. Even a Hi-D line only sinks
about one foot in three seconds and it takes a
minute and a half to go down 30 feet. Count or
time as the line goes through the water. By doing
this we should be able to return the lure to the
same depth again and again with subsequent casts.
This method was specifically developed for the
capture of rainbow trout, especially plankton-feeding
ones. By mid- to late-June, the rainbows should
have begun their assault on a rapidly growing
plankton population. It would be quite impossible
to represent daphnia or any other planktonic animal
on a hook, and even if we could there would still
be little chance of persuading the fish to select
our artificial from amongst the vast host of naturals
in the water. But, by some extraordinary stroke of
good fortune, plankton-feeding rainbows are remarkably
susceptible to bright, flashy lures. Gold, orange,
yellow and red seem almost always to be the most
effective colors, and a Whiskey Fly or a Dunkeld
fished at the right depth and retrieved quickly
will frequently provide the answer to an otherwise
almost insoluble problem.
The pioneers of stillwater fly fishing in the
United Kingdom perfected the Count-Down Method
with sinking lines. It's a consistent technique
for taking trout feeding deep on a variety of
foods, not just zooplankton; and it's one of
the keys for taking large trout in many western
reservoirs in this country. The Count-Down and
bright streamer patterns work on plankton-feeders
in our lowland waters, too. ~ GL
To be continued, next time: More From the Bottom of the Food Chain
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