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The main factors that hurt the productivity of
high-mountain lakes are the cold water temperatures,
hard-rock geology, and configuration (amount of
shallow water versus amount of deep water). A
fertile lake contradicts that profile in one,
two, or three ways:
Configuration -
Most mountain lakes, made by man or glacier, sit
in bowls or canyons and the shallows, or littoral
zone, may be no more than a rim surrounding a
plunging center. The shallow areas produce most
of the aquatic food on a lake. The fishery blessed
with expansive edges, flats, or shoals is richer
than the normal high-mountain hole.
Geology
Much of the Rocky Mountain region before upleft
was the bottom of an ocean. In places the rock
is soft fissured sedimentary limestones and
sandstones. As water filters through layers
of these rocks it combines with carbon dioxide
in the closed spaces and forms carbonic acid the
acid in turn eats away at the rock, releasing
nutrients into the water, and this rich, high-pH
soup raises the basic productivity of any stream
or lake it issues into. There is an abundance of
food, including some forms (scuds and snails)
that can't live in low-pH environments. Trout
grow faster and larger.
Water temperature
Sometimes the simple position of the lake
makes a big difference in productivity. If
it sits so that the early and late sun stays
on the water, there is more photosynthesis
among the basic algae at the bottom of the
food chain. The water warms up faster in the
spring and cools off slower in the fall. Two
lakes can be within a mile of each other, on
opposite sides of the mountain, and the one
that gets more sunlight grows significantly
bigger trout.
Springs entering the lake also create a
warmer temperature zone. A tributary that
dumps from one lake down into another might
be warmer than normal if the water coming
off the surface of the upper lake is heated
by the summer sun. Or a lake just might sit
in the path of prevailing winds that are more
temperate than the surrounding mountain air.
RELATIVELY INFERTILE HIGH-MOUNTAIN LAKES:
The typical high-mountain lake has low
primary productivity, colder than optimum
water temperature for fish growth even
during the summer, and a very brief growing
season overall for the trout (as much as nine
months spent under the ice). Surprisingly,
such a lake can still grow a trophy specimen.
A trout may live many years and, if the
competition for food is low because of a
small population, individual fish may get
relatively large. Larger, at least, than the
average high-mountain trout of 10 to 14 inches.
It becomes a game to catch and release a couple
of the best fish, maybe 18 inches or more, on
a given body of water. A search for the biggest
trout is a good way to make high-lake fisheries
a greater challenge.
For me the worst of the high-mountain lakes
are those overpopulated with 6- to 9-inch,
thin-bodied, big headed runts. This sometimes
happens in cutthroat lakes, but it is more of
a problem in brook trout lakes. The spawning
grounds can be too good there might be miles
of ideal gravel runs on which fish can deposit
eggs. These are great lakes for a beginner.
Those hungry trout rush anything that hits the
water in their mad competition for food. These
are also great lakes for taking out a limit of
trout. On some western lakes the regulations
specifically allow high harvests of fish.
The only way infertile waters can produce the
occasional large fish is with minimal
competition for food. Lakes with poor
spawning sites are good places for big fish.
Lakes with no spawning areas are even better.
Biologists stock lakes without natural
reproduction, and the plant dates and numbers
are public record. If a water is stocked every
eight years, it's going to have a lot of small
fish at the beginning of the cycle and a few
large fish at the end of the cycle.
Here are my final log notes on a nine-day
trip up to the Beartooth Plateau with Bernie
Samuelson and Ken Mira:
It's late July and we're still hitting lakes
with ice patches. There is plenty of snow near
10,000 feet. The search is not just for ice-out
waters. We have stocking records and we're
hitting lakes that haven't received fish for
a number of years. Rock Island Lake is planted
every three years and - this is the third year;
Black Canyon Lake is planted every six years and
this is the fourth year; Lake of the Winds is
planted every eight years and this is the seventh
year.
Without Rufus (goat) and Cheesecake (alpaca), we
couldn't carry the float tubes and extra fishing
equipment, and we need everything we have with
us to catch some of these fish. As it is we're
each toting 55-pound backpacks. A size-20 Halo
Midge Emerger on a 7X tippet is the hot combination;
and we have to use neutral density lines the
cutthroats won't put up with any wind drag. None
of the lakes have a lot of trout in them and the
few cutthroats that are left have long outgrown
the habit of rushing for food. There's a lot of
just watching the water and a lot of prospecting.
At Lake of the Winds we didn't catch anything
smaller than 18 inches and Ken got a 24-incher.
Rock Island kicked out big fish, too, but Black
Canyon was a bit disappointing, with cutts up to
15 inches tops, and it doesn't seem to have the
food base to grow bigger trout even in uncrowded
seclusion.
Both small and large trout cruise to find the
hodgepodge assortment of terrestrials and aquatic
insects scattered over the surface on these lakes.
There's no pattern to the rise forms, but the
fish don't miss much that looks edible. This
isn't fussy feeding. The fish are hunting, and
the best fly is the one that will pull trout the
longest distance and still trigger the strike.
Specific hatches on these waters are seldom
thick enough for trout to gorge themselves,
but rising fish might begin to show a preference,
if not rigid selectivity, for a particular type
of insect. They rush after skittering caddis adults
or sip spent mayfly egg-layers. If they become
fussy over any food type, it is usually a midge
pupa (and just like the natural, an imitation
has to hang half in and half out of the surface
film). It never hurts to match the action and
conformation of a prevalent prey item.
This constant feeding is the key to finding
big fish. Even the biggest trout have to be
obsessed with the surface from ice-out to
ice-up on infertile waters. The best fish
are easy to spot in the clear lakes if the
wind isn't blowing.
I get up high and use binoculars to scan a
lake when the water is flat. When I see
either a nice trout or a big rise form, I
mark the spot. That same trout will probably
be in the same area even when the breeze is
kicking the surface and it's impossible to
sight fish. The bigger the trout the more
likely it is that he travels alone and has
a set territory. ~ GL
To be continued, next time: More on the productivity of lakes
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