.......................  ......Fly Fishing Yellowstone National Park

09/22/09

Catching Yellowstone Trout in Cold Water - Part 2

Trout do not position themselves or hold in cold water in the same places that
they occupy in warm water. Several factors account for this. One is that oxygen
is not a problem. Cold water holds more dissolved oxygen than warm water.
From an oxygen standpoint, the trout could position themselves anywhere in the
stream if the water is cold. In warm water they must position themselves in water
that is aerated enough to provide the oxygen they need. This is usually the
faster moving water of runs and riffles.

Trout in warm water have a high rate of metabolism. They must eat a lot of food
to survive. They will position themselves where ever they can acquire the most
food. This is usually the current seams and almost always is in faster or
moderately moving water. In cold water, the trout have a lower rate of
metabolism. They need less food to survive and they don't have to position
themselves in the faster moving water to acquire enough food to survive. If they
did, they would expend more energy and need even more food. In cold water
they position themselves in the slower moving water.

That seems to make it simple until you try to determine where slow moving water
exist in a stream. In the freestone streams of Yellowstone National Park,
slow water exist not only in the places you can observe from above the surface
but also in the area of fast moving water below the surface. Every rock or
boulder in the stream changes the flow of current and the speed of the water.
There is water moving very slow, some almost still and some that moves only
moderately even in the fast runs of the streams. In fact these obstructions can
cause the water to flow in the opposite direction. If we see this situation on the
surface, we refer to it as an eddy.

Determining where the slower moving water exist in the streams is not exactly
easy to do. The trout don't necessarily hold in shallow water around the edges
of the stream, behind large boulders and other places where the only slow water
in a stream appears to be. They can find slow moving and even still water within
areas of the stream that from the surface appears to be only fast moving water.
In many cases they can position themselves near or on the bottom and be in
water that is barely moving downstream. The deepest spots in a stream usually
have slower moving water due to obstructions upstream that are located at a
higher level or elevation. That is why they are the deepest spots. That is why
you will often see trout in clear, cold water appear to be lying on the bottom of
pools and areas of water where you can clearly see the bottom. They can also
be near or on the bottom in areas of the stream that is moving very fast on or
near the surface. In those cases, you cannot spot them. In fact there are usually
more trout holding in those areas than they are in the deeper areas of slower
moving water such as pools.

Copyright 2009 James Marsh