Yuji Sakuma wrote:

Chas,

I don't know it for a fact but in presentations by biologists my is
impression that winter is indeed stressful for resident brown and brook
trout in my local streams. How stressful probably varies from year to year
and from stream to stream. For example, intuitively I would think that
trout in spring creeks might withstand winter better than trout in freestone
rivers because of the availability of food and more constant temperatures.
I believe that very severe winters that result in anchor ice formation are
deadly. A report that sticks in my mind was a radio-tracking experiment on
brown trout in a local stream. The loss in body mass from fall to spring
was very high, double digit percentages - don't quote me on this but it
might have been of the order of 20-30%. I am not sure of the significance
of the result because the sample size was very small and it was only for one
winter in one stream. I am not sure how fishing regulations were developed
over the years but it seems to me that closed trout seasons, while probably
intended primarily to protect spawning fish, probably also serve to protect
them during a period when they are most highly vulnerable.


I'm pretty sure that catching fish at low water temps is less stressful
than at high ones. (I'll see if I have any info on that)

However, like you state, Winter can be tough on the fish. In streams and
rivers, if anchor ice forms, there can be significant loss. Overall,
although there is weight loss during the Winter, trout deal just fine
with low water temps. The trout have evolved to be able to handle it.
Shallow lakes do often fish kill during the Winter, but this is do to
oxygen depletion and not temperatures that are too low. There are some
sections of tailwaters where the temps "never" get out of the forties
and the fish populations are high and the trout prosper.

Higher water temps are generally the limiting factor in where trout can
survive. As a river flows downstream, average temps generally rise until
they reach the point where the trout can't survive. Today, most of the
trout water that has been lost has been due to increased water temps
caused by changes that man has made. Some of these things a removing
water for for irrigation so water temps rise more easily, the removal
of tree cover, etc.

Willi