During the past many years of trout fishing, we have been concerned with the warm water
temperature issue while fly fishing for trout every year. Water temperature is very
important anytime of the year but especially during the hot Summer season.
The subject of water temperature and oxygen content of the water has come up many,
many times with most anglers. The water temperature issue even becomes important in
many of the Rocky Mountain western trout streams. There, the early morning air
temperature often starts out at about thirty-five degrees but reaches as high as
ninety-five in the afternoons. I could write a book about the subject of fishing for trout in
warmer than normal water, but I will get straight to the point. We don’t catch or release
trout when there is a reasonable doubt as to whether or not the fish will live after being
released. We don’t have to worry about whether they will live or die because we know
what we are doing.
When you frequently catch trout and release everyone of them, you would have to be
plain stupid not to realize when the trout were stressed. We never guess at the water
temperature. We carry two thermometers and check the water temperature almost every
day we fish, especially if there is a question about it being too warm or too cold.
The amount of dissolved oxygen in the water is directly related to the water temperature.
In case you don’t already know, cold water holds dissolved oxygen much better than
warm water. The effects of water temperature on the amount of dissolved oxygen doesn’t
change at a constant rate. It changes at an accelerated rate. In general, for most species
of trout, the fish are most active when the water ranges from about 50 to 65 degrees.
The cold-blooded trout feed at the maximum rates due to their metabolism level in this
temperature range. From 65 to 70, the accelerated rate I referred to begins to take place
to the point it becomes a big factor. In simple terms, at 65 there’s no problem and the
trout feed aggressively. At seventy degrees, there can be a problem depending on the
type of water. The dissolved oxygen content can be low.
Still water is one thing and fast, turbulent water is another. The amount of dissolved
oxygen will vary greatly. That’s why you hear advise to “fish the oxygenated water” all the
time. When the trout start hurting for oxygen, they will begin to cease their feeding
activity. It’s not a great deal different from the way they react in very cold water, just due
to a different reason.
When the water temperature reaches about seventy-four degrees, the trout just about
have to have highly oxygenated water to survive. Again, keep in mind that these
temperatures are guidelines. Again, the particular species of trout and its location and
more specifically the type of water it is in will vary this somewhat – not greatly, but a little.
All of us that want the fish to survive want a safety margin. We don’t want to catch a fish
that shows signs of being stressed. Just like when you climb a high mountain and give out
of breath (especially out West at ten thousand feet), you will have to sit down and you will
struggle for breath – the trout will stop fighting as hard. If it’s in your hands being
released, it won’t be difficult to hold. When you put it back in the water (which should be
done just as quickly as possible), it may hesitate before leaving. A trout that isn’t stressed
won’t swim off slowly. It will shoot off like a rocket, as Angie often says. If it rolls over, or
slows down and doesn’t shoot off like a rocket, it may be stressed.
Does this mean the trout will die? Not any faster than you when you give out of breath
climbing the mountain. It puts the fish at some risk, but just how much risk depends on a
lot of things. To shorten this, in bass tournaments with big dead fish penalties, there have
been many times that I have wanted to give bass mouth to mouth recitation, only to see
them active as they could be minutes later.
Will they swim off and die? According to many studies on just this subject, the answer is
usually no. The great majority of them will be just fine. Of course, every once in a while,
one may die. In my opinion, they will die at about the same rate as you if you give out of
breath climbing the mountain. Far more will die from anglers taking pictures and/or
mishandling the fish otherwise – far more.
Next Summer, if there’s any question about the water temperatures, fish at the highest
elevations. Take the water temperature. Don’t guess at it. If it’s below (lets say, sixty-eight
degrees) catch all you want and just make sure you release them as quickly as possible.
If it’s higher than that, or has the chance of getting any warmer, I would suggest you look
for another location. The trout will not be easy to catch and it is possible, if the fish is
mishandled, for one to die.
Some anglers have blown the problem of fish stress and mortality completely out of
proportion – some unintentional and some trying to impress anglers as the “savior of
trout”.
Copyright James Marsh 2013