Here in Montana rivers and streams are not stocked
with hatchery-reared trout. We rely on natural reproduction
of wild trout populations in our rivers and streams.
The Department of Fish, Wildlife and Parks, anglers
and irrigators have long known that many wild trout
are annually lost from river systems during irrigation
season. When water is diverted from a river to an
irrigation ditch, many trout follow the diverted
flow and are eventually "trapped" in the
ditch. The problem is especially acute during times
of low river flows when a high percentage of the
existing stream flow is diverted into the irrigation
canals.
Irrigators and help save wild trout!
Irrigators who gradually shut down their diversions
and headgates can save trout by affording the time
they need to return to the river.
Investigations conducted in the 1950's by the then
Montana Department of Fish and Game, and the recent
application of gradual headgate shut down methods
by irrigators in south-western Montana, show that
timely headgate manipulations saved substantial
numbers of trout that would surely have died had
the ditches' water flow been cut off suddenly.
Trout need three days to move out of a ditch
To help save trout, FW&P recommends that ditch
companies and irrigators gradually reduce the flow
in irrigation ditches in three equal increments,
at least three days prior to the headgate being
completely closed. The gradual, three-day shutdown
is based on the time it takes the maximum number
of trout to move up and out of an irrigation canal
or ditch.
The gradual flow reductions are remarkably beneficial
to trout and can be applied anytime the ditch is
scheduled to be closed, or when conditions favor
decreased flow during the irrigation season. F
For most effective results, the procedure should
be followed before each cutting of hay and at the
end of the irrigation season.
Open-channel diversions
On open-channel diversions, irrigators can simply
remove equal portions of the diversions over a three-day
period. During the first day, irrigators can remove
a portion of the diversion farthest from the ditch
and follow the same procedure over the following
two days until the diversion is removed and closed.
Plank headgates
For plank-type headgates, on the fist day irrigators
can place a board horizontally across the bottom
of the diversion to reduce flows by one-third. On
the second day, another board on top of the first
to reduce flows by an additional one-third. On the
final day, the headgate can be shut down.
For twin headgate systems, completely close one
side on the first day and follow the same procedure
for the headgate remaining open as outlined above.
Screw down headgates
For screw down headgate systems, on the first day
irrigators can place a board vertically over the
diversion to reduce flows by one-third. On the second
day, a second board can be placed vertically over
the diversion to again reduce flows by one-third.
On the final day, the headgate can be shut down.
For twin headgate systems, completely close one
side on the fist day and follow the same procedure
for the headgate remaining open as outlined above.
Additional trout-saving measures
These methods work because the slow, staggered
shutdown of an irrigation ditch gradually reduces
trout living space in the ditch and prompts trout
to move up the ditch until they reach the river
or until they find temporary hiding places in the
form of pools and rocks.
Trout will travel faster and farther up a canal
whenever a uniformly smooth channel bottom exists.
So, an even greater number of trout can be saved
by filling holes and removing rocks from the ditch.
This is especially important in the area immediately
behind a headgate.
Anglers are willing to help
If irrigators or water managers believe that some
of these practices would take too much time, it
may be possible to cooperatively work with local
anglers or sportsmen's clubs that may be willing
to do the work under the direction of the irrigator.
A phone call to the nearest FW&P office, local
Trout Unlimited chapter or sportsmen's club a few
days prior to the anticipated ditch closure, could
muster up the help needed to begin.
Together, irrigators and anglers might set up a
yearly schedule for carrying out these trout-saving
measures.
Please call the Montana
Fish, Wildlife and Parks office nearest you
for more information.
