Northwest Fishing Magazine September 2025 Volume 5 Issue 1 - Flipbook - Page 15
DUDE: So for the fisheries
folks, it’s “to weir or not to
weir – that is the question.”
KOKANEE: And their task is
not quite that simple either.
Science can make better
predictions if there are
fewer variables. And always
keep in mind that science
and politics don’t mix. To
be considered are also the
factors that affect the food
supply itself. If the food
supply has been constant
over several years, then
manipulating spawning
grounds gives a more
reliable result. Calculations
are made based on the
number of fish desired as
a ratio to the reliable food
source necessary to sustain
that fish population.
DUDE: So you are saying if
many variations affect the
food supply, it becomes
more challenging to use
weirs as a means of birth
control.
KOKANEE: Exactly. And many
fish and game folks are
thrown blame based on
factors they cannot control.
DUDE: So what are some of
the factors that affect the
food supply?
KOKANEE: The pH of the
water and the water
temperature are the first to
be considered. In chemistry,
pH is a numeric scale used
to specify the acidity or
basicity (alkalinity) of an
aqueous solution. Recall
that the primary food for
kokanee is plankton, more
specifically zooplankton.
Kokanee's favorite food
is the zooplankton called
Daphnia. Kokanee fry
devour copepods, a smaller
zooplankton. Zooplankton
can move about in the
water column and are
not dependent upon
wind and wave action
to go on an adventure.
Zooplanktons eat their
share of the phytoplankton.
Phytoplankton needs
sunlight to produce the
carbohydrates that the
zooplankton rely on. If
the pH of the water is too
acidic, the beneficial green
algae cannot survive. Algae,
like other plants, utilize light
to photosynthesize food for
growth. Low temperatures
slow algae growth. During
the day, photosynthesis
takes place due to the
presence of sunlight.
Algae draw carbon dioxide
from the water to utilize
during photosynthesis,
promoting cell growth.
Removal of carbon dioxide
from the water raises the
pH levels, as a result of the
reduction in carbonate
and bicarbonate levels of
water, since they are used
to replenish the lost carbon
dioxide.
