Northwest Fishing Magazine September 2025 Volume 5 Issue 1 - Flipbook - Page 17
is little food for the kokanee
to eat, making them less
active.
KOKANEE: Right. The type
and amount of dissolved
nutrients also affect
algae growth. The most
important one is the
amount of phosphorus
available and dissolved in
the water. Less phosphorus,
less algae.
DUDE: How do the dissolved
nutrients get into the lake?
KOKANEE: You really have to
think in terms of the entire
watershed that comes
into the lake. When the
watershed has wildfires,
nutrients are released that
are washed downstream
and wind up in the lakes.
Heavy storms can cause
significant erosion in
upstream water paths.
Rapid snowmelt can do
the same. While some of
the nutrients are already
dissolved in the water
flowing downstream,
sediments that enter the
lakes will take time to
dissolve, becoming part
of that lake’s ecosystem.
So you can see that there
are a lot of factors. In
the old days, runoff from
agriculture produced too
much phosphates and
other gunk into reservoirs.
DUDE: What other factors
affect size?
KOKANEE: Manipulation of
the natural food supply
has sometimes produced
huge kokes with disastrous
long-term effects. Many
years ago, Mysis shrimp
were introduced into the
Flathead Lake watershed
in Montana. The Mysis
managed to migrate
downstream into Flathead
Lake. The sole purpose was
to be an enhanced food
supply for the resident
kokanee in the upstream
lakes. The goal was to
create large kokanee. Mysis
shrimp pack a lot more
protein than processing
plankton. It is sorta like the
difference between steak
and salad. At least that was
the theory.
DUDE: Let me guess. Things
did not go as planned?
KOKANEE: Not even close.
Glad you are sitting down.
Remember, phytoplankton
is the primary food source
of the zooplankton,
which in turn is the main
food source for kokanee.
Phytoplankton needs
sunlight, so in most waters,
phytoplankton distribution
is limited to about the
top 30 feet of the water
column. Once the sunlight
that penetrates the water
column falls below about
10%, phytoplankton cannot
achieve photosynthesis.
Zooplankton migrate up
