typically devoid of rooted plant life, which limits the
diversity of aquatic invertebrate food sources. The
most abundant insects found living in deep water
are chironomids, as the rich organic bottom or
benthic zone provides ideal larval habitat. It is not
uncommon to have chironomid pupal emergences
occurring in water from 10 to 20 meters in depth.
At other times of the year trout seek out the deep-
water zone in search of diving water boatman and
backswimmers that are in the midst of swarming
and mating flights.
THE IMPORTANCE OF AQUATIC VEGITATION
Aquatic vegetation plays an important role in small
lake ecosystems. Submergent species provide prime
habitat for scuds, mayfly, damselfly and dragonfly
nymphs, caddis larvae, snails, water boatmen,
backswimmers and leeches. Common submergent
plants include potamogeton (Pondweed, Cabbage
Grass), milfoil and ceratophylum (Coontail,
Hornwort). These plants are rooted and grow up
from the bottom of the shoal and drop-off zones.
A quick sweep through these plants with a small
aquarium net or kitchen strainer reveals some or
all of the above mentioned invertebrates. The most
important of these rooted green plants is chara, or
Stonewort, a green algae that forms a skeleton of
calcium carbonate. Chara is easily identified by its
crunchy, brittle texture and strong musty odor. It
often forms a thick covering over the bottom of the
shoal in lakes that are rich in calcium. Chara covered
shoals offer ideal shrimp or scud habitat and its
presence identifies a very nutrient-rich waterbody.
Emergent vegetation, such as cattails, hard-
stemmed bulrushes and lily pads offer cover to fish
swimming in shallow water and also provides the
emergence habitat for damselflies. Mature nymphs
swim up to the underwater stems of these plants and
then crawl up and out of the water. Their nymphal
shucks dry and split open as the adult form emergences
and rests on the plant stems or leaves. Growing around
these plant stems are other submerged vegetation,
which in combination make for ideal foraging habitat
for both juvenile and adult trout.
One can start to see why so much time is spent
chasing trout in shallow water. During the spring-to
early summer period this area is alive with aquatic
insect activity and emergences along with the
ongoing presence of other staple foods, such as
scuds and leeches. Trout return to the shoal zones
again in the fall when water temperatures have
cooled down. They now search of the juvenile or
younger instars of the same aquatic insects and
other invertebrates that made up their spring diet.
SEASONAL CHANGES IN WATER CHEMISTRY
Spring Turnover
Trout are cold-blooded and their metabolism is
directly related to water temperature and associated
dissolved oxygen levels. During the open-water
period there are three limnological events that
occur. These determine where in the lake the trout
can live. At ice-off the entire water column is cold.
But on close examination we find the bottom layers
of water are actually a few degrees warmer than
the surface waters. The benthic water is warmer
due to heat released during the decomposition
process of plant matter that has occurred through
the winter months. Of course some of these lakes
are covered with ice and snow for up to six months
a year. Two major mixing events occur each year
in almost all small trout lakes in the northern
hemisphere. Spring turnover typically occurs
within a few days to a couple of weeks after ice-off.
Warmer air temperatures slowly warm the cooler
upper layers of water until the temperature of the
entire water column is similar. Water is most dense
at 4 degreesC (39 degrees F) and at that point
mixes easily with a little assistance from the wind.
A lake in turnover becomes quite turbid or murky
as detritus is swept off the lake bottom and mixed
throughout the water column. Spring turnover is
an important event as it ensures the entire water
column is saturated with oxygen. However, fishing
during a turnover event is generally not very good
as the overall water chemistry is poor and the fish
generally become dour. It generally takes three-
to five days to complete the turnover and for the
water to clear. The completion of turnover signals
the start of the spring fishing season as continually
warming water initiates the parade of aquatic
insect emergences.
SUMMER STRATIFICATION
Long, hot summers are a key ingredient in producing
a quality stillwater trout fishery. Photosynthetic
energy drives the aquatic ecosystem by stimulating
phytoplankton and zooplankton growth, aquatic
plant production and development and maturation
of insect populations. Under optimum conditions this
all translates into significant fish growth. However,
trout are cold-blooded and their metabolisms are
affected by water temperature and related changes
to water chemistry.
By early summer, the upper layers of water
in many small lakes begin to warm and become
less dense than the colder, deeper water. In other
words, the energy from the sun penetrates to
a certain depth and beyond that the water stays
much cooler. A temperature gradient known as a
thermocline develops where the warmer upper
layers, known as the epilimnion, meet the colder,
deeper water or hypolimnion. Thermoclines are
invisible and typically establish between five and
eight meters deep and they are a barrier to mixing.
Therefore, summer winds continually warm and
circulate the water of the epilimnion while the
deeper hypolimnetic water below remains unmixed.
Ongoing bacterial decomposition occurring within
the benthic or bottom areas of the deepwater
zone results in decreasing levels of oxygen below
the thermocline. In many of the most productive
small trout lakes there may not be enough oxygen
below the thermocline to support fish life. In very
hot weather trout leave the warm shallow shoal
areas and sit just above the thermocline where
the water is colder and well oxygenated. Trout
suspended along the thermocline show up well
on a properly calibrated fish-finder. Trout often
come back onto the shoals to feed at night when
water temperatures are cooler and oxygen levels
hit the appropriate concentrations. That is why we
experience some great late-night summer fishing
in water often less than three meters in