Fish Community Surveys
TWRA reservoir biologists spend many hours each year monitoring sport fisheries and
forage fish communities. Because looking at the entire population of fishes in a lake
is virtually impossible, biologists must depend on sampling to get a snapshot of
population status and make predictions about how it will look in the future. Different
sampling methods (electrofishing, nets, trawls) are used to sample fish populations.
Targeted species surveys may be conducted to obtain information about fish population
size structure, recruitment, growth, density, and mortality.
Information gathered from sampling surveys is coupled with information about the
human and habitat components of sportfisheries and used to make management
recommendations for harvest restrictions and/or stocking. Hatchery managers also
use these gears to collect brood stock from wild populations which can be used in
hatcheries to produce fish for stocking. The following section briefly describes
sampling gear used by TWRA reservoir fisheries and hatchery staff.
Electrofishing
Boat mounted electrofishers are used in Tennessee reservoirs to fulfill various
sampling objectives. Bass, crappie, and sunfish are highly vulnerable to this gear
and surveys are normally conducted during the spring months. A sampling design is
chosen which reflects habitat diversity within a lake and fish are collected after
being stunned by the shocking boat's electrical field. Dip netters at the front of
the boat pick up the fish and hold them in livewells for later analyses.
Trap Netting
Information about crappie populations is often obtained using trap nets. Sunfish
may also be sampled using this method where substantial fisheries exist. Trap nets
are set in the late fall when crappie young move close to the shore. Nets are set
perpendicular to the shoreline and fished over night. This sampling method works
better in reservoirs with gently sloping bottoms and substantial flats in shoreline
areas than steep-sided reservoirs.
Gill Netting
Gill nets are used for a variety of fish species that are difficult to sample with
electrofishing gear. TWRA uses them to collect sauger, walleye, white bass,
striped bass, and Cherokee bass. Most netting surveys are conducted during the
winter months and may be targeted at pre-spawn runs. Like other sampling methods
gill net samples yield important insight into natural spawning success, success of
stocking programs, and sizes of fish available to anglers.
Seining
Like electrofishing, seining is an active sampling method that allows biologists
to look at forage availability, and survival of young sport fish. Seines are really
long, fine-meshed nets that are dragged through the water in shoreline areas. Seine
hauls have also been used by TWRA to evaluate stocking success of striped bass.
Trawling
In recent years, TWRA biologists have been evaluating a surface trawl for sampling
larval crappie. This allows biologists to evaluate crappie spawning success in
reservoirs where other gear types (namely trap nets) have not been an effective
way to sample. The specialized crappie net (neuston net) is dragged behind a boat
for a fixed amount of time. Larval crappie are later identified and counted back at
the lab.
Lab Analysis
Often the work does not stop in the field for TWRA reservoir crews. Fish samples
often must be processed in the lab, species identified, and counted. In addition,
otoliths (ear bones) are routinely used by TWRA biologists to determine age structure
and growth rates for sport fish populations. Data must be entered into computer
databases, analyzed, and summarized for reports. The scenes below illustrate
some of these activities.
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