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.


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.

Photo of Biologists Electrofishing

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.

Photo of Gill Net


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.

Photo of Seine Net


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.

Photo of Larval Surface Trawl

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.

Photo of Larval Fish
Larval Fish From Neuston Net Sample

Photo of Mike at the Microscope
Reading Otoliths Under a Microscope