Backpack or towed electrofishing gear are used for sampling fish in wadeable streams. Backpack electrofishing units consist of electrofishing devices mounted on backpack frames. The power source is either a 24-volt deep cycle battery or a 115-volt gasoline-powered generator. Backpack electrofishing is usually most effective in relatively shallow (less than 1 m), small (not greater than 5 m wide) headwater streams. Towed electrofishing gear consists of a portable generator and electrical output control mechanism, placed within a small boat towed behind (or pushed in front of) an operator. Towed electrofishing gear is usually more effective in relatively wide (greater than about 5 m) wadeable streams with deep pools (greater than 1 m deep). Channel width, channel depth, and access for towed electrofishing gear must be considered in determining the choice between backpack and towed electrofishing methods.
Regardless of the gear chosen, electrofishing procedures for wadeable streams require an electrofishing crew consisting of three to six individuals. Using backpack electrofishing gear, one crew member is the operator of the electrofishing equipment. With towed gear, three crew members are needed to operate the electrofishing equipment. With either gear, two crew members collect fish with dip nets, while an additional crew member is sometimes needed to transfer collected fish to a holding container. All crew members must wear polarized glasses to enhance their ability to see fish that have been stunned by the electrical field.
Procedures for collecting samples using backpack or towed electrofishing gear are similar. Sampling begins at the downstream boundary of the sampling reach and is conducted in an upstream direction. Disturbance caused by electrofishing crews walking in the stream increases turbidity, thereby greatly reducing visibility and collection efficiency. Therefore, sampling in an upstream direction maximizes visibility and collection efficiency. Also, sampling in an upstream direction allows stunned fish to drift downstream, facilitating their capture by crew members. Thus, sampling in an upstream direction in wadeable streams is preferred over sampling in a downstream direction (Hendricks and others, 1980).
All geomorphic channel units and habitat features, such as log jams, macrophyte beds, or large boulders within the wadeable sampling reach, are sampled using pulsed direct current. This may require electrofishing from one shoreline to the other in a "zigzag" pattern, consistently sampling all areas within the sampling reach. Collecting fish from the entire length of the sampling reach is referred to as a "pass" and may require more than one electrofishing operating technique.
A common electrofishing operating technique is to apply electrical current to the water continuously. Fish tend to respond to continuously applied electrical current by attempting to avoid exposure to the electrical field. Thus, continuous application of electricity can result in fish moving just ahead and away from the operator. The operator should be aware of this response and take advantage of natural barriers such as banks or bars, or very shallow areas to "herd" fish into and facilitate their capture. If natural barriers are not available, then seines or other "blocking" nets can be used to create a barrier at the upstream boundary of the sampling reach, thereby increasing sampling efficiency. However, the use of blocking