Electrofishing 101: Understanding Pulse Type, Waveform, and Types of Current

Smith-Root Staff December 08, 2019

The terms "Pulse Type", "Waveform", and "Types of Current" are intermittently used when discussing the shape of the electrical current used for electrofishing. The multitude of terms can often create confusion, when really they are describing the same thing.

For this lesson, I intend to educate and clarify any misunderstandings and confusion associated with these terms.

To start off, I will exclusively call them "Waveforms". The following information is meant to describe the different waveforms and give you practical scenarios where you would typically use each in the field.

Electrical Current is the flow of electricity, namely the movement of electrons. Waveforms are simply the different ways that we create movement of electrons through the water.

Collectively, electrofishers offer the following waveforms:

  • Alternating Current
  • Direct Current
  • Pulsed Direct Current
  • Burst of Pulses Current

Alternating Current (AC) is often only available on Boat and Barge electrofishers because they are powered by generators, and generators create Alternating Current. Over time, experts have come to the conclusion that Alternating Current has the highest capture rates, but also has the highest incidence of injury. Therefore, it is often used only in eradication situations, or situations where water conductivity is at the extremes of effectiveness. Alternating Current has the word "alternating" because the positive (anode) and negative (Cathode) electrodes alternate many times per second. Therefore, the movement of electrons constantly changes direction and amplitude, with the output looking like a sine wave. Because Alternating Current constantly shifts directions, fish do not exhibit Galvanotaxis, which is the phenomenon of fish being "attracted" to the positive electrode. When using Alternating Current, the voltage is measured as the RMS, or Root Mean Square. The RMS voltage is significantly lower than the peak voltage, and only represents the voltage for half of the sine wave. Therefore, the true peak voltage experienced by a fish when using AC is more than twice the RMS value. This is one of the leading reasons why Alternating Current has a higher capture efficiency and has been so injurious to fish at given voltage.

Direct Current (DC) is available on almost all electrofishers and is used with the Electric Fish handling Gloves and when using electricity to immobilize fish during surgery. Experts have come to the conclusion that Direct Current has low capture rates, but also has the lowest incidence of injury. This is partly because Direct Current applies constant, unwavering, movement of electrons in one direction (hence the "direct" word in Direct Current). Since the electrical current is constant, fish muscles and nerves are not stimulated many times per second like they are with other waveforms. Rather, as the electric field gets closer to the fish, the amplitude increases, causing only a single, slower contraction of the muscles. The only other control you can modify when using DC is "Voltage". Since Direct Current applies a constant current, batteries drain at a rapid rate compared to other waveforms. However, because the electrical flow is all in one direction, Galvanotaxis is achieved with this waveform. Additionally, fish recover almost immediately when removed from the electric field created by Direct Current because their muscles are not contracting and relaxing multiple times per second like they are with the other waveforms. Due to low injury rates and rapid recovery, Direct Current is used most often when capturing endangered and threatened species.

Pulsed Direct Current (PDC) is sometimes referred to as Standard Pulse. It is the most frequently used waveform when electrofishing. PDC is seen as the balance between Alternating Current and Direct Current. With this waveform, capture rates are higher than those in DC and injury rates are lower, when used appropriately, than AC. With Pulsed Direct Current, the Direct Current is pulsed multiple times per second. Essentially, it chops Direct Current up and releases small pulses at a given rate, as determined by the "frequency" dial on the electrofisher that sets the number of pulses per second. One then uses the "Duty Cycle" to determine the % of time per second that the electrofisher is applying electricity to the water. The Duty Cycle essentially determines the amount of time each pulse of electricity lasts. Generally, frequency is set to 30 Hz and 12-15% for sensitive species, whereas, 60 Hz and 20-25% are used for more robust species. The low duty cycle provides tremendous battery savings while also increasing catch rates over the use of DC. With PDC, each pulse of electricity stimulates the muscle and nerves of the fish, therefore disabling the fish from controlling its own movements. Additionally, because the electrical flow is all in one direction, Galvanotaxis is achieved with this waveform. When used appropriately, PDC provides tremendous benefits while simultaneously reducing the downsides associated with other waveforms. For these reasons, PDC is the most frequently used waveform when electrofishing.

Burst of Pulses Current is almost exclusively used for removing fish from heavy cover or removing fish from bottom substrates. Particularly, this waveform is used for removing larval/juvenile lamprey from the sediment on the bottom of streams where they live. With Pulsed Direct Current, discussed above, the electrical current is pulsed at a regular and consistent rate. Whereas, with Burst of Pulses, the electrical current is pulsed in small packets with large gaps with no current that occur between the packets. The most typical Burst of Pulses output has three pulses within a "burst" or packet. The pulses stimulate the lamprey, and the period in between packets gives them time to move out of the sediment. Because frequency and duty cycle are so low, this is considered a very safe setting that is very effective at capturing lamprey. Smith-Root backpacks are scientifically proven to have higher capture efficiencies of lamprey when using this waveform.

Hopefully this familiarizes you with these waveforms while helping you understand their differences and typical uses.