Selection of appropriate gear types and models is frequently a difficult task. Often decisions are made with little basis. Here we highlight some factors that we think should be considered when selecting or purchasing electrofishing gear.
By Alan Temple & Jan Dean
At the end of this discussion, we list models that have the attributes we feel are needed for safe and effective sampling. Before we get started, by “type” we mean major equipment categories such as backpack shocker, boat shocker, or electric seine. “Models” are defined as different forms or brands of an equipment type.
The main considerations are associated with logistics/sampling design, capture efficiency/repeatability, and safety.
Logistic elements include the ease of using a particular type of equipment or model and the characteristics of the sample sites. Gear weight and ease of transport are common issues. For example, backpack models, while very portable, differ in weight. In addition, if battery powered, the use of lithium batteries will further reduce weight (up to 55%) since they are much lighter than lead-acid batteries. The physical attributes of the sample sites can narrow your choices. Big considerations are depth (wadeable or non-wadeable) and, especially with streams, width. Electric seines that span the width of a stream may be preferred over backpack shockers if stream width allows excessive avoidance of fish to the electric field. Water conductivity range is a critical factor behind gear selection and will be discussed later.
Sampling design and study purpose play an important role. Are you using 3-pass depletion sampling or are you more interested in quadrat style sampling? Is the purpose of your study to estimate density or abundance and, if so, at what scale? Are you wishing to characterize fish-microhabitat relationships? So, for example, depletion sampling could be accomplished by several different gear types whereas quadrat sampling for density or fish-microhabitat relationships might entail specialized gear as pre-positioned area shockers.
Capture efficiency and repeatability (=”standardization”) are hugely important to the effectiveness of many studies but are more complicated to incorporate into gear selection decisions. The long and short of it is that models need to have fine, independent controls of electrical waveform characteristics important to fish capture and accurate metering (peak volts and peak amperage) to make sure of actual electrical output. A particular piece of equipment also must have the capacity to generate an electric field large enough for successful sampling given the sample site water conductivity.
Here’s various equipment attributes that can give you the capability to improve capture efficiency and precision.
Power, maximum output average: backpacks typically are 200 Watts or 400 Watts average; control boxes for boat units range from 1,700 Watts to 9,000 Watts average and more. Higher power capacity can increase the upper range of water conductivities that you can effectively electrofish.
Waveform type: may have one of more of these types- alternating current (AC), direct current (DC), or pulsed direct current (PDC). Having all three options in a control box provides more capabilities for capture and fish trauma control; AC often extends operating range into lower or higher conductivity waters. DC can be very effective for attraction of fish to the anodes and often is less injurious to salmonids. PDC can be very effective while putting less power demand on your equipment. Some units have a special form of PDC, the gated burst or complex pulse system, primarily used to minimize fish injury potential.
Voltage control: Continuous or small increments (e.g., 5 Vpeak per selection) are desirable. Large increments (>= 50 V) can make it difficult or impossible to apply required outputs for standardization or reduction of fish trauma. A large voltage increment can result in the lower setting resulting in poor catch and the higher setting resulting in shutdown due to excessive power or current draw. Common maximums range from 600 Vpeak to 1000 Vpeak direct pulsed current, and up to 700 Vrms (AC); higher voltage can extend effective fishing range into lower water conductivities.
Amperage: maximum peak current typically ranges from 10 amps to over 75 amps in the higher power units, with the maximum near 600 peak amps in one U.S.-built control box; higher amperage capacity can extend effective fishing range into higher conductivity waters.
Frequency: Typically ranges between 7.5 – 120 pulses per second for PDC (50 or 60 Hz typical for AC). However, higher frequencies, as 300 pps, are showing promise for capture. Some units have capacity up to 1000 pps. The best option is continuously adjustable or fine control by 1 pps increments. Often higher frequencies, at least up to 120 pps, result in lower response thresholds and are more effective (i.e., less power needs to be applied for a particular capture-prone response). Concerning fish trauma, the ability to control frequency enables waveform management to lower fish injury potential.
Pulse width: Units range between less than a millisecond to 10 milliseconds or more; Typical applications use 1 millisecond or more (often up to 4 – 6 milliseconds); pulse width and frequency affect duty cycle.
Duty cycle: Best control is continuous (1% increments) from 1% – 100% (DC); Research has suggested that the optimum range of duty cycle for capturing fish ranges between 20 – 40% so a 40% maximum is sufficient in many cases, although higher duty cycles can increase attraction (taxis). Good control of duty cycle gives you the flexibility to adjust waveforms to improve fish reaction, particularly attraction.
Waveform shape: Shape can vary across models (e.g., capacitor-discharge exponential decay, square, rectified AC) for all three major waveform types. There has been limited research on comparison of capture efficiencies and potential for fish injury among different PDC waveform shapes. Square waves compared favorably in capture efficiency and lower fish injury and stress levels. “Rounded” PDC pulses from rectified AC appear to require higher power than square waves to sample at the same efficiency. The square shape also facilitates accurate metering and description (e.g., duty cycle). Note that square waves can have slanted tops or spikes when under heavy loading, as in high conductivity waters. An operational capacity analysis with a scopemeter can indicate how well a unit keeps the waveform shape intact under various levels of loading.
Metering: It is critical to have good peak reading meters; the best configuration is a peak reading output voltage meter and a peak output amperage meter; however, either a peak volt or a peak amp meter will allow you to standardize by voltage or amperage (of course, really power). If you have an average reading amperage meter, you’ll need a good duty cycle meter or a recently calibrated duty cycle control to convert average to peak. Due to wave non-symmetry, using RMS voltage or current meters for AC is not recommended. You’ll need a peak-reading voltage or current meter for AC as well. Without metering, assuming that the dialed-in values (setting) for voltage is equal to output may be problematic, particularly at high loadings (usually high conductivities); if you don’t have metering, the best option is to incorporate testing equipment (e.g., a scopemeter-current clamp combination to serve as the amp meter). Do not trust the setting value.
Electrodes: The design of electrodes is under your control and preferences. For DC or PDC and often AC electrofishing, typically you want the cathode to have larger surface area than the anode. High resistance can limit power output.
Operational Capacity: Here you are trying to answer the question: “What is the range of water conductivities that can be successfully electrofished with the unit under consideration?” (Do not rely on conductivity ranges given by manufacturers). First determine 1) the range of water conductivities that you will encounter and 2) the level of power required for successful electrofishing across water conductivities with a particular gear (use Excel files EF Goal Power or Electrofishing with Power or the Electrofishing Tool app). Note: a determination of successful electrofishing means that at a given water conductivity and using an effective waveform, you can generate more peak power than you need. Next, run an output analysis of your gear. You’ll need to input certain equipment specifications from the manufacturer and electrode resistance. Use the Excel files Boat Power and Backpack Power to estimate the effective electrofishing range across water conductivity.
Safety features: Saving the most important topic for last, safety features on equipment have been critical to providing safer working environments for crews. Equipment safety requirements is a topic that can be specific to the country or region, depending upon national codes. Features that are standard or desired include construction to electrical standards (wiring capacities, conductors in conduit, water-resistant plugs, etc.), an easily-accessible safety (on-off) switch (e.g., mushroom switch), a “power on” light, safety switch on hand-held electrode handle (backpacks), foot-activated switch on boats (pedal, mat, or kick-plate), tilt-switches on backpacks (forward, backward, and/or sideways), and railings on boat work decks. Additional features to consider include a backpack immersion switch (when operator goes down vertically into the water), anode out-of-water switch, battery compartment splash guard, and enunciator (“power on” sound for battery-powered models). Don’t forget the all-important personal protective gear as insulative gloves.
The following are models that have the desired features we discussed above and are offered as examples. We also have evaluated the output waveforms and metering of these units with scopemeters. (It should be said that our testing has not been limited to models listed below). Any of these models will provide the level of control and metering that is required for efficiency and standardization work. Distinguishing among them for your particular sampling needs requires a power analysis of the units to determine operational capacity. As a guide, units with higher voltage maximums will allow successful fishing in lower conductivities. Units with higher amperage maximums and/or power maximums will extend successful electrofishing into higher water conductivity.
This list is a work in progress, and will be updated from time to time as new models become available and are evaluated. Also, check our buyer’s guide.
ETS Electrofishing, LLC., http://www.etselectrofishing.com/
ABP-3 (backpack shocker)
SDC-1 Stream Barge Electrofishing System (tow-barge shocker)
MBS Boat Series (boat control boxes)
Midwest Lake Companies (Electrofishing Systems), www.midwestlake.com
Infinity Xstream Backpack Shocker
The Infinity Box (control box for tow-barges and boats)
Smith-Root, Inc., www.smith-root.com
LR-24 Backpack Electrofisher
VVP-15B Electrofisher (boat control box)