Effect of Pulsed DC Frequency on Capture Efficiency and Spinal Injury of Trout in Small Streams

Abstract

Electrofishing studies in the 1990s established that higher frequencies of pulsed DC (e.g., 60 Hz) generally result in more spinal injury to fish in comparison with lower pulse frequencies (e.g., 30 Hz). In response to those findings, some agencies adopted low pulse frequency standards to minimize fish injury. However, those earlier studies did not assess whether capture efficiency (CE) was also influenced by pulse frequency. We sampled small trout streams (1–6‐m average width; SE = 0.14 m) by backpack electrofishing with settings of 30 and 60 Hz to evaluate the effect of pulse frequency on both CE and spinal injury rates for Cutthroat Trout Oncorhynchus clarkii, Rainbow Trout O. mykiss, and Brook Trout Salvelinus fontinalis. Duty cycle was held constant at 24% and average power output was held at approximately 100 W. Using a four‐pass removal protocol, cumulative CE (all four passes) averaged 0.84 for 30‐Hz reaches and 0.94 for 60‐Hz reaches. Capture efficiency in pass 1 averaged 0.59 for 30‐Hz reaches and 0.75 for 60‐Hz reaches and declined with successive passes using both pulse frequencies. X‐ray images revealed vertebral compressions and misalignments for 4% of fish captured with 30 Hz (n = 230) and 4% of those captured with 60 Hz (n = 222); no fractured vertebrae were observed. No spinal injuries were observed in control fish that were captured via angling (n = 92). Our results indicate that in small streams where trout are generally less than 300 mm TL, backpack electrofishing with 60 Hz will result in greater CE, improved trout occupancy and abundance estimates, and no increase in spinal injury.

Electrofishing eel, salmon and trout: impact of waveform and frequency on capture-per-unit-effort and spinal damage

“…Voltage decreases during a PEC discharge, however, so the voltage gradient in the water is probably not sufficient (less than 0.1V cm À1 ) to induce a neuromuscular reaction in fishes. During depletion captures, Chiaramonte et al (2020) found greater capture efficiency when they electrofished salmonids with a PDC-60Hz than a PDC-30Hz. This suggests that frequency can influence results (estimation of abundance and capture efficiency with the continual application of electricity) when using depletion sampling, but not, according the present study, when using sampling points (CPUE with a discrete application of electricity).…”

“…Beaumont et al (2000) demonstrated under experimental conditions that PDC captured rainbow trout more efficiently than PEC but that the shape of PDC at a given power had no influence. Moreover, Chiaramonte et al (2020) found a difference in the probability of capturing trout between two PDC frequencies (30 Hz and 60 Hz). Some points still need to be explored, such as the effect of DC on the ability to catch fishes and the relation between higher frequency and injury to fishes.…”

The 100‐Watt Method: A Protocol for Backpack Electrofishing in Small Streams

“…Scatterplots of peak voltage and peak current over the range of water conductivity in stream reaches in the study by Chiaramonte et al (2020). The inverse relationship between voltage and current occurs because average power is held at or near 100 W regardless of water conductivity.…”

“…Second, we used a general linear model to evaluate whether ambient conductivity (as a continuous variable) affected average power output; while we already knew that power output differed between habitat types (i.e., between riffles and pools, as was described above), we included habitat type (as a discrete variable) in the model, as well as a conductivity × habitat interaction term in order to evaluate whether the difference in power output between riffles and pools was affected by changes in conductivity. Finally, we used a general linear model to evaluate whether average power output affected CE; while we already knew (from Chiaramonte et al 2020) that pulse frequency affected CE, we included pulse frequency (as a discrete variable) in the model, as well as a pulse frequency × power output interaction term in order to determine whether the difference in CE between pulse frequencies was affected by changes in power output. To obtain a single power value for each reach to relate to CE, we used the mean of the four average power output values (pool and riffle, start and finish).…”

Spatial distribution and ecological relationships of stream fishes in Iowa's Driftless Area

“…Although other habitat features may affect detection probability of stream fishes (e.g., substrate size proportion, instream habitat complexity, and water clarity; Meyer and High 2011; Lamothe et al 2019), we focused on electrofishing effort because we expected that detection probability of both Brook Trout and Brown Trout would increase with sampling effort. Additionally, detection probability has been estimated to be high for trout in wadeable streams Kanno et al 2015;Chiaramonte et al 2020). After comparing detection model results, we used estimated overall detection probabilities to develop a cumulative detection curve for each species to determine how additional sampling occasions (i.e.…”