A field comparison of different boat electrofishers with comments on standardization

Objective As standardized boat electrofishing methods are adopted, integrating changes in electrofishing equipment at an agency-wide scale is an expensive and protracted process. As a result, many agency offices use a variety of electrofishing control boxes among different boats or interchangeably among boats. Our objective was to compare electrofishing catch data that were collected using different control boxes that are currently in service within and among electrofishing fleets to provide guidance on interchanging between different control boxes and the continued use of out-of-production control boxes for which standardizing power output is difficult. Methods We conducted a field-based assessment of the catch data that were produced by two configurations of a Smith Root Type VI-A electrofisher (low voltage/high pulse width and high voltage/low pulse width) and one configuration of an ETS MBS-1D electrofisher (output standardized to a power goal based on water conditions). The low-voltage Type VI-A configuration was chosen to match the voltage output of the standardized MBS configuration, and the higher voltage configuration consisted of the next highest voltage range on the control box, with the same root-mean-square current as the low-voltage Type VI-A configuration. To isolate the effect of control box configuration, all the data were collected with the same electrofishing boat and equipment, with the same driver and netter, and from the same water body. We tested for differences in the fish assemblage structure, relative abundance, and size structure among the data that were collected by the three configurations. We also mapped voltage gradients surrounding the anode array to assess how the size and strength of the electric field changed with the different configurations. Results The fish assemblages sampled and catch rates of most species were similar among the three electrofishing configurations, but fish <220 mm were consistently underrepresented when electrofishing with the Type VI-A at the lower voltage range. No differences were detected between data that were collected by the standardized MBS and the Type VI-A at higher voltage. The mapped voltage gradients supported the results of calculations that indicated that the Type VI-A configuration required 34% more voltage and current than the MBS configuration for comparable fish capture. Conclusions Inherent differences in settings and characteristics of the waveforms produced by different electrofishers can complicate methods for standardizing power or current outputs that are required for consistent and safe fish immobilization. Although calibration among different control boxes is possible, our results suggest that parabolic pulse shapes require higher peak power outputs than rectangular pulse shapes to produce effectively similar fish catches. Measuring the strength of the electric field provides important methodological context for electrofishing whether users are transitioning from older to newer equipment or relying on out-of-production control boxes.