A Novel Approach for Detecting Minute Electrical Fields Where Blue Catfish (Ictalurus furcatus) and Flathead Catfish (Pylodictis olivaris) Surface When Electrofishing

Electrofishing is a widely used gear that provides efficient samples of Blue Catfish Ictalurus furcatus and Flathead Catfish Pylodictis olivaris throughout their range.  Efforts are underway in Missouri to determine the threshold voltage gradients and power densities for a consistent capture-prone response of these species that exhibit atypical behavioral responses to electrofishing by surfacing at distances over 80 m from the electrofishing boat.  A better understanding of the in-water electric field characteristics at distances where catfish exhibit capture-prone responses is essential to applying the power-transfer model to develop power-based goals specific to these catfish species.  To measure the field intensities (voltage gradients in V/cm), we designed a voltage gradient probe with terminal pins that can be separated up to 1 m apart (compared to the typical 1-cm pin separation) and connected it to a portable oscilloscope.  With a pin separation of 1 m, we measured voltage gradients ranging from 0.00500 to 0.000016 V/cm at distances of 13 m and 108 m, respectively, from the electrofishing boat (fore side) where catfish were actively surfacing.  These are some of the lowest field intensities ever measured and will inform our understanding of the atypical response of these catfish species to electrofishing.