Surfacing Response Thresholds of Blue Catfish Exposed to Low‐Frequency Electrofishing

Increasingly, management efforts are being directed at Blue Catfish Ictalurus furcatus native and invasive populations; however, a lack of standardized sampling procedures using low‐frequency electrofishing (LFE) has hampered the ability to collect comparable data across temporal and spatial scales. Therefore, we conducted wetlab LFE trials to determine optimal power densities that elicit a capture‐prone surfacing response by Blue Catfish. We tested power density applied to the fish (Dm) from 4.69 × 10−6 to 3.65 μW/cm3 and trials with at least one surfacing fish occurred between Dm values of 2.144 × 10−5 and 0.854 μW/cm3. Trials in which ≥50% of fish surfaced all occurred at Dm values between 9.29 × 10−5 and 0.2084 μW/cm3. Even within this narrower range, responses were variable and included trials where no fish surfaced, indicating a wide range of response rates across all power levels tested. Our results suggest that a power density applied to the fish (Dm) between 9.29 × 10−5 and 0.2084 μW/cm3 is most likely to elicit a surfacing response in Blue Catfish, thus exposing them for capture. Further research is needed to map power densities over a range of distances from the electrode (i.e., relating power at the electrode [Pa] with power density in the water [Da]) before standard power tables can be produced. Until this information becomes available, we recommend using the power tables from Bonar et al. (2009) because these allow effective capture of catfishes and will standardize the effectiveness until a better power table could be produced for LFE. Additional research is needed to better understand the Blue Catfish's unique electroreceptive mechanism that drives variability in the response to LFE and whether the proportion of fish surfacing is consistent enough to use catch per unit effort as an index of abundance.