Midwest Fish & Wildlife Conference 2018

AUTHORS. Zach Morris, University of Missouri; Craig Paukert, U.S. Geological Survey, Missouri Cooperative Fish & Wildlife Research Unit; Zach Ford, Missouri Department of Conservation; Andy Turner, Missouri Department of Conservation; Jan Dean, Dean Electrofishing, LLC

ABSTRACT. Standardized sampling is essential to monitor Smallmouth Bass populations. Our objective was to evaluate the effectiveness of different electrofishing settings for collecting Smallmouth Bass by measuring immobilization response thresholds. We compared immobilization thresholds for 12 pulsed DC waveforms (30 to 120 pulses per second (Hz), duty cycles of 15 - 40%), including a commonly used waveform to collect Smallmouth Bass (60Hz/25%). A total of 310 Smallmouth Bass from two size groups (18-28; 35-43 cm) and three temperatures: 11 – 14°C, 17 – 20°C, and 22 – 26°C were collected via electrofishing, rested in a pen for >1 hr, and placed in a tank attached to a backpack electrofisher. Voltage was increased from one volt until immobilization was observed. Preliminary analysis using a 3-way anova testing if immobilization threshold differed by waveform, temperature, and fish size revealed two-way interactions with temperature and size (P=0.01) and temperature and waveform (P=0.071). For the coolest water temperature, the lowest immobilization thresholds were generally with 30 Hz waveforms but did not differ from the commonly used 60Hz/25% waveform (P For the warm water temperature, there was interaction between waveform and size class (P=0.031). Immobilization threshold tended to be the lowest for 60Hz/25% and 120Hz/30% waveforms for small fish (P=0.074) and 60Hz/25% was the lowest for larger fish (P=0.007). A standard waveform commonly used to collect Smallmouth Bass (60Hz/25%) was typically grouped with the waveforms that had the lowest voltage gradients. These results reflect preliminary analysis that will be finalized in 2018.