Electrofishing capture efficiency of four pulse rate/duty cycle Gritters, S. A. 1994. Electrofishing capture efficiency of four pulse rate/duty cycle combinations conducted on Navigation Pool 13, Upper Mississippi River. Report by the Iowa Department of Natural Resources, Bellevue, Iowa, for the National Biological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, October 1994. LTRMP 94-S009. 6 pp. (NTIS #PB95-149225) ABSTRACT An electrofishing efficiency study was conducted on Navigation Pool 13 of the Upper Mississippi River to determine the effects of four pulse rate and duty cycle combinations on electrofishing catch rate. The four combinations of pulse rate (Hz) and duty cycle (%) tested were 60/25, 60/75, 80/25, and 80 Hz/75%. It was found that all settings were effective in the capture of fishes; however, the catch rates differed among settings (X2 = 24.01 P ¢0.05) and 60/25 combination captured more fish than the other settings. The 60/25 setting also showed the least variation between samples. Average lengths and length frequencies of largemouth bass (Micropterus salmoides) collected with the four combinations were similar. KEYWORDS electrofishing, pulse rate, duty cycle, largemouth bass, Mississippi River, galvanotaxis