Influence of Electrofishing on the Mortality of Arctic Grayling Eggs

Abstract

The influence of electrofishing on egg mortality of Arctic grayling Thymallus arcticus was investigated. The hypothesis that electrofishing affects egg mortality was supported by two experiments. Experiment 1 examined the mortality rate of Arctic grayling eggs from parents that were electroshocked before spawning, and experiment 2 examined mortality rates of eggs that were electroshocked after fertilization. For experiment 1, egg mortality rates were significantly higher than the control group. The difference in mean mortality rates was 0.016 (SE = 0.005) compared to the control (P = 0.022). For experiment 2, mean egg mortality varied significantly (P < 0.001) by parents (electroshocked or not electroshocked), level of electroshock, and egg developmental stage. The largest difference in mean mortality rates compared with that of controls was 0.086 (SE = 0.017) for eggs electroshocked at the highest voltage gradient (1.30–1.50 V/cm), at 70 temperature units postfertilization, and from parents that were electroshocked before spawning. Under normal field conditions, only eggs in close proximity to an electrode would experience the highest level of electroshock used in this study. At other stages of development and at lower voltage levels (equivalent to being farther away from the electrodes), egg mortality rates were considerably less (typically <0.05). Arctic grayling eggs experienced less mortality before and after 70 temperature units postfertilization. The results of this study suggest that even in situations when the probability of exposure to electroshock is high, the cost to the population from using electrofishing to sample Arctic grayling is low.