The efficacy of killing developing common carp embryos with electricity: using a laboratory evaluation to assess a potential means of reducing the recruitment of an invasive fish

Concern about electrofishing inadvertently harming the embryos of species of conservation concern has motivated much of the research that describes what electrical conditions can kill fish embryos. As a result, targeted electrofishing might be underutilized as a potential control method to reduce the recruitment of nuisance fishes like common carp (Cyprinus carpio), one of the most widely distributed invasive fish in North America. We evaluate the efficacy of using electricity to reduce common carp recruitment by examining embryonic survival while manipulating the transfer of electric power to developing carp embryos. Embryos were shocked in water from a carp-occupied area (ambient conductivity 127 mu S/cm) using a variety of voltage gradient and waveform treatments common to commercial electrofishing units and generators. Survival of electroshocked common carp embryos was <= 50% at power densities (12,700 mu W/cm(3)) and voltage gradients (10 V/cm) that failed to cause significant mortality in other cyprinid species; however, embryonic resistance to electroshock was first noted at almost 3 d after fertilization (survival <= 50% at 79,375 mu W/cm(3)). Power transfer theory was used to explore optimal water conductivities for the deployment of electrical control of fish embryos at shallow endorheic lakes by using conditions at Malheur Lake as an example. Power transfer theory suggests that at relatively high water conductivities it becomes more difficult to achieve power transfer thresholds sufficient to kill small fish embryos without exceeding the power capabilities of commercially-available electrofishing equipment, and that power transfer to the embryo drops below 50% of the total power applied when water conductivities exceed 325 mu S/cm. Thus, water chemistry conditions most amenable to killing carp embryos with electricity in an arid, endorheic lake like Malheur Lake would most likely occur at lake inflows or more generally when the lake level is elevated. However, when spawning is dispersed or more spawning habitat is available during higher lake levels, the resulting increase in areas that require treatment may present logistical challenges. Managers considering the use of electrofishing to control recruitment of an invasive fish like common carp should consider the spatio-temporal arrangement of spawning sites, the spatial scale of the necessary control treatment, how compensatory effects may influence the overall population response, and the need for concurrent control methods targeting other life stages.