Exposure of Unionid Mussels to Electric Current: Assessing Risks Associated with Electrofishing

Abstract

Electric current is routinely applied in freshwater for scientific sampling of fish populations (i.e., electrofishing). Freshwater mussels (families Margaritiferidae and Unionidae) are distributed worldwide, but their recent declines in diversity and abundance constitute an imperilment of global significance. Freshwater mussels are not targeted for capture by electrofishing, and any exposure to electric current is unintentional. The effects of electric shock are not fully understood for mussels but could disrupt vital physiological processes and represent an additional threat to their survival. In a controlled laboratory environment, we examined the consequences of exposure to two typical electrofishing currents, 60-Hz pulsed DC and 60-Hz AC, for the survival of adult and early life stages of three unionid species; we included fish as a quality control measure. The outcomes suggest that electrical exposure associated with typical electrofishing poses little direct risk to freshwater mussels. That is, adult mussel survival and righting behaviors (indicators of sublethal stress) were not adversely affected by electrical exposure. Glochidia (larvae that attach to and become parasites on fish gills or fins) showed minimal immediate reduction in viability after exposure. Metamorphosis from glochidia to free-living juvenile mussels was not impaired after electric current simulated capture-prone behaviors (stunning) in infested host fish. In addition, the short-term survival of juvenile mussels was not adversely influenced by exposure to electric current. Any minimal risk to imperiled mussels must be weighed at the population level against the benefits gained by using the gear for scientific sampling of fish in the same waters. However, scientists sampling fish by electrofishing should be aware of mussel reproductive periods and processes in order to minimize the harmful effects to host fish, especially in areas where mussel conservation is a concern.