Electrofishing as a potential threat to freshwater cetaceans

Abstract

Electrofishing is an accepted practice for legal fish sampling and surveying, but its use for subsistence food and market fishing has long been illegal in most countries. Illegal use affects freshwater fish populations in many parts of the world, and has been cited as a cause of mortality for endangered freshwater cetaceans in China (Yangtze dolphins and finless porpoises) and Southeast Asia (Ayeyarwady, Mekong, and Mahakam dolphins in Myanmar, Cambodia, and Indonesia, respectively), although the extent of this threat to cetaceans is unclear. Given their threatened status, these populations can ill afford such mortality in addition to the other threats they face (e.g. entanglement in gillnets, habitat deterioration and loss, declines in prey). Here, we review the evidence that electrofishing is a serious threat to freshwater cetaceans. It may alter the behavior of dolphins and porpoises, and contact with electrical currents may even directly kill or injure these animals, although questions remain unanswered concerning the exact nature and scale of the impacts. While other threats may appear more certain and urgent, electrofishing could be playing a significant role in driving the declines of some critically endangered freshwater cetaceans in Asia. Due to ethical and logistical challenges to improving our understanding of the impacts of electrical currents on cetaceans, clear descriptions of lesions in dead animals found stranded are needed to characterize the damage caused by electrofishing, to be more certain about cause and effect beyond spatiotemporal associations, and to determine the extent of this threat. Mortality from electrofishing seems to be uncommon, but in face of the uncertainties and the numerous other threats to these small populations, high priority should be given to enforcing electrofishing bans in the freshwater habitat of dolphins and finless porpoises.