Neonicotinoid pesticide use may have caused the abrupt collapse of two commercial fisheries on Lake Shinji, Japan, in 1993, according to a new study. While the negative impacts of the world's most widely used insecticide on pollinator species are well known, these results highlight new and potential indirect effects on other organisms, including vertebrates. Using more than two decades of data on lake chemistry, biology and fishery yields, Masumi Yamamuro and colleagues tracked the impacts of neonicotinoids through the aquatic food chain of Lake Shinji - from zooplankton to the commercially harvested species of smelt and eel. Yamamuro et al.'s analysis revealed that the very first application of neonicotinoid pesticides in 1993 coincided with an 83% decrease in average springtime zooplankton biomass, which was shortly followed by a complete collapse of the fisheries of the species that feed on them. The smelt harvest alone collapsed from 240 tons per year to 22 tons in a single year after the first use of neonicotinoids. According to the authors, neonicotinoid pesticides indirectly reduced Lake Shinji's fishery yields by decreasing the abundance of invertebrates that serve as food for smelt and eels. What's more, the results show that the precipitous decline in zooplankton could not be explained by other confounding factors, such as nutrient depletion or changes in salinity or oxygen concentration. Yamamuro et al. argue that nationwide decreases in fishery yields in other lakes of Japan during this time were likely also due to food web disruption from pesticide use. Since neonicotinoids are the most widely used pesticide, similar dynamics are likely playing out in bodies of water around the world, the authors say. "Yamamuro et al.'s study, though observational, presents compelling evidence from more than a decade of data both before and after neonicotinoid insecticides were introduced to this region," writes Olaf Jensen in a related Perspective.
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Science