Quantification of Environmental DNA Shedding Rates from Invasive Bighead Carp and Silver Carp

Due to its high sensitivity, environmental DNA (eDNA) surveys hold promise as an early detection method for aquatic invasive species. Quantification of eDNA amounts may also provide data on species abundance, allowing managers the potential to successfully combat the spread of ecologically damaging species. To better understand the link between eDNA and an organism’s presence, it is crucial to know how eDNA is shed into the environment. Our study used quantitative PCR (qPCR) and controlled laboratory experiments to measure the amount of eDNA that two species of invasive bigheaded carps (Hypophthalmichthys nobilis and H. molitrix) shed into the water. We first measured how much eDNA a single fish of known weight sheds and the variability of these measurements. Then, in a series of manipulative lab experiments, we studied how temperature, density (g fish/ L), and diet affect the shedding rate of eDNA by these fish. We found that eDNA amounts exhibit a positive relationship with fish density, and that feeding could increase the amount of eDNA shed by ten-fold, whereas water temperature did not have an effect. Our results demonstrate that quantification of eDNA may be useful for predicting carp density, and possibly other rare or invasive species.