Abstract
The timing and location of spawning events are important data for managers seeking to control invasive grass carp populations. Ichthyoplankton tows for grass carp eggs and larvae can be used to detect spawning events; however, these samples can be highly debris-laden, and are expensive and laborious to process. An alternative method, environmental DNA (eDNA) technology, has proven effective in determining the presence of aquatic species. The objectives of this project were to assess the use of eDNA collections and quantitative eDNA analysis to assess the potential spawning of grass carp in five reservoir tributaries, and to compare those results to the more traditional method of ichthyoplankton tows. Grass carp eDNA was detected in 56% of sampling occasions and was detected in all five rivers. Concentrations of grass carp eDNA were orders of magnitude higher in June, corresponding to elevated discharge and egg presence. Grass carp environmental DNA flux (copies/h) was lower when no eggs were present and was higher when velocities and discharge increased and eggs were present. There was a positive relationship between grass carp eDNA flux and egg flux. Our results support the further development of eDNA analysis as a method to detect the spawning events of grass carp or other rheophilic spawners.
Highlights
Since the developing semibuoyant eggs and the larvae of grass carp (Ctenopharyngodon idella) drift in the current [1,2,3,4], ichthyoplankton tows during the spawning season can be used to detect spawning events [2,5]
Environmental DNA, has been used in determining the presence of aquatic species from water samples taken from a particular waterbody [7]
EDNA technologies could theoretically be used for the detection of spawning or as part of a two-tiered approach with traditional ichthyoplankton sampling
Summary
Since the developing semibuoyant eggs and the larvae of grass carp (Ctenopharyngodon idella) drift in the current [1,2,3,4], ichthyoplankton tows during the spawning season can be used to detect spawning events [2,5]. Ichthyoplankton samples from tows taken during high discharge tend to be debris-laden and are expensive and laborious to process. Grass carp eggs in the drift tend to distribute more densely toward the bottom of the water column [6], where sampling is difficult or dangerous. EDNA technologies could theoretically be used for the detection of spawning or as part of a two-tiered approach with traditional ichthyoplankton sampling
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