Nonlinear relationship between Silver Carp density and their eDNA concentration in a large river

Area of Science:

• Aquatic Ecology
• Environmental DNA (eDNA) Analysis
• Invasive Species Management

Background:

• Environmental DNA (eDNA) is a valuable tool for surveying aquatic ecosystems, but its relationship with fish density in rivers is not well understood.
• Accurate quantification of invasive species like Silver Carp is crucial for effective management strategies.

Purpose of the Study:

• To investigate the relationship between Silver Carp (Hypophthalmichthys molitrix) density and eDNA concentration in a large river system.
• To determine if eDNA detection rates and concentrations can be used to estimate Silver Carp abundance.

Main Methods:

• Conducted hydroacoustic surveys to quantify Silver Carp numerical and biomass density across 460 km of the Illinois River at 23 sites.
• Collected 192 surface water samples for environmental DNA (eDNA) analysis concurrently with fish density surveys.

Main Results:

• A positive, non-linear relationship was observed between Silver Carp density (numerical and biomass) and eDNA concentration (copy number).
• Both eDNA concentration and detection rate increased with Silver Carp density but plateaued at moderate densities.
• The findings suggest eDNA can be used to estimate relative abundance, particularly in low to moderate density populations.

Conclusions:

• Environmental DNA (eDNA) concentration and detection rates are related to Silver Carp density in rivers, though the relationship is non-linear.
• This technique shows promise for estimating invasive fish abundance in newly colonized areas.
• Further research into the causes of the non-linear relationship will enhance aquatic monitoring and management programs.