CSI: Chesapeake Bay

Sampling River Herring

eDNA emerges as powerful tool for tracking threatened river herring in Chesapeake Bay

Using environmental DNA (eDNA) to track the presence of fish in waterways is emerging as a powerful tool to detect and understand the abundance of species in aquatic environments. However, relatively few studies have compared the performance of this emerging technology to traditional catch or survey approaches in the field.

Researchers from the University of Maryland Center for Environmental Science and Smithsonian Environmental Research Center field tested using eDNA--tracking the presence of fish by identifying DNA that has been left behind in the water--to detect river herring in tributaries of Maryland's Chesapeake Bay. They found that tracking and quantifying herring DNA from the environment corresponded well to more traditional field methods and has great potential to assist future monitoring efforts of river herring abundance and habitat use.

"Sampling a single river, you need a net, crew, permits, it can be expensive," said study author Louis Plough of the University of Maryland Center for Environmental Science. "The eDNA approach is an alternative where you just take water and you get an idea of the abundance of fish."

River Herring jumping a small rapid.

Accurate information on how many fish are in a river system and where they travel is essential to understanding their ecology and how to manage the fishery in increasingly human-impacted environments. Environmental DNA (eDNA) sampling has recently emerged as a powerful, non-invasive alternative to capture-based techniques to detect the presence of a species in their environment.

"You can scoop up water and know what's been there," said Plough. "It captures a snapshot of the DNA that has been around in the past couple of weeks."

The researchers developed a genetic probe that targeted and identified the DNA of two particular fish species, alewife and blueback herring, collectively known as river herring, in the waterways. As they swim, the fish slough off cells and waste that contain DNA.

"The eDNA method is especially powerful because it can identify whether alewife, blueback herring, or both species are present at each site," said study co-author Matt Ogburn of the Smithsonian Environmental Research Center. "When we use some traditional methods like collecting fish eggs or larvae, we often aren't able to tell which river herring species they belong to, and they might even be from other local species like hickory shad."

Cool!