Could Fish DNA Tests Replace Population Surveys?

Collecting DNA isn’t just for detectives at the scene of a crime. It’s now being used by environmentalists to track fish species in the water.

Study author Louis Plough takes a water sample. Photo: UMCES

Environmental DNA, or eDNA, comes from the cells or waste that fish leave behind while swimming. Researchers take water samples from tributaries, then test them for the presence of a certain species.

“You can scoop up water and know what’s been there,” said Louis Plough of the University of Maryland Center for Environmental Science (UMCES). “It captures a snapshot of the DNA that has been around in the past couple of weeks.”

In a field test of this new technology, scientists at UMCES and the Smithsonian Environmental Research Center (SERC) took samples to track river herring in Maryland’s Chesapeake Bay tributaries. It’s one of the first times anyone has compared eDNA results to traditional catch-and-release sampling results. They found that the DNA tracking worked well and has “great potential” to monitor the abundance and habitat of river herring in the future.

“Sampling a single river, you need a net, crew, permits, it can be expensive,” said Plough, who authored a study on the recent river herring findings. “The eDNA approach is an alternative where you just take water and you get an idea of the abundance of fish.”

How can one little water sample tell scientists which fish used to be there? Researchers developed a genetic probe that targeted and identified the DNA of two particular species: alewife and blueback herring, which are together known as river herring.

These fish used to be common in Maryland rivers, where they came to spawn every spring. River herring are an important link in the food chain, serving as snacks for striped bass, bald eagles and osprey. But loss of habitat, overfishing, and worsening water quality has caused their population to drop sharply.

The team sampled 196 locations across 12 tributaries in Maryland—nearly 500 waters samples-—in an effort to understand where they are and how many there are.

They found that the eDNA abundance data corresponded well to other field methods and even gave them a finer looks at species distribution. Alewife were more common among Eastern Shore rivers while blueback herring were more common among rivers on the more developed Western Shore.

It’s one of the first times eDNA has been used to create a map of where river herring are spawning in the Bay watershed. Researchers hope to replicate the method with other species of fish, to inform conservation and restoration efforts.

The paper detailing this study was published in scientific journal PLOS ONE. To read it, click here.

-Meg Walburn Viviano