As fish swim around in the ocean, they leave pieces of themselves behind.
“At sort of the least technical level: It’s slime. It’s skin. It’s poop,” said Andrew “Ole” Shelton, a researcher with the Northwest Fisheries Science Center in Seattle. “It’s, you know, all the things you don’t really want to think about being in the water.”
These fragments of genetic material — environmental DNA, or eDNA — collected in bucketfuls of ocean water and analyzed in a lab, cast a sort of shadow about what was in the area hours before. It’s enough to give researchers information about the abundance and distribution of a species without needing the fish to actually be present at the time a sample is collected.
Shelton is the lead author of a recent study by a team that hopes to use eDNA on a large scale for fisheries management and conservation work.
They covered a large area off the West Coast, sampling at various points, and used eDNA to measure populations of Pacific hake, or whiting.
Pacific hake is a major commercial fishery, one of the West Coast’s largest in terms of pounds landed and money generated. Population and distribution assessments are key when it comes to running and working in the fishery.
Until the research done by Shelton and his team, eDNA had mostly been used on a smaller scale — to assess the presence of certain species in lakes, rivers and coastal waters, for instance.
Last year, scientists used eDNA to show a beluga whale that made an appearance in Puget Sound was likely from a population of beluga whales in Arctic waters.
Traditional fishery survey methods use trawl nets or sonar. Researchers catch or see what they can at a particular time in a particular place. For eDNA, the fish could have been there and gone several hours ago.
The water samples collected can be stored and studied again and again. Researchers can even look for the presence of different species using the same water samples.
The archive of water samples needs to grow and data collected must accumulate over time before eDNA surveys of species like hake will be as useful to fishery managers as the more traditional surveys. Hake trawl surveys have a long time series attached to them with information that can be compared over years of surveying. Environmental DNA does not have this history — not yet.
There are also limits to what eDNA can reveal. It can’t tell researchers about the age, sex or size of the individual fish. But after the success at surveying for hake, Shelton sees opportunities to put the eDNA approach to work.
It can be a more cost-effective way to sample, he noted, saving researchers expensive ship time. At it’s most basic, you’re dropping a bucket into the ocean and pulling it up filled with water.
Collection of eDNA could also prove especially useful for tracking the distribution and populations of fish and marine mammal species that are difficult to find or difficult to survey.
For example, on the West Coast there are rockfish species that were historically overfished. Environmental DNA could be a way to help fishermen avoid them.
“That’s a big question,” Shelton said. “How do you mitigate bycatch of these species that you’re concerned about? And how do you better target your fisheries management to deal with these species that it’s just hard to figure out where they are?”
This is a gap — a bucket, if you will — that Shelton believes eDNA could fill.