Words by
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Finprints
Artwork courtesy of Gulf of Maine Research Institute
Using DNA to Weigh Climate Change Impact on Maine Seafood

Ever wonder what happened to Maine shrimp? You might see these tiny, sweet shellfish listed on menus, but they were likely caught in Canada because Maine’s commercial shrimp fishery closed in 2014 after the species fell off the sonar screen in state waters. If you’re extremely lucky this winter, you may find a pound of local shrimp in a Portland fish shop. But if you do, it would be sourced from research vessels conducting extremely limited trawl surveys in the Gulf of Maine.


Trawl surveys—taken by dropping a net in randomly selected segments of the sea and pulling up the catch—are used to gauge the health of fish stocks. But they’re notoriously imprecise. An empty net doesn’t mean a huge school of cod wasn’t there just a couple of hours before the net was dropped.


Accurately determining what species are where and when in the open ocean is difficult. Climate change is happening so fast that scientists have a hard time identifying ecosystem shifts like disappearing Maine shrimp and changing migratory patterns of cod, lobster, and black sea bass in real time.


“A lot of these species evade our notice,” says Dr. Graham Sherwood, a research scientist at the Gulf of Maine Research Institute. He is working with a team on a project to assess whether studying DNA left behind in the ocean after fish swim through an area can help identify when, where, in what quantities, and even why they were there.


The endgame of DNA sampling is to have a more accurate understanding of how climate change affects commercially important species so we can make smarter seafood management decisions.


An ocean of DNA

Environmental DNA (eDNA) is the trace signature that any organism leaves in the ocean as it passes through the water or nestles in the sediment. Scientists match sampled eDNA to known species genomes. eDNA degrades at different rates, so it can be hard to tell exactly when a fish passed through a water sample.


Sherwood and his team are specifically studying Atlantic herring populations to see if eDNA can reliably indicate where and when herring swim through several areas in the Gulf of Maine. They’re benchmarking the quality and accuracy of the eDNA sampling against known acoustic patterns for herring migration.


Using sonar waves to get an acoustic “image” of schools of marine species is a common measure of where fish and shellfish are congregating, and it seems to render a more accurate portrait than trawl surveys. Researchers can look at a sonar screen of a school of fish and see its shape, depth, speed, and behavior; then they can match that data to the time of year to determine what species they may be looking at.


Scientists are confident they can identify spawning herring acoustically because the small fish tend to school in very large shoals toward the bottom in deep water during late fall. So if Sherwood and his team can first find a big school of spawning herring acoustically, and then verify the presence of herring in that school using eDNA, they will have proven that eDNA sampling can work in that application.


Other groups are also studying the use of eDNA for other species throughout the Gulf of Maine. A University of Maine team is using eDNA to gauge what restoration of migratory paths up once-dammed rivers will mean for alewives and everything up the food chain that depends on them. Other studies are focusing on the early lifecycle of lobster, the impact of toxic algal blooms, and the prevalence of invasive species like green crabs.


“We’re just trying to add to the body of knowledge that eDNA is a valid tool for understanding trends in distribution and abundance of marine species,” says Sherwood. He hopes to finalize his research and provide conclusions in the next year or so.


“This is the very early stage of eDNA research in relation to management outcomes,” says Sherwood. We won’t see management decisions based on eDNA studies for years.


But the possibilities could be significant because any tool that can help fishermen and women navigate climate change in the Gulf of Maine will be a welcome one.

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Colles Stowell is president of One Fish Foundation, a 501(c)3 non-profit that brings the sustainable seafood message into classrooms (from elementary through college) and communities.

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