Native Americans in the Chesapeake Bay area harvested oysters sustainably for thousands of years before Europeans arrived. That's what scientists say they've discovered by measuring oyster size and population changes over time. And modern conservation plans based on these methods may offer hope for both rebuilding the bay's oyster population and preserving the other species that benefit from their presence.
Modern fishing practices in the Chesapeake Bay have reduced Maryland’s wild oyster population by 99 percent since the late 1800s. Deepwater trawlers dredge the bottom of the bay, destroying the oysters' ecosystem, which once played a major role in keeping the water clean and supplying reefs for other ocean life. And they've impaired a once thriving bivalve industry.
Over the last two centuries, the devastation has been so complete that some researchers argue that the bay isn’t possible to save. But a study outlining the oyster’s history going back about 300,000 years suggests that conservationists still have a shot.
“The past has this incredible database that tells us what the landscape looked like when there were [Native Americans] harvesting resources differently than we do today," says Catherine West, an archaeologist at Boston University who wasn’t involved with the research. "It might give us some ways to solve current conservation problems.”
The study, published in the Proceedings of the National Academy of Sciences, took eight years to complete and is the first interdisciplinary work of its kind. Scientists braved bad weather, mosquitos, and bugs to examine 50,000 oyster shells at archaeological sites around the Chesapeake Bay. They measured shells dating back thousands of years and found that the oysters are slightly bigger now than they were back then, suggesting that the Native American harvest was sustainable. (See "From Oysters to Kelp: The Evolution of Aquaculture")
“We were surprised,” says Torben Rick, an archaeologist at the Smithsonian Museum of Natural History and lead author of the study. Rick received a grant from the National Geographic Society's Committee for Research and Exploration to support the archaeological portion of his research.
“We thought we’d see a decline [in shell size] throughout time," he says. Instead, "We saw a [small] size increase."
Usually, a species gets smaller over time when it’s been overharvested. For example, people have overfished the Atlantic cod, plucking the largest individuals from the sea to grace dinner plates. Now, says Matt Ogburn, an ecologist at the Smithsonian Environmental Research Center, the fish don’t get big as quickly as they used to.
No one knows why oysters in the Chesapeake Bay have so far escaped this fate, because there’s little disagreement over the fact that they've been overharvested, but there are a couple of theories.
Native Americans were probably hand-collecting oysters from shallow water, allowing those living in deeper waters to grow longer and therefore increase in size. Those were the ones to reproduce, leading to the modern oyster.
Oyster size may have also remained relatively stable over time because oysters have been feeding on the excess nitrogen in the bay, put there in the last 200 years or so by deforestation and pollution. A future study will test these theories.
Though not indicative of the average oyster, the largest oyster measured in this study was 259 millimeters (about 10 inches) tall. Ogburn lays down a dare to all the foodies out there salivating over the mere thought.
“I would challenge you to slurp that oyster in one slurp,” Ogburn says. (See "Like Swallowing a Baby")
Nowadays, even oysters left alone to fend for themselves seldom live long enough to grow to such proportions. There are two oyster diseases—MSX and Dermo—that rarely allow oysters to survive more than four years in the wild, Ogburn adds.
The odds are long to restore the oyster population to its previous glory, but the state of Maryland has imposed restrictions on harvesting methods that disturb the oyster beds.
And there are some modern commercial oyster farmers who are seeking to repopulate the Chesapeake Bay while also earning a living.
“Our mission is to increase the number of oysters grown throughout the Chesapeake,” says Travis Croxton, co-owner of Rappohanock Oyster Company. “We want to go beyond sustainable and be restorative.”
He farms two types of oysters—diploid and triploid. Growing the two types means Croxton can rotate his harvest, which gives diploids the opportunity to spawn and create new, wild oysters.
Croxton and his team keep the oysters in cages and let them grow at the bottom of the bay, elevating them to keep them free of the mud.
“Chesapeake oysters are the best thing you can do for the environment," he says. "For every oyster we take out, we put about 12 back into the water.”
Rick says scientists must learn from the bay’s previous caretakers in order to create the best possible future, but he’s not suggesting oyster harvesting stop altogether. Conservationists must consider the needs of the environment along with the needs of the industry.
Mollie Bloudoff-Indelicato is a science, health, and environmental reporter. Follow her on Twitter.