Times are tough for Chesapeake oysters.
For one thing, they used to be bigger. "If you look at what people were saying back in the 1600s and 1700s about oysters, people had to cut them in half before they could even eat them," says Denise Breitburg, an ecologist with the Smithsonian Environmental Research Center.
What's more, these oyster behemoths were so plentiful that they formed tall towers stretching up to the water's surface. But today, after decades of overfishing, oyster populations in Maryland's waters have dropped to 1 percent of what they were around 1900.
To see how much the population has changed over the years, Breitburg and other biologists and archaeologists undertook the largest survey to date of any shellfishery, chronicling the Chesapeake Bay's oyster population from almost 800,000 years ago to the present day. The researchers were surprised to find thousands of years during which oyster populations stayed stable – the era of Native Americans. The stability suggests Native Americans figured out how to farm oysters sustainably, and their techniques could help support our oyster habit today, according to a study published earlier this summer in the Proceedings of the National Academy of Sciences.
The archaeologists began by studying Native American trash pits, which speckle the Chesapeake Bay coast and are full of oyster shells.
By using radio carbon dating, researchers found the oldest trash pit surveyed to be 3,200 years old, and the most recent to date no later than 1900. Next they measured the height of each oyster as a proxy for past human pressure on oysters. (Humans tend to harvest bigger oysters first, so if the average oyster size is smaller, it likely means that oysters were being harvested too fast for many of them to reach a large size and produce a lot of baby oysters.)