Seas have generally been rising in Maine since the glaciers retreated 15,000 years ago. Rising waters had transformed the Damariscotta estuary into an optimal oyster habitat by the time this midden, and another across the river, were created.
The middens around Damariscotta are the largest examples north of South Carolina, said Arthur Spiess, senior archaeologist with the Maine Historic Preservation Commission.
From about 2,200 to 800 years ago, Native Americans visited this site in late winter and spring. The inhabitants discarded the shells in heaps that grew year after year, century after century.
“They were eating oysters like crazy and catching alewives,” Dr. Spiess said, referring to a type of herring.
In later centuries, European settlers viewed the middens as a resource. One company burned the oyster shells for lime; another smashed them for chicken feed.
As the shells were unearthed, however, archaeologists found ceramics, bones and stone tools, and the remains of animals on which the tribes feasted. (Many of the artifacts went to the Peabody Museum of Archaeology and Ethnology at Harvard University.)
This and other middens have revealed much of what is known about Native Americans in Maine over the past 4,000 years. The best-studied site, Turner Farm, on North Haven Island in Penobscot Bay, has yielded artifacts more than 5,000 years old.
The inhabitants ate shellfish, of course, mostly soft-shell clams. But they also had a taste for deer, bear, moose, porpoise and seal; cod, sturgeon and swordfish; and even extinct species like sea mink and the flightless great auk.
Donald Soctomah, the historic preservation officer for the two Passamaquoddy tribes in eastern Maine, said middens tell important stories.
“To the Passamaquoddy, the shell middens are a link to the past, and give us an idea of how life was at a certain time and what people consumed,” Dr. Soctomah said in a phone interview. “To us, any information about our past is very important, because we didn’t have a written record.”
In an effort to more rapidly assess middens, Dr. Kelley has developed protocols to survey them using ground-penetrating radar. She thinks of the surveys as a sort of triage, a way of determining which sites are at greatest risk of erosion and which are best to study. With funding from Maine Sea Grant, she has surveyed six middens so far.
“If you want to know what was in the western Gulf of Maine 3,000 years ago, this is how you’re going to figure that out,” Dr. Kelley said.
To survey a site, Dr. Kelley and graduate student Jacque Miller pushed a wheeled radar unit about the size of a jogging stroller across the area, and followed a grid pattern at a walking pace. This allowed them to map a midden without excavating in just two or three days (longer for forested or brushy sites).
The radar not only shows the extent and thickness of the middens, but also reveals the detailed layering, including what may have been floors in historic settlements.
Ms. Miller said in addition to the cultural information buried in the middens, the shells are also a record of ancient climate. Researchers can analyze them to determine historic water temperatures and salinity in the Gulf of Maine.
Still, she said, the middens do not get much attention. “A lot of people just don’t know these things exist,” said Ms. Miller. “It’s just not a focus.”
During the radar surveys, Dr. Kelley’s team had some unpleasant surprises. In one case, they arranged permission to survey a southern Maine midden that had been recorded 49 years ago. When the crew arrived with their equipment, they found it had vanished into the sea.
At the conference, Tom Dawson and Joanna Hambly of the University of St. Andrews described the Shorewatch program, which enlists citizens to monitor archaeological sites in Scotland that are threatened by coastal erosion.
Florida has developed a similar network, called Heritage Monitoring Scouts. Dr. Kelley hopes to develop such a program in Maine.
Dr. Soctomah said he keeps an eye on middens in eastern Maine. “We try to do a walk-by after a bad storm, when you are going to see a site getting more damage,” he said.
“It’s bad because they are disappearing so fast, and the knowledge that is within those middens will be washed out to sea.”