Ancient clam beaches not so natural, study shows

Lepofsky's research team has discovered that Northwest Coast Indigenous people didn't make their living just by gathering the natural ocean's bounty. Rather, from Alaska to Washington, they were farmers who cultivated productive clam gardens to ensure abundant and sustainable clam harvests.

In its new paper published by American Antiquity, Lepofsky's team describes how it isolated novel ways to date the stone terraces that created clam beaches. These beaches are certainly more than 1,000 years old and likely many thousands of years older. The researchers identified many places where people built gardens on bedrock -- creating ideal clam habitats where there were none before. This, the researchers concluded, clearly challenges the notion that First Nations were living in wild, untended environments.

"We think that many Indigenous peoples worldwide had some kind of sophisticated marine management, but the Pacific Northwest is likely one of the few places in the world where this can be documented," says Lepofsky. "This is because our foreshores are more intact than elsewhere and we can work closely with Indigenous knowledge holders."

The researchers, who worked with First Nations linguistic data, oral traditions and memories, geomorphological surveys, archaeological techniques and ecological experiments, belong to the Clam Garden Network. It's a coastal group interested in ancient clam management.

"Understanding ancient marine management is relevant to many current issues," says Lepofsky.

Her team is comparing clam garden productivity to that of modern aquaculture and assessing whether the shell-rich beaches of clam gardens help buffer against increasing ocean acidification. The team will also build experimental clam gardens, applying many of the traditional cultivation techniques learned from First Nations collaborators as a means of increasing food production and food security today.

This latest study is on the heels of one done a year ago by Lepofsky and her collaborators. The original three-year study published in PLOS ONE found that these ancient gardens produced quadruple the number of butter clams and twice the number of littleneck clams as unmodified clam beaches. It was the first study to provide empirical evidence of the productivity of ancient Pacific Northwest clam gardens and their capacity to increase food production.

The Tula Foundation, Parks Canada, the Social Sciences and Humanities Research Council and Wenner Gren, among other groups, are funding the team's studies.

Key highlights of new study:

Northwest Coast Indigenous peoples from Alaska to Washington State managed clam beaches in a variety of ways. These included replanting of small clams and building rock terrace walls at the low-low tide line to create clam gardens.

Northwest Coast First Nations language terms indicate clam gardens were built in specific places by rolling the rocks for two purposes. One was to create rock-walled terraces ideal for clam growth. Another was to clear the beaches of unwanted rubble that would limit clam habitat.

The researchers developed novel ways to date the clam gardens and their preliminary excavations revealed that many date to more than 1,000 years ago.

Working on these clam gardens posed some logistical challenges since many are only visible for about 72 daylight hours per year.

Extensive air and ground surveys revealed that clam gardens can be found from Alaska to Washington State, but in some places, such as the Gulf Islands, recent rising sea level obscures the rock walls. In some areas, clam gardens made possible the dense ancient First Nations settlements that dot our coastline.