Quirks & Quarks

Clam gardens have been cultivated by Indigenous people for millennia

Clam gardens have existed for a long time on the west coast of Canada, but until now, we haven't known for how long. Now, a team of Canadian archaeologists, using carbon dating, found that the gardens have existed for at least 3,500 years.

Archaeologists have dated the oldest clam gardens to 3,500 years ago

Aerial view of the research team working at a clam garden (Keith Holmes/ Hakai Institute)

Originally aired on March 9, 2019.

Clam gardens have existed for a long time on the west coast of Canada, but until now, we haven't known for how long.

They're an ancient aquaculture innovation invented by the Indigenous coastal people to cultivate clams, and also barnacles, crabs, sea cucumbers, kelp and even fish.

The coastal First Nations have built, maintained and harvested seafood from these shallow water structures all over the west coast. But nobody knows how old they are.

Now, a team of Canadian archaeologists, using carbon dating, found that the gardens have existed for at least 3,500 years. They also believe that a better understanding of this long experience of aquaculture could teach us a great deal, as we move forward in a world plagued by climate change and food security challenges.

Life in the gardens

Clam gardens function by expanding the shallow water beach habitat of different species of clams. Different species of beach clams establish themselves at different elevations along the beach, so that they're covered and uncovered by incoming and outgoing tides for just the right amount of time.

Indigenous people built rock walls, and backfilled behind them at just the right tidal height to create a flattened plateau in order to expand space that clams could live in. 

Dr. Dana Lepofsky and Ginevra Toniello excavating within a clam garden wall. (Nicole Smith)

Clam gardens can be two to four times more productive than a regular beach, according to Nicole Smith, the lead author of the paper and an archaeologist at Hakai Institute.

"They encourage the clams to grow faster, and are more beneficial for clam recruitment, so the baby clams will settle more commonly in clam gardens compared to unwalled beaches."

Beyond clams, a number of other species also take up residence in the gardens. The structures were a rich source of food for ancient Indigenous communities.

Looking back and moving forward

To determine the age of the clam gardens, the research team investigated nine different gardens on Quadra Island, B.C. a small island off the east coast of Vancouver Island.

They carbon-dated shell samples of clams, snails and barnacles found within or beneath the garden walls and terraces, and ended up with 35 radiocarbon dates ranging from at least 3,500 years ago to the 20th century.

The team radiocarbon dated whelks, limpets, and clams trapped within and below the rock walls and terraces to help establish ages of the clam gardens. (Nicole Smith)

"In some ways, it's not surprising that clam gardens began to be built at least 3500 years ago because the coastal First Nations have always known about clam gardens," Dana Lepofsky. a co-author of the paper and a professor in the department of archeology, Simon Fraser University, said in an email to Quirks & Quarks . 

"What is remarkable is that some individual gardens were used for thousands of years and were still being used until very recently."

A time-lapse video of Aboriginal community and SFU researchers racing against the tide to investigate clam gardens on the shores of Quadra Island. The wall of the clam garden can be seen at the lowest tide moment. The rock wall serves the purpose of flattening out the beach to increase clam habitat.

An incredible amount of work needed to go into maintaining these gardens, from tilling the settlements to removing older and larger clams and keeping the beach clean so that the clams below can breathe.

"When you think about the implications of this — that knowledge about clam stewardship was passed down orally over 100's of generations — there remains no question about the longevity and sustainability of traditional management practices," said Lepofsky.

"Clearly, we have much to learn from these practices going forward."


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