A team of SFU researchers, working alongside coastal First Nations, has revealed that ancient clam gardens along the northwest coast were cultivated by coastal indigenous people — not naturally occurring, as previously thought.
By comparing clam growth rates in the stone terrace gardens and in other non-walled beaches, they determined that clams grow better and more densely within the altered environment than without.
Their findings show that the First Nations people along the coast — from Washington to Alaska — were not simply hunter-gatherers. They created food security by increasing clam productivity through creating ideal clam habitats.
“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,” said SFU archaeologist Dana Lepofsky in a media release.
Lepofsky has been working to accurately date these gardens by assessing the last time the deepest part of the rock was exposed to sunlight during the clam gardens’ construction. While the team can’t provide specific dating, the clam gardens are estimated to be 1,000 years old in the least.
It was local geomorphologist John Harper who first noticed that coastline didn’t look as it should, having undergone only natural processes. While flying over the coast approximately a decade ago, he saw that there were walled structures that didn’t fit in with the natural coastline — human-made clam gardens.
The team, working in conjunction with the Clam Garden Network and knowledge holders from the Tla’amin First Nation and Laich-kwil-tach Treaty Society, focused their research on two bays on Quadra Island.
In an experiment, the team placed baby clams in clam gardens and in non-walled beaches and then compared their growth rates, biomass, and densities over a season of growth.
Lead author of the three-year study and a graduate from SFU’s School of Resource and Environmental Management, marine ecologist Amy Groesbeck, joined the team and started her master’s thesis on clam gardens in 2010.
“We found that there were much higher densities of clams, especially culturally and economically important clams, butter clams and littleneck clams in clam gardens,” said Groesbeck. “They’re extremely innovative structures, very innovative engineered environments.”
She added that they are looking into many potential mechanisms that contribute to clam productivity, including tidal height, increased beach slope, and sediment composition.
When they dug up the sand from clam garden beaches, they found a significant amount of crushed shell. Coastal First Nations members revealed that these ground up shells were indeed added to the beaches to increase clam productivity.
The team is also looking into the possibility that the shell hash in the sediment, through releasing calcium carbonate into the water, “acts as a localized buffer against ocean acidification,” said Groesbeck.
Not only will their research have implications for ocean acidification research, but it could help in applying ancient techniques to increase food production and security.
