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Many populations have sustained their diet for thousands of years on the mariculture, a diet based mainly on seafood. Until now it had been thought that these ancient communities ate mollusks and crustaceans because they had an abundant and nearby natural source at their disposal.
A new study, published in PLoS ONE, now proposes a new theory.
A team of scientists from different Canadian institutions suggests that these seafood harvests were not possible just because they were close to these natural nurseries. Too influenced the ability of indigenous people to practice mariculture, that is, the cultivation or breeding of marine plants and animals such as, for example, clam gardens - a rock wall and a flat terrace - which serve as protected artificial habitat to favor and increase the development of these mollusks on the beaches .
For five years, within the framework of The Clam Garden Network project, the researchers analyzed nine ‘orchards’ of clams built by coastal indigenous peoples and found by archaeologists on Quadra Island, located in northwestern Canada.
The authors believe that on this remote island, as in other parts of the world, these techniques have been practiced to encourage the growth of these small animals, for at least 3,500 years.
New criteria for dating
Normally, the dating is obtained thanks to the analysis of carbon - an organic element that remains in the fossilized remains of the deposits - by radiocarbon techniques. But the walls and terraces of the clam gardens are not organic so it is impossible to directly decipher the age of these constructions.
Despite being a real challenge, Dana Lepofsky from Simon Fraser University (Canada) and her team of archaeologists went into these settlements in order to find the age of these indigenous constructions.
"The elements that make up clam gardens are not organic, but clams are," explains Sinc Lepofsky. "We had to create innovative trainers to find out how old they are," emphasizes the scientist.
The team analyzed shell samples from inside and under walls and terraces. In all, they collected 35 radiocarbon dates from clam shells, snails, and barnacles that go from 3,500 years old to the 20th century.
“The clam garden walls are only visible during a few hours of daylight. We had to dig and collect samples in a hurry, head down and focused for three hours, before the tide rose again, ”says Lepofsky.
According to study co-author Nicole Smith of the Hakai Institute (Canada), the clams found in the center or near the top of the wall were discarded, as this position in the structure meant that they had appeared after it was built.
On the other hand, "if we found them trapped, we knew that they appeared earlier, so it gives us a limited age for the wall, that is, it had to be built some time after the clam grew underneath," he explains to Sinc Smith.
Furthermore, the scientists also compared these results with data on the history of sea level and marine management in the region. According to Smith, "the radiocarbon dates, in combination with the knowledge of the position of the previous coastline gave us evidence to establish the ages of the clam gardens."
Mariculture: a sustainable and safe model
Although these dating methods are just the beginning, the research supports what the First Nations of the Pacific Northwest have always known: that clam farming, in the form of gardens, is a fundamental practice for long-term food security.
"In these times of climate change and changing ocean conditions, clam gardens can provide information on food security in the future," says Lepofsky.
"This traditional form of mariculture has been used continuously for 3,500 years to the present and has the potential to become a model for how local and sustainable food systems could function in the future," concludes Smith.
Smith, NF, Lepofsky D et al. "3500 years of shellfish mariculture on the Northwest Coast of North America”, February 2019, PLOS ONE, DOI: https://doi.org/10.1371/journal.pone.0211194.
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