Digging Into Ancient Clam Aquaculture

IRA FLATOW: If you live on or near the coasts, you may have a real nice clam bake every now and then. And you know what? Thousands of years ago, Indigenous peoples on this continent were the same way. Clams were an important part of the coastal diet and culture. In fact, inhabitants of the Pacific Northwest developed techniques for essentially farming clams in constructed clam gardens.

Dana Lepofsky is one of the authors of a study published this week in the journal Proceedings of the National Academy of Sciences on the success of those clam growing techniques. She’s a professor of archaeology at Simon Fraser University in Burnaby, British Columbia. Welcome to Science Friday.

DANA LEPOFSKY: Thank you.

IRA FLATOW: So tell us about these colonies. What did you know about them?

DANA LEPOFSKY: Oh, goodness. Well, we knew from the Indigenous elders of this region, that they used to cultivate clams in something called– or that we call– clam gardens. But they had traditional names depending on the Indigenous group, like [INAUDIBLE], which means to roll rocks in the [INAUDIBLE] language.

And basically, these are features that we now know were developed some 3,000 or 4,000 years ago, that when Indigenous people would roll the rocks at the lowest intertidal from the sloped beach down to the water edge to create a rock wall. And in doing so, when the tides came in, they brought sand and gravel, and they filled in that rock wall to make a flat terrace. So if any gardeners are out there, you can understand why that would be really great, because you’ve created this flat terrace where there was a sloped beach before.

But why it’s so ingenious is because in the intertidal, there are zones where different critters flourish. And there is a particular zone in the beach as you’re walking down the beach where butter clams and little necks flourish, these two species that were so important to Indigenous food systems. And by building this terrace and flattening out that slope, you’ve basically expanded the zone at a particular tidal height where these clams do the best. So you’ve increased the habitat, the zone where those clams can really flourish. So you’ve really expanded your food source.

IRA FLATOW: Well, they were sort of clam scientists then.

DANA LEPOFSKY: Very much. I mean, Indigenous peoples worldwide were our scientists, were scientists. Because their knowledge developed over thousands of years of observing how the world worked and doing trial and error on different kinds of things and then passing that knowledge on intergenerationally, so definitely scientists.

IRA FLATOW: And so they actually sculpted the ground, knowing how to best raise the clams, shaping the garden, as you say, and getting the best production they could out of the clams.

DANA LEPOFSKY: That’s right. And what’s really neat about clam gardens or [INAUDIBLE] is that not only did people put them on an already existing beaches that had a kind of a mediocre, natural abundance of clams, they also built these rock walls on bedrock shells. And then through time, when they filled in with sediment, with sands and gravels, beaches were created where there was none before. So they created gardens where there was bedrock, thereby multiplying the food source in a sustainable way over incredible numbers over what was available naturally.

IRA FLATOW: But the people did stop farming them, right? They stopped using the farming technique. Why? What happened?

DANA LEPOFSKY: Yeah, that’s right. So we actually have a sequence of study that takes us from post-glacial times 11,500 years ago to current times. And what we see is basically right around the late 1700s, early 1800s, people stopped farming in an intensive way these clams. And that’s because the Indigenous population plummets as a result of introduced European diseases. So a lot of that knowledge and that daily practice gets lost, although today, there’s a huge, huge effort among Indigenous peoples up and down the coast from Alaska to Washington to actually reinstate these clam gardens, and in doing so, reconnect with that cultural tradition.

IRA FLATOW: Is there a way of rediscovering how they did what they did?

DANA LEPOFSKY: Yeah, and that’s basically what we do as archaeologists is we listen to Indigenous peoples and hear what they have to tell us. And they have a lot to offer to the discussion. And then we combine that with Western scientific techniques, which, in our case, is archeology and paleoecology. We dig in the ground. We measured clams over the 11,000 year period. Basically, we measured the growth rings and asked how fast did they grow, how big did they grow, when did they die, that kind of thing. And we can track through time, through these interactions with people, how well did clams do.

And what we find is that the clams just after the glacial age, when beaches are really [INAUDIBLE]– there’s not much gravel and sand and not much microorganisms on them– that those clams are growing very slowly, very poorly, and dying young. And they look the most similar to the clams today. And in between, when people were managing them and harvesting them intensively and passing on that Indigenous knowledge, clams were thriving.

IRA FLATOW: So there was a golden age of clams, some time ago.

DANA LEPOFSKY: Yeah, just a couple hundred years ago.

IRA FLATOW: [LAUGHS] For everybody who likes clams, they wish they were back then.

DANA LEPOFSKY: Yeah.

IRA FLATOW: Well, I want to thank you very much for taking the time to talk to me. Is there anything else that you need to study on this?

DANA LEPOFSKY: Oh, goodness, yes. So we know that in our region, people developed and really finetuned this technology around 3,000, 4,000 years ago. But now we want to ask, and we’re starting to ask, what was the relationship between that, and population numbers, and climate change, and various other kinds of ecological changes? Because of course, in this dramatic time that we live in today of changes environmentally brought on by changing climate, we need to know how these traditional techniques can help us into the future.

So we’re finding when we do experiments today that these clam gardens are, even though they hadn’t been worked and tended, even today, they’re way more productive, many, many times more productive than the beaches without these clam gardens. So what can we learn about that in this time where clams are actually suffering? Because with ocean acidification, they’re having trouble putting on their shells. Clam gardens are very rich in calcium carbonate because of broken up barnacle shells. So what can we learn from that? What can Indigenous peoples tell us, either by talking to them and listening carefully, or combining that with Western science that can bring us forward into this next age that we’re facing.

IRA FLATOW: Do you think there are Indigenous peoples in other parts of the world that raised claims the same way?

DANA LEPOFSKY: There are Indigenous peoples in other parts of the world for whom clams were really important and who cultivated clams, but not exactly in this way. So what’s neat about clam gardens is that even naysayers can’t deny the fact that they are traditional management techniques. There has been a whole wave of scientists who believe that indigenous peoples didn’t really manage their environment for the long term. Because these rock walls persist, they can’t deny it.

But there are other kind of techniques that were used globally, like cultivating, tilling the soil and size selection, and determining what times of year you can harvest and when you can’t, what species you can harvest. That’s worldwide. It’s just harder to track in the archaeological record, but there is no doubt in my mind that [INAUDIBLE] Bay was full of large, large archaeological sites with meters high of shells.

Clams are that important all over the world and for millennia. And that they sustain people over that time, despite the fact, people were harvesting them intensively and that populations were very dense in the past, it really reflects the fact that there was traditional management techniques. And I think we just need to stop long enough to talk to Indigenous peoples around the world and ask them, how should we do this?

IRA FLATOW: There’s something to be learned there. That’s a great lesson. Wow. We have hubris about how well we do things. We can learn stuff that’s hundreds of years old. Thank you–

DANA LEPOFSKY: Absolutely.

IRA FLATOW: Yeah, thank you very much for taking the time to talk with us, Dr. Lepofsky.

DANA LEPOFSKY: My pleasure. Take care.

IRA FLATOW: Dana Lepofsky is professor of archeology at Simon Fraser University in Burnaby, British Columbia.

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