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calendar   Friday - January 10, 2020

Ancient Tidal Farming

Study: Paleo Clam Gardens More Productive Than Natural Mud Flats

Well duh. That’s the whole idea of farming, right?

Yeah, I’m weird. This kind of stuff interests me. We’ve all read those articles about how anthropologists have found evidence of ancient First Peoples by the shell midden heaps they left everywhere. I guess the idea was that them old injuns would walk around every year or two to some productive spot by the water’s edge, and chow down on clams and oysters, toss the shells in a pile, and move on. And lather, rinse, repeat, for thousands of years. “Move to where the food is” is a great idea.

Well, it turns out that in some places, at least the Pacific northwest, folks had been doing aquaculture for thousands and thousands of years. At least as far back as the end of the last Ice Age.

Changing the very shape of the seashore by building and maintaining clam gardens. Clam gardens? What are they? Let’s go right to the PNAS and find out.

That Extra Special Human | Clam Relationship

Our understanding of the historical ecology of humans and butter clams on Quadra Island not only illustrates the long-term and intertwined relationships of these 2 species but also, serves as a model for studying the intricacies of other human–species relationships. In the case of butter clams, a culturally valued species, there was a myriad of ecological and cultural factors that influenced population viability throughout the Holocene.

...

On the Northwest Coast of North America, as in coastal communities worldwide, the human–clam relationship is age old and continues today. Tracing that history and situating these relationships in the context of modern management decisions take bringing together data from multiple sources and using diverse types of analyses. They also require recognizing the sometimes-active role of humans in modifying coastal ecosystems of the past as well as the present and that not all long-term human–ecological interactions have negative ecological consequences on biological diversity.

In our study area, our analyses of shells from intertidal death assemblages, archaeological shell middens, and modern clams provide insights into how clams, clam habitats, and human–clam relationships changed through time in a specific place. More specifically, the analyses reveal how clam life histories have responded to shifts in harvesting, habitat alterations, climate and environmental factors, and management practices. Taken together, the temporal and spatial variability that we document is another reminder of the need to gather site- and time-specific baselines for modern management. We have demonstrated that ocean temperatures and substrate play a role in butter clam life history. Thus, it is no surprise that there is considerable variation in estimates of butter clam size in the literature (46⇓⇓–49), just as there are in our modern data and paleodata. Management plans based on local, modern, and paleoecological data are likely to be more robust than those based on more general spatiotemporal data from the literature. However, under future climate change scenarios, environmental variables are likely to resort in different combinations than those of recent history and perhaps, with few analogs in the past.

Previous research on clam gardens in our study area demonstrated that clam gardens today are at least twice as productive as nonwalled beaches. This has implications for the numbers of people who can be locally supported by this ancient innovation in mariculture. Our data, however, show that clams in clam gardens today are far less productive than they were before European contact and industrial logging—that is, when traditional management systems were active and shell–sand–gravel vs. silt-rich beaches dominated clam habitats. This highlights the possibility that, if traditional mariculture methods were applied to clam beaches today, they could produce even greater yields than those estimated based on current ecological conditions—assuming similar pelagic production and oceanic conditions. In fact, many Indigenous communities along the Pacific Northwest Coast are exercising their rights to access and collective choice by restoring clam gardens and the traditional protocols associated with them.

Paleo Pete and Holocene Harry built up low walls of barely submerged stone across mud flat beaches at the low tide line. When the tide would rise, fresh silt and nutrients would wash in, but stay there when the tide went out, filtering through the loose stone walls. This made a perfect clam habitat.

In time the accumulation of silt changed the slope of the beach, flattening it out and growing the land. Clams thrived in this protected environment. People would come in and harvest them, safe behind the walls in the water. The more big clams they dug up and ate, the more room there was for the little clams to grow. Pretty soon you had clams enough for the multitudes, and some of these clam gardens stretched for miles. There are thousands of them along the coast, from Alaska down to Washington. And that’s the ones we can find today. How many more were lost beneath the waves as the post-glacial oceans slowly rose?

image

Indigenous people of the west coast of North America used a range of techniques and practices to maintain or increase the production of culturally important foods, including clams. These practices are encompassed within age-old social, economic, and spiritual beliefs and practices of coastal First Peoples. One long-lasting and visible practice was the building of clam gardens.

Clam gardens are ancient intertidal features constructed by the coastal First Nations of British Columbia (Canada) and Native Americans of Washington State and Alaska (USA), to enhance shellfish productivity. These features are made by constructing rock walls at the low tide line along the edges of bays and inlets, transforming naturally sloping beaches or rocky shorelines into productive, level beach terraces.

Coastal First Nations knowledge holders note that the very act of harvesting clams keeps clam beaches productive.  Digging for clams creates healthy bivalve habitat by turning over the beach sands and silts, exposing these sediments to oxygen. In an unworked beach, seaweed and dead clams can accumulate on the surface of the beach, suffocating live clams.  When digging, people ensured that populations were healthy by thinning clams or preferentially harvesting larger ones to allow younger clams to grow. We learned from Indigenous harvesters that some people added broken shells back to the beach to augment the sediments as needed.

image

Amy Groesbeck’s recent investigation into these ancient structures found that clams are more plentiful, and grow bigger inside of clam gardens. Butter clams are known to grow four times as big in clam gardens compared to non-walled beaches (Groesbeck et al, 2014). There is speculation that the rock walls could also provide a home for other creatures including young fish, sea cucumbers, and other invertebrate species. Current observations suggest that building clam gardens may change the types of species surrounding the clam garden, but will not likely have a harmful impact on the species already present.
Clam gardens have recently caught the attention of many academics, researchers, resource managers, and First Nations along the Vancouver coast – who has joined forces and formed “The Clam Garden Network”.

And you know what else? Clams fight both pollution and global warming. Well, the things are filter feeders, so they suck the yuck out of the ocean and live on it. And as clams grow, their shells grow. The shells are made of calcium carbonate. This means that clams reduce greenhouse gas by locking up huge amounts of carbon dioxide by building their shells. So they’re good for the environment. And good to eat.

Seriously, we don’t need to go all Greta and destroy our world to reduce our Evil Carbon Footprint. Just plant more trees, and farm clams and oysters.  It’s organic. It’s sustainable. And it costs hardly a thing.


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Posted by Drew458   United States  on 01/10/2020 at 03:50 PM   
Filed Under: • Archeology / AnthropologyEnvironmentFoodGardens and plants •  
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