Restoring Ancient Clam Gardens in the Pacific Northwest

What if the key to sustainable seafood lies in ancient practices we’ve nearly forgotten? Discover how Indigenous clam gardens are coming back to life.

Clam gardens are ancient mariculture systems. You could think of them as underwater farms which people have built and cared for over thousands of years. For example,  people in the Pacific Northwest region built rock walls at the shoreline, creating the perfect conditions for clams to grow big and fast with the coming and going of the tide. It’s an example of how, working with nature, people could ensure they’d have plenty of food without damaging the environment. 

For thousands of years, Indigenous People sustainably managed these clam gardens. However, colonisation and industrialisation have led to a significant decline in these practices as coastal areas were developed and communities were disrupted and displaced. Today, Indigenous communities in Washington state (USA) and British Columbia (Canada) are drawing upon ancestral knowledge to restore these clam gardens. In this way, they can revitalise the environment and cultural traditions while producing an abundance of nutritious food.¹ 

‘Clam’ is the common name given to several kinds of bivalve mollusc. They live as infauna, meaning they spend most of their lives halfway buried in the seafloor or riverbeds. 

How are traditional clam gardens built?

Recently, scientists have identified ancient clam garden remains stretching over several kilometres in the Northwest Pacific coast, some dating back to at least 3,500 years.² 

These gardens were constructed by building rock-walled terraces on gently sloping intertidal zones, at the lowest low tide line. The rock walls retained sediment, creating a flat, stable environment for clams to settle and grow. 

The maintenance of these clam gardens involved careful, ongoing management to ensure their productivity and ecological balance, such as optimising sediment quality and temperature.³ 

The techniques varied amongst Indigenous groups: some added shell-rich sediments and gravel to help build up terraces, while others removed shells post-harvest to maintain balance. Additionally, clearing large rocks from beach sections, increasing sandy areas for clams, and thinning out clams reduce competition and help younger clams thrive.⁴ 

The Kwakwaka’wakw nation also employed a unique method of aerating the ground by inserting and wiggling a wooden stick, which helped clams grow bigger and faster.⁵ These methods, passed down through generations, are an example of achieving food security through sustainable resource management. 

Clam garden shown from above. Quadra Island, British Colombia. Photo by Keith Holmes, Hakai Institute.

Unfortunately, with the arrival of European colonists and the displacement of Indigenous populations, clam gardens fell into disuse. Professor Dana Lepofsky, from the Department of Archaeology at Simon Fraser University, Canada, told FoodUnfolded, “Largely, they really stopped being used. People collected clams on them, but they weren't cultivated since about the fifties. They fell out of use even before then, with lots of changes in the governance systems, removal of people from the shore and disconnection from heritage.”

What are the ecological benefits of traditional clam gardens?

Besides food security and cultural value, restoring these gardens can positively impact the local ecology. Clams, like other bivalves, are filter feeders. This means they can filter chemicals and particles from the surrounding water. By doing so, the clams improve the local water quality, which benefits other organisms that inhabit the area. 

Bivalves also play a crucial role in nutrient cycles, particularly for nitrogen and phosphorus, by removing them from the water. Some nutrients are incorporated into their tissues, while the rest are buried in the surrounding sediments. Given their ability to cycle nutrients, bivalves are often used as a tool in marine restoration projects to combat eutrophication in areas with nutrient-polluted water. This ability to capture nutrients from the local environment also means that bivalves require no feed or synthetic inputs to grow, so their cultivation is one of the most environmentally friendly forms of aquaculture.⁶ 

The filter-feeding abilities that mean bivalves improve water quality also means that clams can accumulate harmful toxins, bacteria, and pollutants from their environment - posing a risk to food safety. This problem is getting worse as climate change intensifies harmful algal blooms. One of the main concerns is the Paralytic Shellfish Poison (PSP), a naturally occurring marine biotoxin that is produced by some species of microscopic algae.This danger must be balanced with the cultural rights of First Nation communities to consume their clams. One notable program involves the Sitka Tribe of Alaska, which runs a tribally owned and controlled Environmental Research Lab (STERL). This lab tests shellfish samples sent in by residents from various small communities and villages throughout Southeast Alaska to make sure they are safe for consumption. Initiatives like this are important to balance food safety while also empowering local communities.

As well as feeding people, clams are a crucial food source for many wild species.⁷  

Professor Marco Hatch is a marine ecologist at Western Washington University and a member of the Samish Indian Nation. He told FoodUnfolded, “We spend a lot of time thinking about clams in clam gardens. But I like the term sea garden(…) If you're thinking about what was there before clam gardens, it was primarily a two-dimensional habitat. When we build a clam garden, all these rocks piled up at the low tide line create a lot of space between the rocks. And one of my former students worked to see what other types of traditional foods also live within that rock wall. There are things growing there like red sea cucumber, red rock crab, cockles, large snails, limpets, and seaweeds, showing that the rock wall itself is also a major source of food.” This contrasts with other types of seafood farming practices, which often lead to a decrease in local biodiversity.⁹ 

Indigenous communities are leading the way

In recent years, the restoration of clam gardens in British Columbia and Washington has gained momentum. The move is primarily driven by a commitment to revive Indigenous traditions and enhance marine ecosystems and as part of broader efforts to reclaim Indigenous governance and achieve food sovereignty. According to Professor Dana Lepofsky, when the First Nations are asked why they wish to revitalise clam gardens, their reasons are usually “to connect youth and elders, to reconnect with heritage, to gain food sovereignty and rights and title.”

Projects like the Clam Garden Network bring together Indigenous communities, scientists, and conservationists to revive these ancient mariculture systems. Professor Marco Hatch, who is also a member of the Clam Garden Network, explains how something that started as a platform to exchange information transformed into a network of people working for a common goal, “Initially, it was a way for us to connect to talk about different research questions related to clam gardens and to think about ways to share data and standardise methods. But over the past ten plus years, it's grown and changed shape into a network that is trying to use our expertise and resources to help communities reconnect to clam gardens, and in some cases, restore and build them in their home territory.”

A team of archaeologists, lead by Dr. Dana Lepofsky, collecting samples in order to date indigenous rock walls. Quadra Island, British Colombia. Photos by Keith Holmes, Hakai Institute.

Indigenous groups are at the forefront of this movement, utilising traditional knowledge to restore and maintain these rock-walled terraces. For example, the Hul’q’umi’num’ and W̱SÁNEĆ Coast Salish communities are pioneering the first experimental clam garden restoration in the Southern Gulf Islands of British Columbia, working in partnership with Parks Canada. In Washington State, the Swinomish Indian Tribal Community is leading the first modern clam garden construction as part of its climate change adaptation strategy.

These efforts extend beyond environmental restoration; they are acts of cultural revitalisation. Across the Pacific Northwest, Indigenous people continue the tradition of rolling rocks to build low-tide walls, tending to beaches, and harvesting clams from these gardens, keeping their heritage alive. “You see kids on the beach, rolling rocks together with Elders. It's just magic,” Professor Dana Lepofsky tells us.

"You see kids on the beach, rolling rocks together with Elders. It's just magic" - Professor Dana Lepofsky

Professor Marco Hatch adds, “When you're working on a clam garden that you know might be thousands of years old, and you're rekindling that connection between the community and that ancestral feature, it's hard not to think about the magnitude of that. And to think about how many generations have touched those rocks that have done exactly what we're doing today. And so, then you're looking backwards, reactivating something that's been practised and managed continuously for thousands of years but also looking forward, trying to ensure that it's practised continuously for thousands of years more. I think that is an impactful, profound thing to think about.”