Prehistoric fisheries offer clues to sustainable catch

Efforts to reform fisheries in the present just got a boost from the past. Two quantitative studies of prehistoric fisheries show that some early cultures figured out how to get high yields without overexploitation.

Jack Kittinger of the University of Hawaii in Honolulu and Loren McClenachan of Simon Fraser University (SFU) in Vancouver, Canada, studied the reef fisheries in Hawaii since the islands were first colonised 700 years ago.

With little archaeological evidence of farming, the earliest Hawaiians were reliant on the sea for much of their food. Previous estimates suggest they each consumed about 182.5 kilograms of seafood per year ? similar to levels in Pacific island countries which rely on seafood today. Kittinger and McClenachan worked out the total annual catch, assuming a conservative estimate that Hawaiian population reached 160,000 before contact with European settlers. It is thought that the population was probably more like 250,000 at its pre-settler peak.

"The coral reef fisheries yielded three to four times what people think is the sustainable yield for reef fisheries today," Kittinger says. "And we were very conservative in our yield estimates ? it's crazy."

Historical accounts and ethnographic studies suggest why the Hawaiian fishing operations were so successful. The pre-European society had a complex set of rules that saw reefs regularly closed to fishing, strict regulations on fishing gear, and restrictions on eating vulnerable species ? all remarkably prescient of modern regulations.

There is also archaeological evidence that they built extensive fish ponds stocked with juvenile mullet and milkfish as insurance against famine. The regulations make sense, given that Hawaii is at the mercy of tsunamis, floods, hurricanes and droughts, requiring sophisticated risk management strategies.

The Hawaiians were not the only Pacific community to fish sustainably. SFU researchers Anne Salomon and Amy Groesbeck have been studying the ancient "clam gardens" in the territory of the Kwakwak'awakw and K'?moks First Nations along the coast of British Columbia, Canada. Such structures were built and maintained for 2000 years, from Washington State to Alaska, until European settlers disrupted the practice.

Clam, clam and more clam

Clams are filter feeders and thrive on pebbly beaches that trap nutrients brought in with the tide. The gardens provide them with these preferred conditions. They are walled structures built in the intertidal zone of shores. As the tide rises, water cascades over the walls and washes nutrients into the beach behind, which has been artificially extended to create a clam-friendly pebbly habitat. At low tide, the area is exposed and easy to harvest.

The terraced beaches are extensive platforms that provide the clams with perfect living conditions, so in theory the shellfish there should grow faster and live longer, allowing for more sustainable cultivation. To test the claim, Salomon and Groesbeck seeded 11 walled and unwalled beaches with clams in the spring and then in the autumn dug them up to compare growth.

Their as-yet-unpublished work shows that the gardens work, says Salomon. "Our experimental data shows quantitatively that you get more clams from clam gardens, with higher survival rates and higher growth rates." She adds that it is clear that the people heavily exploited this method ? the bay under study has over 50 original clam gardens.

Salomon thinks this research could change how we cultivate shellfish. "We're going to need to double the world's food supply by about 2040," she says. "We can use the technology from ancient times to feed people today. Clam gardens are a perfect example of how people can do more with less."

Kittinger and McClenachan think their Hawaiian study also holds lessons. "They had basically the same tools in the toolbox, in terms of reef management strategies, but they used them differently and managed more effectively, with locally developed rules and regulations," Kittinger says. "It is evidence that coral reef fisheries can be sustainable. Ancient Hawaiian societies gave us the road map for how to achieve that in today's context."

Not all early societies had sustainable practices, though. Kittinger and McClenachan also looked at ancient fishing in the Florida Keys. Lack of freshwater probably limited the pre-European population to around 1000 people, and so they did not face food shortages ? and the locals had strong trade connections with the Caribbean. They had little need for Hawaiian-style regulations or sustainable fishing practices. Once European settlers arrived, however, an unsustainable fish export economy quickly emerged.

"Florida is a really good example of what happens when there's a lot of focus on one or two fisheries for export," says McClenachan. "It's a cautionary tale of what happens when you don't manage and don't diversify."

Journal reference: Fish and Fisheries, DOI: 10.1111/j.1467-2979.2012.00465.x

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