Salmon has been on the American menu for 11,800 years, says a new chemical investigation of prehistoric hearths.
Researchers from the University of Alaska Fairbanks (UAF) made the discovery as they excavated a total of 17 hearths from different time periods at the Upward Sun River site near the Tanana River in central Alaska.
To identify the fish remains, a team led by UAF postdoctoral researcher Kyungcheol Choy employed the same technique used to reconstruct ancient diets from cooking pottery and food residues. In this case, they analyzed the chemistry of sediments from each hearth.
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"Most of archaeologists are interested in bone remains, human bones and pottery residues to reconstruct the food consumption in ancient people. However, fishbone remains are not preserved well and it's difficult to detect fish consumption in pre-pottery people," Choy told Discovery News.
The researchers examined chemical profiling of the hearth residues by carrying out stable isotope analysis and lipid residue analysis. In this way, they determined whether the food cooked there came from land animals and plants or aquatic ones.
"We confirmed the Upward Sun River site was used for cooking salmon and freshwater fish even though the site is located in the central Alaska," Choy said.
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High nitrogen values in hearths indicated that fish was cooked in hearths dating to 11,800 and 11,500 years ago.
More in detail, the carbon ratios from lipids in hearths pointed to both marine and freshwater fish. Given the site location in central Alaska, far away from the ocean, the researchers concluded the marine species must have been salmon, which migrate from the ocean into rivers each year to spawn on gravel beds.
"DNA analysis of chum salmon bones from the same site on the Tanana River had previously confirmed that fish were part of the local indigenous diet as far back as 11,500 years ago," UAF said in a statement.
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The new 11,800-year-old dating confirms central Alaska as the earliest site of salmon consumption in the Americas.
Finding ancient salmon traces in Alaska might not sound that surprising, but Choy and colleagues noted that Alaska's ice age residents were previously thought to have a diet dominated by terrestrial mammals such as mammoths, bison and elk.
"Our results demonstrate that salmonid and freshwater resources were more important for late Pleistocene hunter-gatherers than previously thought," the researchers wrote in the Proceedings of the National Academy of Sciences.
Ben Potter, a professor of anthropology at UAF and co-author of the study, said the findings suggest a more systematic use of salmon than DNA testing alone could confirm.
"This is a different kind of strategy. It fleshes out our understanding of the people of Upward Sun River in a way that we didn't have before," Potter said.
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