If you think most fish stinks after 3 days, try 11,500 years: That’s the age of salmon bones that archaeologists have uncovered at the Upward Sun River site, one of Alaska’s oldest human settlements. They say the cooked bones provide the first clear evidence of salmon fishing among the earliest Americans, Paleoindians, who crossed from Siberia into Alaska over the Bering Land Bridge more than 13,000 years ago. The finding, published online today in the Proceedings of the National Academy of Sciences, helps debunk the idea that America’s first fishermen relied primarily on big game for food. It also explains how they managed to survive in an ice age Arctic environment and adapt to life on a new continent.
These days, salmon is a staple for native Alaskans, but evidence for the origins of salmon fishing has been hard to come by. Wood and rope fishing tools decompose quickly, as do salmon bones. And until recently, most researchers hadn’t been doing the kind of careful excavation necessary for discovering fragile fish skeletons. But building on recent work that suggests big-game hunting was just one part of a “broad-spectrum” strategy among America’s first people, researchers have begun searching for other remains. These include creatures like migratory waterfowl, small mammals, and salmon that would have been part of a more seasonally based diet. Archaeological sites across the Bering Strait region—including Siberia—support this idea, says John Hoffecker, a University of Colorado, Boulder, archaeologist who specializes in the region.
But finding ancient salmon leftovers has been a challenge. “It’s difficult to capture ancient fishing because of the nature of fish bones—they’re small, fragile bones,” says Carrin Halffman, a biological anthropologist at the University of Alaska (UA), Fairbanks, and the lead author of the new study. And if archaeologists do turn up any fishy remains, she says, it’s hard to know just what kind of fish it was. As the team tried to find out how the people at Upward Sun River used the resources of the nearby Tanana River, they carefully excavated parts of the site, sifting soil through fine-meshed screens. In the same fire pit where they found the buried remains of two infants, they discovered the salmon bones. Analyzing DNA in a piece of uncooked fish bone, Halffman and her team found that it was chum salmon (Oncorhynchus keta), a hefty fish that weighs 5 to 10 kilograms and grows roughly 60 centimeters long. Thousands of chum salmon still swim up the Tanana River every summer to spawn, and the run remains a central cultural event for the indigenous Athabascan people who live there today.
But could the find be evidence for the beginnings of this annual ritual? It was possible that the salmon were not part of the annual saltwater-to-freshwater migration, but instead were freshwater fish that lived in the river their entire lives. To find out, Halffman analyzed carbon and nitrogen isotopes in the fish bones. Because different versions of the two elements—both with different weights—are found in varying concentrations in seawater and fresh water, that compositions is reflected in the fish bones. The bones that Halffman analyzed had higher ratios of heavier carbon and nitrogen isotopes, meaning the fish had lived in the ocean and must have been caught during a spawning run. “What we’re looking at is probably the beginnings of the utilization of salmon,” says Ben Potter, an archaeologist at UA Fairbanks, and a co-author of the study.
The discovery boosts the view of Paleoindians as generalists who ate a variety of foods, Hoffecker says. “I don’t think it was possible for people to occupy these environments without this broad-based diet and without this kind of high-tech economy,” he says. Herb Maschner, an Arctic archaeologist at the University of South Florida in Tampa, agrees and says the careful excavation methods and analysis serve as a good example of what archaeologists need to do to answer questions about ancient people living in central Alaska where the conditions for preserving bones and artifacts are “notoriously” bad.
Potter and the other researchers are already busy answering other questions. Eventually, they say, the abundance of salmon and the ability to store fish allowed the indigenous people of the Pacific Northwest to settle in large permanent villages, a lifestyle that typically requires agriculture. The team suspects that salmon fishing became more important over time as big game became scarcer in central Alaska, an idea they hope to test with further excavations. For now, little is known about salmon fishing in the period between 11,500 and 1000 years ago, but Upward Sun River gives the research team a start. Potter says: “You need that beginning to see how the end came about.”