Some 10,000 years ago, humans first migrated into the mountains of modern-day Norway. Steep waterfalls left behind by the last Ice Age should have prevented fish from traveling upstream, making seafood an unlikely item on the Neolithic menu. But archaeological evidence seems to suggest otherwise.
In 2022, archaeologists spotted what looked like fish traps at the lakebed of Lake Tesse in Norway. Subsequent dating and analysis of five excavated traps and associated wooden fragments revealed that the artifacts were between 5,000 and 7,000 years old. The results, published today in Antiquity, represent the first known evidence that prehistoric humans introduced freshwater fish to upstream lakes and rivers—an old hypothesis bolstered by new evidence.
“For more than 100 years, it has been known that the fish inhabiting watercourses in the Norwegian mountains are descended from specimens translocated by humans,” Axel Mjærum, the study’s lead author and an archaeologist at the University of Oslo in Norway, said in a statement.
An odd hotspot for trout
Before becoming a hydropower reservoir in the 1940s, Lake Tesse was famous for being home to an impressive population of brown trout, according to the paper. The abundance of fish likely made the lake a prime location for fishing. This was supported by the fact that, every spring, lower water levels would expose areas with buried archaeological items of interest at the lakebed.
Going back thousands of years, however, exactly how the trout ended up in this lake was a mystery to scientists. During the last glacial period (between 115,000 and 9,700 BCE), the ice coverage in the area “rendered inland habitats inhospitable to freshwater fish,” the researchers explained in the paper. So, researchers hypothesized since as early as 1918 that humans most likely relocated brown trout from their natural habitat to mountainous lakes.
“However, until now it has remained unclear when people first began transporting fish upstream into lakes and rivers that originally lacked natural fish,” Mjærum said.
Putting a date to the traps
The latest results offer a long-awaited clue into the timeline of this artificial trout migration. According to the study, radiocarbon dating of the traps dated the oldest sample to roughly 5,000 BCE, whereas the youngest trap was dated to 2,700 BCE. The traps were held together by wooden poles, with the best-preserved samples including cut marks, splits, and general signs of having been crafted.
The team pointed out that, realistically, it would have taken several decades for the translocated trout to reproduce. In other words, these early humans appeared to have successfully transported fish and anticipated this “delayed return,” the researchers wrote in the paper. If true, this shows how early “hunter-fisher-gatherers,” as they put it, were effectively managing their environment to control their food supplies.
“By introducing brown trout, a strong and lasting entanglement was established between people and aquatic resources in the mountains,” the team concluded in the paper. “These ties continued to shape activities in the region during the Neolithic […] and the results of this early environmental management can still be harvested by sport fishers and professional fishermen today.”
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