Prehistoric Humans May Have Stocked Mountain Lakes With Trout, Study Finds

Stone Age Fish Traps Found at a Norwegian Mountain Lake

Archaeologists have uncovered the first known evidence that prehistoric humans stocked freshwater fish in upstream mountain lakes. In 2022, researchers spotted what appeared to be fish traps on the lakebed of Lake Tesse in the mountains of modern-day Norway. Dating and analysis of five excavated traps and associated wooden fragments revealed the artifacts were between 5,000 and 7,000 years old. The findings, led by Axel Mjærum, an archaeologist at the University of Oslo, were published in Antiquity.

Humans first migrated into these Norwegian mountains around 10,000 years ago. Steep waterfalls left behind by the last Ice Age should have prevented fish from traveling upstream, which made seafood an unlikely item on the Neolithic menu. During the last glacial period, between roughly 115,000 and 9,700 BCE, ice coverage rendered inland habitats inhospitable to freshwater fish.

A Trout Hotspot With a Long History

Before it became a hydropower reservoir in the 1940s, Lake Tesse was famous for an impressive population of brown trout. That abundance likely made the lake a prime fishing location. Every spring, lower water levels would expose areas of the lakebed containing buried archaeological items, including sections of a Stone Age settlement.

How the trout ended up in the lake had long puzzled scientists. As early as 1918, researchers hypothesized that humans most likely introduced brown trout into mountainous lakes from their natural habitat. “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,” Mjærum said. Until now, though, it remained unclear when people first began transporting fish upstream into waters that originally lacked them.

Dating the Traps

Radiocarbon dating placed the oldest trap sample at roughly 5,000 BCE and the youngest at 2,700 BCE. The traps were held together by wooden poles, with the best-preserved samples showing cut marks, splits, and other signs of having been crafted.

The team noted that it would realistically have taken several decades for translocated trout to reproduce. These early humans therefore appear to have transported fish while anticipating a delayed return, a sign that hunter-fisher-gatherers were effectively managing their environment to control food supplies. “By introducing brown trout, a strong and lasting entanglement was established between people and aquatic resources in the mountains,” the researchers wrote. Those ties continued to shape activity in the region through the Neolithic, and the results of that early environmental management can still be harvested by sport fishers and professional fishermen today.

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