Around 7,000 years ago, Stone Age hunter-gatherers carried live brown trout up into the steep highlands of Norway to stock an isolated mountain lake, marking the earliest known instance of human-mediated fish translocation in the world.
The discovery, made at Lake Tesse in central Norway, reveals that prehistoric humans were actively managing their local ecosystems to secure reliable food sources long before the advent of agriculture in Scandinavia. Located at an elevation of approximately 850 meters, Lake Tesse was covered by the massive Fennoscandian ice sheet until roughly 8,400 years ago. Once the ice retreated, it left behind a barren ecological blank canvas.
While the lake historically boasted a remarkably rich brown trout population—yielding up to nine metric tons of fish annually before it was converted for hydropower storage in the 1940s—how the fish first arrived had long baffled researchers. Natural migration was ruled out due to impassable geographical barriers, including massive downstream waterfalls. Furthermore, the exclusive presence of brown trout in Tesse and other nearby mountain lakes discredited the theory of accidental transport by birds.
The breakthrough came in 2022 when a temporary lowering of the lake's water levels exposed the partially buried remains of elaborate wooden fish traps. Axel Mjærum and a team of archaeologists from the University of Oslo subjected the wood to radiocarbon dating, tracing the oldest trap structures back to approximately 4950 BC.
Additionally, by correlating younger wooden posts with pine tree ring chronologies from the central Scandinavian mountains, the researchers pinpointed the felling of one post to 2669 BC, and another to 2657 BC. This 12-year gap, combined with the overall age span of the site, indicates that these sophisticated traps were continuously maintained and operated for well over two millennia.
To transport the trout to such a high altitude, hunter-gatherers likely utilized waterskins. Archaeologists believe these mobile groups stayed in the mountains during the summer months to hunt reindeer and harvest fish, before retreating to milder coastal areas or low-lying valleys for the winter. Securing a predictable, self-sustaining population of trout in the highlands would have transformed their seasonal migrations, enabling entire family groups—rather than just hunting parties—to stay in the mountains for extended periods.
While even older fish management systems have been documented elsewhere—such as 8,600-year-old eel channels in Australia—the Lake Tesse findings stand as the earliest concrete evidence of humans intentionally moving fish to populate a new, isolated habitat.