Stone Age hunters stocked Norway’s mountain lakes with trout

The trout could not have reached that spot on their own: the route from the lower-lying bodies of water was blocked by rapids and high waterfalls. Consequently, the fish must have been brought there and released by people. Radiocarbon dating has shown that the traps were in use as early as around 5000 BC.

The discovery challenges the conventional view of hunter-gatherers as people who merely took ready-made resources from nature. Many centuries before the spread of agriculture in Norway, they were already deliberately altering ecosystems and creating more reliable sources of food.

Details

Lake Tesse is situated in the mountains of southern Norway, not far from Jotunheimen National Park. Today it is known as a place rich in trout. However, following the retreat of the glacier, the lake and the associated upper reaches of the rivers should have remained fishless.

Natural obstacles prevented fish from migrating upstream from lower water bodies. Waterfalls posed a particularly serious barrier: trout were physically unable to navigate certain sections of the current.

For over a century, researchers had assumed that humans had introduced the fish into the mountain lakes. The exact time when this occurred remained unknown.

Wooden structures on the bed of Lake Tesse helped provide the answer. They were spotted following a seasonal drop in water levels caused by the operation of a hydroelectric power station. Usually, the remains of such traps are hidden under several metres of water, which is why the wood was so well preserved.

Archaeologists discovered several fishing structures. Each consisted of dozens of sharpened stakes, driven forcefully into the lake bed. Branches or other material were placed between them to prevent the fish from slipping through the barrier.

A long fence guided the trout into a narrowing passage, beyond which lay a holding chamber. Fish that entered this chamber could be retrieved with a net whilst standing in shallow water or from a small boat.

Traces of stone-axe carving remain on some of the stakes. Wooden objects of this age are rarely found in Norway: on land, they usually decay quickly. Underwater, the traps have been so well preserved that individual parts look almost as good as new.

Radiocarbon analysis has shown that the oldest elements date back to around 5000 BC. Other samples indicate that the traps were repaired and used in later periods. This was not a one-off event, but a sustained and well-organised fishing operation.

How the trout ended up in the lake

The traps themselves prove that fish were already present in Tessa around seven thousand years ago. However, archaeologists have not found any containers in which the fish might have been transported, nor any other direct evidence of ancient stocking.

This conclusion is based on a combination of evidence. The waterfalls rule out the natural arrival of fish, whilst the ancient traps indicate that by 5000 BC there was a sufficiently large population in the lake to justify regular fishing.

The most likely species was brown trout – Salmo trutta. It grows to a considerable size, is rich in nutrients and reproduces relatively easily in suitable bodies of water.

People may have transported live fish or roe from rivers further downstream. The exact method remains unknown. Nor has it been established how long before the construction of the traps trout had appeared in Lake Tessa. Therefore, 5000 BC is not the date of the first introduction of fish, but the latest point by which they were definitely already present in the lake.

Nor can one speak of full-scale fish farming. There is no evidence that hunter-gatherers controlled trout reproduction or selected individuals with desired traits. They stocked a suitable body of water with fish and then utilised the resulting population.

Why this is important

The research shows that active management of the natural environment began long before the emergence of agricultural societies. Hunter-gatherers were able to plan years in advance and alter the environment to make food provision more predictable.

Hunting reindeer depended on the season, the weather and luck. Fish traps provided a more consistent yield. Trout could sustain people during prolonged hunting camps in the mountains.

Transporting the fish also required an understanding of its life cycle. People needed to know in which lakes the trout would survive, where it would spawn, and in which part of the water body it was best to set traps.

The authors suggest viewing this as an early form of food production. People were not yet growing crops or rearing domestic animals, but were already creating a new resource that had not previously existed in the local ecosystem.

The consequences of this decision are still felt today. The trout found in Lake Tesse today belong to a population that originated from this ancient relocation of fish. Seven thousand years later, the lake remains a popular fishing spot.

Background

After the end of the last ice age, the glaciers began to retreat, leaving behind new lakes and rivers. People arrived in the inland mountainous regions of southern Norway around 8,000 BC.

Archaeologists have found campsites, tools and evidence of large-scale reindeer hunting in these areas. Fishing probably supplemented the hunting lifestyle and allowed people to stay away from permanent settlements for longer periods.

Stone tools, net weights and the remains of settlements from various periods had previously been found near Lake Tesse. The wooden traps have, for the first time, provided direct evidence of just how sophisticated local fishing practices were some seven thousand years ago.

The discovery also serves as a reminder that the distinction between ‘hunter-gatherers’ and ‘food producers’ was not always clear-cut. People may not have practised agriculture, but they did deliberately relocate useful species and reshape ecosystems to suit their needs.

Source

A study by Axel Mjørum, Ellen Fries, Trugve Hesthagen, Andreas Kirchhefer and their colleagues, ‘The introduction of fish to the Scandinavian mountains by hunter-fisher-gatherers 5000 BC’, was published in the journal Antiquity in 2026.