Released fish into mountain lakes 7,000 years ago: "It was a form of simple fish farming"
People have always had the ability and capacity to influence and change their surroundings, says an archaeologist.
The dried-up bay of Lake Tesse, with Stone Age fish traps.(Photo: Magne Samdal / Museum of Cultural History. Photo of Axel Johan Mjærum: Museum of Cultural History)
The fish living in the lakes of the Norwegian mountains did not get there by themselves.
We have known that for a long time, says archaeologist Axel Johan Mjærum.
But we did not know when they got there or how.
A theory that the fish must have been carried up there and released by humans is nearly a hundred years old. Mjærum himself has been working on these questions for almost 15 years.
And now he has the answers.
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In a groundbreaking study published in the journal Antiquity, Mjærum shows that Stone Age people in Norway released fish into mountain lakes at least 7,000 years ago.
"It's quite a bit earlier than most people had imagined," he tells Science Norway.
Stone Age people created mountain fishing
The study does not just tell us when Norwegian mountain lakes became filled with trout.
It also shows how complex and knowledgeable Stone Age people were, according to the archaeologist from the Museum of Cultural History in Oslo.
"This tells a very important story about how hunter-gatherer and fishing communities related to nature," says Mjærum. "They were not just passive harvesters of nature – they also went in and changed it. They made quite significant interventions."
The traditional view of Stone Age people is that they were nomads who moved in search of food. When agriculture took over, people instead began producing food by manipulating and controlling nature, which in turn became crucial for the development of more complex and advanced societies.
But this division turns out to be too simplistic.
"Some of what we think of as natural today was actually created by Stone Age people, for example, mountain fishing," says Mjærum. "If we take the idea a bit further, we can see this as a form of simple fish farming or food production in the natural environment."
Inland, traces of several Stone Age settlements have been found, and just out in the water here, the remains of four fish traps have been discovered. But the fish did not make their way up into the mountains on their own. The photo is from the excavation of the fish traps in 2023.(Photo: Magne Samdal / Museum of Cultural History)
Discovered by a hiker
It was mountain hiker and hobby-archaeologist Reidar Marstein who, in 2022, discovered fish traps thousands of years old in the mountain lake Tesse in Jotunheimen, Eastern Norway.
The water in the lake is drained every year to produce power. On the bottom of the lake, Marstein saw numerous thin wooden poles, arranged in a distinct pattern. He realised they had to be the remains of ancient fish traps.
And now the results of all the examinations of the timber are available.
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5000 BCE
Four fish traps were excavated that summer. Of these, 113 samples were sent for dendrochronological analysis. This method provides very precise dating based on the growth rings in the wood.
The oldest poles have been dated to 5000 BCE. In other words, they are 7,000 years old.
Other thin wooden poles are younger. According to the calculations, the fish-trapping installation was in use for at least 2,300 years.
The poles show clear signs of having been worked. And within the same fish trap, the researchers found poles that were felled 12 years apart. This shows that the structures were maintained and used over time.
Poles from the fish traps had been driven deep into the bottom of the lake at some point 7,000 years ago.(Photo: Ellen K. Friis / Museum of Cultural History)
A reconstruction of what the fish traps may have looked like. The traps stood in shallow water and formed a kind of catch chamber. Here, people could scoop up the fish from a boat, or catch them by wading out into the water.(Illustration: Ingvild Tinglum Bøckman)
They transported the fish in leather bags
But before these complex structures for catching fish were built, the fish were actually released into the water here in Tesse. Far inland, high up in the mountains, 850 metres above sea level.
How did they do it?
"We haven't actually found the bags they carried the fish in," says Mjærum. "But they were skilled at working with hides. So one possibility is that they simply used watertight bags made from animal skin. Evidence of hide processing is commonly found at Stone Age settlements."
It goes without saying that the fish could not survive for very long in such a bag. Mjærum believes the journey up to Tesse probably happened in stages.
"There were probably trout farther down in the Gudbrandsdalslågen river. Then a few decades would have passed while the fish established themselves there. After that, they could have carried them farther upstream," he says.
Mjærum estimates that it may have taken a few decades, or perhaps even a hundred years, before the fish reached Tesse.
"This wasn't something they did to get a return the same year, but for the future. It took many years before they could begin to reap the benefits of this work," he says.
The journey up to Tesse probably happened in stages, Mjærum believes.(Map: Mjærum et al.)
They used nature and produced food
The fish in Norwegian mountain lakes are not the only example showing that Stone Age people knew how to use nature to produce food.
The spread of hazelnuts across Europe around 8000 BCE was partly driven by humans, Mjærum explains. It is also known that people at that time deliberately started forest fires to improve grazing areas for prey animals.
"Stone Age people actively shaped and made use of nature. And this discovery of ours, that they introduced trout into the mountain lakes, is a very concrete example of that," says Mjærum.
Technology, investment, and cooperation
Eventually, once the fish had established themselves in Tesse, Stone Age people built the fish traps.
Each fish trap consisted of around 40–50 poles, with woven branches forming a larger chamber, and a fence that guided the fish into it.
Prestigious reindeer hunting was probably one of the main reasons for being up here in the mountains. The fish provided food security. Even if they did not manage to kill an animal, they still had food. This also meant more people could travel into the mountains, and they could stay there for longer. Some groups may even have lived permanently in these areas.
“They had, by their own standards, the ability to make use of complex technology,” says Mjærum. “They invested resources in order to gain returns later. And they quite clearly cooperated – this is not something one person can do alone. This is something that has to be done as a group.”
The fish traps in Tesse were excavated in 2023. Here, the archaeologists are working to uncover the posts in one of them.(Photo: Ellen K. Friis / Museum of Cultural History)
Excavating the lakebed is hard work, but it is precisely these sediments that have created the unique conditions preserving the wooden posts. Well-preserved wood from the Early Stone Age is exceptionally rare.(Photo: Ellen K. Friis / Museum of Cultural History)
The fish could not get past the waterfall
Mjærum is absolutely certain that the fish could not have made it up here without human help. In fact, this has also been the prevailing theory since it was first put forwards by a fish biologist in 1918.
All freshwater fish in inland Scandinavia arrived after the ice from the Ice Age disappeared, a melting process that continued until around 8000 BCE in the mountainous regions of southern Norway.
In lower-lying areas, fish were able to spread gradually from the coast and inland through brackish water as the glaciers retreated and rivers and lakes formed. But it is not possible for fish to move farther upstream. There are waterfalls here that the fish have no way of passing, according to Mjærum and his colleagues.
Another theory suggests that fish and fish eggs may have been transported by birds, allowing them to establish themselves in mountain lakes.
But the higher you go, the fewer fish species there are. Why would the birds only have carried trout? And how is it that the fish became established in the mountains at exactly the same time, from 5000 BCE onwards?
"Through the work we have now done, we have a good understanding of when the fish were introduced. And it gives us some valuable insights into what it meant to be a Stone Age person during the Early Stone Age, before agriculture," says Mjærum.
"An important study"
"These are very exciting and important results," says Knut Andreas Bergsvik.
The professor of archaeology at the University of Bergen is an expert on the Stone Age and has studied hunting and fishing communities along the Norwegian coast.
"This is the first time that this type of fishing installation from the Early Stone Age has been found in Norway. And the researchers present a clearly convincing argument for the dating," he says, adding:
“It has long been known that people fished in the mountains during the Early Stone Age. But it has never before been known that it was done in the way they have documented here."
According to Bergsvik, the article quite clearly shows that the fish were carried here and released by people.
Stone Age people were clearly more closely connected to the landscape than we previously thought, according to Knut Andreas Bergsvik. “It's not impossible to imagine that it was the grandfather who made the trapping installation, and that it was now being used by younger generations,” he says.(Photo: University of Bergen)
“It would not have been possible for the trout to get up here on its own. So as early as the Early Stone Age, they transported the fish here with the intention of returning and harvesting the resource," he says.
Returned to the same place
Bergsvik believes the discovery tells us something about society that we did not really known before.
People have imagined Stone Age communities constantly moving around and hunting, continually seeking out new places. A kind of restless wandering from one location to another.
“This study shows that people had a clear intention of returning and using the same places again and again,” says Bergsvik. “It says something about these people that they were able to plan all of this."
According to Bergsvik, the article helps change the view of how hunters and fishers interacted with nature, and the knowledge they had about species and animal behaviour.
“This blurs the distinction between hunter-fisher-forager societies and farming communities,” he says. "They managed natural resources, planned ahead, and harvested in much the same way that farmers do. They had a stronger attachment to landscapes and to particular places than previously thought. And it supports the idea that these were far more complex societies than we had previously believed."
