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Farmers brought fish up the mountains of Europe as early as the 7th century, ancient DNA reveals

Ancient DNA extracted from a sediment core from a high-altitude Pyrenean lake in Spain reveals that fish may have been added to the lake by humans as early as the 7th century CE. The findings, in Nature Communications, suggest that fish were present in Lake Redon much earlier than previously suggested by historical evidence and provide further insight into the impact of human activity on these ecosystems.

High-mountain lakes were historically fishless due to natural barriers, but historical documents began to record fish stocking in European high-mountain lakes during the 14th and 15th centuries CE. These records mostly detail fishing rights and trade for specific lakes, but whether the practice of stocking fish began earlier is unclear.

To investigate, Elena Fagin and colleagues examined a 30cm-long sediment core spanning 3,200 years from Lake Redon in the Pyrenes Mountains of Spain, which is currently host to a population of approximately 60,000 brown trout. No fish DNA was preserved in the lake sediments, but the authors identified DNA from fish parasites and fish prey, which they used as a proxy for the fish, enabling them to investigate their introduction.

They identified DNA belonging to fish parasites as early as the 7th century CE, with a more consistent signal beginning in the 9th century CE, approximately 500 years before historical records begin to document fish stocking in this area. This coincides with evidence from nearby archaeological excavations suggesting that the region was used as sheep pasture in the Late-Roman and Visigothic periods.

The authors suggest that the population of fish living in the lake remained consistent despite changes in the human population in the surrounding area, from which the authors infer that the fish were well-established but could have been impacted by climatic trends.

These findings demonstrate the potential of ancient DNA to help understand historical human activity and document previously unclear impacts of settlements on high-mountain ecosystems.