Ancient fish ponds built by humans in the Bolivian savanna helped settlements to survive dry periods – Science Story

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Tribes in the Amazon basin constructed fishing ponds to cope with months of continuous droughts 1,000 years, new research has found.

A network of ponds connected by canals that captured rainfall and stored it was thought to feed local settlements all year round.

By studying fish fossils, scientists also found fish species with adaptations that allowed it to live in these ponds all year round.

Scientists from universities in France and Brazil think these ponds were cultivated to support a permanent human settlement in the region. 

 

The study looked at the Llanos de Mojos region in central Bolivia, a vast plain which receives flooding rains from October to April, and then virtually no rainfall the rest of the year.

Beginning about 500AD, humans began to create earthen mounds in the region which were established as permanent settlements. 

One of these is Loma Salavtierra, located more than 31 miles (50 km) from the nearest major river, has become an important archaeological site as well as the focus of the current study. 

Scientists studied more than 17,000 fish remains in Loma Salavtierra occupied between 500 and 1,400 AD. 

A team of researchers  – led by Gabriela Prestes-Carneiro of Federal University of Western Para, Brazil -studied the bones of the remains of over 17,000 fish found in midden piles at the pond site.

These man made constructions are thought to be used as fishing ponds but how these fisheries may have functioned is still poorly known. 

Using a comparative collection, scientists from the Muséum national d’histoire naturelle in Paris identified more than 35 different taxa of fish, with four types of fish predominating in the find: swamp-eels, armoured catfish, lungfish, and tiger-fish.  

The study is the first to document the full range of fish species kept in these constructed ponds in the settlement area and offer new insights into how humans modified the savanna environment to cope with the months-long droughts.

The author of the study wrote in the latest report: ‘Although many studies have drawn attention to how Pre-Hispanic inhabitants of these savannas managed to deal with excess water, little attention has been paid to understanding how large and permanent populations were sustained during long periods of drought.

‘In Loma Salavtierra, a network of circular walled ponds connected to system of canals has been identified, raising questions about a possible use of these structures for fishing.’ 

Referring to the four dominant species of fish found, the authors said that all four are characteristic of shallow and stagnant waters.’ 

Previous work has established the existence of a series of shallow ponds rimmed by low earthen walls and connected by canals, which are believed to have captured rainfall and stored it throughout the dry season, potentially built to serve multiple purposes including water storage, drainage, and fish management.

All four of these are adapted to conditions of low oxygen and fluctuating water levels, as would be expected to arise in the ponds during the long dry period between annual rains.

Together with evidence of similar pond networks elsewhere in the region, the authors suggest that their results point to the use of these ponds for harvesting fish year-round, far from any rivers, permanent natural ponds, or other open-water habitat. 

The authors added: ‘The savanna, in contrast to the large Amazonian rivers, presents a distinct set of fishing habitats where humans likely established specific fishing strategies.’

Further studies will be needed to investigate fish storage and holding activities, and whether these activities changed in response to precipitation and landscape fluctuations. 

 

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