The oldest historical records on the presence of fish in the mountain lakes in Europe are from the fourteenth and fifteenth centuries. Now, a job supported by ancient DNA has found signs that they should be in a lake of the Pyrenees about 700 years before. The authors of the study, published in Nature Communications, have not found remains of fish, but genetic material of their parasites since the beginning of the seventh century, in the High Middle Ages. Then there was an outstanding grazing activity on the peaks and the shepherds were able to take them up there to have what to eat. The orography and gravity had to prevent the colonization of high mountain lakes by the strict species, such as salmonids, in the distant past. The lakes like Redon should be impossible to reach them. Located at 2,240 meters above sea level, in the central Pyrenees (northwest end of Catalonia), it is isolated by its origin of glacial. “It has no other body of water nearby, when you go up there, it is at the top, it is impossible for them to arrive naturally because they cannot overcome any course,” says Creaf Elena Fagín researcher, first author of this investigation. There is only one exit stream, but it falls through a waterfall of about a hundred meters. There is no fish that climbs so much. There are currently about 60,000 trout. Between the first historical references to populate the lakes with fish are the time of the Emperor of the Holy Roman Empire, Maximiliano I (Father of Felipe el Hermoso, who will marry Juana La Loca). “Illustrated books are preserved in which porters are observed with tonles full of fish uploaded to the tyrol lakes,” says the CSIC researcher at the Creaf Jordi Catalan, senior author of the study of the fish of Lake Redon. “The emperor wanted the lakes to have life and for that he believed they needed to have fish,” he adds. Maximiliano reigned since the end of the 15th century, but Catalan mentions other even older documents, from the previous century. One shows how the authorities granted a family of the place the rights of fishing and marketing of what they fish in Lake Redon. But the fish must arrive before. Lake Redon Plan, surrounded by steep mountains and with an exit stream with a waterfall of about a hundred meters. “The Redon is a manual lake, idealizations that do not really exist,” says Catalan. They have sediments for 10,000 years, which make it a window to the past. From the list of things that have known thanks to the mud, are the first traces of livestock activity in the area thousands of years ago. One of his works, directing the thesis of researcher Pere Mascé, now a professor at the Australian University Edith Cowan, found lead traces in the sediment. “We think it would come from gasoline.” But when calibrating the layer they verified that it was from the times of the Romans, of mining. In more recent dates, the clay cylinder has witnessed how the Saharian dust neutralizes the acid rain or the presence of pollutants of the so -called persistent or microplastic chemicals. The lake has also allowed to rebuild the weather since the end of the last glaciation, detecting some climatic optimal and confirming others, which have served to compare the current warming with those of the past. The arrival of ancient DNA techniques have revitalized the study of the lake bed looking for life that has housed. “But we do not find fish and that I have spent two years looking for them, every day,” says Fagín, the first author. There is no fossil record, that is, physical remains of fish, until recent dates. But there is also no genetic soup that is formed as organisms die, they fall into the background, they decompose and, hopefully, there are portions of their genetic material that allow them to identify them. Previous works had shown that their genetic material degrades easily. Fagín obtained the DNA of a recent trout. “I detected it very well, but once it went through an environmental filter and degraded, there was no way to detect it,” he says. At least, they had more luck with their parasites. Among all the genetic material that is accumulated in the mud, they have identified a third. The cylinder they extracted is barely 30 centimeters, but due to the slow sediment deposition rate, that height corresponds to about 3,300 years of lake history. Masqué, who did that thesis on lead pollution directed by Catalan has been responsible for chronology and dating. To get an idea of the task, masqué compares the rhythm of sedimentation in the submarine cannons close to the coast, which is around “a centimeter per year, with that of the Redon, about a hundred years for every centimeter, of average”, he highlights. The dates put them thanks to the carbon-4 technique. In the mud circle there is life from the beginning, but little. They have found genetic material of microscopic crustaceans, microalgae, dafnias or fleas of water … but in the early eighth century they see something new. “Before this century we see little primary productivity, it is something with little nutrient contribution,” says Fagín. Until him, little material comes by air and his own ecosystem generates little material, hence the slow sedimentation rate. But since then they detect the presence of a group of ectoparasites, species that live in the skin or the guts of fish, such as those known as the Ichthyobodos. In the following centuries there are three other groups of fish parasites, although discontinuously. “The Ichthyobodo are preserved very well in the registry,” adds the researcher. In fact, it is still present in the lake. It is to know how and who took the trout up there. There are no records or writings, although everything points to the shepherds. “Even today they continue to rise to shepherd in summer, when the grass is extinguished downstairs,” says Fagín. Over time, fishing would be formalized, recognizing the exclusive right to exploit fishing for different clans. In fact, Fagín ends up remembering that “until a few decades ago, in a lake (near) Aigüestortes National Park, a family of the place retained fishing rights.” (Tagstotranslate) DNA
