Researchers from the University of Oviedo have proven the decrease of the size and the average age of native Asturian salmonids since the Paleolithic until our days. The comparison of archeological remains and modern samples of salmons and trouts has allowed them to determine that their size is smaller and their average age lower due to the increase in the temperatures, the continuous fishing activity and the fragmentation of the habitats that has taken place throughout the centuries.

The research, part of the activity of the Marine Observatory of Asturias, has been conducted by researchers from the Departments of Functional Biology and Geology of the University of Oviedo in collaboration with scientists from the University of Swansea (United Kingdom). The article includes the conclusions of the research, which has been published in Royal Society Open Science and referenced at the website of the National Geographic magazine.

Tenured Professor of Genetics Eva García Vázquez, and the geologist Pablo Turrero have studied remains of salmonids from the Paleolithic belonging to the collection of the Archeological Museum of Asturias, and they have compared them with modern samples fished in the Principality. "In general terms, we see a significant decrease in the average size of these species, which would range between 50 to 33 cm", explains Pablo Turrero.

The measuring of the vertebrae allows the specialists to determine equations that relate the size of these bone structures to the total length of the individual, and these calculations lead to observe how this decrease in size takes place. The research conducted also reveals notable changes in the average time that these migrating individuals spend at sea, while the duration of their fresh water phase remains stable. "We have seen that every time they come back earlier from the sea, and, therefore, their size is smaller", concludes Turrero.

The fishing activity that has been taking place for millenia may have affected the populations by removing the bigger-sized individuals, which are the most lucrative ones, from the competition for reproduction. Thus, the individuals that manage to reproduce are the smaller and younger ones, causing bigger-sized fish to be more uncommon.

The steady increase in the temperature and the intense fishing activity condition the evolution of the species affected

The progressive increase of the temperature of the water is another explanation offered by the scientists to justify the decrease in the average size, at least in the concrete case of salmons, since their biology itself makes them grow less in warm waters. Finally, the pollution that exists in the flow of rivers is another great difference between them and the environments in which the salmonids of the Paleolithic lived, and a possible determining factor to explain their changes in size and average age.

The Marine Observatory of Asturias, promoted by the Campus of International Excellence, is configured as a Strategic Coalition of Research Groups in which cross-curricular groups and teams of the University of Oviedo work in order to gather and facilitate the information on the sea of Asturias to the scientific community, the citizenship, the professionals and the administrations.

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To the left, a vertebra of a sample of modern salmonid; to the right, one of the archeological vertebrae maintained since the Paleolithic and used for the research.