Study: fish species endangered if dams built on the Puelo River

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Puelo River. Photo: Andres AmengualPuelo River. Photo: Andres Amengual
By Iván Vera Escalona
Translation by Zoe Baillargeon

Vestiges of a remote past, glaciers tell us about a different time scale, alien to the human one. Reminiscent of what they once were, the glaciers that hypnotize us so with their celestial flashing, with their roughness or dimensions that at times seem overwhelming, are survivors of another era.

In the Pleistocene, between 2.5 million and 10 thousand years ago, the world was very different in relation to what we observe today. Most high-altitude areas and those near the poles were partially or totally covered by glaciers during the period we call glacial cycles. The Patagonian ice fields are the most palpable living example of those times.

During the period of the glacial cycles, the habitable areas for animal species were drastically reduced, affecting the connectivity between populations, the genetic diversity, and finally the very existence of the species. Many of the species that exist today survived in what we call glacial refuges, areas where conditions were favorable for shelter and that could ensure the survival of the species despite low temperatures and the presence of glaciers.

After the Pleistocene, the current geological period, the Holocene, began, characterized by an increase in global temperature and the decline of glaciers. This phenomenon left large areas free of ice, polishing and slowly carving the landscapes we observe today. This was how different species were able to colonize new areas and expand their ranges of distribution to those places where we can find them today.

All these processes that have happened during the last thousands of years have left their mark at the genetic level (in the DNA of the species). Almost as if it were a forensic case, these genetic traces, when taken together with geological information, allow us to understand how those processes affected the species, what places the species might have inhabited during the past, and in what period of time they inhabited a specific site.
Puye grande (Galaxias platei). Photo: Iván Vera EscalonaPuye grande (Galaxias platei). Photo: Iván Vera Escalona

With this in mind, researchers from Dalhousie University in Canada and the University of Concepción in Chile worked together to better understand what happened to the puye grande (Galaxias platei) in the Puelo River basin in the past. The puye grande is a fish species found only in Patagonia, and which is relatively unknown to most of the population. However, it has a wide distribution and an interesting history.

Thanks to our study, we determined that the puye grande populations of the Puelo River basin were more connected during the past than at present, and that they were strongly affected during the glaciations. They faced complex and inhospitable environmental conditions during the Pleistocene, managing to survive with a very low genetic diversity.

The genetic diversity is a very important indicator on the state of a species: it allows us to determine the effort that we must put forward in its conservation. A species with populations that have a high genetic diversity tells us that the natural processes that affect the species will not present a great threat. In contrast, low genetic diversity implies that certain populations are highly sensitive to natural processes, as well as to changes in their environment. Under this scenario, the low genetic diversity of the puye grande tells us that it is highly sensitive to changes in the lakes and rivers where it lives.

What would happen if hydroelectric power plants are built in the habitat of the puye grande in the Puelo River basin? Several scientific studies have shown the negative effects of dams on different fish species in terms of reduced connectivity among their populations, but their implications at the genetic level are poorly documented.

Using a series of genetic methods and simulations performed on supercomputers to develop a scientific instrument capable of addressing the effects of dam construction on native species, we conclude that in this case the connectivity between puye grande populations would be altered, leading to an extinction rate between 50-75% in the next 40 to 75 years. In addition to affecting the connectivity between the populations of puye grande of the area of ​​study, the construction of dams would cause great changes in the environmental conditions, among them the flooding of the shores of the lakes and an increase in the temperature of the water.

Although there are mitigation measures that could be effective in maintaining the movement of the fish through fish passages or translocation of individuals with the aim of reproduction with specimens from other populations, the truth is that very little work has been done in Chile in this area. Great efforts are required to protect the diversity of native species in our rivers and lakes. It is part of the path that our country must still travel.
The author, Iván Vera Escalona, is a Chilean biologist currently studying for a Ph.D. in biology at Dalhousie University, Canada.