André Luis Regolin talks us through the latest research from themselves and colleagues on conserving the rare Williams’ side-necked turtle. The study uses a new methodological approach to evaluate how current and future scenarios of hydroelectric generation affect the species’ distribution.

The problem

The Williams’ side-necked turtle (Phrynops williamsi) was only described to science in 1983 and since then little attention and research efforts have been directed to the species. It is restricted to rivers in the Atlantic Forest and Pampas and, for about two decades, scientists have suggested that it is at risk of extinction.

Its geographical distribution includes Uruguay, southern Brazil, northern Argentina and southeastern Paraguay. On sunny days, individuals aggregate on rocks in rivers with with rocky beds and high water flow to regulate their body temperature. The species is rarely found outside the watercourse; the use of the terrestrial environment is limited to the breeding season, when females lay eggs in nests built along riverbanks. 

Currently, the species is categorized as Vulnerable mainly due to the installation of hydroelectric plants. Unlike most species of turtles, the Williams’ side-necked turtle is part of a rare group of chelonian species specialized in inhabiting lotic environments. The high flow of water is fundamental for the maintenance of hydrodynamic processes in these ecosystems, driving the occurrence of species of plants and animals that are resources for the turtle.

Hydroelectric plants cause habitat loss by severely altering water flow, which is essential for maintaining the species’ environmental conditions. In addition to converting parts of rivers into lakes, dams isolate populations by preventing the gene flow that is essential for long-term survival. Additionally, by flooding the banks of rivers, hydroelectric plants destroy areas where the species builds its nests. Thus, hydroelectric plants cause direct impacts on the species on a small, medium and large scale.

Our study

We built ecological niche models to estimate the species’ distribution and then compared the predicted species’ distribution with current and planned hydropower plants in Brazil to

• verify if the locations of the hydropower plants coincide with areas of high suitability
• evaluate the difference in the magnitude of impacts on species caused by hydroelectric plants in relation to their licensing phase and type
• identify priority areas for the conservation of the species in places where new hydroelectric plants are planned based on an integrative analysis of ecological niche models and hydrological connectivity

Finally, we assessed the risk of extinction of the species at several levels (regional, national, and global).

What we found

The results demonstrate that hydroelectric plants overlap areas of high suitability for the species, regardless of the type or licensing stage. It should be noted that areas of high suitability represent only 20% of the species’ total distribution area. Differences in adverse impacts between hydropower plant types were determined by the area affected and the degree of interruption in river connectivity.

Our predictions suggest that habitat loss from the installation of hydroelectric projects could be greater than 30%. In the future, the area impacted by small hydroelectric plants will be almost equal to that of large hydroelectric plants, which currently have the highest impacts on the species. The assessment of the species’ conservation status partially corroborated previous assessments and suggested that the risk of extinction was underestimated at some levels.

The results suggest that the species is “Vulnerable” at several levels (ie, regional, national, and global) due to hydroelectric expansion plans in its range in Brazil. The situation is more serious in Argentina, Uruguay and Paraguay, where we reveal that it is “Endangered” due to its very restricted distribution.

What is new in this approach?

The approach we adopted is innovative and allows for a more comprehensive and reliable analysis of the impacts of power plants on the species. By combining environmental descriptors and occurrence records using ecological niche models, a more accurate and complete view of the effects of developments on the habitat and geographic distribution of the large-scale turtle can be obtained. This type of evaluation had not yet been performed for this species.

Another differential of our study was the inclusion of connectivity disruption estimates between populations. Unlike most works that focus solely on assessing the impacts at the site of the project (local scale), our work addresses the impacts across the entire geographic distribution of the target species and also assesses the cumulative or synergistic impacts of the dams on this species (large scale).

In this way, our results are an important step towards the development of more effective and informative conservation strategies, helping managers to understand the cumulative effect of hydroelectric dams on biodiversity at a large scale. With an improved understanding of the environmental impacts of dams on this species, we will be able to plan and implement more appropriate mitigation programs, preserving both the species and the ecosystem in which it inhabits. In addition, the methodology used can serve as a model for analyzing impacts on other species and in other ecosystems.

Can we prevent future impacts?

Our results revealed that it is possible to partially prevent the impacts of hydropower plants on the species. Our work explicitly categorized the 233 planned hydropower plants considering the negative impacts on the species considering the environmental suitability and the degree of isolation of populations.

Future impacts can be partially avoided if the expansion of the hydroelectric matrix focuses on the implementation of less impactful projects. We found differences between the impacts generated by different types of plants. Large hydropower plants cause the highest loss of habitat and also interrupt the connectivity in locations that are key points for the movement of individuals.

It should be noted that, in the future, the estimates of habitat loss caused by Small hydropower plants could almost equal those of the Large hydropower plants. Although the impacts of Small hydropower are of lesser magnitude, their impacts will be large due to the high number of planned projects.

Conclusion

The modeling methodological approach used in this study highlights potential conflicts between hydroelectric generation and conservation of the species. This analysis can be a complementary tool to guide decisions on the environmental sustainability of hydroelectric power plants, revealing the patterns of cumulative impacts of projects on river species and freshwater ecosystems, subsidizing the planning of sustainable energy supply.

Our study also highlights the importance of modern and advanced scientific approaches in the assessment of environmental impacts, reinforcing the continuous need for research and monitoring for the conservation of species threatened by hydroelectric projects. Through collaborative efforts between scientists, managers and other stakeholders, we can work towards a more sustainable future. 

Read the full article “Integrating ecological niche and hydrological connectivity models to assess the impacts of hydropower plants on an endemic and imperilled freshwater turtle” in Journal of Applied Ecology