River dolphins: Species that indicate the state of health of the aquatic ecosystems of the Amazon and Orinoco regions

Abstract

In the present study, we used the population sizes of river dolphins (Inia and Sotalia) as indicators of the state of health of 20 aquatic ecosystems associated with the basins of the Amazon and Orinoco Rivers. The information was collected during 30 scientific expeditions carried out during 2006 and 2017 in Colombia, Ecuador, Perú, Bolivia, Brazil, and Venezuela. The results show intense processes of ecosystem degradation in the Caquetá, Putumayo, Iténez, and Grande Rivers in the Amazon basin and the Tocantins-Araguaia and Guaviare Rivers, as well as in the upper basin of the Orinoco River. This condition may be increased in the coming decades due to the loss of connectivity between the Andes and the Amazon due to the presence of 142 already existing hydroelectric dams and other 160 which are in the planning stage on the rivers running from the Andean headwaters to the Amazon. The ecosystemic impacts of this type of infrastructure on the aquatic trophic networks of these systems have been poorly studied. Our results provide important elements for understanding the degradation processes caused by the fragmentation and the loss of fluvial connectivity in the Amazon and Orinoco regions using the population sizes of river dolphins as indicators. These cetaceans have extensive ecological requirements and are evolutionarily adapted to predictable seasonal changes. These ecological characteristics make river dolphins excellent indicators to understand the effects on flood pulses and their effects on the ecosystem functionality of the complex hydrographic systems of the Amazon and Orinoco basins.