INTRODUCTION:

As a consequence of population isolation by the presence of geomorphological barriers, dolphins from northern South America are subdivided into three species: I. geoffrensis (Amazon and Orinoco Rivers), I. boliviensis (Madeira River in Bolivia), and the recently described I. araguaiaensis inhabiting the hydrologic complex of the Araguaia -Tocantins Rivers in the northeastern Brazilian Amazon. The importance of pink dolphins at the ecosystems they inhabit is supported by: 1) its position as top predators in the food chain; 2) bioindicators for ecosystem health; 3) its cultural and mythological meaning for the local ethnic groups, such as Sikuanis from the Orinoco, and Ticuna for the Amazon; and 4) their economic value, mainly as a touristic attraction. The conservation status of Orinoquian populations of river dolphins (i. g. humboldtiana), has not been fully established. However, we know their populations are threatened by a series of human activities on both aquatic and terrestrial environments, affecting their occurrence across the basin. This research is part of an inter-institutional effort conducted between the Corporación para el Desarrollo Sostenible del Área de Manejo Especial de la Macarena (CORMACARENA) and Fundación Omacha, to monitor pink dolphin populations inhabiting the rivers: Meta, Manacacías, Yucao, and Cusiana, in order to identify conservation tensors affecting the species in the study area.

METHODS:

We conducted a multitemporal study to determine anthropogenic threats affecting dolphin populations during two hydrologic periods along 317.2 km-1 across the middle Meta River basin. We calculated the degradation index for streams of continental waters and density of the river dolphins, developed by Gómez-Salazar et al. (2012). Water quality, habitat transformation, species exploitation, and the increment in number of human settlements were identified as the main conservation tensors in the analyzed area.

RESULTS:

We obtained a high value in the index of degradation, with a potential increment in value through time. River confluences were identified as priority areas for the conservation of the species. The development of infrastructure projects on the main streams was identified as a future threat on freshwater ecosystems in the basin. Differences in hydrologic periods were identified as an important variable, not only affecting the ecological dynamic of the species, but also determining the anthropogenic tensors through time. Water quality, habitat modification, and species exploitation were particularly intense at low water level periods, while boat traffic, and fishing activities are more frequent at periods of high water levels in the region.

DISCUSSION AND CONCLUSIONS:

For the Meta River, water quality and species exploitation appear to be the major tensors for dolphins and they may explain the low densities recorded for the area in comparison with densities reported for the Amazon basin. Even though, we consider this analysis is not definite and more samplings are necessary to confirm this hypothesis. Finally, river confluences were identified as conservation hot spots for dolphin populations. We point out on the importance of river dolphins as umbrella species, ideal to develop conservation strategies in the region.