Risks of dam construction for South American river dolphins: a case study of the Tapajós River

Hj Pavanato,M Marmontel,F Trujillo,M Paschoalini,G Melo-Santos,M Portocarrero-Aya,R Meneses,Ds Lima,F Mosquera,C Maretti

doi:10.3354/esr00751

Abstract

River dolphins are strongly affected by the construction of hydroelectric dams. Poten- tial isolation in subpopulations above and below such dams and the resulting low genetic variability of these subpopulations can cause extinction at a local level. Here we aimed to estimate density and population size of South American river dolphins (boto Inia geoffrensis and tucuxi Sotalia fluviatilis), map their distribution, and estimate potential biological removal (PBR) limits in order to evaluate the effects of population fragmentation between planned dams in the Tapajos River, Amazonian basin, Brazil. Boat-based surveys were conducted following a line transect sampling protocol covering dif- ferent dolphin habitats in 2 stretches of the river divided by rapids. The mark−recapture distance sampling method was applied to account for animals missed on the trackline. After the estimation of population sizes by habitat, PBR was calculated. The farthest upriver sighting of tucuxis was close to the Sao Luiz do Tapajos rapids, whereas the farthest upriver sighting of botos was upstream of the rapids, suggesting that botos move upstream through the rapids. Estimated abundance of tucuxis (3372 ind., CV = 0.38) was twice as high as that estimated for botos (1815 ind., CV = 0.4). The PBR ranged from 11 to 18 ind. for boto and 21 to 34 for tucuxi. Throughout this study, we identified low abundances of river dolphins compared to other Amazon rivers. Boto may not be sustainable at a population level, due primarily to population fragmentation which would result from the construc- tion of the proposed dams. Precautionary measures are urgently needed before construction of dams begins in the Tapajos River.

Highlights

The building of dams and barrages to enable the generation of hydroelectric energy and the creationPublisher: Inter-Research · www.int-res.comEndang Species Res 31: 47–60, 2016 of land, and increase the impact of sewage and industrial effluents (Dudgeon 1992, Kondolf 1997, Rosenberg et al 1997, McCully 2001, Sabir et al 2013, Kondolf et al 2014)
Based on the Akaike’s information criterion (AIC), the less parameterized model was chosen for inference
Throughout this study, we confirmed that the distribution range of boto extends to the upper reaches of the Tapajós River, above the São Luiz do Tapajós rapids

Summary

Introduction

The building of dams and barrages to enable the generation of hydroelectric energy and the creationPublisher: Inter-Research · www.int-res.comEndang Species Res 31: 47–60, 2016 of land, and increase the impact of sewage and industrial effluents (Dudgeon 1992, Kondolf 1997, Rosenberg et al 1997, McCully 2001, Sabir et al 2013, Kondolf et al 2014). Possible impacts on river dolphin populations are reduced prey fish diversity and abundance (Luz-Agostinho et al 2008), and possible displacement to unusual areas while searching for prey. River dolphins may be affected at a population level by the formation of subpopulations and/or reduction in their distribution range (Reeves & Leatherwood 1994, Smith & Reeves 2012, Braulik et al 2015). Dams and barrages divide rivers, disrupting dolphin movements upstream and downstream, isolating individuals above and below dams and reservoirs. This process leads to the isolation of subpopulations with low genetic variability (da Silva & Martin 2010, Gravena et al 2014), which can cause local extinction

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