Amazon river dolphins Inia geoffrensis are on the path to extinction in the heart of their range A. R. MARTIN and V. M. F. DA S IL VA
Abstract Riverine cetaceans are threatened globally by increasing anthropogenic impacts, and the Yangtze river dolphin Lipotes vexillifer is already extinct. The Amazon river dolphin Inia geoffrensis is widely distributed, but is ca- tegorized as Endangered on the IUCN Red List. Drowning in gillnets and being hunted for fish bait are probably the main causes of its decline. A long-term (25-year) study of the biology and ecology of I. geoffrensis in and near the Mamirauá Reserve in Amazonas state, Brazil, has produced estimates of survival and reproductive rates based on the individual recognition of .650 animals. Concurrently, monthly standardized counts of dolphins along a fixed tran- sect in the Reserve over 22 years demonstrated a sustained, profound decline. In this study we tested whether the mea- sured rate of population decline is consistent with popula- tion parameters estimated from independent data, using population viability analysis. With the known parameters as input, programme Vortex predicted population extinc- tion in all scenarios and a 95% loss of dolphins within 50 years. With default parameters, the model predicted a 5.5% annual decline, which is consistent with that observed. We conclude that the Amazon river dolphin population is in severe decline because of human pressures, even in one of the better protected parts of its range. Unless the accidental and deliberate killing of this species is rapidly reduced, it is highly likely that the Amazon river dolphin will follow its Yangtze counterpart to extinction.
Keywords Amazon river dolphin, Brazil, Endangered spe- cies, extinction, fishery interactions, Inia geoffrensis, popu- lation viability analysis
Introduction
escape them. Almost everywhere they live, river dolphins are subject to frequent and persistent anthropogenic threats, including chemical pollution, fragmentation of waterways,
R A. R. MARTIN (Corresponding author,
orcid.org/0000-0003-1158-6919)
Centre for Remote Environments, University of Dundee, Perth Road, Dundee DD1 4DY, UK. E-mail
boto@live.co.uk
V. M. F. DA SILVA (
orcid.org/0000-0002-1774-0393) Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil
Received 27 July 2020. Revision requested 14 October 2020. Accepted 7 December 2020. First published online 25 October 2021.
iver-dwelling cetaceans are particularly vulnerable to human pressures in many forms because they cannot
reduced availability of food resources because of fishing and damming, hunting, and accidental entrapment in fishing nets (Reeves & Martin, 2018). Consequently, the Yangtze river dolphin Lipotes vexillifer was the first cetacean to be rendered extinct by humans (Turvey et al., 2007), and the remaining two taxa of river dolphins in Asia, Platanista gangetica and Platanista minor, are now categorized as Endangered on the IUCN Red List (Braulik et al., 2012; Smith et al., 2012). In South America, the boto or Amazon river dolphin Inia geoffrensis is also categorized as Endangered (da Silva et al., 2018b). The species has a wide geographical distribution that extends from the Andes to the Atlantic, including hundreds of rivers with varying levels of connectivity in Brazil, Colombia, Ecuador, Bolivia and Venezuela. Some of the more isolated populations have evolved distinct characteris- tics that may justify recognition as separate species or sub- species. Although the detailed taxonomy of the Amazon river dolphin is not yet resolved, it is certain that there is not one homogenous meta-population (Gravena et al., 2014; Hrbek et al., 2014; Siciliano et al., 2016). A continuous 25-year study of botos in and near the Mamirauá Reserve, Amazonas state, Brazil (Fig. 1), has resulted in estimates of key reproductive parameters and annual survival rates (Mintzer et al., 2013; Martin & da Silva, 2018). Data from the Reserve show a prolonged and steep population decline (da Silva et al., 2018a), probably driven by harmful fishery practices. These practices are widespread, and pressures outside the Reserve could be worse, not only because regulations applicable within the Reserve may offer some protection, but because some threats (e.g. damming and gold mining) have no known impact in the Mamirauá region (da Silva et al., 2018a). Estimates of the key reproductive parameters (Martin &
da Silva, 2018) and survival rates (Mintzer et al., 2013)of botos from Mamirauá provide an opportunity to test whether these population characteristics are consistent with the decline in animal numbers observed during 1994–2017 (da Silva et al., 2018a).
Study area and species
We collected data in an area of seasonally flooded lowland forest, and in the rivers that drain this landscape, one of which is the mainstem of the Amazon River (Fig. 1). The focus of the work was the Mamirauá Sustainable Development Reserve, Amazonas state, Brazil.
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Oryx, 2022, 56(4), 587–591 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320001350
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