Amazon river dolphinsInia geoffrensisare on the path to extinction in the heart of their range

A R Martin,V M F Da Silva

doi:10.1017/s0030605320001350

Abstract

AbstractRiverine cetaceans are threatened globally by increasing anthropogenic impacts, and the Yangtze river dolphinLipotes vexilliferis already extinct. The Amazon river dolphinInia geoffrensisis widely distributed, but is categorized 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 ofI. geoffrensisin 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 transect in the Reserve over 22 years demonstrated a sustained, profound decline. In this study we tested whether the measured rate of population decline is consistent with population parameters estimated from independent data, using population viability analysis. With the known parameters as input, programmeVortexpredicted population extinction 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.

Highlights

River-dwelling cetaceans are vulnerable to human pressures in many forms because they cannot escape them
The Yangtze river dolphin Lipotes vexillifer was the first cetacean to be rendered extinct by humans (Turvey et al, ), and the remaining two taxa of river dolphins in Asia, Platanista gangetica and Platanista minor, are categorized as Endangered on the IUCN Red List (Braulik et al, ; Smith et al, )
In South America, the boto or Amazon river dolphin Inia geoffrensis is categorized as Endangered

Summary

Introduction

River-dwelling cetaceans are vulnerable to human pressures in many forms because they cannot escape them. Almost everywhere they live, river dolphins are subject to frequent and persistent anthropogenic threats, including chemical pollution, fragmentation of waterways, reduced availability of food resources because of fishing and damming, hunting, and accidental entrapment in fishing nets (Reeves & Martin, ). In South America, the boto or Amazon river dolphin Inia geoffrensis is categorized as Endangered (da Silva et al, b). 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, ; Hrbek et al, ; Siciliano et al, )

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Conclusion