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SC/69B/SM/06
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Resource ID
22167
Access
Open
Document Number
SC/69B/SM/06
Full Title
Range-wide decline in Amazonian river dolphin abundance: are we seeing a mirror of Asian river dolphins? fate?
Author
Mariana Paschoalini Frias, Fernando Trujillo, Maria Jimena Valderrama, Miriam Marmontel, Fabiola La Rosa-Camino, Oscar Quispe Hure, Cedric Gilleman
Authors Summary
Boto (Inia geoffrensis) and tucuxi (Sotalia fluviatilis) are endangered small freshwater cetaceans species that may being facing the same declining curve in population than its Asian counterparts. Trends in density and abundance for these species are pointed out as key information to guide conservation planning actions. However, this information is only available for a small area of its distribution. This paper presents the population trends of freshwater species in the Amazon and Orinoco river in a basin-wide approach, using standarized methodology and following protocols validaded under the IWC for other species (e.g., Distance Sampling). This information might help in the decision-making under the current CMP River Dolphins and guide efforts towards effective management actions targgeting the direct threats to each of the areas discussed (Amazonian Trapezium, Tapaj s River, Meta River).
Publisher
IWC
Publication Year
2024
Abstract
Freshwater cetaceans are a small and endangered group of dolphins distributed in 14 countries in Asia and northern South America river basins. All species are classified by the IUCN as endangered and most of them face deep population declines (mainly in Asia). In South America basin-wide data on population trend of Inia geoffrensis (boto) and Sotalia fluviatilis (tucuxi) is unlike to be assessed due to their wider range. However, small scale studies have indicated population declines for both species in the Mamirau Reserve and suggest declining to the upper Amazon River (the Amazon Trapezium). In this study we provide data on trends in abundance for two new sites: the Meta River in the Orinoco basin, and the Tapaj s River in the Southern Amazon basin, adding basin-wide approach to the population status for these two species. Additionally, we provide new systematic data collected in the Amazonian Trapezium confirming the indications of population declined evidenced in previous years. 52% and 30% decline was perceived to boto and tucuxi respectively in the Amazonian Trapezium over a period of 30 years. In the Tapaj s River, the population decline was estimated near 11% and 34% for boto and tucuxi, respectively over a period of eight years. In the opposite way, the population of boto in the Meta River, Orinoco basin, showed signs of population stability (possible increase 18%) over a period of 16 years. This paper is still preliminary, and no model was applied considering the generation-time either population availability analysis. This is a work in progress that may provide in the mid-term understanding on how severe the declines for the assessed areas and supports effective management actions targeting to reverse the curve.