They “listen” to the Amazon dolphins to save them from extinction

delfin rosa

Echolocation tracking, which is the sound that animals such as cetaceans make to orient themselves, can be used to track the movements of freshwater dolphins that live in inaccessible areas of the Amazon basin. This is what a team from the Bioacoustic Applications Laboratory of the Polytechnic University of Catalonia has done. The results have been published in the journal Scientific Reports

Researchers listen to Amazon dolphins to save them from
A pink dolphin in the Mamirauá sustainable development reserve, in the Amazon. / Marina Gaona, IDSM.

He boot (Inia geoffrensis) or pink river dolphin and the tucuxi (Sotalia fluviatilis) are two species of freshwater dolphins in danger of extinction that live in inaccessible places in the world. Amazon. These species are threatened by human activity derived from the fishing, the agriculture, the mining and the construction of dams.

During the wettest period of the year, between the months of April and August, both species of dolphins move to the rivers in the areas of rainforests of the Amazon (várzeas) in search of freshwater fish. However, the floodplain and vegetation make it extremely difficult to observe dolphins with boats or drones.

The researchers have used data obtained through five hydrophones submerged at depths of between three and five meters in the Solimões and Japurá rivers.

The researcher Florence Erbs and other scientists Bioacoustics Applications Laboratory from the Polytechnic University of Catalonia (UPC) have studied some 800 square kilometers of the booking sustainable development of Mamirauá, in Brazil. For this they have used the data obtained through five hydrophones submerged at depths of between three and five meters in the Solimões and Japurá rivers.

The results of the study, which were published this week in the journal Scientific Reports, reveal new knowledge about the river dolphin movements, which could contribute to improving the conservation of these species. The work has been developed together with scientists from the Instituto de Desarrollo Sustentável Mamirauá (IDSM) and the National Marine Mammal Foundation, in San Diego, in the USA.

 
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A specimen in the Mamirauá sustainable development reserve (Amazon)./ Marina Gaona, IDSM

The article analyzes bioacoustic data from the river channels, bays, lakes and flooded forests of this reserve. These were recorded in different periods, during the wet and dry seasons, between June 2019 and September 2020.

The experts used deep learning algorithms—known as Convolutional Neural Network either convolutional neural network— and manually collected bioacoustic data to automatically classify dolphin echolocation sounds, boat noises and also rain noises, with accuracy levels of 95 %, 92 % and 98 %, respectively.

They thus detected that the presence of dolphins increased from 10 % to 70 % in the bay and the river, as water levels were rising, between November and January.

Another behavior that the researchers highlight is that the dolphins were using these waterways to enter the floodplain of this Amazon basin. The young botos and females with calves of these dolphin species spent more time in the floodplains than the males, either due to rich abundance of prey or as a safeguard against aggressive behavior of males.

The authors of the study encourage other scientists to use the methodology they have used to understand better and protect preferences and habitat needs of the Amazon river dolphins. In particular, they recommend these techniques to be used within the framework of the project. Providence, which carries out exhaustive bioacoustic monitoring of aquatic and terrestrial biodiversity in one of the most threatened tropical forests on the planet.

Reference: André, M. et al. “Towards automated long-term acoustic monitoring of endangered river dolphins: a case study in the Brazilian Amazon floodplains.” Scientific Reports (2023)