Use echolocation to track endangered dolphins in the Amazon

Spanish scientists use echolocation signals to track the movements and interactions between the two endangered freshwater dolphin species in the Amazon basin, the pink puffer fish and the Turku dolphin, and their interactions with humans, which could be used to develop conservation strategies for these species. The study was recently published in Scientific Reports.

Both the pink puffer fish and the Turku dolphin are threatened by human activities, including conflicts with fishermen and pressure from agriculture, mining and dam construction. During the wet season from April to August, these dolphins enter floodplain forests that connect different river channels in order to feed on freshwater fish. However, floodplains and vegetation make these dolphins difficult to investigate with boats or drones.

Florence Erbs, Michel Andre and colleagues from the Bioacoustics Applications Laboratory of the Polytechnic University of Catalonia, Spain, surveyed the 800-square-kilometer Mamilawa Sustainable Development Reserve in Brazil, where the Solimonis and Yapura rivers meet, using five hydrophones that dive to depths of 3 to 5 meters.

The researchers collected data on river channels and confluence bays, floodplain lakes, and flood forests at different times during the wet and dry seasons between June 2019 and September 2020. Using deep learning algorithms and survey of acoustic data collected by hand from surveying vessels, they automatically classified the detected sounds as echolocation signals of dolphins, boat engine noises or rain sounds, with 95%, 92% and 98% accuracy, respectively.

The study found that as the water level rose between November and January, the daytime presence of dolphins in Confluence Bay and rivers increased from 10% to 70%. They believe that the dolphins used these channels to enter the floodplains. Pubertal pink puffer fish and female pink puffer fish with young dolphins spend longer than males in the floodplains, either because of the abundance of prey or because it serves as a shelter from aggressive behavior by male dolphins. The researchers hope to use this method to further understand the habitat preferences and requirements of Amazon river dolphins.

In the Milawa Sustainable Development Reserve, a pink puffer fish demonstrates the act of vacating. Image courtesy of Marina Gaona

In the Milawa Sustainable Development Reserve, two pink puffer fish explore the floodplain. Photo by Wezddy Del Toro

(Source: China Science News, Jinnan)

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