Endangered Ganges River dolphins are still surviving and breeding in parts of the heavily polluted Buriganga River near Dhaka despite intense vessel traffic and extensive human activity, a study has found.
Researchers from Jahangirnagar university zoology department recorded 57 dolphin sightings, indicating the presence of at least 20 dolphins, during a year-long survey from September 2023 to August 2024 along a 27-km stretch of the river.
Excerpts from the study titled ‘Population status, spatiotemporal distribution, and habitat drivers of endangered Ganges River dolphins in the Buriganga River, Bangladesh’ were published in the ‘Journal of Asia-Pacific Biodiversity’ in May.
According to the study led by the university’s zoology professor Abdul Aziz, dolphins were found mainly in deeper sections of the river with comparatively less boat traffic and human activity.
Concentrations of the river mammal were recorded in three areas, namely the Kholamura-Basila stretch, the Buriganga Riverview-Nabinagar Housing area and the stretch from Pagla to the Buriganga-Dhaleshwari junction.
Kholamura-Basila recorded the highest number of sightings, while sightings were lowest between Pagla and Kholamura.
Ganges River dolphins are functionally blind, with eyes that can detect only light.
They rely on echolocation to navigate, locate prey and communicate, making them particularly vulnerable to underwater noise.
Therefore, three river segments around the busy Sadarghat area recorded no dolphins.
Professor Abdul Aziz said, ‘At least 665 heavy transporters run through Sadarghat every month. The absence was due to heavy vessel traffic and their noise.’
The study found that dolphin occurrence also varied by season.
December recorded the highest number of sightings, while none were recorded in October 2023 or from July to August 2024. Winter had the highest seasonal count and the monsoon the lowest.
At least 20 dolphins survive
57 dolphin sightings recorded during year-long survey
Suckermouth catfish key prey
The findings also indicate that the population is reproducing despite severe pollution. Adults accounted for 84.21 per cent of the recorded population estimate, while calves accounted for 15.79 per cent.
‘Calves were observed from November to January and again from April to June, indicating that reproduction and recruitment continue despite the river’s multiple habitat pressure,’ Aziz said.
The researchers also observed a shift in the dolphins’ social behaviour.
Unlike earlier observations in which they were generally seen alone, about 80.70 per cent of sightings during the study involved groups, with an average group size of about five dolphins.
‘The grouping among dolphins could be linked to greater pressure from human activities,’ Aziz said, adding that the interpretation required further study.
The study identified 57 effluent discharge points along the river as a vital driver for deteriorating water quality. Researchers said chronically low oxygen levels could reduce fish populations and indirectly limit the dolphins’ prey.
Fishing activity was also found to be almost absent in several heavily polluted sections, including areas receiving tannery effluent.
‘The dolphins may have been feeding on invasive suckermouth catfish as they are the only possible prey in some sighting areas,’ Aziz said.
The researchers recommended establishing conservation zones in key dolphin habitats, particularly the Kholamura-Basila and Pagla-Buriganga-Dhaleshwari stretches.
They also called for stricter control of waste discharges, regular water-quality monitoring and enforcement of vessel speed limits below 5 kilometres per hour in core dolphin habitats to reduce disturbance.
Earlier, a separate survey by the Wildlife Conservation Society and the Forest Department, funded by the World Bank, covered 4,893km across 45 rivers between 2024 and 2025 and recorded 2,307 Ganges River dolphins across the country’s river systems.