The post-mortem, conducted by the Rajiv Gandhi College of Veterinary and Animal Sciences (RAGACOVAS) on the 15 long-nosed dolphins that were washed ashore on April 11 near Veerampattinam, has revealed that the cause of their death was “pneumonia,” which was the result of “massive congestion” of the lungs owing to inhalation of sea water.

The incident in April was the third time in 10 months that dolphins were found dead on the shores, which had led to apprehension among the local fishing community, and environment activists in the region, who demanded a complete probe into the matter.

According to Deputy Conservator of Forests A. Anil Kumar, the report confirms the preliminary assessment of the department that the death could have been the result of the phenomenon of “mass stranding,” where an entire group of dolphins drift to shallow parts of the ocean and fail to get back to their original route.

The dolphins were especially vulnerable near the Puducherry harbour, where there are sudden and marked changes in the depth of the water as sand had accumulated on one side of it owing to suspension of the dredging process.

“When the waters become shallow suddenly, the mammals get confused. They are unable to get back to their original route and the shallow waters make it difficult for them to breathe,” he said.

Mr. Kumar said that the autopsy report also pointed to damages to the muscular system as the dolphins were deprived of oxygen for an extended period of time before death.