Noise pollution is killing whales off Maharashtra coast: Study

MUMBAI: Increased shipping, seismic blasting and lack of regulatory provisions for noise pollution at sea has caused several instances of whale beaching and deaths in the last three years, a study by the Indian Maritime Foundation (IMF) in Pune has found.

“Permanent degradation of acoustic habitat for large marine mammals along the Maharashtra coast is leading to navigation issues and recurring stranding,” a research paper published in the National Maritime Journal of India earlier this month stated. “The average decibel levels off the coast of Maharashtra, in close proximity to shipping activities, are nearly 80 decibels (db). The average noise level at sea due to shipping traffic is 170 db.”

The study group assessed individual whale-stranding incidents at Mumbai, Alibaug, Ratnagiri and Raigad.

A 2017 study by the IMF found that noise can harm whales depending on their proximity to the source, such as ships, seismic survey air guns and sonar. While noise levels over 120 db causes discomfort, anything above 170 db could lead to internal injuries, bleeding and haemorrhaging. Noise levels beyond 200 db can result in instant death.

“Since 2009, the west coast of India has seen a significant increase in maritime activities with a high density of ships due to multilateral coalitions engaged in anti-piracy. When these ships move in a convoy, the noise in the entire region goes up significantly,” said Arnab Das, who authored the paper. “At the same time, large marine mammals were never known to frequent areas along the west coast… Over time, their migratory pattern has been disturbed by excess shipping.”

The study identified the vocalisation signal characteristics (the frequency at which large mammals communicate) of the blue whale as being up to 160 Hz and that of the Bryde’s whale as between 50-150 Hz. “The low-frequency ambient noise (less than 300 Hz) is reported to have been rising at an alarming rate of 3 db per decade since the industrial era (1950s), primarily driven by shipping noise. The shipping noise spectral characteristics have been found to directly overlap with the vocalisation of large cetaceans, the baleen whales,” the study said.