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 the 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 in January stated. “The average decibel levels off the Maharashtra coast, in close proximity to shipping activities, is nearly 80 decibels (dB). The average noise level at sea owing to shipping traffic is 170 dB,” said the study. The study group under the Maritime Research Centre of the IMF assessed individual whale-stranding incidents at Mumbai, Alibaug, Ratnagiri and Raigad.
The study 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 120dB causes discomfort, anything above 170dB could lead to internal injuries, bleeding and haemorrhaging. Noise levels beyond 200dB 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 engaged in anti-piracy. When these ships move in a convoy, the noise in the entire region goes up significantly,” said Arnab Das, authored of the paper. “Large marine mammals were never known to frequent areas along the west coast. Over time, their migratory pattern has been disturbed by excess shipping,” he said.
The study identified that shipping noise overlaps with the vocalization signal characteristics (frequency at which large mammals communicate) of the Blue Whale and the Bryde’s whale, thus, affecting their navigation. As per the Maharashtra Maritime Board, almost 30,000 large ships and vessels travel along the Indian coastline every year. “Anthropogenic (manmade) noise is a documented threat to the survival of these species as it hinders their communication,” said Das.