Study reveals marked decline in noise levels in Indian Ocean Region during lockdown

By, Mumbai
May 21, 2020 06:57 PM IST

A slump in shipping traffic during the lockdown has resulted in a marked decline in noise levels across the Indian Ocean Region (IOR) – which includes Arabian Sea, Bay of Bengal and the Indian Ocean – a study by Pune’s Maritime Research Centre (MRC) has revealed.

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The average noise levels in IOR fell from 103.6 decibels (dB) during March to 73.4 dB in May, revealed the study conducted by MRC along with the Foundation for Underwater Domain Awareness, a non-governmental organisation working on marine ecosystem concerns due to acoustic habitat degradation.

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For a comparison, 103 dB is as loud as a jet flying at 1,000 feet, while 73.4 dB is the sound of a vacuum cleaner. However, measurements in air and water use separate references for dB calculations (1 micro pascal in water and 20 micro pascal in air).

Comparative heat maps of shipping traffic during March and May indicated a sharp decline in ocean noise, especially across the east coast and southwestern coastline.

“A surge in the shipping traffic witnessed over the past three decades has suddenly plummeted to a level where background ocean noise can be measured. It calls for a major policy rethink on how we can redistribute the traffic to control noise. Using this data, solutions can be put in place to navigate development through a sustainable growth model,” said Arnab Das, author of the study, former commander in the Indian Navy and director, MRC.

The reduction in the noise will benefit the marine ecosystem, leading to habitat improvement, the study concluded.

“The low frequency ambient noise due to shipping has been documented to have doubled (3 dB) every decade since 1950 forcing the marine ecosystem to bear the brunt of unsustainable development,” said Das.

Noise levels more than 120 dB cause discomfort to marine mammals, above 170 dB causes injury (internal injuries, bleeding and haemorrhages) and beyond 200 dB can lead to instant death.

“Low frequency ambient noise overlaps with the hearing of marine mammals, particularly big whales. They use sound [sonar] for multiple biologically critical functions like navigation, communication, foraging, finding mates, for breeding and avoiding predators. Increasing ocean noise masks these characteristic abilities. While the lockdown may have its negative impacts, noise reduction comes as a silver lining for relaxed marine environment even if it is for a brief period,” said Das.

However, peak noise levels of 94.5 dB had been recorded along the Gujarat and Maharashtra coasts even during the lockdown. The peak was more than 120 dB prior to the lockdown for the entire IOR. A percentage comparison cannot be done in case of dB levels, as it is a logarithmic conversion of the linear scale, and will give a false sense of high or low.

“Higher noise towards the Gujarat and Maharashtra areas may be due to cargo movement, which is marginally higher in this region than the rest of the IOR. Oil exploration is also going on as an essential activity,” said Amitabh Kumar, director general (shipping).

According to Kumar, the findings of the study were accurate as international trade plummeted considerably during the lockdown months.

“We must realise that this traffic constitutes shipping activities in high seas. These are not the ships coming to India, but are the ones using the important IOR route with cargo emanating from the Gulf to be supplied to Asian, Southeast Asia and Eurasian countries. With the reduction in the international trade due to lockdown across countries in these regions, ocean noise is bound to fall. At the same time, many of the ships are being used as storage points for petroleum cargo that use this route, and are currently stationary closer to ports,” said Kumar.

However, he also added that the lockdown period was not the apt time to ascertain the safe limits for ocean noise.

“The reduction required in activities should be adjudged after the lockdown when international trade is fully functional again. The current drop in noise level is consequential to the slowdown in traffic, which will be nowhere near the levels when operations resume,” Kumar said.

MRC’s study used an assessment tool to evaluate real-time low frequency ambient noise variation in the IOR during both time periods using an automated identification system (AIS) which provides the geo-location of ships and catches individual frequency levels through calibrated noise monitors to record the average and peak noises.

According to the Indian National Shipowners’ Association, between 2017 and 2019, the estimated capacity of shipping traffic increased from 27,500 metric tonnes (mt) to 35,383 mt, which included navy ships, security vessels, export-import goods, dry cargo, petroleum products, gas load and crude oil.

In December 2019, global regulatory body International Maritime Organisation (IMO) had decided to implement noise abatement measures for safe standards at sea, but the decision was opposed by major Southeast Asian countries such as China.

An independent expert, who was not part of the study, said that such noise measurement studies were futile if IMO does not declare safe standards.

“Only when there is regulation and penalty, can there be restriction in shipping operations to conserve the marine ecosystem. To avoid a surge in marine mammal deaths, shipping operations and international trade needs to be opened up gradually and country specific caps should be in place for movement of vessels within their region,” said E Vivekanandan, marine biologist and emeritus scientist at Central Marine Fisheries Research Institute.


    Badri Chatterjee is an environment correspondent at Hindustan Times, Mumbai. He writes about environment issues - air, water and noise pollution, climate change - weather, wildlife - forests, marine and mangrove conservation

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