Identifying Hotspots for Acoustic Habitat Degradation in the Indian Ocean Region (IOR)

Dolphins are among the species endangered by increased noise levels due to shipping in the IOR. PC: NOAA. Source: Unsplash.

India’s Exclusive Economic Zone (EEZ), 18th largest globally, extends over 23 lakh sq kms across the Arabian Sea, Bay of Bengal, and the Indian Ocean. Such a huge mass of water body also presents a mammoth challenge in ensuring sustainable growth for ourselves as well as the entire Indian Ocean Region (IOR). Maritime ecosystems cannot be bound by manmade boundaries; actions in one part will affect the entire region. Hence national regulatory actions are inadequate in addressing regional sustainability concerns.

Thanks to geopolitical churnings and economic growth, an increasing number of littoral nations and extra-regional powers are deploying more and more assets in the IOR. Maritime activities, both military and non-military, have reached unprecedented levels, and along with them, so have noise levels in the underwater domain.

Ocean noises originate from sources which are categorized into natural and manmade. Marine mammals get accustomed to the natural sources as they are a part of their habitat, however manmade sources deeply impact their population size.

Marine species, particularly mammals, use sound for multiple functions such as foraging, navigation, communication, finding mates for breeding, avoiding predators and more, many of which are biologically critical. They perceive their environment through sound, and high noise levels can disrupt their acoustic habitat, resulting in Acoustic Habitat Degradation (AHD).

There are primarily three sources of anthropogenic noise in the ocean: distant shipping, seismic surveys by oil and gas industry, and sonars on-board naval and non-military marine platforms.

Distant shipping is the single ubiquitous source of noise in the ocean. It creates a low frequency ambient noise that has been recorded to have doubled every decade since the pre-industrial period. However, records are available 1950 onwards.

G V Frisk in his much-acclaimed work named ‘Noiseonomics’ worked out the relationship between growth of gross tonnage in shipping, global GDP growth and low frequency ambient noise up to year 2015. The plot below shows his findings and the results do match with the 3 dB increase per decade reported by famous acoustician Donald Ross.

Long-term trends in ambient noise levels, gross tonnage of the world fleet, and world gross domestic product. Source: Frisk, George. (2012). Noiseonomics: The relationship between ambient noise levels in the sea and global economic trends. Scientific reports. 2. 437. 10.1038/srep00437.

It is alarming to see such a substantial increase in the low frequency ambient noise due to shipping despite scientific and technological advances in ship design and building. Low frequency noise caused by shipping has the unique characteristic of minimal attenuation in the ocean. It is able to spread far (in the order of 1000 kms) and thus can influence very large regions.

Dealing with this noise is not as straightforward as it seems. Shipping has always been a driver of economic engines and a direct contributor to global GDP growth. Given that IOR nations are still in various developing stages, the evolving eco-political system does not encourage proactive action towards regulations that in any way could restrict shipping activities.

Naval platforms have used Underwater Radiated Noise (URN) management extensively for acoustic stealth requirements. However, due to absence of regulatory requirements in the merchant marine and fear of slimming profit margins, URN management technology has not penetrated into commercial shipping. Human beings are essentially terrestrial animals who somehow feel insulated from the acoustic habitat degradation. However, this “ostrich effect” will not take us far; we must take urgently address the issue of acoustic habitat degradation caused by shipping.

The Automatic Identification System (AIS) can be used to capture shipping traffic data comprehensively. It provides details of both, the ship and its voyage, vital inputs for computing the URN of a ship spatially and temporally. At the Maritime Research Centre (MRC), Pune, we have developed algorithms to extract the AIS inputs for grids of 5×5 sq. kms. We then compute the radiated noise at source for each grid using the estimation techniques Ross and Wittekind proposed.

We then pass this noise through underwater channel propagation models, with real time inputs on local, site-specific surface sea and bottom parameters. Ultimately, we obtain a spatio-temporal map of low frequency ambient noise.

Spatial Noise Mapping for IOR (Noise in dB re 1 µPa 2). Source: Author.

The map gets updated every 6 minutes and is of a very high resolution. It also addressed the source (distant shipping noise) and path (underwater propagation) for the specific low frequency spectrum which impacts marine species. It is a real-time AHD assessment tool for monitoring the impact of low frequency noise on the specific marine species and can effectively identify hotspots for AHD in the IOR.

The International Union for Conservation of Nature (IUCN) is the global body authorized to declare endangered species. In the IOR, species with hearing range below 1 kHz, such as blue whales (>100 Hz), fin whales (10-200 Hz), sperm whales (0.9-30 Hz) and the Indo-Pacific bottlenose dolphin (0.2-150 kHz).

In the recent past, we have seen some of these species stranded on India’s west coast. It is possible that they are connected to the anti-piracy operations in the IOR since 2009. In the year 2016-2017, there were over 80 incidents of whale stranding on Maharashtra’s coastline alone.

Left: 42 ft Blue Whale stranded off Alibaug Coast in Jun 2015. Right: 50 ft Bryde Whale stranded off Mumbai Coast in Jan 2016.

PM Narendra Modi announced the Security and Growth for All in the Region (SAGAR) vision in May 2015. It is a first-of-its-kind apex-level announcement visualizing a leadership role for India in the IOR, and it also recognizes both, security threats and the massive growth potential, that exist in the region.

In the entire process of growth, sustainability is inseparable, and it has to be an integral component of the capacity and capability initiative. Realising SAGAR vision will also require effective implementation of the Underwater Domain Awareness (UDA) framework. Acoustics in the tropical waters of the IOR have traditionally not been easy and require special efforts. Tools such as the AIS will go a long way in meeting these two objectives.

Dr Arnab Das

Dr Arnab Das is a former Naval Officer and has obtained a PhD on Underwater Technology from IIT Delhi. He is Founder & Director of Maritime Research Centre (MRC), Pune and also runs a startup called M/S NirDhwani Technology Pvt Ltd (NDT). Both MRC and NDT focus on the Underwater Domain Awareness (UDA) Framework.

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The views and opinions expressed in the above article belong to the author(s) and do not necessarily represent the official opinion, policy or position of Lokmaanya.

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