18 Sep 2022  |   06:03am IST

Fish in troubled waters

Sound is critical for communication between all living creatures. While soft chatter indicates happy atmosphere, loud noise levels signify signs of disturbance. SHASHWAT GUPTA RAY reports on two different studies related to sounds observed underwater off Goa shores and their implications on marine life, especially the fish, which are critical for the people of Goa. While the first study deals with the issue of marine sound pollution caused by human activities, the other establishes a direct link between variations in sound emitted by fish and temperature change underwater
Fish in troubled waters

While harmful impact of noise pollution on land is well documented, however very little is known to the common people about the impact of marine noise pollution caused by human activities.

Now, a study has been done by researchers at BITS Pilani, Goa campus in which noise levels were recorded from under water off Goa coast. The study found high anthropogenic noise levels under water caused by human activities like movement of ships, tourism activities, and construction activities viz building of bridge amongst others. This is going to have long-term impact on the fish availability in Goa.

The research was carried out by Commodore (retd) K Laxmi Narasimha Chary in pursuit of his PhD degree, under the supervision of Dr (Prof) Mukund K Deshmukh and Dr (Prof) Nitin Sharma at the Department of Electrical and Electronics Engineering of BITS, Pilani K K Birla Goa Campus, is the first ever attempt to develop a comprehensive marine soundscape at the marine site near the coast of Goa. 

“The marine site is characterised in terms of measured values of the existing noise levels and corresponding frequencies, and also their variation over time of the day, time of month, time of the season, and time of the year. I have undertaken the study as part of my PhD thesis to develop underwater soundscape in shallow tropical coastal waters near Grande Island biodiversity site,” Commodore Chary told Herald.

There were many challenges encountered while taking the underwater measurements of sound levels as part of the study.

“Main was monsoon weather. No underwater measurements could be undertaken during May to October due to rough seas and the instruments getting damaged. This is the first underwater soundscape developed based on long term measurements in Indian waters,” the Indian Navy veteran officer said.

This will be useful to monitor the human made underwater noise pollution in marine environment that is increasing and threatening marine life. Noise radiated by ships, fishing and tourist boats can be monitored and noise control regulations can be implemented near Grande island to protect marine life.

“Goa coastline provides livelihood to fishermen communities, and it should be ensured that fish species are not threatened by underwater noise pollution. Marine ecosystem in estuaries also needs to be protected from underwater noise pollution. Noise maps are required to be generated for bio diverse zones to monitor underwater noise pollution,” he said.

A marine soundscape is essentially a comprehensive representation of existing sound (or noise) levels in an underwater environment.  Study of soundscapes is an emerging field of research that attempts to provide important baseline information on environmental conditions and also biological composition of the underwater environment. 

The measurements have been carried out at the site using three distinct innovative methods. The measurement site is located close to Grade Island Archipelago near the coast of Goa, about 16 km west of the Dabolim International Airport. 

“The measurements have been recorded over a long period, spanning many years.  It is found that the measured noise is mostly a low frequency noise ranging from near zero to 10 kHz, which confirms the presence of the diverse biophonic sources, including variety of fish, snapping shrimps, dolphins, near the site,” said Dr Deshmukh, who was the research guide for the study. 

It may be noted that the Grande Island Archipelago is globally recognized as the biodiverse site. Also, the existence of higher levels of noise in the range 10 Hz to 10 kHz is recorded at the site, which confirms that the noise levels due to anthropogenic sources such as shipping and boat traffic and off-shore constructions, etc, are regularly contributing to the soundscape at the site.

“The trends in the measured noise levels at the site clearly show that the noise levels due to anthropogenic sources are increasing over the period of measurement and these may interfere with the frequencies used by the aquatic species for their livelihood. It is well known that the consistent excessive noise levels may be fatal to the aquatic ecosystem as these hamper communication between the marine animals and, in the long run, may be a major threat to the existence of a bio diverse marine site near the Grande Island Archipelago,” the senior faculty said.

In may be noted that in contrast to environmental regulatory practices in the advanced countries such as the USA, Europe, New Zealand and Australia, the inclusion of underwater noise in Environment Impact Assessment in India, is of recent origin.  

“There is urgent need to measure underwater noise levels and establish baseline soundscapes for the site. To this end, there is scope for developing appropriate measurement schemes using the available technologies and appropriate formats of soundscapes for standardization. 

“Also, there is wide scope for developing Artificial Intelligence-based computer models for prediction of noise levels over short and long terms, using the data generated through extensive measurements. The present research emphasizes need to continue efforts in this direction,” he said.

Scientist-Emeritus at National Institute of Oceanography Bishwajit Chakraborty, an authority on marine soundscape, said behaviour of the fish gets affected due to noise created by human activities. 

“Due to the constant noise pollution, the communication system fails and their ears get affected. Their otolith bone sare getting adversely affected, degrading the hearing system of the fish. The impact is already seen on ground. For example, off Goa coast, you find that fish are coming up at night and going down in the daytime. This is affecting their breeding due to the noise as they are unable to hear each other mating calls,” Dr Chakraborty said.

This according to him, will result in the fish species moving out of their current location in search of more peaceful environment, which will result in unavailability of fish that are found now.

“Moreover, Fish are important members of aquatic ecosystems and indicators of water quality..A healthy aquatic ecosystem contains a good balance of producers (like algae and aquatic plants), consumers (like zooplankton and invertebrates), and predators (like fish)”Dr Chakraborty said.

Director of NIO Sunil Kumar Singh said there are different kinds of fish that are found underwater which produce different kinds of sounds to communicate with each other. 

“Their sound frequency is very low. The source level and frequency of the signals generated by human activities is very harmful for their biology. Their daily activity is affected since noise pollution acts as a barrier in their communication process. This will also affect the fish productivity,” Dr Singh said.

International Quite Ocean Experiment (IQOE) is an international program of research, observation, and modelling to characterize ocean sound field to promote understanding of sound on marine life initiated from 2016 through the funding from the Sloan Foundation to SCOR (Scientific Committee on Ocean Research).Dr Chakraborty represented India in the IQOE founding committee (2016-2018).


Idhar Udhar