UNDERWATER NOISE EMISSIONS

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Context:  The rising man-made (anthropogenic) underwater noise emissions (UNE) from ships in the Indian waters are posing a threat to the life of marine mammals like Bottlenose dolphin, Manatees, Pilot whale, Seal and Sperm whale.

Details:

Form of energy:

• The main form of energy for multiple behavioural activities of marine mammals, which include mating, communal interaction, feeding, cluster cohesion and foraging, is based on sound.
• However, the sound that radiates from ships, on a long-term basis, affects them and results in internal injuries, loss of hearing ability, change in behavioural responses, masking, and stress.
• There are Acute and Chronic noise categories in the emissions.

UNE:

• The UNE or underwater sound pressure levels in the Indian waters are 102-115 decibels, relative to one microPascal (dB re 1Pa).
• The East Coast level (10 dB re 1Pa) is slightly higher than that of the West.
• There is an increase by a significant value of about 20 dB re 1Pa.
• Continuous shipping movement is identified to be a major contributor to the increase in the global ocean noise level, according to a new study titled “Measuring Underwater Noise Levels Radiated by Ships in Indian Waters” at the Visakhapatnam Port (for the East) and Goa’s Mormugao port (for the West).

Masking:

• The frequencies of ships’ underwater self-noise and machinery vibration levels are overlapping the marine species’ communication frequencies in the low frequency range of less than 500 Hz.
• This is called masking, which could have led to a change in the migration route of the marine species to the shallow regions and also making it difficult for them to go back to the deeper water.

https://epaper.thehindu.com/ccidist-ws/th/th_delhi/issues/25634/OPS/GEDAT59AD.1+G7MAT60FB.1.html