Oceanographer Divya Panicker deploying an acoustic recorder off the Kavaratti reef in Lakshadweep islands. Credit: Sayed Abdullakoya
The first study tracking underwater sounds around Lakshadweep islands in the Arabian Sea has provided sonic snapshots of reef activity that might help reveal climate change impacts on marine life1.
From the mid-ocean scientists captured loud dusk choruses of fish, a midnight chorus of lanternfish, and a night chorus of snapping shrimp, says lead researcher, Divya Panicker, at the School of Oceanography, University of Washington, in the United States.
“As we track oceanic soundscapes over multiple years, we can begin to understand the sonic signature of a changing climate and its impact on marine species,” Panicker says.
Marine animals use sound to mate, communicate, and navigate. Underwater soundscapes — a mix of biological sounds (biophony), natural Earth sounds (geophony), and sounds of human activities (anthropophony) — are a new way of understanding how animals perceive their environment.
Oceans have become substantially noisier2 over time, as shipping, resource exploration, and infrastructure development increase anthropophony. Meanwhile, biophony levels have reduced, due to hunting, fishing, and habitat degradation. Climate change is altering both geophony and biophony.
The Lakshadweep islands are vulnerable to changing rainfall patterns, increasing cyclonic activity and coral bleaching. Soundscapes are helping scientists track and predict impacts of climate change by measuring these changing patterns over time. The results of such studies could inform development projects to minimize underwater noise pollution, a growing threat to marine species.
Soundscapes generate information during rough -weather such as the southwest monsoon season, when diving is a challenge, but Indian waters have hardly been studied. To fill this gap, the researchers lowered two acoustics recorders (hydrophones) off the outer reef of Kavaratti atoll in Lakshadweep at depths of 11 metres and 18 metres. Acoustic data were collected from January to October 2019 between 20 Hz to 48 kHz.
Although anthropogenic sounds from vessels were recorded, they did not influence the overall soundscape, the researchers say. However, island tourism, mechanized fisheries and increased connectivity will trigger more vessel traffic and reef fishing, they observe.
Sound sources correlate with ocean parameters differently during monsoon and non-monsoon months. For instance, the researchers found that the chorus of snapping shrimp increased when wind speeds were low.
Warming oceans make sound travel faster in water, accounting for higher levels of noise pollution in oceans, says marine scientist Bishwajit Chakraborty at the International Quiet Ocean Experiment that studies ocean soundscapes and their effects on marine organisms. This speeding up of sound in water deviates from historic sonic conditions and may disorient marine life in the rapidly warming Arabian Sea.
Chakraborty used hydrophones to tune into the Grande Island coral reefs off the coast of Goa3. Using artificial intelligence to assess the reef’s acoustic diversity, he and his team marked loud grunts of tiger perch (Terapon theraps) at dusk, snapping shrimp, choruses of plankton-eating fish species, drumming sounds of fish of the Sciaenidae family and a mysterious “buzz”.
Chakraborty’s team call for the installation of more hydrophones along India’s coast to help maintain archival data on fish sounds and analyze underwater acoustic metrics.
