Do fish bay at the moon? Can their odd songs identify Hawaiian mystery fish?

Using hydrophones to eavesdrop on a reef off the coast of Goa, India, researchers have helped advance a new low-cost way to monitor changes in the world's murky marine environments.

Reporting their results in the Journal of the Acoustical Society of America (JASA), the scientists recorded the duration and timing of mating and feeding sounds—songs, croaks, trumpets and drums—of 21 of the world's noise-making ocean species.

With artificial intelligence and other pioneering techniques to discern the calls of marine life, they recorded and identified:

• a medium sized "grunter," loudest at dusk, Terapon theraps (audio https://bit.ly/41LQmn);
• fish of the Sciaenidae family (audio: https://bit.ly/3KWtawy);
• choruses of plankton-eating fish species (audio: https://bit.ly/3oAsGo5); and
• snapping shrimp (audio: https://bit.ly/3mTQ0gd), including commercially-valuable tiger prawns.

Some species within the underwater community work the early shift and ruckus from 3 am to 1:45 pm, others work the late shift and ruckus from 2 pm to 2:45 am, while the plankton predators were "strongly influenced by the moon."

The degree of difference in the abundance of marine life before and after a monsoon was also recorded by the scientists.

The paper concludes that hydrophones are a powerful tool and "overall classification performance (89%) is helpful in the real-time monitoring of the fish stocks in the ecosystem."

The team, including Bishwajit Chakraborty, a leader of the International Quiet Ocean Experiment (IQOE), benefitted from archived recordings of marine species against which they could match what they heard, including:

• a cacophony of spawning tiger perch: (audio: https://bit.ly/3LkZYkj), and
• snapping shrimp (audio: https://bit.ly/41NZWH2), whose sounds baby oysters reportedly like to follow

Also captured was a "buzz" call of unknown origin (https://bit.ly/3GZdRSI), one of the oceans' countless marine life mysteries.

With a contribution to the International Quiet Ocean Experiment, the research will be discussed at an IQOE meeting in Woods Hole, MA, USA, 26–27 April.

Advancing the Global Library of Underwater Biological Sounds (GLUBS)

That event will be followed April 28–29 by a meeting of partners in the new Global Library of Underwater Biological Sounds (GLUBS), a major legacy of the decade-long IQOE, ending in 2025.

GLUBS, conceived in late 2021 and currently under development, is designed as an open-access online platform to help collate global information and to broaden and standardize scientific and community knowledge of underwater soundscapes and their contributing sources.

It will help build short snippets and snapshots (minutes, hours, days-long recordings) of biological, anthropogenic, and geophysical marine sounds into full-scale, tell-tale underwater baseline soundscapes.

Especially notable among many applications of insights from GLUBS information: the ability to detect in hard-to-see underwater environments and habitats how the distribution and behavior of marine life responds to increasing pressure from climate change, fishing, resource development, plastic, anthropogenic noise and other pollutants.

"Passive acoustic monitoring (PAM) is an effective technique for sampling aquatic systems that is particularly useful in deep, dark, turbid, and rapidly changing or remote locations," says Miles Parsons of the Australian Institute of Marine Science and a leader of GLUBS.

He and colleagues outline two primary targets:

• Produce and maintain a list of all aquatic species confirmed or anticipated to produce sound underwater;
• Promote the reporting of sounds from unknown sources

Odd songs of Hawaii's mystery fish

In this latter pursuit, GLUBS will also help reveal species unknown to science as yet and contribute to their eventual identification.

For example, newly added to the growing global collection of marine sounds are recent recordings from Hawaii, featuring the baffling:

• Mystery fish 1 (audio: https://bit.ly/3LjHDUJ),
• Mystery fish 2 (audio: https://bit.ly/3UW24u0), and
• Mystery fish 3 (audio: https://bit.ly/3KWtVpo)

These recordings are now part of an entire YouTube channel (https://bit.ly/3H5Ly54) dedicated to marine life sounds in Hawaii and elsewhere (e.g., this "complete and total mystery from the Florida Keys" (https://bit.ly/41w1Xbc) (Credit: Annie Innes-Gold, Hawai'i Institute of Marine Biology; processed by Jill Munger, Conservation Metrics, Inc.)

Says Dr. Parsons, "Unidentified sounds can provide valuable information on the richness of the soundscape, the acoustic communities that contribute to it and behavioral interactions among acoustic groups. However, unknown, cryptic and rare sounds are rarely target signals for research and monitoring projects and are, therefore, largely unreported."

The many uses of underwater sound

Of the roughly 250,000 known marine species, scientists think all fully aquatic marine mammals (~146, including sub-species) emit sounds, along with at least 100 invertebrates, 1,000 of the world's ~35,000 known fish species, and likely many thousands more.

GLUBS aims to help delineate essential fish habitat and estimate biomass of a spawning aggregation of a commercially or recreationally important soniferous species.

In one scenario of its many uses, a one-year, calibrated recording can provide a proxy for the timing, location and, under certain circumstances, numbers of "calling" fishes, and how these change throughout a spawning season.

It will also help evaluate the degradation and recovery of a coral reef.

GLUBS researchers envision, for example, collecting recordings from a coral reef that experienced a cyclone or other extreme weather event, followed by widespread bleaching. Throughout its restoration, GLUBS audio data would be matched with and augment a visual census of the fish assemblage at multiple timepoints.

Oil and gas, wind power and other offshore industries will also benefit from GLUBS' timely information on the possible harms or benefits of their activities.