Researchers listen in on fishy conversations

Scuba diving pioneer Jacques Cousteau famously described life beneath the ocean’s surface as “the silent world.” But it turns out life beneath the waves may not be so quiet after all. 

International researchers have discovered that different fish use grunts, chirps and pops to communicate. 

Now the Cayman Islands Department of Environment is listening in on fish sounds to help build data on the number and variety of species at various sites. 

Using specialized underwater devices called hydrophones, the Department of Environment, the Reef Environmental Education Foundation and the Darwin Initiative are identifying fish species that visit designated spawning sites. 

The hydrophones act like microphones that pick up sounds that fish make and convert them into audio signals and measurable data. The scientists use the data to determine which species, such as Nassau grouper, and the number of fish that frequent the sites. 

Department of Environment Marine Research Officer Bradley Johnson said the hydrophones provide stronger data than the methods used previously.  

“We have been tracking fish species via in-water monitoring and acoustic tagging for many years now,” he said. “However, this allowed us to only track fish that we tagged while they passed by the monitoring stations. With these hydrophones, we can now record underwater sounds at the spawning sites every five minutes. The data is more comprehensive and, ultimately, they provide greater understanding of which species use the sites, and their abundance.” 

Three hydrophones, which were funded by the Scripps Institution of Oceanography, are deployed in Little Cayman. A fourth, in Grand Cayman, was purchased through the Darwin Initiative grant, funded through the U.K. Department for Environment, Food and Rural Affairs.  

A fifth hydrophone will be installed in Cayman Brac within the next few months. All of the hydrophones will be deployed for six months at a time. 


Marine Research Officer Bradley Johnson, from the Department of Environment, checks out the new hydrophones.