Muñoz-Duque, S., Fonseca, P. J., Quintella, B., João Gama Monteiro, Fernandez, M., Silva, R., Vieira, M., & Amorim, C. P. (2024). Acoustic fish community in the Madeira Archipelago (North Atlantic Ocean): Characterization of sound diversity and daily patterns. Marine Environmental Research, 199, 106600–106600. https://doi.org/10.1016/j.marenvres.2024.106600
The ocean is a noisy place, and not just because of boat motors and whale songs. Although fishes may seem to be relatively quiet animals, over 980 species have been reported as vocal, and it is thought that about a third of all fish species make deliberate vocalizations. Fishes make sounds for a variety of purposes, such as seeking a mate, spawning, or defending territory.
Much like bird songs, the sounds made by different fish species are distinguishable from each other. These sounds differ by tones and pulses which help fish within the same species recognize and communicate with each other. Researchers use passive acoustic monitoring (PAM) sensors that record underwater sounds to identify fishes by their vocalizations.
In the Madeira Archipelago, a small chain of islands off the coast of Morocco, scientists investigated the vocalizations of fishes. They focused on two marine protected areas (MPAs) surrounding the islands, the Garajau and the Desertas. MPAs are swaths of the ocean that are managed and protected from destructive human activities to restore marine resources and ecosystems. These two MPAs in particular help to protect important species, like the endangered dusky grouper.
Soundscapes Unveiled
In June of 2021, PAM sensors were deployed at each MPA site, with the goals of identifying vocal fishes in the region, creating an inventory of fish sounds, and analyzing the abundance and diversity of fish vocalizations. The sensors were collected after three and a half months of recording. In addition to these recordings, scientific divers made regular visits to document the most prominent fish species observed around the sensors.
Using a random selection of 30-minute recordings from the PAM sensor, scientists detected the presence of 35 vocal species of fish and 102 potentially vocal species, which are species closely related to known vocal species. There are just over 188 documented fish species in the Madeira Archipelago waters, so about 70 percent of the fish in the region are vocal or potentially vocal.
Forty-three fish sound types were distinguished, most of which were sound pulses—brief, sharp sounds that are often repeated. This has helped to build the first catalog of fish sounds for the region. Between the two MPAs, Garajau had a greater diversity of fish vocalization types and greater vocalization activity than Desertas. However, it is still unclear which sounds correspond to which fish species.
The recordings also indicated a difference in the vocalizations based on the time of day, demonstrating that different fish species dominate the soundscape during the day versus night. Damselfish and clownfish are thought to be responsible for the majority of sounds during the day, and scorpionfish are thought to dominate the soundscape at night.
What does this mean for the future of MPA monitoring?
A greater understanding of marine ecosystems can be gained from passive acoustic monitoring. This study shows that passive acoustic monitoring is a promising non-invasive method for studying the biodiversity of fish species in marine protected areas. Researchers hope that this study and the catalog of vocal species and sound types will serve as a base of knowledge for long-term monitoring of the Desertas and Garajau MPAs. Future studies may also involve matching fish sounds to fish species, which will be important for determining the state of endangered or threatened species of fish, like the dusky grouper.
There is still much to learn about fish acoustics – globally, just 4 percent of fish species have been studied for sound production. As demonstrated in this study, fish vocalizations provide useful information for understanding fish biology and will be helpful for scientists working to develop better conservation strategies.
I am a recent graduate of Oregon State University with a bachelor’s degree in marine biology. I am most interested in marine ecology, sex-changing fishes, and intertidal nudibranchs. I also recently earned my AAUS scientific diving certification which has sparked my interest in the different applications of SCUBA diving in science. In the near future, I hope to pursue a master’s degree in tropical fish ecology. Outside of science, I also enjoy hiking, reading, and doing the wordle.