Researchers at Johns Hopkins University have discovered that fish swimming in schools exhibit a surprisingly stealthy behavior underwater, able to sound like a single fish when moving together in just the right way. The study, published in Bioinspiration & Biomimetics, sheds light on why fish swim in schools and offers promise for designing quieter submarines and autonomous undersea vehicles. Senior author Rajat Mittal explains that while swimming in groups already provides fish with added protection from predators, the reduction in their acoustic signature when swimming in groups may be another reason for the formation of fish schools.
Using a high-tech simulation of schooling mackerel, the team created a 3D model to explore how different numbers of fish swimming together, their formations, proximity to each other, and synchronized movements impact their noise levels. They found that a school of seven fish moving in sync was able to sound like a single fish, potentially fooling predators like sharks into thinking they are only hearing one fish instead of a group. The key to sound reduction was found to be the synchronization of the fish’s tail fin movements – specifically, alternating tail flaps cancelled out each other’s sound, resulting in a significant decrease in the overall noise produced.
Lead author Ji Zhou, a graduate student studying mechanical engineering at Johns Hopkins, emphasized that the tail fin movements not only reduce sound but also generate flow interaction between the fish, allowing them to swim faster using less energy. This shows that reductions in noise do not have to come at the expense of performance, as the hydrodynamic interactions between the swimmers lead to noticeable increases in per capita thrust. The team was surprised to find that even one swimming fish joining another could lead to sound reduction benefits, indicating that simply swimming together without coordination already plays a role in reducing the sound signature.
The researchers plan to further enhance their models by incorporating ocean turbulence and creating simulations that allow the fish to swim more freely. By studying how these factors affect the stealthiness of swimming fish, they hope to gain a deeper understanding of the mechanisms behind noise reduction in schools of fish. Ultimately, these findings could inform the design and operation of quieter underwater vehicles, as well as provide insights into the benefits of collective behavior in aquatic environments. The team’s work contributes to the growing body of research exploring the bioinspired capabilities of marine creatures and their potential applications in engineering and technology.
