In schools, fish have mastered the skill of moving without sound

Have you ever wondered how a swirling school of fish can move with such grace and coordination? What if someone told you that they’re actively working to become invisible…or at least invisible to the ears of predators? New research suggests that fish schooling together can drastically reduce the sound they make.

Fish schools without sound

“It’s widely known that swimming in groups provides fish with added protection from predators, but we questioned whether it also contributes to reducing their noise,” said senior author Rajat Mittal, a researcher at Johns Hopkins University.

Think about it – a school of fish should be noisier than a single fish, right? Yet, something fascinating is happening beneath the waves. It seems our intuition might be leading us astray.

Fish schools are quieter than a whisper

Mittal and his team at built a sophisticated 3D model of mackerel to crack the code behind silent schools. They experimented with the number of fish, swimming formations, proximity, and even how synchronized their movements were. The results were astonishing.

A school of seven fish, when swimming with just the right coordination, could effectively sound like a single fish to a predator like a shark.

“This could have significant implications for prey fish,” noted Mittal. After all, becoming harder to detect means a better chance of survival in the unforgiving underwater world.

Sound waves and stealthy swimmers

The secret to this underwater stealth mission lies in how the fish move their tail fins. “Sound is a wave,” explained Mittal. “Two waves can either add up if they are exactly in phase or they can cancel each other if they are exactly out of phase.”

The researchers were surprised to discover that even two fish swimming together can make a difference. Imagine the advantage when hundreds or even thousands of fish are involved. The team believes the noise reduction likely plateaus as the school gets significantly larger, but the benefits are clear.

“Simply being together and swimming in any manner contributes to reducing the sound signature,” Mittal said. “No coordination between the fish is required.”

Sound travels in waves, which have alternating regions of high and low pressure. These pressure fluctuations are what our ears (or a predator’s ears) pick up as sound.

Uneven fish movements

When two sound waves meet, they can interact in different ways. If the high-pressure region of one wave overlaps with the low-pressure region of another wave (out of phase), they effectively cancel each other out, reducing the overall sound.

When fish in a school alternate their tail flaps, they create tiny pressure waves that interact with the pressure waves caused by other fish. With the right timing, a significant portion of this sound can be canceled out, making the school as a whole much quieter.

Fish school benefits beyond minimal noise

The sound reduction isn’t the only surprising benefit schools of fish receive. Ji Zhou and his team discovered an additional advantage to the precisely timed tail fin movements. “We find that reduction in flow-generated noise does not have to come at the expense of performance,” Zhou explained.

As fish move through water, they experience drag, a force that opposes their movement. This drag is partly caused by the friction between the fish’s body and the water, and partly by the way water flows around the fish’s fins and body.

When fish in a school move their fins in a coordinated way, they can create smoother water flow around each other’s bodies. This smoother flow reduces drag, allowing the fish to swim with less effort and expend less energy.

Remarkably, the same tail fin movements that create the sound-canceling effect also contribute to this drag reduction. Essentially, by swimming together with precise timing, the fish achieve both stealth and increased efficiency.

This discovery highlights the incredible adaptations fish have developed to survive in their environment. Schools benefit from a double advantage: becoming quieter to evade predators while simultaneously using less energy to travel further or maneuver more quickly. It’s a testament to the power of natural selection and the elegance of biological design.

Underwater vehicles inspired from fish school

This discovery extends far beyond simply understanding the wonders of the natural world. By studying the remarkable way fish schools achieve quiet movement and efficient swimming, researchers believe we can unlock valuable insights that can be applied to human technology. This field of study, known as biomimicry, essentially involves mimicking nature’s ingenious solutions to solve human challenges.

In this case, the research on fish schools has the potential to revolutionize the design and operation of underwater vehicles, including submarines and autonomous underwater vehicles (AUVs). Here are some potential applications:

Quieter submarines

Traditional submarines rely on powerful propellers that generate significant noise. This noise can disrupt marine life and limit a submarine’s ability to operate undetected.

By understanding how fish schools achieve noise reduction, engineers could develop quieter propulsion systems for submarines, allowing for more discreet underwater exploration and potentially reducing the impact on marine ecosystems.

More efficient AUVs

AUVs are increasingly used for various tasks, from oceanographic research to underwater search and rescue. However, battery life remains a limiting factor for these vehicles.

By mimicking the way fish schools reduce drag through synchronized movements, engineers could potentially design AUVs that operate more efficiently, requiring less energy and extending their operational range.

Potential benefits of knowing fish school sounds

The potential benefits of this research are vast.:

• Exploring the depths discreetly: Quieter submarines could allow scientists to study deep-sea environments and marine life with minimal disruption. This could lead to significant advancements in our understanding of these fragile ecosystems.
• Minimizing environmental impact: Reduced noise from underwater vehicles could help protect marine animals that rely on sound for communication and navigation. This could be particularly important for species like whales and dolphins that are known to be sensitive to underwater noise pollution.
• Extending AUV capabilities: More efficient AUVs could be deployed for longer periods and cover wider areas, expanding our ability to conduct oceanographic research, monitor marine resources, and perform underwater inspections.

The research on fish schools offers a glimpse into the power of biomimicry. By studying nature’s ingenious solutions, we can develop new technologies that are not only more effective but also more sustainable and environmentally friendly.

This discovery highlights the importance of fundamental scientific research and the potential for groundbreaking innovation when we take inspiration from the natural world.

The next time you see a school of fish, remember they’re not just mesmerizing, they’re masters of stealth and efficiency. Nature, as always, continues to surprise and inspire with its brilliant designs.

The study is published in the journal Bioinspiration & Biomimetics.

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