Comprehensive Report on Fish Startle Response to Low-Frequency Sound for Sonus Fishery System

Introduction

Traditional bottom trawling involves contact with the seabed, which can cause significant damage to benthic habitats and result in unwanted bycatch. By utilizing the natural "startle response" of fish to low-frequency sound, the Sonus Fishery system has the potential to revolutionize bottom trawling by eliminating the need for seabed contact. The system will focus on using low-frequency sound to scare fish off the seabed and guide them up towards the trawl opening, allowing fish to swim into the net without the need for trawl doors or contact with the seabed.

This report examines how fish react to different frequencies and sound levels (dB) in order to apply low-frequency sound to scare fish off the seabed and optimize bottom trawling without seabed contact.

Fish Hearing and Response to Sound

Fish have different hearing abilities depending on the species, with most fish sensitive to low-frequency sound (typically between 100 Hz and 300 Hz). Research shows that species like cod, haddock, pollock, and similar fish have a well-developed ability to detect low-frequency sound, which they use to avoid predators or identify threats.

Low-Frequency Sound and Startle Response

When exposed to intense low-frequency sounds (typically under 1,000 Hz, often between 50 Hz and 300 Hz), fish exhibit a "startle response," where they rapidly move away from the sound source. This reaction is well-documented and can be used to scare fish off the seabed. Several studies, including Chapman (1973) and Popper et al. (2019), have documented strong fish reactions to sounds in this frequency range.

• Haddock showed high sensitivity to low-frequency sound, with strong reactions observed between 110 Hz and 310 Hz, with threshold levels as low as -20 dB.
• Cod typically reacts to sounds in the 100-300 Hz range and avoids areas with high-intensity noise, which can trigger a startle response.

Sound Levels (dB) and Response Intensity

Various studies suggest that fish begin to react strongly when sound levels exceed 160-180 dB. The sound intensity must be sufficient to overcome the natural background noise of the marine environment, which can mask lower sound levels.

• Rapid flight response: At sound levels ofover 180 dB, especially in the low-frequency spectrum (e.g., 250 Hz), fish have shown a strong flight response away from the sound source. This can be used to scare fish upwards from the seabed towards the trawl opening.

Application of Low-Frequency Sound in the Sonus Fishery System

Sonus Fishery system can leverage these characteristics of fish startle response to avoid seabed contact during trawling. By generating powerful low-frequency sounds in front of the trawl, fish will be scared off the seabed, removing the need for trawl doors, which typically drag along the bottom to herd fish into the net. This offers several advantages:

1. Environmental benefits: Reducing seabed contact significantly lessens the damage to benthic ecosystems, including impacts on the seabed's flora and fauna.
2. Fuel savings: Since trawl doors no longer need to be dragged along the seabed, resistance is reduced, leading to lower fuel consumption.
3. Reduced bycatch: Fish startled upwards by low-frequency sound can be more precisely targeted, reducing the amount of bycatch.

Technical Implementation

The system would require specially designedunderwater speakersmounted in front of the trawl. These speakers should be capable of generating sounds in the 100-300 Hz range at a sound level of at least 180 dB, ensuring an effective startle response from fish close to the seabed. The duration and intensity of the sound can be adjusted in real-time to optimize fish response in different marine environments.

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Practical Trials

Research, as described in Björnsson (2018), shows that fish can be trained to respond to sounds, indicating that even naïve fish instinctively react to specific low-frequency sounds without the need for long training periods. This makes the Sonus Fishery system practically applicable in commercial fisheries.

Conclusion

Overall, research shows that low-frequency sound can be effectively used to trigger a startle response in fish, causing them to move off the seabed. By implementing the Sonus Fishery system in commercial bottom trawling, fishermen can reduce their environmental impact, save fuel, and achieve more targeted catches without bycatch. The system capitalizes on fish’s natural response to danger in the form of low-frequency sounds, enabling more sustainable fishing practices.

References

• Chapman, C.J. (1973).Field Studies of Hearing in Teleost Fish. Marine Laboratory, Aberdeen.
• Björnsson, B. (2018).Fish Aggregating Sound Technique (FAST): How Low-Frequency Sound Could Be Used in Fishing and Ranching of Cod. ICES Journal of Marine Science.
• Popper et al. (2019).Examining the Hearing Abilities of Fishes.
• Hastings & Popper (2005).Effects of Sound on Fish.