
4 February 2025
Researchers develop a new seal deterrent for sustainable fishing
Commercial fishermen along the coasts of Sweden have long struggled with seals that damage fishing gear and eat the catch. To address this challenge, a three-year research project was launched in autumn 2023 aimed at developing a new type of seal deterrent.
The project is led by Eva-Lotta Blom, a marine biologist at the Swedish University of Agricultural Sciences (SLU) in Umeå, in close collaboration with Örjan Johansson, Professor in Engineering Acoustics at Luleå University of Technology.
“Sound is crucial to creating an effective seal deterrent. Current models emit sound in the frequency range of 10,000–15,000 Hertz, but research shows that seals are most sensitive to frequencies between 25,000–30,000 Hertz, and even higher. We are now working to find the right frequency ranges and a time structure that creates maximum discomfort without harming the seals,” says Örjan Johansson.
The seal deterrents available on the market today are primarily designed for fish farming. The project aims to develop a smaller, lighter, and more portable solution better suited for small-scale fishermen. The goal is to create a deterrent that can be easily carried and used by fishermen when setting their nets.
“One of the major problems with current deterrents is that they become ineffective over time because seals can get used to the sound. We therefore need to design a deterrent that is both acoustically effective and difficult for the animals to ignore,” explains Örjan Johansson.
Tailored ultrasonic sound with motion detector
The new design of the seal deterrent will include a strong ultrasound, similar to a siren, and a motion detector. The purpose of this is to create a shock effect that triggers when seals approach, which should prevent them from becoming accustomed to the sound.
Research has shown that seals' hearing is most sensitive to sounds in two specific frequency ranges. One is related to resonances in the closed air-filled ear canal, and the other involves frequencies that cause irritation in their whiskers. By targeting these areas, the researchers hope to create an effective disruption without affecting other species. Fish will not be impacted by the sound, as their hearing is sensitive to much lower frequencies compared to seals. Additionally, there is potential for other marine mammals, such as harbour porpoises, to be positively affected by the deterrent, as these animals also tend to avoid fishing gear when they hear loud sounds.
The challenge lies in optimising the spread of sound underwater, as factors such as gas bubbles, plants, salinity, and water depth can influence how sound waves move.
“Sound behaves very differently in water than in air. Therefore, we need to carefully test and adjust both frequencies and sound intensity to ensure it works in different environments,” says Örjan Johansson.
Prototype testing in spring 2025
In spring 2025, the researchers plan to test an initial prototype in the field. They will also experiment with different frequencies to identify the most effective solution.
Through this research, the team hopes not only to solve a significant problem for commercial fishermen but also to contribute to a more sustainable and conflict-free interaction between humans and seals in our seas.
Contact
Örjan Johansson
- Professor and Head of Subject
- 0920-491386
- orjan.johansson@ltu.se
- Örjan Johansson
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