Sounds alerts for seals
Acoustic technology that could more effectively protect marine installations from unwanted sea life has been unveiled at St Andrews University. The system could be used to keep dolphins away during turbine installation offshore or to protect fish farms from seals — a major problem for the seafood industry.
Group leader Vincent Janik, a specialist in communication in marine mammals, said his team has found the optimum target-specific signals to irritate sea mammals just like 'nails on a chalkboard' can grate on a person's nerves.
The sound can be produced by an under-water transducer attached to a fish farm cage submerged 4m-5m in the water. The battery of the transducer control unit would need to be changed every few days.
Janik said the kit would include a detection system that would trigger the sound only when a marine mammal approaches.
He said there are two possible methods that could be used for the initial detection of nearby sea mammals. One is an active method such as sonar, where a distinctive 'ping' is transmitted and an echo is then listened for. The other is a passive method, such as acoustic daylight imaging technology, which uses the ambient noise in the ocean to create an image.
Janik said with that technology an underwater dish would reflect the acoustics collected from the surrounding ocean area back to a series of underwater microphones facing inward on the front of the dish. The microphones would convert the acoustic image into a set of electrical signals that could be used to alert the deterrence system of a new object in the area.
'If you play a sound continuously even in the absence of animals it is an issue of not only noise pollution under water but also, it makes the method potentially less effective because the animals may get use to the sound,' he said.
Janik claimed their system is more effective than others being used. 'The usual systems work in a way where they just produce loud sounds to exceed the pain threshold for the animals so the animal experiences physical pain and tries to avoid the source of it,' he said.
'One of the problems with that kind of method is if you are exceeding the pain threshold you are also damaging the hearing system of animals. So an animal that becomes exposed to this will become gradually more and more deaf.'
The animal, Janik said, will therefore become immune to the deterrence system over time. 'As the animal's hearing threshold goes up the sound that is produced by the existing devices doesn't exceed the pain threshold any more so the animals will quite happily swim up to the farm and help themselves to fish,' he said.
The other problem with existing systems, Janik added, is that they tend to have effects on other animals in the sea.
'So while they don't necessarily work with seals they work very well keeping small whales and dolphins away from a farm,' he said.
'Hearing sensitivity of whales and dolphins is much lower than that of seals so the sound appears even louder to the dolphin than it does to the seal. There is a serious problem in areas where you have a lot of fish farms. You basically exclude porpoises and dolphins from entire coastlines that are usually available for them to forage in.'
The St Andrews acoustic system does not produce sounds near the pain threshold of sea mammals. Janik's team did this by producing a sound that is adverse but not loud. He said there are many examples of these kinds of sounds for humans.
'The famous example is the fingers over the chalkboard,' said Janik. 'It's not a very loud sound but, nevertheless, we have a very strong physiological response when we try to avoid the sound.'
He added: 'We've exploited these kinds of phenomenon to develop systems that work in the same way for seals.'
In addition to protecting fish farms, another application for these systems could be offshore construction sites. Janik said the noises created during the construction of offshore wind farms, for example, can be extremely loud and they can cause injury to sea mammals like dolphins.
'So devices like this could be used to keep dolphins away from sites for the duration of construction,' he said.
The group is trying to license the technology, which can be implemented by modifying existing devices, and is in discussions with interested companies.