MOHN AQUA
CONTAINMENT SPECIAL
SEAL SCARERS W
A DESIGN THAT KEEPS PREDATORS AWAY BY USING PHYSIOLOGICAL, NOT PSYCHOLOGICAL, TECHNIQUES
ith seal attacks being cited as one the pri- mary reasons for fish
escapes, farmers today have to make every effort to reduce or remove the issue of seal predation. Today in Scotland the AIRMAR dB plus II acoustic deterrent continues to be the most commonly used system. The system was developed in the mid-90s by US firm AIRMAR Technology Corp. One of the world’s leading producers of marine transduc- ers for the leisure, industrial and military markets, AIRMAR
had been involved in sup- plying transducers for use in seal scarers made by other manufacturers in aquacul- ture for several years prior to this. What had become clear by this point was that the traditional method of using underwater acoustics to create a psychological seal scarer was proving ineffective if used for any timespan longer than a couple of months. AIRMAR engineers recog- nised that a new approach was needed and that a physi- ological deterrent would be the best way forward. Using their extensive experience in marine ultrasound, combined with assistance from respected marine biologists, they devel- oped the first dB plus system. By going down the physi- ological route, all of the traditional theories about seal scarers were now made irrelevant. The system causes seals significant discomfort as they get close to the farm, particularly when they get to within 40m of the transducer. Beyond 40m the system has almost no effect on the seal, and at 100m represents the same level of noise as an
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outboard motor produces. As a result transducer place- ment is critical – correctly placed transducers around the outside of the farm create an ‘electric fence’ of protection, while incorrectly placed trans- ducers create a fence with holes in it, vastly reducing the effectiveness of the system. Preliminary tests on the east coast of the USA proved highly successful. Some im- provements were made to the system, including the addition of soft start that slowly ramps up the output when the unit is
CORRECTLY PLACED
TRANSDUCERS CREATE AN ‘ELECTRIC FENCE’
www.fishfarmer-magazine.com
PHOTO: ANDREAS TREPTE
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