Acoustic Monitoring of Fish: CTG's hydrophone arrays used to study the reactions of fish to sound
“Chelsea has been working with the Norwegian University of Science and Technology (NTNU) for a number of years,” said CTG’s acoustics specialist Paul Bolton, “they initially commissioned us to custom design a 6m vertical acoustic hydrophone array in order to conduct novel underwater acoustic experiments. This was followed by the design of three 8m long, active hydrophone arrays. These arrays are now being used by the Institute of Marine Research in Bergen to map the sound field inside a fish pen at Austevoll, just south of Bergen.
The reactions of a school of herring (ca. 10000 fish) to waterborne acoustic signals and noise of various types is currently being studied to get a better understanding of the environmental impact human-made noise can have on fish. The primary objective of the project is to gain an understanding of the interaction between direct stimuli and the information transfer between individuals in schooling fish, and to understand how this affects their behaviour.
"With over 50 year's experience in the design and manufacture of underwater acoustic transducers including hydrophones, projectors, pingers and sidescan sonar arrays we are ideally placed to custom design systems to meet the expectations of the most demanding research programmes", said Chelsea's Paul Bolton.
Find out more about the fish study:
The research project conducted by the Institute of Marine Research involves observing the collective behaviour of penned herring and investigating the effect of various sound stimuli. The primary aim is to understand the interaction between direct stimuli and information transfer between individuals in schooling fish and to understand how this affects the collective behaviour, with special emphasis on noise induced behaviour. An area of particular interest is to understand how information is transferred in animals groups, and how stimuli is amplified or dampened through social interactions.
The project will perform lab experiments on schooling fish in response to external stimuli, and investigate the role of the social interactions. The fish will be observed using video cameras, and techniques to extract the behavioural information will be further developed.
An important aspect of the proposal is to establish a link between the highly controlled laboratory observations to in situ experiments. The results from the laboratory will be used to form rigorous hypotheses on the collective behavioural rules in herring, a key species both economically and ecologically. These will be tested on herring in a net pen setup. We will use both video cameras and acoustic cameras to observe the behaviour, and the methods developed from the laboratory experiments will be refined to fit the herring net-pen system.
The Institute are particularly interested in sound stimulated collective behaviour, since anthropogenic noise pollution is an increasing concern worldwide. To achieve this a range of different sound sources will be used, and the different noise fields will be modelled and verified before being exposed to the fish. The role of near field effects and range effects will be investigated, and the results will be related to in situ sound exposure experiments, in particular where sound pressure levels has failed to explain the behaviour.
The eight metre long, oil filled array (shown above), houses eight omni directional identical hydrophones. The array is designed to be deployed to depths of 100 metres.
Where does all the noise come from? There is growing interest in understanding the effects of human-generated sound on fish and other aquatic organisms. Boats and ships are a major source of noise. Sonars systems used by navies, shipping companies, fishing industries and the oceanographic research community are also a significant sound source. Pile driving and seismic airgun arrays are also high-intensity sources.