INSTITUTE OF MARINE RESEARCH
The use of biological sounds for selective fisheries.
A project was carried out from 1999 to 2001 in order to explore the possibilities for using biological sounds from fish as a tool for developing selective fishing gears. The main goals have been:
1 Development of technology.
Even though the basic instruments needed for recording of underwater sound, for visual studies of fish behaviour and for replay of sounds do exist, there were no previous history of connecting them in a way that made it suitable for recordings of sound and behaviour in the open sea. Therefore, in the first phase of this project, a large effort took place in improving instrumentation. A remote-controlled instrument platform for fish behaviour studies and sound monitoring was developed.
Figure 1 Remote controlled instrument platform
2 Recording of sound
During the project we managed to obtain field recordings of biological sounds from several different fish species,. The recordings of cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens) and tusk (Brosme brosme) are the most important. Several of the registered sound sequences have not earlier been documented.
Behaviour studies were carried out simultaneously to the sound recordings to document in what behavioural contexts these sound signals were used. We also managed to obtain recordings of sound and behaviour patterns of spawning cod in net cages that have not earlier been registered.
In addition to the field surveys, more basal studies of cod sounds were carried out in net cages. Examples of parameters that have been studied are differences in the frequency and spectral characteristics with age, size, season and time of day.
Table 1 Seasonal variation in diurnal grunt-rhythm
3 Playback of acoustic recordings.
In the last phase of the project playback experiments using several of the recorded sounds were carried out to observe if the behavioural pattern of fish was affected by these sounds.
Playback experiments have been completed in field surveys on wild fish under surveillance of underwater video. Similar trials were also done where the swimming behaviour of fish was monitored by means of acoustic tagging. The data from the experiments are not yet fully analysed, but the immediate impression is that the results are complex and difficult to interpret.
During the last phase of the project we wished to employ potential behavioural responses to develop more environmental friendly and selective capture methods. There was a wish to use acoustic signals in pots and traps instead of or in addition to - bait.
Figure 2 Vemco buoy recording signals from acoustic tagged fish during trials with playback. Aim was to observe fish behaviour when acoustic sound was playback.
Figure 3 Instrumental room onboard F/F Fangst, during playback trials in October 2001.
The project was closed the 31st of December 2001, but our goal has not yet been achieved - to develop selective capture devices using biological sounds.
Norway has a short history of studies on biological sound from fish, and our basic knowledge about the vocal production of our main commercial fish species was very limited when the project started. This called for thorough basic studies of acoustic signals, and behaviour patterns linked to these signals. The basic studies turned out to be more complex and more time demanding than expected.
The fish behaviour response to acoustic signals in playback experiments was also more complicated than first expected. There were no consistent attraction responses detectable when exposing fish to acoustic signals, which is essential when designing capture devices using acoustic stimuli as "bait".
Figure 4 Future capture-pot based on biological sound?