A stationary acoustic system for monitoring undisturbed and vessel affected fish behaviour
Original version
This report is not to be cited without prior reference to the authorsAbstract
Thorough knowledge of the dynamics of natural fish behaviour and distribution
within a survey and among surveys is fundamental for reliability of time series of
abundance indices. Further, vessel/trawl affected avoidance may greatly affect density
estimates from trawl and acoustic surveys. Means for monitoring behaviour of fish
during surveys or in special experiments have been limited, time consuming and
expensive.
This paper describes an acoustic buoy system for monitoring undisturbed distribution
and behaviour of fish as well as avoidance reactions of fish in relation to passing
surveying or trawling vessel. Operation and results from the first trials are described.
The buoy could easily be operated in connection with a standard trawl haul,
prolonging the haul time with approximately 30 minutes for launching, retrieval and
extra cruising distance. Information on fish distribution and behaviour , i.e. vertical and horizontal movements, is stored in the buoy and can easily be downloaded for
later processing and analysis. Observations on cod demonstrated avoidance away
from the vessel of variable intensity.