ABSTRACT
This paper describes a hydroacoustic system for monitoring and feeding control in cage rearing of Atlantic salmon.
An echo-sounder, linked to an upward-facing transducer mounted under the cage, provides echo signals from the caged fish. The signals are processed by a PC-based echo integrator which monitors the change in echo intensity at different depths in the cage. Before feeding the highest fish densities are found at medium depths. When feeding starts, fish density and thus echo intensity close to the surface increase significantly and stay at a high level as long as the appetite remains high. When the echo intensity in the upper layer of the cage decreases to a certain preset threshold, the feeders are automatically shut off. The downward migration of the fish, as shown by the reduced echo intensity, is thus used as an indicator of satiation.
Besides the direct feeding control application, amount of feed is logged, and the software allows different feeding strategies for example with respect to number of daily feedings, feeding intensity, total daily feed limits, and level of automation to be implemented. The system is designed to monitor and control twelve cages and feeder units.
Other useful applications as continuous monitoring of the fish with possible alarm functions, observation of dead salmon and wild fish, as well as possible biomass estimation, are described and discussed.
