Deployment of hydroacoustic feeding control in salmon sea-cages; biological and technical considerations

Abstract

Automation of feeding control for sea-caged Atlantic salmon is important to reduce waste feed. Hydroacoustic appetite-led feeding, or echofeeding, uses echo sound to monitor fish biomass in a defined feeding area. As the fish become satiated and begin to leave the feeding area, the monitored biomass falls, enabling the setting of threshold levels of biomass at depth. Software then decides to continue or stop feeding. Here, we implemented a fully autonomous echofeeding system in 3 sea-cages with salmon during summer (900 g, ~14 °C) and winter (5300 g, ~5 °C). To find the best signal of feeding activity, fish biomass was monitored with two echo sounder transducers at different depths and echo beam widths, directed upwards towards the feeding area. Prior to echofeeding, we trained salmon to consume their daily ration in short, intense feeding bouts. The fish adapted to consume their daily food ration in just 1 h and sustained their feeding activity close to the surface under the echofeeding regime. The feeding response was positively correlated with feeding intensity and was strongest at the surface (0–1.5 m), with a narrow echo beam from 8 m depth giving the best proxy of fish appetite. Appetite varied between meals and days, yet echofeeding prevented waste feed while fish maintained strong growth rates. Echofeeding is simple to deploy, as farmed salmon, independent of fish size or season, can adapt to changes in feeding regimes. Both feeding intensity and the biomass threshold for feeding cessation were kept static under echofeeding, which challenge the industry's standard manual feeding control practice where feeding intensity is adjusted by visually assessing appetite within meals. Our results provide novel insight into basic principles for hydroacoustic-based and autonomous feeding control in general and highlight echofeeding as a promising technology.