Oceanographic processes control dissolved oxygen variability at a commercial Atlantic salmon farm: Application of a real-time sensor network

Abstract

Open ocean fish farming involves containment of cultured animals under environmental conditions influenced by seasonal variation and water quality. Recently, an important area of research focus has been on water quality monitoring to improve aquaculture management. The development of novel sensors that report in real-time is critical to improve the monitoring capacity of farms, while increasing the understanding of the dynamics of environmental variables. In this study, commercially available, real-time dissolved oxygen and temperature sensors were distributed in the center of 19 cages at a commercial Atlantic salmon (Salmo salar) farm located within Shelburne Bay, Nova Scotia (Canada) and four reference sites. The site had an average depth of 15 m, while the cages consisted of nets 10 m deep. The dense deployment allowed for insight into the spatial and temporal variability of dissolved oxygen throughout the farm. Tide was determined to have the most significant impact on dissolved oxygen levels, with its influence varying depending on cage location within the farm. As waters flow from one end of the farm to the other, driven by tidal advection, fish behaviour and physiology, as well as flow restriction from cage infrastructure reduce oxygen levels in cages downstream. This results in oxygen concentrations out of phase on opposite ends of the farm, with higher oxygen levels at one end of the farm (i.e. 8.24 ± 0.29 mg L−1) and lower oxygen levels at the other (i.e. 5.38 ± 0.34 mg L−1) at any given phase of the tidal cycle. As Atlantic salmon become stressed and exhibit a reduced appetite at oxygen levels below 4–6 mg L−1, depending on temperature, it is important to accurately monitor the entirety of the farm. This study examined the patterns and drivers, specifically tide, of dissolved oxygen throughout a commercial salmon farm to understand the oxygen dynamics and make informed decisions that impact fish growth and welfare.