AEI prepress abstract  -  DOI:

Cage size affects dissolved oxygen distribution in salmon aquaculture

Tina Oldham*, Frode Oppedal, Tim Dempster


ABSTRACT: Atlantic salmon aquaculture is shifting toward larger cages, but the water quality implications of this shift are unknown. While larger cages could improve profitability through economies of scale, they may increase the risk of low dissolved O2 (DO) conditions due to reduced water exchange. Low DO conditions reduce feed intake, meaning that the benefits of shifting to larger cages must be weighed against potential negative impacts on fish growth. To test the impact of cage size on DO distribution, we recorded DO saturation in several circular cages of two different sizes on a commercial salmon farm: six 168 m and four 240 m circumference. Static strings of DO loggers at 1, 4.5, 8, 12 and 16 m depths recorded DO saturation once every 60 seconds throughout a 10 day period in mid-summer. Overall, DO levels in standard 168 m circumference cages were suitable for salmon feeding and growth. Mean DO levels were highly variable (57 – 134% saturation), and were lower in cages than at the reference site. On average, DO saturation decreased with depth, and was lowest during the early morning hours. Lowest DO measurements occurred in the large 240 m circumference cages, where 1 in 20 of all recordings were at levels known to reduce salmon feeding and growth. DO levels in larger cages can suit salmon production, but site specific environmental conditions throughout the year must be considered to ensure there is sufficient capacity to support reduced water exchange.