Skirt around a salmon sea cage to reduce infestation of salmon lice resulted in low oxygen levels

Oxygen gradients affect behaviour of caged Atlantic salmon Salmo salar

“…The results of our manipulative experiment align with previous observations that salmon remained in the warm surface waters of a cage despite DO saturation being 20 to 30% lower than in the deeper, cooler water (Stien et al 2012). During our trial, the hetero- and dissolved oxygen (% saturation).…”

“…However, an alternate study at 4 commercial farm sites found that salmon avoided specific depth ranges in the water column where lowest DO concentrations (60% saturation at 15°C) occurred . Given that DO concentrations reach severely hypoxic levels in commercial cages for extended periods of time (Oppe dal et al 2011a, Burt et al 2012, Stien et al 2012, and that commercially viable mitigation options are limited (Bergheim et al 2006, Srithongouthai et al 2006, Oppedal et al 2011b, it is critical to know whether salmon avoid hypoxic areas for farmers to maximize welfare and production performance.…”

Sea lice infestation levels decrease with deeper ‘snorkel’ barriers in Atlantic salmon sea‐cages

“…By exploiting this aspect of their behaviour, a possible solution is to prevent or limit the contact of sea‐caged salmon with surface waters. Mismatching host–parasite encounters is the principle behind most depth‐based lice‐barrier technologies such as fully enclosed floating tanks where the water is pumped from the deep, cages that incorporate plankton‐shielding skirts, or lice ‘snorkel’ barriers that stop encounters in surface waters, and fully submerged cages …”

Evidence for ‘escape through spawning’ in large gilthead sea bream Sparus aurata reared in commercial sea-cages

“…The use of a curtain-like egg collector, such as that manufactured in the present study, could prevent the dispersal of eggs away from the cages. Whether such devices could practically be implemented at a commercial scale requires further investigation; however, skirts that restrict water flow through sea-cages reduce oxygen levels, which has implications for fish welfare and production (Stien et al 2012). Future studies that look into filtration as a method to remove spawned eggs must therefore also take into account the welfare of cultured fish.…”