Two different carrying capacity models were applied to commercial mussel raft systems in two sea lochs on the west coast of Scotland. The mean currents were found to be 0.052 m/s in Loch Etive (LE) and 0.05 m/s in Loch Kishorn (LK). The mussel filtration rate ranged from 0.54 to 2.26 l/h in LK and 0.93 to 2.07 l/h in LE (p>0.05). The assimilation efficiency was 19.64% in May and 25.02% in August in LK (P>0.05). However, the assimilation efficiency was significantly higher in May (28.23%) than August (21.17%) in LE. Based on the seston clearance model, the carrying capacity was estimated to be 5.7 times greater in LE than the present mussel culture system utilitizes, while the carrying capacity was about 3 times greater in LK than the present culture system utilizes. According to the particulate organic matter model, the Loch Kishorn mussel farm is producing more mussels than the estimated carrying capacity of the system (by a factor of 20-40%), while, in contrast, the mussel production in Loch Etive is considerably below the carrying capacity (by about 40% to more than 100%). The production capacities were found to be more accurate in the particulate organic matter model than in the seston based model at both sites.