Monitoring regional benthic environment of Norwegian salmon cage farms

ABSTRACT: The influence of cage aquaculture on the benthic environment is a crucial concern for sustainable development. The impacts are affected by multiple environmental factors and aquaculture operations. Our main objective was to comprehensively analyze the interaction between Norwegian salmon aquaculture and the benthic environment, involving prolonged temporal observations and wide-ranging spatial assessments, achieved through reviewing government-regulated environmental assessment reports. A total of 3480 reports from 759 farms operating between 2016 and 2022 were analyzed. Our main finding was that the impact of Norwegian salmon cage aquaculture on the benthic environment varied significantly across the Northern, Central, and Southern regions (p < 0.001). This variability was significantly associated with factors such as water depth (p < 0.05), maximum allowable biomass density (p < 0.001), and length of the production cycle (p < 0.001), and was slightly correlated with current velocity (p = 0.067). Additionally, we observed that the most severe environmental degradation often occurred during the summer-autumn period under maximal annual feeding rates. Further, we traced 2922 reports to investigate the changes in the state of the benthic ecosystem over multiple production cycles. We found that the environmental impact of seafloor ecosystems was recoverable, with more effective recovery rates in the early stages of degradation compared to the later stages. We suggested that the optimal biomass levels, production cycle arrangement, and farming practices should differ depending on specific environmental factors. It is imperative to consider these factors for adapting farming operations and take early action when the benthic environment shows signs of degradation.