WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2024 67 of salmon farms, potentially becoming heavily infested with sea lice that have spread with the currents. The sea lice feed on the mucus, skin and blood of the fish and can cause lethal effects on the salmon individuals. The battle against sea lice and their impact on wild salmon has stirred considerable discussion in the world of aquaculture. While numerous studies have confirmed the detrimental effects of sea lice on individual Atlantic salmon, evidence of their impact on entire wild salmon populations remains scarce. Stringent Measures: Norwegian Regulations on Sea Lice Amidst a global decline in wild Atlantic salmon populations, with Norway hosting about one-third of these, the country stands at a crossroads. Balancing the conservation of wild salmon with the flourishing aquaculture sector, Norway has progressively implemented an increasingly stringent regulatory framework, aiming to safeguard its marine legacy while supporting sustainable aquaculture growth. By implementing strict sea lice thresholds within net pens at aquaculture sites and introducing the innovative Traffic Light System to assess the environmental viability of further production growth, Norway has undertaken a comprehensive strategy to tackle the issue of sea lice. Yet, as regulations grow increasingly strict, the effectiveness of Norway’s approach in combating sea lice remains an open question. In 2017, the Norwegian government tightened regulations on sea lice in salmon farms, reducing the allowable limit from an average of 0.5 to 0.2 sea lice per farmed fish during the spring season. Stricter than any other salmon farming nation, the procedure for monitoring involves counting sea lice on 20 fish from each net pen and calculating the average number of sea lice per fish at the site. If this average exceeds the 0.2 threshold, measures must be implemented. The stricter thresholds were not established based on a scientific foundation, and there was no prior evaluation of the potential effects of reducing the threshold to 0.2. The aim of our study was thus to assess the environmental effectiveness of these more stringent sea lice limits. Evaluating Impact: The Environmental Effectiveness of Sea Lice Regulation The coastal regions of Norway have been partitioned into 13 separate production areas (PAs) under the aquaculture management framework (Figure 1). Our study focused on PAs 3, 4, 5 and 7, which are known for their extensive salmon farming activities. All salmon farmers are mandated to submit bi-weekly reports detailing the average sea lice count at their sites. Additionally, each spring, the government undertakes a monitoring campaign of the migrating wild salmon smolt, trawling the fjords to assess the lice burden on these juvenile fish. This allows us to explore the association between farmers’ compliance with stricter sea lice thresholds and the resulting impact on infestation levels in wild salmon smolt. Industry Compliance First, we assessed the extent to which fish farmers have adopted and complied with lice management requirements, that is, whether stricter lice regulations affect the lice levels at farm sites. Figure 2 illustrates the percentage of farm sites within the production areas that managed to stay below a 0.2 threshold in the period before and after the regulatory shift in 2017. According to the figure, more than 90 percent of the farm sites maintained lice levels under the 0.2 limit in 2017 and about 95 percent in 2018, indicating effective implementation of the more rigorous standard by the farmers. Infestation Pressure on Wild Atlantic Salmon Next, we examined the association between adherence to these stringent lice limits and their impact on infection pressure among wild salmon populations. Despite more than 90 percent of farmers successfully adhering to the stricter sea lice thresholds, which has led to reduced sea lice levels in the net pens — we did not observe a corresponding decrease in the portion of severely infested wild salmon smolts within the fjords, as illustrated in Figure 3 a. Should the lice limit prove effective, we would anticipate that fewer sites exceeding the 0.2 threshold coinciding with a lower portion of (CONTINUED ON PAGE 68) FIGURE 3. Figure 3 Sea Lice sites. Source: Institue of Marine Research 20152019, Sea lice infestation on wild salmon [Laskelusinfestasjon på vill laksefisk]. TOP: Proportion of sites exceeding the 0.2 lice per fish and the corresponding proportion of severely infested wild salmon (smolt with more than 0.1 lice per gram fish). The color indicates the production area (PA); blue is PA 3, orange is PA 4, grey is PA 5 while yellow is PA 7. BOTTOM: The total number of sea lice within each PA and the corresponding proportion of severely infested wild salmon (smolt with more than 0.1 lice per gram fish). The color indicates the production area (PA); blue is PA 3, orange is PA 4, grey is PA 5 while yellow is PA 7.
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