68 JUNE 2024 • WORLD AQUACULTURE • WWW.WAS.ORG heavily infested wild smolt, and vice versa. Figure 3b explores the relationship between the total number of sea lice within each production area and the percentage of severely infested wild salmon. We hypothesize that an increase in overall sea lice level would result in a higher percentage of severely infested salmon. Yet, the data do not confirm this relationship, showing no evident correlation. Unintended Consequences of Stringent Measures The drive for stricter sea lice regulations might not be translating into substantial environmental gains. Yet, these stringent rules have prompted a rise in delousing efforts. A decade ago, chemical treatments dominated the battle against sea lice, as shown by the grey line in Figure 4a. However, as these chemical methods were used more frequently, sea lice began to develop resistance, the effect vanished, and the lice problem escalated. This forced the industry to develop new, nonmedical methods, which we categorize as “biological” or “mechanical”. The biological solution involves “cleaner-fish” like lumpfish and wrasse, known for their appetite for sea lice. In 2018, Norway farmed approximately 42 million of these helpful fish, alongside capturing some 20 million wild wrasse (Labridae), to place them in salmon pens for cleaning purposes. Yet, this solution has not been without its challenges with more than 40 percent of the cleaner-fish dying related to significant health and welfare problems. Meanwhile, mechanical methods, including various flushing techniques, freshwater treatments and heated water are gaining ground. The impact on the farmed fish welfare of these newer methods is currently under scrutiny. As depicted in Figure 4a, which illustrates the shift from medical to mechanical and biological delousing methods between 2013 and 2019, mechanical approaches are becoming increasingly dominant. Over the same period, we observe a strong correlation between the intensity of lice-reduction operations at production sites and the farmed salmon mortality (Figure 4b). Although the stricter lice regulations have reduced lice levels at farm sites, successfully, they have also led to substantial unintended consequences for the health and survival of farmed fish. The trade-offs between the effectiveness of these regulations and their broader impacts, particularly on farmed fish welfare, merit careful consideration in evaluating the true success of these regulation efforts. The Future of Salmon Farming Regulation and Environmental Effectiveness The Norwegian authorities have implemented a stringent lice threshold across all salmon farming sites with the goal of managing an element within the ecosystem. The effectiveness of this measure is judged not by the sheer numbers of sea lice in the pens, but how much it aids in diminishing mortality risks for nearby wild salmon populations, and ultimately, ensuring their survival. Our analysis indicates that the environmental effect of strict lice limits has been limited or absent; successful compliance with the lice requirements does not seem to reduce the infection pressure on the wild salmon in the areas we have examined. Yet, in striving to meet these demanding standards, salmon farmers have resorted to delousing methods that introduce a new set of problems, such as reduced welfare and higher mortality rates among the farmed fish. Moreover, the seemingly less invasive approach of using cleaner- fish has resulted in poor welfare and high death rates for these auxiliary species. Our study suggests the association between regulating on FIGURE 4. Fig. 4 Numbers of delousing measures. TOP: Number of various types of delousing measures BOTTOM: Number of de-lousing measures and farmed fish mortality. Source: Based on data from Barentswatch, January 2020. URL: https://www.barentswatch.no/nedlasting/fishhealth/treatments, Directorate of fisheries, January 2020. URL: https://www.fiskeridir.no/ Akvakultur/Tall-og-analyse/Biomassestatistikk/Biomassestatistikk-etter-fylke Our analysis indicates that the environmental effect of strict lice limits has been limited or absent; successful compliance with the lice requirements does not seem to reduce the infection pressure on the wild salmon in the areas we have examined.
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