Epidemiological description of the sea lice (Caligus rogercresseyi) situation in southern Chile in August 2007

Salmon sea lice represent one of the most important threats to salmon farming throughout the world. Results of private monitoring efforts have shown an increase in the number of positive cages and cage-level abundance of sea lice in southern Chile since 2004. As a consequence, the Chilean Fisheries Service implemented an Official Surveillance Program in the main salmon production area of southern Chile to assess the situation of sea lice in fish farms. Results showed that the prevalence of sea lice in the fish farms was 53.4%, ranging from 3.5% in Puerto Aysen to 100% in the Seno de Reloncavi zone. The average sea lice abundance was 11.8 per fish (Geometrical mean (GM) = 8.61, 95% CI (2.1-6.9)). The highest levels were found in Seno de Reloncavi (GM = 24.99, 95% CI (15.9-39.2)), Hornopiren (GM = 14.7, 95% CI (10.4-20.8)) and Chiloe norte (GM = 9.75, 95% CI (1-1.9)), and the lowest loads were observed in Puerto Aysen (GM = 1.35, 95% CI (1-1.9)) and Puerto Cisnes (GM = 1.67, 95% CI (1.1-2.6)). Salmo solar and Oncorhynchus mykiss had the highest abundance levels (GM = 6.93, 95% CI (5.7-8.5), and (GM = 5.55, 95% CI (3.6-8.5), respectively). O. kisutch showed lower levels (GM = 1.34, 95% CI (1-1.7)), apparently being more resistant to infestation. Sea lice in farmed salmon are widely distributed in different zones of southern Chile, and are becoming a serious threat to this industry. Prevalence and abundance levels were found to be generally high, decreasing in southern zones