Sea Lice Infestation Of Salmonids In Chile Between 2011 And 2017: Use Of Regulatory Data To Describe Characteristics And Identify Risk Factors

Sea lice infestation is a chronic production issue for the majority of salmonid farming industries worldwide. In Chile, Caligus rogercresseyi is the main sea lice species of concern. It is associated with poor welfare, reduced productivity, high treatment and management costs, and increased susceptibility to other diseases within the salmonid aquaculture industry. In response to increasing sea lice abundance, the Servicio Nacional de Pesca y Acuicultura (`Sernapesca', the Chilean National Fisheries and Aquaculture Service) implemented an official national surveillance program for C. rogercresseyi in 2007. Epidemiological studies were conducted in the early stages of this program and described the distribution of and risk factors for lice abundance. Since that time, there have been no further studies. The performance of the program compared to long-term trends in sea lice abundance is unknown. Our study used seven years of industry-wide regulatory data held in Sernapesca's Sistema de Fiscalizacion de la Acuicultura (SIFA) and Informe Ambiental para la Acuicultura (INFA) databases to confirm that previously identified risk factors for lice abundance are still relevant to the Chilean salmonid industry, and to generate hypotheses about previously unidentified risk factors for future investigations. A total of 63,437 sea lice sampling records were analysed within 1397 production cycles for Atlantic salmon, rainbow trout, coho salmon and king salmon. We used information-theoretic approaches for risk factor analysis and post hoc modelling to generate hypotheses for future investigations. Compared to Atlantic salmon, coho salmon were significantly (p < .001) less likely to have higher levels of lice abundance (odds ratio 0.0029, 95% CI 0.0014-0.0062). Lice abundance was significantly (p = .001) lower in the most southern farming region of Chile (odds ratio < 0.001, 95% CI 0-0.0023). The influence of fish density on abundance requires further investigation; if found to be a risk factor, it could be manipulated by industry to improve health. There has been an industry-wide reduction in the abundance of C. rogercresseyi in farmed Chilean salmonids since the implementation of the program and national levels continue to decline. Further hypotheses for investigation include the assessment of whether improved lice control has resulted in reductions of other production diseases within the industry.