title: Space-time modelling of the spread of salmon lice between and within Norwegian marine salmon farms.
abstract: Parasitic salmon lice are potentially harmful to salmonid hosts and farm produced lice pose a threat to wild salmonids. To control salmon lice infections in Norwegian salmonid farming, numbers of lice are regularly counted and lice abundance is reported from all salmonid farms every month. We have developed a stochastic space-time model where monthly lice abundance is modelled simultaneously for all farms. The set of farms is regarded as a network where the degree of contact between farms depends on their seaway distance. The expected lice abundance at each farm is modelled as a function of i) lice abundance in previous months at the same farm, ii) at neighbourhood farms, and iii) other, unspecified sources. In addition, the model includes explanatory variables such as seawater temperature and farm-numbers of fish. The model gives insight into factors that affect salmon lice abundance and contributing sources of infection. New findings in this study were that 66% of the expected salmon lice abundance was attributed to infection within farms, 28% was attributed to infection from neighbourhood farms and 6% to non-specified sources of infection. Furthermore, we present the relative risk of infection between neighbourhood farms as a function of seaway distance, which can be viewed as a between farm transmission kernel for salmon lice. The present modelling framework lays the foundation for development of future scenario simulation tools for examining the spread and abundance of salmon lice on farmed salmonids under different control regimes.
authors.affiliation: Norwegian Computing Center, Oslo, Norway. magne.aldrin@nr.no
authors.forename: Magne
authors.initials: M
authors.lastname: Aldrin
authors.forename: Bård
authors.initials: B
authors.lastname: Storvik
authors.forename: Anja Bråthen
authors.initials: AB
authors.lastname: Kristoffersen
authors.forename: Peder Andreas
authors.initials: PA
authors.lastname: Jansen
mesh_terms: D000465:Algorithms; D000818:Animals; D003198:Computer Simulation; D033342:Copepoda; D062665:Epidemiological Monitoring / Q000662:veterinary*; D005260:Female; D005393:Fish Diseases / Q000453:epidemiology / Q000469:parasitology* / Q000635:transmission; D005398:Fisheries; D008297:Male; D015233:Models, Statistical; D009664:Norway / Q000453:epidemiology; D059208:Parasite Load; D012306:Risk; D012474:Salmon / Q000469:parasitology*; D013029:Space-Time Clustering