Finite volume ocean circulation and particle tracking models are used to simulate water-borne transmission of infectious hematopoietic necrosis virus (IHNV) among Atlantic salmon (Salmo salar) farms in the Discovery Islands region of British Columbia, Canada. Historical simulations for April and July 2010 are carried out to demonstrate the seasonal impact of river discharge, wind, ultra-violet (UV) radiation, and heat flux conditions on near-surface currents, viral dispersion and survival. Numerical particles released from infected farm fish in accordance with IHNV shedding rates estimated through laboratory experiments are dispersed by model oceanic flows. Viral particles are inactivated by ambient UV radiation levels and by the natural microbial community at rates derived through laboratory studies. Viral concentration maps showing temporal and spatial changes are produced and combined with lab-determined minimum infectious dosages to estimate the infective connectivity among farms. Results demonstrate that neighbouring naïve farms can become exposed to IHNV via water-borne transport from an IHNV diseased farm, with a higher risk in April than July, and that many events in the sequence of farm outbreaks in 2001-2002 are consistent with higher risks in our farm connectivity matrix. Applications to other diseases, transfers between farmed and wild fish, and the effect of vaccinations are also discussed.

A finite volume, ocean circulation model was applied to the Discovery Islands region of British Columbia and used to simulate the three-dimensional velocity, temperature and salinity fields required by a companion biological transport model. The circulation model was initialized with a combination of climatological data and recent temperature and salinity observations, and forced with i) winds measured at seventeen weather stations, ii) the discharges from twelve rivers, and iii) five tidal constituents. A simulation for the period 1 April to 28 April 2010 was evaluated using simultaneous observations from three current meter moorings and the harmonics computed from historical measurements at twenty-four tide gauges. Though the model tidal elevations were shown to be in excellent agreement with the observations, profiles of model tidal speed versus depth generally did not capture observed vertical variations as well. Mean and low-pass filtered flow fields, though reasonably accurate near the surface, were also found to deteriorate farther down the water column. However, near-surface, model current harmonics were shown to be in reasonable agreement with those used to produce annual predictions at five sites in the Canadian Tide and Current Tables. Though the winds were not found to be a significant contributor to mean flow fields over the simulation period, tidal rectification was. Numerous residual and transient eddies that may lead to retentive regions in subsequent Lagrangian studies were predicted by the model. Future work and improvements to overcome model deficiencies are briefly outlined.RÉSUMÉ [Traduit par la rédaction] Nous avons appliqué un modèle de volume fini des courants océaniques à la région des îles Discovery en Colombie-Britannique et nous nous en sommes servis pour simuler les champs de la vélocité, de la température et de la salinité en trois dimensions, exigés par un modèle de transport biologique d'accompagnement. Le modèle de circulation a été initialisé au moyen d'une combinaison de données climatologiques et d'observations récentes liées à la température et à la salinité et il a été forcé avec les vents mesurés à 17 stations météorologiques, le débit de 12 cours d'eau et cinq composantes de marées. Nous avons évalué une simulation pour la période allant du 1 er avril au 28 avril 2010 à l'aide d'observations effectuées simultanément par trois courantomètres, et les harmoniques ont été calculées à partir des mesures effectuées dans le passé à 24 marégraphes. Bien que les hauteurs de la marée établies par le modèle concordent parfaitement avec les observations, les profils de la vitesse de la marée dans le modèle en fonction de la profondeur ne réflétaient généralement pas aussi bien les variations verticales observées. De plus, nous avons constaté que les champs de courant moyens et auxquels on avait appliqué un filtre passe-bas perdaient en précision plus bas dans la colonne d'eau bien que leur valeur près de la surface soit raisonnablement exacte. Cependant, les harmoniques des c...

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