Understanding how pathogenic organisms spread in the environment is crucial for the management of disease, yet knowledge of propagule dispersal and transmission in aquatic environments is limited. We conducted empirical studies using the aquatic virus, infectious hematopoietic necrosis virus (IHNV), to quantify infectious dose, shedding capacity, and virus destruction rates in order to better understand the transmission of IHN virus among Atlantic salmon marine net-pen aquaculture. Transmission of virus and subsequent mortality in Atlantic salmon post-smolts was initiated with as low as 10 plaque forming units (pfu) ml−1. Virus shedding from IHNV infected Atlantic salmon was detected before the onset of visible signs of disease with peak shed rates averaging 3.2×107 pfu fish−1 hour−1 one to two days prior to mortality. Once shed into the marine environment, the abundance of free IHNV is modulated by sunlight (UV A and B) and the growth of natural biota present in the seawater. Virus decayed very slowly in sterilized seawater while rates as high as k =  4.37 d−1 were observed in natural seawater. Decay rates were further accelerated when exposed to sunlight with virus infectivity reduced by six orders of magnitude within 3 hours of full sunlight exposure. Coupling the IHNV transmission parameter estimates determined here with physical water circulation models, will increase the understanding of IHNV dispersal and provide accurate geospatial predictions of risk for IHNV transmission from marine salmon sites.

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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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