Modeling parasite dynamics on farmed salmon for precautionary conservation management of wild salmon

Conservation management of wild fish may include fish health management in sympatric populations of domesticated fish in aquaculture. We developed a mathematical model for the population dynamics of parasitic sea lice (Lepeophtheirus salmonis) on domesticated populations of Atlantic salmon (Salmo salar) in the Broughton Archipelago region of British Columbia. The model was fit to a seven-year dataset of monthly sea louse counts on farms in the area to estimate population growth rates in relation to abiotic factors (temperature and salinity), local host density (measured as cohort surface area), and the use of a parasiticide, emamectin benzoate, on farms. We then used the model to evaluate management scenarios in relation to policy guidelines that seek to keep motile louse abundance below an average three per farmed salmon during the March-June juvenile wild Pacific salmon (Oncorhynchus spp.) migration. Abiotic factors mediated the duration of effectiveness of parasiticide treatments, and results suggest treatment of farmed salmon conducted in January or early February minimized average louse abundance per farmed salmon during the juvenile wild salmon migration. Adapting the management of parasites on farmed salmon according to migrations of wild salmon may therefore provide a precautionary approach to conserving wild salmon populations in salmon farming regions

The relevance of larval biology on spatiotemporal patterns of pathogen connectivity among open-marine salmon farms

Warming waters are changing marine pathogen dispersal patterns and infectivity worldwide. Coupled biological-physical modelling has been used in many systems to determine the connectivity of meta-populations via infectious disease particles. Here we model the connectivity of sea lice larvae (Lepeophtheirus salmonis) among salmon farms in the Broughton Archipelago, British Columbia, Canada, using a coupled biological-physical model. The physical model simulated pathogen dispersal, while the biological component influenced the survival and developmental rates of the sea lice. Model results predicted high temporal variability in connectivity strength among farms; an emergent effect from the interacting parts of the simulation (dispersion vs. survival/development). Drivers of temporal variability were disentangled using generalized additive modeling, which revealed the variability was most strongly impacted by the spring freshet, which can act as a natural aid for sea lice control in the Broughton Archipelago. Our results suggest that farm management strategies can benefit by taking into account short-term spikes in regional pathogen connectivity among farms. Additionally, future scenarios of a warming climate with reduced snowpack can make sea lice control more challenging

Seabed attributes and meiofaunal abundance associated with a hydrodynamic gradient in Baynes Sound, British Columbia, Canada

Sutherland, T.F.; Garcia-Hoyos, L.M.; Poon, P.; Krassovski, M.V.; Foreman, M.G.G.; Martin, A.J., and Amos, C.L., 2018. Seabed attributes and meiofaunal abundance associated with a hydrodynamic gradient in Baynes Sound, British Columbia, Canada. The distribution of seabed geotechnical, biochemical, and meiofauna attributes was examined in Baynes Sound, British Columbia, between 2009 and 2014. Among attributes measured were sediment porosity, organic carbon and nitrogen, and trace element concentrations (e.g., zinc, copper), which increased with increasing sediment fines content toward the head of the Sound. A ternary plot (sand-silt-clay percentages) revealed a constant clay/silt ratio across a range of sand proportions with textures ranging from well-sorted sand at the high-energy SE entrance to silt-dominated mud in the depositional basin. These sediment textures were related to modeled maximum velocity values within 5 m of the seabed (Umax,5), with highest values (restricted entrance) and lowest values (deep basin) representing sand depositional and mud depositional facies. Sediment porewater sulfide fell into an oxic category (0-700 μM), exhibiting a lack of variation and organic enrichment within the Sound. The first principal component analysis (PCA) factor described the alignment between fine sediments, organics, Cu and Zn, and meiofauna attributes and accounted for 49% of the total variance. The second PCA factor (19% of total variance) described the relationship between Umax,5 and sediment grain size fractions &gt;0.5 mm and an indirect association with water depth and fine sand (0.105-0.250 mm). Meiofauna were associated with a medium sand fraction (0.25 mm) characterized by low-porosity and low-organic sand loam textures. Although the range in abundance was relatively greater for nematodes, harpacticoid copepods revealed a stronger response to changes in sediment geotechnical and organic attributes, suggesting these taxa may be used to describe seabed variations or potential perturbations.</p