Salmon Parasite In Linnhe, Lorn, and Shuna (SPILLS)

The SPILLS Project developed and compared different models designed to predict distribution of sea lice in Scottish sea lochs. Visualising the model outputs is very much limited using simple maps because of the variation (patchiness) of dispersing lice across both time and space. We have generated some video images that show how lice are predicted to disperse.

The animated lice video shows the modelled dispersion of sea lice larvae from 8 active salmon farms in Shuna Sound, Argyll, west Scotland. The time period of the animation is 1st April - 30th October 2021. The video is divided into three sections: the first (“All Lice”) shows total lice densities (lice m^-3) calculated from both lice stages, nauplii and copepodid; the second section shows predicted densities of the infective copepodid stage only (“Copepodids”); and the final section show predicted densities of the non-infective nauplius stage (“Nauplii”). Densities were calculated in a near-surface layer 2 m deep (0 – 2 m), where lice are predominantly found. The simulation was produced using outputs from the UnPTRACK lice dispersal model (Gillibrand et al., 2023), using flow fields from the WestCOMS hydrodynamic model (Aleynik et al., 2016).

The lice dispersal simulation incorporated temperature-dependent maturation and hourly mortality, and behaviours including phototactic (movement towards or away from a light stimulus) vertical swimming (diel migration) and low-salinity avoidance. Sea lice development into infective copepodids is dependent on water temperature: following release from adult female lice on farms, the larvae spend a few days in the water as nauplii before moulting into the infective copepodid stage. The animations show the streams of nauplii from the farms, with the wider distributions of copepodids following later.

The animations reveal the high spatial and temporal variability of sea lice larvae distributions. By gathering at the surface during daylight hours, the larvae are subject to tidal and wind-driven currents, and may accumulate in localised high densities at fronts and other areas of convergence. The patches of lice larvae are then advected around the coastal zone by wind and tide. The localised high densities of lice are transient, making sampling of planktonic lice very challenging.

References

Aleynik D, Dale AC, Porter M, Davidson K (2016). A high resolution hydrodynamic model system suitable for novel harmful algal bloom modelling in areas of complex coastline and topography. Harmful Algae 53:102–117

Gillibrand, PA. Moriarty M., Brain S. (2023). Final Report: Sea Lice Dispersal Modelling in the Sound of Shuna. SPILLS project.

SPILLS Team

The SPILLS project involved collaboration between farm operators (Mowi Scotland Ltd., Kames Fish Farming Ltd.), a number of local fisheries trusts and organizations (Argyll Fisheries Trust, Argyll District Salmon Fishery Board, Fisheries Management Scotland), an academic research organization (The Scottish Association for Marine Science (SAMS)) and Scottish Government (Marine Scotland) . Staff changes during the project led to participation from Scottish Sea Farms Ltd. in an advisory capacity.