Salmon Parasite Interactions in Linnhe, Lorn and Shuna (SPILLS): final project report

Annex 1 – Summary of the objectives of the work packages

Work package 1: The development of sea lice dispersal modelling for Shuna Sound.

The main objectives of this work package were to:

• simulate the sea lice infection risk to wild salmonids from salmon farms in the Shuna Sound area.
• assess the performance of the models against planktonic sea lice data collected by SAMS at sites in Shuna Sound in 2021 and sea lice count data from wild fish monitoring by AFT (WP 3) in the same year.

Four different hydrodynamic model configurations coupled with three lice dispersal models were used.

The comparison between models and field data aimed to test the performance of the various models and propose areas for improvement.

Preliminary modelling was carried out prior to the field season to develop a field sampling strategy for the monitoring strategy work package (WP 2).

The report for the work package describes in detail the modelling methodologies and results from this work.

Work package 2: Development of a monitoring strategy for infective sea lice stages.

The main objective of this work package was to develop a coherent field sampling strategy for the Shuna Sound area to generate field data for the validation of the models.

The outcomes of the work package are included in the work package 3 report.

Work package 3: Wild fish monitoring and planktonic lice sampling in the coastal water catchment.

The main objective of this work package was to collect field data to help validate and refine sea lice dispersal models developed for the Shuna Sound area.

It involved:

• sampling pelagic sea lice larval distributions in Shuna Sound.
• recording attached sea lice on wild-caught salmonids (primarily juvenile sea trout) in Shuna Sound .

The report on this work package describes in detail the monitoring methodologies and results.

Delivery of the work package developed the skills of Scottish based researchers in sea lice larvae sampling, identification, and enumeration.

Work package 4: Model inter-comparison and validation in the Loch Linnhe and Firth of Lorn study area.

The main objective of this work package was to assess the robustness of the three sea lice dispersal models.

The results of the lice dispersal models for the Loch Linnhe and Firth of Lorn study area were compared against field data collected between 2011 and 2013. The field data consisted of sentinel caged fish counts and planktonic sea lice larvae data.

The sea lice dispersal models were all coupled with the Wider Loch Linnhe System (WLLS) model^[2] configured to give the best fit to observations on temperature, salinity, water elevation and currents for the period concerned.

Sensitivity analysis led to a better understanding of the degree of bio-physical complexity required in the particle tracking models to have confidence in the outputs.

This included developing an ensemble approach using the three particle tracking models. Ensemble approaches are widely used in other modelling fields such as weather forecasting and epidemiology (Probert et al. 2022), where multiple models are used to identify areas of low and high agreement and thus identify where forecasts are likely to be most reliable (high agreement). This is the first ensemble application in sea lice modelling and demonstrates potential for improving communication on model uncertainty and variability.

Project synthesis and reporting

Final detailed work package reports are available for WP 1 (Gillibrand et al., 2023), WP 2 and 3 (Reinardy et al., 2023), and WP 4 (Moriarty et al., 2023).