The interactions and effects of sea lice on wild salmon

Salmon smolt movement map

To understand the risk of interaction between farm origin sea lice and wild salmon smolts, information must be obtained on the distribution of both. On going work to determine salmon migration patterns is described below.

Tracking acoustically tagged wild salmon smolts

Tracking work will be performed on migrating smolts.  Wild salmon smolts will be trapped and acoustically tagged as they migrate down rivers.  Acoustic receivers will be deployed in the marine environment to detect the tagged salmon and determine their migration routes.  Initially it is planned to deploy curtains of receivers (i.e. regularly spaced in open water between two defined points) on the west coast near the Isle of Mull and the mainland.  These will be used to determine the migration routes of locally tagged salmon, to see how they travel around the Isle of Mull, whether travelling northward close to the coast or if they migrate straight to open waters.  As the project develops, tagging experiments will continue in order to build up a picture of migration routes, and migration times, of salmon from different geographical areas.  It is planned to collaborate where possible on other national and international tagging projects e.g Ocean Tracking Network.

The red lines on the map to the right indicate example areas where curtains of acoustic receivers could be deployed around the Isle of Mull to detect acoustically tagged migrating wild salmon smolts.  Deployment will depend on local bathymetry and the usage of different areas – e.g. high traffic throughput etc. Feasibility studies are ongoing.

Modelling wild salmon smolt movements

In addition to collecting data on smolt movement in the field, an attempt to predict smolt migration routes using models will also be made.  The models will consist of a hydrodynamic model, representing water movement, coupled with a particle tracking model.  The particles within the model will be given biological and behavioural properties representing what is currently known on salmon swimming behaviour in the marine environment, e.g. speed and depth. Behaviours such as seeking currents in which to swim, or swimming against water current, can be included as more information on swimming behaviour becomes available.

Some of this information will be obtained from the data generated by monitoring of acoustically tagged fish. Having information on water movements and knowing how “salmon particles” behave in relation to these movements should allow salmon distribution and time to migrate to be simulated. By using the modelled hydrodynamics of different areas, salmon migration patterns around Scotland may then be predicted.