Fish farm environmental impacts

Impact of aquaculture on wild fish populations

This project aims to investigate and quantify the risk to wild sea trout populations in Scotland from sea lice originating from salmon farms. It involves scientists from Marine Scotland Science (MSS) Marine and Freshwater Laboratories and builds on the work of the latter, who have monitored the sea trout population in the River Shieldaig for several years.

Since 1999, scientists from MSS Freshwater Laboratory have sampled littoral waters close to river mouths in Loch Shieldaig and Loch Torridon in order to estimate the abundance of infective sea lice. Sampling has been carried out weekly during spring and summer months, with slightly reduced sampling frequency during autumn and winter. With this sampling regime it is hoped to quantify the infective pressures on sea trout post-smolts migrating from the rivers into the marine environment. MSS Freshwater Laboratory scientists have also monitored lice levels on post-smolts returning early to the river Shieldaig.

Modelling Loch Torridon

Complementing this work, scientists at MSS have been sampling for sea lice nauplii and infective stages in the open waters of Loch Torridon. The aim of this work is to establish the abundance of lice in the wider marine environment, both close to and further from local fish farms.

A coupled hydrodynamic and biological model of Loch Torridon, which simulates the water circulation and transport pathways of lice larvae from fish cages is being developed.The models will be used to identify convergence and accumulation points in the loch and to understand the mechanisms, physical and biological, by which the lice are transported to these areas. The ultimate aim of the project is to try and identify cost-effective management strategies to reduce the infestation risk to sea trout without unacceptable impacts on the environment.

Results to date have recently been presented at the ICES Annual Science Conference (Copenhagen 2002) and the Challenger Society UK Marine Science Conference (Plymouth, 2002).