Scottish Marine and Freshwater Science Vol 1 No 14

The Scottish Government has ambitious targets for renewable energy production, to which offshore renewables could make a substantial contribution. However, the new marine energy industries must develop on a sustainable basis, ensuring that environmental impacts are assessed, and if necessary, minimised through appropriate mitigation. The likelihood of any impacts on Atlantic salmon, sea trout or European eels will depend on interactions between (1) migratory routes and behaviour (2) the distribution of offshore developments (3) the technologies deployed and (4) the dynamics of the relevant fish populations. This report summarises available information on the migratory routes and behaviour of salmon, sea trout and eels in a Scottish context.

Broad scale patterns of migration are identified for adult Atlantic salmon, although the resolution of available data is unlikely to be sufficient to inform site specific risk assessment. Less extensive information is available on juvenile migratory routes and no information is available on juvenile migration from important east coast rivers. The limited information available on sea trout migration suggests predominantly inshore and local use of the marine environment, although wider ranging migrations have been observed from some rivers. No specific migratory routes can be discerned for either juvenile or adult sea trout. European eels in Scotland are part of a single European population for which there is considerable uncertainty regarding migratory routes. The limited evidence which is available suggests that eels from a number of European countries may migrate through Scottish waters. For all the species considered, there is only very limited information on behaviour and swimming depths. Most of this information has been generated outwith Scotland and it is uncertain whether it can be reliably transferred to the Scottish context given differences in the life stages observed and local geography.

Significant knowledge gaps remain for all three species considered in this review. These knowledge gaps should be considered as part of an overall assessment of research needs in relation to offshore renewable developments and diadromous fish.