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Conservation Limits

Salmon are an important species for Scotland in terms off both economics and conservation. To make informed decisions on current and future management, it is necessary to understand the health of the salmon stocks at various spatial scales and consequently the levels of mortality (e.g. fisheries, losses to marine renewable energy, predation) that can tolerated for a given set of management objectives. For salmon this is often achieved through the use of conservation limits.

Previous projects have developed conservation limits based on data collected from the River North Esk. However, applying such limits throughout Scotland assumes that all Scottish rivers behave in the same way as the North Esk. Due to the range of habitats found in rivers throughout Scotland, such an assumption seems to be unreasonable and likely to give spurious results. For this reason, Scottish Government has thus far resisted pressure to produce and use conservation limits. Although a direct transfer from the North Esk is unreasonable, some appropriate method for transferring the data needed to generate a conservation limits foir each rivers needs to be developed.

Currently conservation limits tend to apply to the whole stock of salmon within a river. However, Scotland has noted spring runs of salmon that are not found elsewhere in Europe, enabling Scotland to have economically important spring fisheries. In addition to their economic value, spring fish are important components of the stocks within a number of SAC rivers. These spring sub-stocks appear to be doing less well than salmon returning to rivers later in the year. The use of a single river conservation limit, as suggested by NASCO, could suggest an overall level of harvest that is deterimental to spring fish stocks. Methods are therefore required for producing conservation limits at a sub-river catchment level to facilitate effective management of spring fish, which tend to rear in specific geograpohic regions.

In 2014, a five year research project will commence aimed at exploring a number of different approaches for producing conservation limits. Current data (from rod catches and a limited number of counters) will be explored to assess how conservation limits can be produced in the short term. In addition potential longer term options will be examined. The first option involves the use of electrofishing data to determine the carrying capacity of different habitat types. A second option is to examine the utility of data collected from additional counters in producing conservation limits. Finally the use of genetics to identify areas of rivers which produce spring fish will be examined. The results of this work will be used to inform management of salmon at a national level.