Riparian Owners of the River Carron spearheading scientific research into management of wild Atlantic salmon.

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A study has been published today by the River Carron Conservation Association (RCCA), representing the Riparian owners of the Carron River. The study, carried out by the Rivers & Lochs Institute (RLI) of Inverness College, University of the Highlands and Islands (UHI), points to the positive contribution that the use of carefully-managed native Atlantic salmon broodstock programmes could make in mitigating the growing human impact on populations, such as climate-change affected spate flooding. It also indicates that this can be achieved while maintaining the genetic diversity of declining wild populations.

Atlantic Salmon catches on the Carron declined precipitately from the mid-80’s to a point at which the population was considered at risk of extinction. A complete catch-and-release policy and a supplementary stocking programme was initiated, starting in 1995, supplemented annually by returning adults from the Carron rod catch. The salmon population has since revived and catches are now higher than those at the previous peak in the 80s & 90s. The continued spate flooding of the Carron and the low numbers returning to adjacent west coast rivers, raises the question of whether wild salmon would have persisted in or naturally re-colonized the Carron without this intervention.

While it is accepted that supplementary stocking programmes can have negative effects on wild salmon, these do not necessarily outweigh the potential positive effects for populations threatened with extinction. The balance of threats and benefits is likely to be population specific and depend on programme management. To date, relatively few supplementary stocking programmes have been properly evaluated. Using a method known as ‘Parentage-based tagging’ (PBT), which allows stocked fish to be effectively discriminated from wild-spawned salmon, the RCCA plan to follow the fate of stocked vs. wild spawned fish over multiple years and life history stages.

The RLI previously partnered with the Carron Riparian owners in an evaluation programme (Phase I) using monitoring data collected up to 2014 to assess the reasons for the population decline and the subsequent rebound. Results showed a strong correlation between the number of juveniles stocked and the number of adults returning to the river. Phase II seeks to use information from Phase I to investigate whether the observed increase in adult returns is the direct result of the stocking programme, whether genetic composition of the population has been altered and which stocking strategies can be recommended in terms of population abundance and genetic health. The ultimate aim is to integrate the results with other information sources to develop an adaptive framework for future management of the River Carron that conserves its native wild Atlantic salmon population for the long term, while maintaining the security and integrity of the wild fishery.

The study released today (Phase IIa) represents an evaluation of how stocked fish from a single year of broodstock crossings (2014) have contributed to the returning adult catch. The report’s authors at UHI state that “fish stocked in the Carron clearly survive to adulthood and make a substantial contribution to the fishery. The results also show no major differences in measures of genetic diversity and inbreeding”.