New Marine Directorate paper gives new insights in farm-to-wild genetic introgression in Scotland’s wild Atlantic salmon populations

The Marine Directorate have published a new peer reviewed paper entitled “Spatial variability in farm-to-wild introgression in Scotland’s wild Atlantic salmon populations: Integrating a novel spatial statistical survey design, juvenile sampling by electrofishing and genetic methods”. The paper is published in the ICES Journal of Marine Science and can be accessed here. 

This work builds on a previous, preliminary study which undertook a site-level analysis of introgression pressures in Scotland (available here). Members of FMS contributed to data collection for both papers under the National Electrofishing Programme for Scotland (NEPS). 

The current paper represents a significant scientific advance, integrating a bespoke panel of genetic markers, the NEPS survey design, and novel statistical approaches to characterise introgression at both the national and regional scales. Two new metrics of introgression are reported that describe the spatial extent of impacts (percentage of rivers in the NEPS sample frame where hybrids are present) and the severity of impacts (mean percentage introgression Nationally and within regions), with a new statistical test for the significance of the latter. 

In summary: 

• The paper describes an analysis of farm to wild introgression in Scotland and for the first time quantifies impacts at national and regional scales. 

• The new methods are sensitive in detecting even low levels of regional introgression, with associated significance tests that incorporate sample sizes and the NEPS survey design. 

• Impacts were concentrated in areas of aquaculture production, but were also detected at lower levels across most of Scotland. 

The paper recognises that genetic samples are not available in Scotland prior to aquaculture development, so there is potential that the wild reference baseline used in the study may include some hybrids and admixed individuals. The paper states that as a consequence, the overall effect of introgression will likely be underestimated and the introgression pressures reported in the paper will be driven by contemporary hybridization (likely over a few generations). 

Dr Alan Wells, CEO of Fisheries Management Scotland said; “We welcome the publication of this paper which provides important Scotland-specific information about the extent and impact of farm-to-wild introgression at national and regional scales. This paper once again demonstrates the importance of Scotland meeting its International commitments under the North Atlantic Salmon Conservation Organization (NASCO) including, 100% of farmed fish to be retained in all production facilities.”