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'Norwegian' genes found in wild salmon populations in Wester Ross

Posted: Monday 4 March, 2013 @ 16:03:52

Escaped farm salmon, recognised by scale reading, Tournaig August 2008 (Ben Rushbrooke).

[Please also see link to quiz at end of this news item . . . ]


The results of a study to learn more about the occurrence of genes with a Norwegian signature in wild salmon populations in the West of Scotland have just been published.


The study, ‘Genetic Tool Development for Distinguishing Farmed vs. Wild fish in Scotland’ was led by Mark Coulson as part of the RAFTS Managing Interactions with Aquaculture Project [MIAP] and supported by WRFT and other fishery trusts. The report can be downloaded by clicking here or via the link at the end of this item.


The results of this study demonstrate the ability to distinguish between Norwegian and Scottish fish as well as identify individuals of mixed ancestry with high accuracy. 


For samples collected in the West of Scotland, the presence of Norwegian genetic signatures was identified from most sites.  Several cases of putative direct aquaculture escapees were genetically consistent with field-based identification, including samples from the River Balgy (2006 and 2007) and the Tullich burn near Lochcarron (2011).  It was also possible to distinguish individuals of mixed ancestry versus those of either pure Scottish or Norwegian origin. For rivers sampled in Wester Ross, juvenile salmon of mixed ancestry represented the following % of the samples from respective rivers (where n = number of fish in the sample): Gruinard 2005, 15% (n=20); Kerry 2011, 27% (n=33); Torridon 2007, 26% (n=44); Kishorn 2011, 30% (n=27); and Carron [River Lair] 2011, 34% (n=32). 


Concerns about the genetic impacts of escaped and deliberately released farm salmon spawning in the wild in Scotland date from the 1980s. Following a large escape of farmed salmon in Loch Eriboll in Sutherland in 1989, Webb et al 1991 demonstrated spawning by escaped farmed female salmon in the nearby River Polla by identifying the artificial pigment canthaxanthin (used in salmon feed) in salmon eggs taken from redds located in the river. Subsequently canthaxanthin was found in salmon fry in many rivers in the west of Scotland in 1991 (Webb et al 1993). Within the WRFT area, canthaxanthin was found in samples of salmon fry taken from respective rivers, as follows: Gruinard, in 9.6% of sample (n=180); Kerry, 17.8% (n=45); Torridon, 11% (n=144); Elchaig, 1.9% (n=160). This study demonstrated that female farmed salmon had spawned successfully in 1990 (and noted that any contribution to spawning by escaped males would not have been detected).


Between 1990 and 1995, the proportion of ‘reared’ salmon recorded in samples of salmon taken in nets at Red Point near Loch Gairloch varied from 14.5% to 37.5% (Youngson et al 1992). Rod catches of salmon in many Wester Ross rivers fell to their lowest levels at the end of the 1990s by which time recorded escaped farm salmon were in some years 30% more of the rod catch of salmon. For example, of just 13 salmon that were caught in the River Carron in 1999, 8 were recorded as ‘escaped farm fish’.


Since the turn of the century, however, and particularly during the years from 2004 to date, there has been a substantial recovery in rod catches of wild salmon in many rivers in Wester Ross, most notably in the River Carron. The proportion of ‘escaped farm salmon’ in recorded rod catches for most rivers has been much less than 5% in recent years (2008-2012).  That genes with a Norwegian signature were still widespread in samples taken between 2005 & 2011 may indicate that escaped farm salmon were still entering rivers in greater numbers that rod catches suggested, and/or that some of the wild salmon in Wester Ross rivers carried genes of Norwegian origin one or more generations on from when escaped farm fish spawned. The recent occurrence of several unusually large salmon of over 30lb in rod catches from several Wester Ross rivers may also be partly a reflection of Norwegian genes within the Wester Ross wild salmon population.


While the latest MIAP study offers a promising tool for the identification of wild vs. farmed or intermediate individuals in Scotland, the current analysis is limited in its ability to distinguish Scottish strains in aquaculture from wild Scottish fish. For the tool to be developed further, a comprehensive baseline of aquaculture strains and possible addition and/or refinement of the make-up of genetic markers used in this panel is required. 


The study should also be seen as reminder of the importance of minimising the number of escaped farm salmon that spawn in the wild to maintain the health and productivity of wild salmon populations. Anglers should continue to kill any salmon that does not look like a 100% wild fish.


*There may be opportunities for follow up investigations. Anglers interested in learning about whether there are ‘Norwegian genes’ in any salmon they catch should retain a genetic sample. This could be of a few scales (5-10 is ideal) or an air-dried fin clip (of about 5mm2) put into a paper envelope. Currently the cost of analysing a sample is about £25 (this may come down a bit!). For further information, please contact


** Can you recognise an escaped farm salmon?

Jennifer Murphy-O'Connor (a Spanish student at Stirling University) needs your help for her final year project. It's about farmed salmon escapes into Scottish rivers. The recapture of farmed salmon by anglers is reported but there is no knowledge on how accurate the data is. How good are anglers and biologists at telling the difference between farmed and wild salmon?

Jennifer wants to find out and has developed a survey in order to collect her data.

Please follow the link below to participate. It should not take more than 10-15 minutes and she would very much appreciate it! At the end of the quiz there are several photographs of salmon some of which are escaped farm fish, others which are wild: can you tell the difference?


Main report:


Coulson, M. (2013). Report on Genetic Tool Development for Distinguishing Farmed vs. Wild Fish in Scotland. RAFTS Managing Interactions Aquaculture Project 2011/12, February 2013


Some other references:


Butler, J. R. A., Cunningham, P. D., & Starr, K. (2005). The prevalence of escaped farmed salmon, Salmo salar L., in the River Ewe, western Scotland, with notes on their ages, weights and spawning distribution. Fisheries Management and Ecology, 12(2), 149-159.


Webb, J. H., Hay, D. W., Cunningham, P. D., & Youngson, A. F. (1991). The spawning behaviour of escaped farmed and wild adult Atlantic salmon (Salmo salar L.) in a northern Scottish river. Aquaculture, 98(1), 97-110.


Webb, J. H., Youngson, A. F., Thompson, C. E., Hay, D. W., Donaghy, M. J., & McLaren, I. S. (1993). Spawning of escaped farmed Atlantic salmon, Salmo salar L., in western and northern Scottish rivers: egg deposition by females. Aquaculture Research, 24(5), 663-670.


Youngson, A. F., Webb, J. H., MacLean, J. C., and Whyte, B. M. (1997). Frequency of occurrence of reared Atlantic salmon in Scottish salmon fisheries. - ICES Journal of Marine Science. 54: 12161220