Norges Forskningsrad (Grant Numbers 200510 and 216105); Japan Society for the Promotion of Science (KAKENHI Grant Number JP262921020); Det Frie Forskningsrad (Natural Sciences Grant Number: 1323-00158A); Department of Agriculture, Food and the Marine (Beaufort Marine Research Award)

https://onlinelibrary.wiley.com/doi/pdf/10.1111/faf.12214

Half a century of genetic interaction between farmed and wild Atlantic salmon: Status of knowledge and unanswered questions

Hindar, K., Fleming, I. A., McGinnity, P., and Diserud, O. 2006. Genetic and ecological effects of salmon farming on wild salmon: modelling from experimental results. � ICES Journal of Marine Science, 63: 1234e1247. Cultured salmonids are released or escape into the wild in large numbers and may make up significant proportions of wild salmonid populations in fresh- and saltwater, causing considerable concern for the fitness and productivity of these populations. This paper focuses on the effects of escaped farmed Atlantic salmon (Salmo salar) on wild salmon. Farmed salmon have been under artificial selection for growth and other economically important traits for 30 years and are genetically different in their origin at the molecular and quantitative genetic levels. Escaped farmed salmon spawn in the wild with limited success. Their offspring outgrow those of wild origin but suffer higher mortality. Whole-river experiments in Ireland and Norway have shown that the lifetime success of farmed salmon is reduced relative to wild salmon. Based on data from these experiments, we model the future of wild salmon populations experiencing invasions of escaped farmed salmon. Simulations with a fixed intrusion rate of 20% escaped farmed salmon at spawning suggest that substantial changes take place in wild salmon populations within ten salmon generations (w40 years). Low-invasion scenarios suggest that farmed offspring are unlikely to become established in the population, whereas high-invasion scenarios suggest that populations are eventually mixtures of hybrid and farmed descendants. Recovery of the wild population is not likely under all circumstances, even after many decades without further intrusion. Managers of wild salmon will have difficulty in obtaining broodstock of the original wild population after a few generations of high intrusion. We conclude that further measures to reduce escapes of farmed salmon and their spawning in wild populations are urgently needed.

Genetic and ecological effects of salmon farming on wild salmon: modelling from experimental results

Electrophoretic studies of proteins remain a primary source of insight into genetic diversity in many species including the Atlantic salmon Salmo salar, one of the most culturally and economically important fish species of the North Atlantic region. Since 1966, >350 scientific papers on protein variation have been published encompassing 25 000+ salmon from over 400 locations in >200 river systems across the species' distribution. Variation has been detected at 30% of the 110 protein loci screened, though most studies examine <40. The method has been applied largely to the investigation of population structure and differentiation, but work has also led to the systematic revision of the genus Salmo and remains the primary source of insight into hybridization in the wild with brown trout Salmo trutta. Spatial patterns of differentiation show temporal stability, both within and among river systems, and strongly support structuring of the species into river and tributary specific populations and the designation of European and North American populations as distinct sub-species. They also show widespread regional differentiation within both continents, beyond the marked subcontinental differences between Baltic Sea and Atlantic Ocean populations in Europe. Most of the differentiation probably reflects gene flow and founder events associated with colonization following the retreat of the glaciers from much of the species' modern range. However, variation at MEP-2* shows strong correlations with environmental temperature, both within and among rivers, and associations with phenotypic performance. This suggests selection is acting on the locus and provides compelling evidence for the local adaptation of populations. Protein studies have led to more population centred management of the species and have been exploited in the discrimination of regional stocks in mixed stock analysis in high seas fisheries, particularly in the Baltic Sea, and as markers for the assessment of stocking success. They have also advanced insight into how the genetic character of populations can be changed in cultivation and the potential impact of salmon aquaculture and stocking on wild populations. The method has been largely superseded by DNA based analyses, but the results remain highly relevant to Atlantic salmon management and conservation and are an irreplaceable data set for studying genetic stability of populations over time.

Population structure in the Atlantic salmon: insights from 40 years of research into genetic protein variation

– Stable isotopes of carbon and nitrogen (δ13C and δ15N) were examined in wild and aquaculture origin Atlantic salmon, Salmo salar, to evaluate their utility to identify escaped farmed fish. Samples of muscle tissue obtained from wild Conne River, Newfoundland, salmon were significantly more enriched in nitrogen (δ15N: mean = 12.75; SD ± 0.38‰) but depleted in lipid corrected carbon (δ13C′: mean = −20.51; SD ± 0.23‰) by comparison with aquaculture specimens obtained from Bay d'Espoir, Newfoundland (δ15N = 10.96 ± 0.19‰; δ13C′ = −19.25 ± 0.17‰) resulting in a complete separation of the two groups. Aquaculture specimens differed in δ13C′ from analyses of commercial salmon diet by 0.24‰, within the enrichment range associated with trophic transfers, while the δ15N values in salmon muscle were enriched by 5.01‰. Although differences occurred in direct comparisons of white muscle and adipose tissue (N = 49), the average δ13C′ and δ15N signatures varied in absolute amounts by only 0.5‰, supporting the use of adipose tissue as a nonlethal means to determine isotopic signatures of Atlantic salmon.

Resumen

1. Examinamos isotopos estables de carbono y nitrogeno (δ13C y δ15N) de ejemplares de Salmo salar procedentes de una poblacion natural y de acuicultura para evaluar su utilizacion en la identificacion de individuos que se escapan de granjas.



2. Muestreos de tejido muscular obtenidos de ejemplares del Rio Conne (Terranova, Canada) mostraron estar significativamente enriquecidos en nitrogeno (δ15N: media = 12.75; SD ± 0.380/00) pero no contuvieron carbono lipidico (δ13C′: media = −20.51; SD ± 0.230/00) en comparacion con individuos de acuicultura procedentes de Bay d'Espoir, Terranova (δ15N = 10.96 ± 0.19; δ13C′ = −19.25 ± 0.170/00), resultando en una separacion completa de ambos grupos de ejemplares.



3. Los ejemplares de acuicultura difirieron en δ13C′ de analisis de dietas comerciales para salmon en un 0.240/00, dentro del rango de enriquecimiento asociado a trasferencias troficas mientras que los valores de δ15N en musculo aparecieron enriquecidos en un 5.010/00.



4. Aunque aparecieron diferencias en comparaciones directas de musculo blanco y tejido adiposo (N = 49), el promedio de senales de δ13C y δ15N vario en cantidades absolutas por solo 0.50/00, hecho que apoya el uso de tejido adiposo como un medio no letal para determinar senales isotopicas en Salmo salar.

Use of stable isotopes to distinguish farmed from wild Atlantic salmon, Salmo salar

In Norway, there have been restrictions on salmon farming in several fjords to reduce the potential negative impact on important stocks of wild Atlantic salmon. Little is known about the incidence of escaped farmed salmon in fisheries and broodstocks relative to the extent of fish farming in nearby areas. In this study, we analysed data on the incidence of escaped farmed Atlantic salmon in angling catches and broodstock fisheries in rivers for a 16-year period (1989e2004). These data were weighted using official catch statistics and combined at the county level, and the incidence of escapees was correlated with both the stock of farmed salmon in net pens and the reported number of escapees in different Norwegian counties. Our results indicate a significant positive correlation between the incidence of escaped farmed salmon in the rivers at the county level and the intensity of salmon farming, measured as the number of farmed salmon in net pens, suggesting that protection areas may reduce the impact of escapees in salmon populations nearby.

/pdf/relationships-between-the-frequency-of-farmed-atlantic-4ul9jimmr5.pdf

Relationships between the frequency of farmed Atlantic salmon, Salmo salar L., in wild salmon populations and fish farming activity in Norway, 1989–2004

External morphological characteristics were used to identify escaped farmed Atlantic salmon, Salmo salar L., in a coastal salmon fishery in County Antrim, Northern Ireland during four fishing seasons and at an adjacent freshwater location (R. Bush) during a 5-year period. Out of a total of 36 326 adult salmon examined in the fishery, 883 (2.4%) were identified as having escaped from sea cages. Annual average values ranged from 0.26% to 4.04% of the fish caught. Occurrence of escapees entering an adult trap in fresh water averaged 0.88%, with a range of 0.13–2.62%, depending on year. No correlation between presence in the marine fishery and in fresh water was evident, the latter year-round figures probably being more indicative of presence of escapees in spawning stocks. Entry to fresh water was significantly later on average for escaped farmed salmon, compared with wild salmon.

Crozier

Papers

Incidence of escaped farmed salmon, Salmo salar L., in commercial salmon catches and fresh water in Northern Ireland