Escaped farmed Atlantic salmon replace the original salmon stock in the River Vosso, western Norway

Aquaculture escapees represent a threat to the genetic integrity of native populations, may spread infectious agents and display ecological interactions with wild fish. DNA-based identification methods are well established for tracing Atlantic salmon escapees back to their farms of origin. However, traditional genetic assignment approaches are not always able to single out the farm of origin in cases where several potential farm sources rear fish from the same genetic line, and display strongly overlapping allele frequencies. We investigated whether an alternative statistical approach, which involves ad hoc identification of sibling relationships, circumvents the challenge of overlapping allele frequencies. We analysed the following samples collected in 2013: (1) 221 farmed escapees captured in several rivers in the Ryfylke region of Norway, (2) 139 farmed escapees captured some 150 km away in an upstream fish migration trap in the River Etne, and (3) 779 farmed salmon sampled from 17 cages on 10 farms in Ryfylke. Siblingship tests increased the precision of identification of escapees back to their farm of origin over genetic assignment and population statistic approaches. Together with other non-genetic data, siblingship tests were also able to connect 2 seemingly independent escape events, demonstrating that some of the salmon escaping from 1 or 2 farms in Ryfylke took approximately 1 mo to migrate 150 km northwards before entering the River Etne. Finally, we demonstrated that the genetic background of the escapees captured in the River Etne during the course of an entire season was represented by the 3 major breeding programs in Norway.

Section: Introductionmentioning

confidence: 99%

Siblingship tests connect two seemingly independent farmed Atlantic salmon escape events

Quintela¹,

Wennevik²,

Sørvik³

et al. 2016

“…Escapees have been observed spawning with wild salmon (Lura & Saegrov 1991, Webb et al 1993, Saegrov et al 1997, but experiments suggest that their spawning success, compared to wild salmon, is much lower (Fleming et al 1996(Fleming et al , 2000. Nevertheless, genetic changes implying successful spawning of farmed salmon have been observed in wild populations in Norway , 2013, Ireland (Crozier 1993, Clifford et al 1998a and Canada (Bourret et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Genetic introgression of farmed salmon in native populations: quantifying the relative influence of population size and frequency of escapees

Heino¹,

Svåsand²,

Wennevik³

et al. 2015

Farmed escapees may threaten the genetic integrity of native salmon populations through interbreeding. However, introgression requires survival until maturation, successful reproduction and successful early development. These traits are often compromised in domesticated animals selected for high performance in captivity. This makes it difficult to predict introgression levels in native populations. A recent study estimated genetic introgression of farmed escaped Atlantic salmon Salmo salar in 20 Norwegian rivers and found highly population-specific levels of introgression. The underlying causes of these patterns, however, remain unknown. Here, using a modeling approach on empirical and demographic data, we demonstrated that a combination of the observed relative frequency of escaped farmed salmon and the average annual angling catch weights for rivers, provides a significantly better predictor for cumulative introgression of farmed salmon in wild populations than the frequency of farmed salmon alone. Our results suggest that the demography of the native population is a significant factor influencing the relative success of farmed salmon in the wild.

“…Escaped salmonids may spread diseases (Johansen et al 2011) and parasites such as salmon lice (Heuch & Mo 2001, Skilbrei 2012). If they enter rivers to spawn (Saegrov et al 1997), they may compromise the genetic integrity of local wild salmon populations (Crozier 1993, Clifford et al 1998, Skaala et al 2006. Young farmed salmon that escape from net pens in the sea as smolts or post-smolts during spring and summer migrate rapidly towards the feeding areas of wild salmon in the open sea, returning after 1 to 3 yr to spawn (Skilbrei 2010a,b).…”

Section: Introductionmentioning

confidence: 99%

Use of fatty acid profiles to monitor the escape history of farmed Atlantic salmon

Skilbrei¹,

Normann²,

Meier³

et al. 2015

Farmed Atlantic salmon can escape from fish farms at various stages of their life, from juveniles to large mature fish. Escapees that enter rivers to spawn pose a threat to the genetic integrity of wild populations. Knowledge about the timing of these escapes can provide important information for wildlife management and the aquaculture industry, enabling them to prevent or mitigate the negative impacts of escapees. Farmed salmon food has a high content of terrestrial lipids; thus, we used fatty acid (FA) profiling to monitor the escape history of farmed salmon. Escaped salmon captured in rivers (n = 251) presented a wide range of FA profiles that we used to classify the fish as (1) early-escaped wild-like fish that were assumed to have escaped at smolt or early post-smolt stage (24%), (2) recently escaped fish with high levels of FAs typically found in commercial salmon food (61%) and (3) intermediate escapees whose FA profiles lay between those 2 groups (15%). To estimate the size at escape of the intermediate escapees, we performed a feeding experiment that monitored the development of FA profiles after a shift in diet from terrestrial to marine lipids. Most intermediate escapees appeared to have escaped when they were < 3 kg, and ranged from 3 to 11 kg when recaptured in rivers. We conclude that FA profiling is a promising tool to monitor escape histories, and that the proportion of post-smolt escapees in this study was high compared to official escape statistics which include very few reports of young fish escaping.