Interactions between domesticated escapees and wild conspecifics represent a threat to the genetic integrity and fitness of native populations. For Atlantic salmon, the recurrent presence of large numbers of domesticated escapees in the wild makes it necessary to better understand their impacts on native populations. We planted 254,400 eggs from 75 families of domesticated, F1‐hybrid, and wild salmon in a river containing up‐ and downstream traps. Additionally, 41,630 hatchery smolts of the same pedigrees were released into the river. Over 8 years, 6,669 out‐migrating smolts and 356 returning adults were recaptured and identified to their families of origin with DNA. In comparison with wild salmon, domesticated fish had substantially lower egg to smolt survival (1.8% vs. 3.8% across cohorts), they migrated earlier in the year (11.8 days earlier across years), but they only displayed marginally larger smolt sizes and marginally lower smolt ages. Upon return to freshwater, domesticated salmon were substantially larger at age than wild salmon (2.4 vs. 2.0, 4.8 vs. 3.2, and 8.5 vs. 5.6 kg across sexes for 1, 2, and 3 sea‐winter fish) and displayed substantially lower released smolt to adult survival (0.41% vs. 0.94% across releases). Overall, egg‐to‐returning adult survival ratios were 1:0.76:0.30 and 1:0.44:0.21 for wild:F1‐hybrid:domesticated salmon, respectively, using two different types of data. This study represents the most updated and extensive analysis of domesticated, hybrid, and wild salmon in the wild and provides the first documentation of a clear genetic difference in the timing of smolt migration—an adaptive trait presumed to be linked with optimal timing of entry to seawater. We conclude that spawning and hybridization of domesticated escapees can lead to (i) reduced wild smolt output and therefore wild adult abundance, through resource competition in freshwater, (ii) reduced total adult abundance due to freshwater competition and reduced marine survival of domesticated salmon, and (iii) maladaptive changes in phenotypic traits.

The global increase in the production of domestic farmed fish in open net pens has created concerns about the resilience of wild populations owing to shifts in host-parasite systems in coastal ecosystems. However, little is known about the effects of increased parasite abundance on life-history traits in wild fish populations. Here, we report the results of two separate studies in which 379 779 hatchery-reared Atlantic salmon smolts were treated (or not) against salmon lice, marked and released. Adults were later recaptured, and we specifically tested whether the age distribution of the returning spawners was affected by the treatment. The estimates of parasite-induced mortality were 31.9% and 0.6% in the River Vosso and River Dale stock experiments, respectively. Age of returning salmon was on average higher in treated versus untreated fish. The percentages of fish returning after one winter at sea were 37.5% and 29.9% for the treated and untreated groups, respectively. We conclude that salmon lice increase the age of returning salmon, either by affecting their age at maturity or by disproportionately increasing mortality in fish that mature early.

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.

There is an error in the abstract of this paper: 'Age of returning salmon was on average higher in treated versus untreated fish'. Should instead read: 'Age of returning salmon was on average higher in untreated versus treated fish'. There is also an error in the first paragraph of the Results section; the last two sentences of the paragraph should read as follows: 'In the Vosso experiment, more treated fish than untreated fish were recaptured every year except from releases in 2009 (table 1). The number of recaptures from releases in 2009 amounted to 38.3% of all of the recaptures during the study period, which may be partly explained by the high marine survival rate throughout the northeast Atlantic that year [14]'.

The effect of nocturnal and diurnal releases on survival and migration of wild and hatchery‐reared Atlantic salmon, Salmo salar, L., smolts (n = 82) was investigated by releasing acoustically tagged smolts at the lower end of the River Vosso, Norway. Hatchery smolts was registered in the estuary within hours of their release, whereas wild smolts migrated over a prolonged period. The time of estuary exit was affected by river discharge but not by time of release. Progression rates were slow through the estuary (0.25 BL/s ± 0.18 SD) and fast through the fjord (1.80 BL/s ± 0.69 SD), and they were not affected by the time of release or origin. Survival to the fjord was low (0%–15%). Survival was not affected by body length but was lower for wild smolts than for hatchery smolts, and survival of the former was lower when the fish were released in daylight.