Norway is the world’s largest producer of farmed Atlantic salmon and is home to ∼400 rivers containing wild salmon populations. Farmed escapees, a reoccurring challenge of all cage-based marine aquaculture, pose a threat to the genetic integrity, productivity, and evolutionary trajectories of wild populations. Escapees have been monitored in Norwegian rivers since 1989, and, a second-generation programme was established in 2014. The new programme includes data from summer angling, autumn angling, broodstock sampling, and snorkelling surveys in >200 rivers, and >25 000 scale samples are analysed annually. In 2014–2017, escapees were observed in two-thirds of rivers surveyed each year, and between 15 and 30 of the rivers had >10% recorded escapees annually. In the period 1989–2017, a reduction in the proportion of escapees in rivers was observed, despite a >6-fold increase in aquaculture production. This reflected improved escape prevention, and possibly changes in production methods that influence post-escape behaviour. On average, populations estimated to experience the greatest genetic introgression from farmed salmon up to 2014 also had the largest proportions of escapees in 2014–2017. Thus, populations already most affected are those at greatest risk of further impacts. These data feed into the annual risk-assessment of Norwegian aquaculture and form the basis for directing mitigation efforts.

Understanding how demographic processes influence mating systems is important to decode ecological influences on sexual selection in nature. We manipulated sex ratio and density in experimental populations of the sex-role reversed pipefish Syngnathus typhle. We quantified sexual selection using the Bateman gradient (β ss ), the opportunity for selection (I), and sexual selection (I s ), and the maximum standardized sexual selection differential (s max ). We also measured selection on body length using standardized selection differentials (s ) and mating differentials (m ), and tested whether the observed I and I s differ from values obtained by simulating random mating. We found that I, I s , and s max , but not β ss , were higher for females under female than male bias and the opposite for males, but density did not affect these measures. However, higher density decreased sexual selection (m but not s ) on female length, but selection on body length was not affected by sex ratio. Finally, I s but not I was higher than expected from random mating, and only for females under female bias. This study demonstrates that both sex ratio and density affect sexual selection and that disentangling interrelated demographic processes is essential to a more complete understanding of mating behavior and the evolution of mating systems. K E Y W O R D S :Bateman's principles, intrasexual competition, mating system, operational sex ratio, Syngnathus typhle.

We report on the data from an extensive monitoring programme for the occurrence of escaped farmed Atlantic salmon (Salmo salar) in Norwegian rivers for 25 years. This monitoring started as a 3-year research programme in 1989 and was followed by management authorities to cover the proportional occurrence of escaped farmed Atlantic salmon in rivers during summer and autumn before spawning. Farmed salmon were distinguished from wild salmon by growth patterns in the scales. More than 362 000 salmon were registered by this programme. Here we present the historical data on escaped farmed salmon in catches 1989–2013 and a methodology for calculating averages across summer and autumn capture in rivers, across years and in regions, using weighted and unweighted observations. Catches of escaped farmed salmon show large spatial and temporal variation, with the early 1990s and early 2000s being periods of large influxes of farmed fish. Western Norway and parts of middle and northern Norway have shown particularly high incidences of escaped farmed fish. Because escaped farmed Atlantic salmon are competing and interbreeding with wild Atlantic salmon, as well as increasing the spread of disease-causing agents, they have become a major force driving the abundance and evolution of Atlantic salmon.

We compared the within-river movements and distribution of wild and escaped farmed Atlantic salmon Salmo salar before and during spawning in the Namsen river system of Central Norway. A total of 74 wild and 43 escaped farmed salmon were captured at sea, tagged with radio transmitters and released. Based on our examinations, most, if not all salmon (farmed and wild) entering the River Namsen were sexually mature. Farmed salmon entering the river system had a higher probability than wild individuals of reaching the migration barrier in the upper part of the river, 70 km from the sea. During the pre-spawning and spawning periods, farmed salmon were located mainly in the upper parts (50 to 70 km from the sea), whereas wild salmon were evenly distributed along the entire river during both periods. Consequently, the probability of farmed × wild inter-breeding varied among river sections. Our finding that the distribution of escaped farmed salmon may differ from that of wild salmon and among river sections in the prespawning and spawning periods-and that it may also vary over time-must be taken into consideration when (1) designing monitoring programs aimed at estimating the proportion of escaped farmed salmon in rivers and (2) when interpreting monitoring results. Furthermore, targeted fishing in the river aimed at reducing the number of farmed salmon prior to spawning may be more effective in upper rivers sections, and below major migration barriers.

Escaped farmed Atlantic salmon interbreed with wild Atlantic salmon, leaving offspring that often have lower success in nature than pure wild salmon. On top of this, presence of farmed salmon descendants can impair production of wild‐type recruits. We hypothesize that both these effects connect with farmed salmon having acquired higher standard metabolic rates (SMR, the energetic cost of self‐maintenance) during domestication. Fitness‐related advantages of phenotypic traits associated with both high SMR and farmed salmon (e.g., social dominance) depend on environmental conditions, such as food availability. We hypothesize that farmed offspring have an advantage at high food availability due to, for example, dominance behavior but suffer increased risks of starvation when food is scarce because this behavior is energy‐demanding. To test these hypotheses, we first compare embryo SMR of pure farmed, farmed‐wild hybrids and pure wild offspring. Next, we test early‐life performance (in terms of survival and growth) of hybrids relative to that of their wild half‐siblings, as well as their competitive abilities, in semi‐natural conditions of high and low food availability. Finally, we test how SMR affects early‐life performance at high and low food availability. We find inconclusive support for the hypothesis that domestication has induced increased SMR. Further, wild and hybrid juveniles had similar survival and growth in the semi‐natural streams. Yet, the presence of hybrids led to decreased survival of their wild half‐siblings. Contrary to our hypothesis about context‐dependency, these effects were not modified by food availability. However, wild juveniles with high SMR had decreased survival when food was scarce, but there was no such effect at high food availability. This study provides further proof that farmed salmon introgression may compromise the viability of wild salmon populations. We cannot, however, conclude that this is connected to alterations in the metabolic phenotype of farmed salmon.