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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.

The Ryman-Laikre (R-L) effect is an increase in inbreeding and a reduction in total effective population size (NeT ) in a combined captive-wild system, which arises when a few captive parents produce large numbers of offspring. To facilitate evaluation of the R-L effect for scenarios that are relevant to marine stock enhancement and aquaculture, we extended the original R-L formula to explicitly account for several key factors that determine NeT , including the numbers of captive and wild adults, the ratio of captive to wild Ne/N (β), productivity of captive and wild breeders, and removal of individuals from the wild for captive breeding. We show how to provide quantitative answers to questions such as: What scenarios lead to no loss of effective size? What is the maximum effective size that can be achieved? and What scenarios insure that NeT will be no smaller than a specified value? Important results include the following: (1) For large marine populations, the value of β becomes increasingly important as the captive contribution increases. Captive propagation will sharply reduce NeT unless the captive contribution is very small or β is very large (∼103 or higher). (2) Very large values of β are only possible if wild Ne/N is tiny. Therefore, large wild populations undergoing captive enhancement at even modest levels will suffer major reductions in effective size unless wild Ne is a tiny fraction of the census size (about 10-4 or lower).

The present study aimed to investigate the morphological and genetic differentiation of lowland and montane populations of the Pieris napi species complex in Norway and to make inferences about the subspecific status of Pieris napi adalwinda and Pieris napi napi. We measured 22 morphological characters on 228 individuals from eight populations in Central Norway (20–1100 m a.s.l.). In addition, lowland and mountain animals were reared at a high altitude locality. Half the animals from either locality were reared on mountain plant, and the other half on a lowland plant. Finally, a fragment of the mitochondrial cytochrome b gene was sequenced for individuals from Central and South-eastern Norway and Germany. Principal component analysis of morphological characters showed a zone of abrupt change from lowland to mountain morphological character states between populations at 506 m and 730 m a.s.l., respectively. The transplant experiment showed that the morphological differences have a genetic basis and that food plants have no impact on morphology. Limited, but significant, molecular genetic differentiation was found between lowland and mountain animals, but the phylogenetic analysis, however, showed that the lowland form (P. n. napi) is paraphyletic and the montane form (P. n. adalwinda) is monophyletic. Further study is required before taxonomic recognition can be applied. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 727–745.

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.

Management of a group of Atlantic salmon (Salmo salar) populations that are harvested together in the ocean, but separately in freshwater, is looked at from a genetic perspective. A model that estimates total effective population size from local effective population sizes and migration patterns is applied to a system of ten salmon populations in the Sognefjorden district, western Norway. This population system is dominated numerically by the River Lærdalselva population, which may act as a source of migrants into nine smaller populations in a “source–sink” metapopulation. The total effective population size of this system is to a large extent dependent on the effective population size of the Lærdalselva population, but the contribution per spawner to the total effective population size is greater for a fish from the smaller populations than for a fish from Lærdalselva. The results are discussed in light of conservation genetic theory, and empirical results on the fitness consequences of loss of genetic variation in salmonids. The genetic consequences of harvesting need to be assessed both at the levels of local populations and the metapopulation.

Lycaenid butterflies of the Aricia agestisartaxerxes complex pose an unresolved taxonomic and conservation problem in northwestern Europe. Two key issues require resolution: (i) how many species of Aricia occur in northwestern Europe and what are their distributions?; (ii) how is the morphological variation observed in northwestern Europe best explained? We investigated phylogenetic relationships and phylogeographic patterns in this species group using mitochondrial and nuclear markers in comparison with morphological variation. A 325 bp fragment of the mitochondrial cytochromeb gene was sequenced from 179 individuals representing 18 populations from the UK and Scandinavia. Seventeen enzymecoding loci were analysed from 538 individuals from the same populations. Highly congruent phylogenies between mitochondrial and allozyme markers demonstrate that the sample is composed of two closely related species, A. agestis and A. artaxerxes. Both marker types also suggest that Scottish and northern Scandinavian A. artaxerxes populations are conspecific, and consequently do not support the endemic status of A. artaxerxes in the UK. The subspecies division of British populations of A. artaxerxes is also not supported by phylogenetic analyses. Allozyme and mitochondrial analyses cluster two populations from the Peak District, UK, differently. The former suggests that they are A. artaxerxes whilst the latter suggests they are A. agestis. Further research is required to find the reason for this disagreement, which could be associated with the different dynamics of nuclear and mitochondrial genes across a hybrid zone between the two species. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 27–37.

A model of the migration pattern in a metapopulation of sea beet (Beta vulgaris L. ssp. maritima), based on the continuous distributions of seed and pollen movements, is fitted to gene frequency data at 12 isozyme and RFLP loci by maximum likelihood by using an approximation of the simultaneous equilibrium distribution of the gene frequencies generated by the underlying multivariate stochastic process of genetic drift in the population. Several alternative restrictions of the general model are fitted to the data, including the island model, a model of complete isolation, and a model in which the seed and pollen dispersal variances are equal. Several likelihood ratio tests between these alternatives are performed, and median bias in the estimated parameters is corrected by using parametric bootstrapping. To assess the fit of the selected model, the predicted covariances are compared with covariances computed from the data directly. The dependency of estimated parameters on the ratio between effective and absolute subpopulation sizes, which is treated as a known parameter in the analysis, is also examined. Finally, we note that the data also appear to contain some information about this ratio.

Eggs and alevins were collected from 36 redds in the River Vosso in late March 1996. The redds had been made by 20 individual female Atlantic salmon and 12 female brown trout. Species-specific allozyme variation was used to distinguish trout from salmon and egg size and pigment analyses were used to distinguish farmed from wild salmon females. Nine (45%) of the 20 female salmon spawners in the sample were of confirmed farmed origin, because their offspring contained synthetic astaxanthin which is an additive to commercial fish feed. Most of the remaining female salmon were also likely to have been farmed escapees because only about half of the actual farmed spawners can be identified by their astaxanthin content due to intake of carotenoids from natural food sources. The estimated peak spawning for both confirmed and putative farmed females was 32 d earlier than peak spawning of wild females. Egg survival was high and similar to previous estimates for wild and farmed salmon in the River Vosso. Based on the astaxanthin content in sampled eggs and the time of peak spawning it is concluded that most Atlantic salmon fry that hatched in the River Vosso in 1996 were produced by escaped farmed females. The frequency of redds made by farmed females was in accordance with their estimated representation (81%) in the population of spawners during autumn 1995.

Arctic charr, Salvelinus alpinus (L.), commonly exhibits two coexisting morphotypes, dwarf and normal charr, which are characterized by differences in adult body size and colouration. We tested whether or not the morphotypic differences were genetically determined in rearing experiments with offspring of the two morphs and of their crosses. The experiments suggest that this ecological polymorphism in Arctic charr is largely environmentally determined. When reared under similar conditions, offspring of each of the two morphs differed little in size at the same age, and they had the same early developmental rate and maturation pattern. Moreover, the presence of parr marks along the flanks of the fish, one characteristic of dwarf charr, depended on body size and not on parental morph. Genetic differences between the morphs were suggested for growth rate during the second year of life, and for jaw morphology. Comparisons between charr life histories in captivity and in the wild suggest that ecological polymorphism in Arctic charr is chiefly a result of variation in growth conditions between different habitats.

The farming of salmon and other marine finfish in open net pens continues to increase along the world's coastlines as the aquaculture industry expands to meet human demand. Farm fish are known to escape from pens in all salmon aquaculture areas. Their escape into the wild can result in interbreeding and competition with wild salmon and can facilitate the spread of pathogens, thereby placing more pressure on already dwindling wild populations. Here we assess the ecological, genetic, and socioeconomic impacts of farm salmon escapes, using a risk-assessment framework. We show that risks of damage to wild salmon populations, ecosystems, and society are large when salmon are farmed in their native range, when large numbers of salmon are farmed relative to the size of wild populations, and when exotic pathogens are introduced. We then evaluate the policy and management options for reducing risks and discuss the implications for farming other types of marine finfish.

The systematica of coexisting morphotypes of Arctic charr, Salvelinus alpinus, has been a matter of dispute ever since the days of Linnaeus. Widespread allelic variation at an esterase locus has led some investigators to propose that the morphotypes reflect a complex of at least three sibling species. We tested this hypothesis by examining 42 electrophoretically detectable loci in natural and transplanted charr populations from 15 localities in S Norway. The absolute values of Nei's genetic distance between morphotypes and populations are small (typically in the order of 0.001), and morphotype changes may occur without accompanying changes in frequencies of esterase alleles. Differentiation among localities explains far more of the total gene diversity than differences between morphotypes in the four cases of naturally occurring sympatric morphotypes examined. The data are consistent with an intraspecific population structuring based on locality, and the multiple species hypothesis is rejected.