Evaluation of a new management scheme for Norwegian Atlantic salmon Salmo salar

Atlantic salmon, Salmo salar L., stocks are decreasing worldwide, and major efforts are underway to conserve populations that are threatened. In a recent effort to conserve the Norwegian salmon, the Norwegian government implemented in 2007 a scheme called National Atlantic Salmon Watercourses and Fjords (NASW), where 52 rivers were given special protection. Here, the scheme is described and it is evaluated if and to what extent the scheme has led to changes in management practice. After the implementation of the NASW scheme, fewer plans for development (e.g. hydropower plants, water abstraction, flood and erosion control) at the within‐river level were accepted for NASW‐rivers than for rivers not in the scheme. However, at the same time, there was a tendency for fewer plans overall being sanctioned in all types of rivers probably due to overall changes in management practices not related to the NASW scheme. In total, these changes could lead to increased protection of Norwegian Atlantic salmon populations.     

Atlantic salmon living on the edge: Smolt behaviour and survival during seaward migration in River Minho

The Atlantic salmon (Salmo salar) population of the River Minho represents the southern natural distribution edge of the species. In line with the general trend for Atlantic salmon, this population has been declining over the years and is now at a critically low level. With river connectivity compromised by a large dam just 80 km upstream the River Minho's outlet, and an expected deterioration of climatic conditions, it is urgent to increase our knowledge of this population and identify survival bottlenecks that can be addressed. In this study, we used radio and acoustic telemetry to track Atlantic salmon smolts during their migration towards the sea and record both survival rates and possible causes of mortality. The recorded survival for the tagged migrating Atlantic salmon remained below 55% in the three studied years, indicating that the in‐river loss of smolts is likely a strong constraint to this population. From the smolts to which a likely cause of mortality could be attributed (34%), most appear to have been removed from the river (25%), with two confirmed events of bird predation and one of mammal predation. Interestingly, eight tags were recorded moving back upstream, likely indicating predation by larger fish. Increasing predator populations (e.g. cormorants, Phalacrocorax carbo) and invasive predators (e.g. American mink, Neovison vison) lead to elevated predation pressure on this already strained Atlantic salmon population, and further studies quantifying their impact in more detail could prove crucial for future management considerations.     

Prospects for the future of pink salmon in three oceans: From the native Pacific to the novel Arctic and Atlantic

While populations of other migratory salmonids suffer in the Anthropocene, pink salmon (Oncorhynchus gorbusca Salmonidae) are thriving, and their distribution is expanding both within their natural range and in the Atlantic and Arctic following introduction of the species to the White Sea in the 1950s. Pink salmon are now rapidly spreading in Europe and even across the ocean to North America. Large numbers of pink salmon breed in Norwegian rivers and small numbers of individuals have been captured throughout the North Atlantic since 2017. Although little is known about the biology and ecology of the pink salmon in its novel distribution, the impacts of the species' introduction are potentially highly significant for native species and watershed productivity. Contrasts between pink salmon in the native and extended ranges will be key to navigating management strategies for Atlantic nations where the pink salmon is entrenching itself among the fish fauna, posing potential threats to native fish communities. One key conclusion of this paper is that the species' heritable traits are rapidly selected and drive local adaptation and evolution. Within the Atlantic region, this may facilitate further establishment and spread. The invasion of pink salmon in the Atlantic basin is ultimately a massive ecological experiment and one of the first examples of a major faunal change in the North Atlantic Ocean that is already undergoing rapid changes due to other anthropogenic stressors. New research is urgently needed to understand the role and potential future impacts of pink salmon in Atlantic ecosystems.     

Competitive interactions among multiple non‐native salmonids and two populations of Atlantic salmon

Competitive interactions with non‐native species can have negative impacts on the conservation of native species, resulting in chronic stress and reduced survival. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (Sebago and LaHave) that are being used for reintroduction into Lake Ontario were placed into semi‐natural stream tanks with four non‐native salmonid competitors that are established in Ontario streams: brown trout (S. trutta), rainbow trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha) and coho salmon (O. kisutch). Brown trout and rainbow trout reduced the survival and fitness‐related traits of Atlantic salmon, whereas Chinook salmon and coho salmon had no impact on these traits. These data support theories on ecological niche overlap and link differences in observed aggression levels with competitive outcomes. Measurements of circulating hormones indicated that the Atlantic salmon were not chronically stressed nor had a change in social status at the 10‐month time point in the semi‐natural stream tanks. Additionally, the Sebago population was better able to coexist with the non‐native salmonids than the LaHave population. Certain populations of Atlantic salmon may thus be more suitable for some environments of the juvenile stream phase for the reintroduction into Lake Ontario.     

Vitamin K-dependent γ-glutamylcarboxylase in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.)

Due to problems with bone deformities in farmed Atlantic salmon, there is a growing interest in the possible involvement of vitamin K in normal bone development, and sensitive biomarkers for evaluating vitamin K status are therefore needed. The vitamin K-dependent (VKD) enzyme γ-glutamylcarboxylase (GGCX, EC 6.4.x.x) requires vitamin K as a cofactor for its post-translational modification of glutamic acid (Glu) residues to γ-carboxyglutamic acid (Gla) residues in VKD proteins, and is required for their function in haemostasis and bone metabolism. The present study was designed to evaluate the enzyme assay for GGCX activity in isolated liver microsomes and its distribution in the tissues of Atlantic salmon. The effect of KH₂ and menadione on the GGCX activity in salmon liver was also compared. Results from the present study show a widespread tissue distribution and expression of GGCX in Atlantic salmon. The GGCX activity and ggcx expression in all bony tissues examined imply the presence of vitamin K, and suggest the involvement of vitamin K in bone metabolism of Atlantic salmon. We propose the GGCX assay as a sensitive marker for vitamin K status, and confirm that menadione does not work as a cofactor for GGCX in Atlantic salmon liver.     

Competitive effects between rainbow trout and Atlantic salmon in natural and artificial streams

Competition with non‐native species may impede the restoration of native species, but differences in competitive abilities among intraspecific native populations may make some populations more suitable for reintroduction than others. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (LaHave and Sebago) being used for reintroduction into Lake Ontario were placed into two natural stream sites differing in the presence of ecologically similar rainbow trout (Oncorhynchus mykiss). We assessed the effects of competition in the natural streams on fitness‐related traits and habitat use of the Atlantic salmon. We then compared these effects to those observed in artificial streams from a previous study. Atlantic salmon in natural streams had reduced fitness‐related traits that were associated with suboptimal microhabitats in the presence of rainbow trout, but utilised optimal microhabitats in their absence. In the presence of rainbow trout, the two Atlantic salmon populations exhibited comparable recapture proportions to each other, but the individuals from the Sebago population had better performance (body size and condition) than those from the LaHave population. Responses of both Atlantic salmon populations to competition with rainbow trout were generally similar in both direction and magnitude when compared to results from the artificial stream study. The combined results suggest that native species restoration efforts should be focused on candidate populations that are ecologically suitable to reintroduction environments, as well as on suitable habitats that do not contain exotic competitors. Moreover, this study highlights the value of controlled experiments in artificial environments for predicting fitness‐related performance in natural environments.     

Evidence for spatial coherence in time trends of marine life history traits of Atlantic salmon in the North Atlantic

A hierarchical Bayesian life cycle model is presented that considers spatial covariation of marine life history traits of Atlantic salmon (Salmo salar) populations in the North Atlantic. The model is based on a collective analysis of the dynamics of 13 stock units (SUs) from two continental stock groups (CSGs) in North America and Southern Europe in a single hierarchical model over the period 1971–2014. The model sets up a new assessment framework for Atlantic salmon stocks. It also provides a framework to investigate the drivers of changes in Atlantic salmon population dynamics including disentangling the effects of fisheries from those of environmental factors in a hierarchy of spatial scales. It is used to test the hypothesis of a strong spatial synchrony in marine life history dynamics of Atlantic salmon populations. The trends in two key parameters associated with the early marine phase of the life cycle are estimated: (i) the marine survival during the first summer–autumn spent at sea and (ii) the proportion of fish maturing after the first winter at sea. The results provide evidence of a decline in the marine survival together with an increase in the proportion of fish that mature after the first winter at sea, common to all SUs. Our results show an increased coherence in the covariations of trends in these two marine life history traits related to geographic proximity of SUs which support the hypothesis of a coherent response of geographically proximate Atlantic salmon populations that likely share similar migration routes.     

Increased abundance of European eel (Anguilla anguilla) in acidified Norwegian rivers after liming

The prevalence and abundance (density 100 m^?2) of European eel (Anguilla anguilla) were studied by means of electrofishing in 13 acidified rivers in Norway that had been limed to restore acceptable water quality for Atlantic salmon (Salmo salar). Status of Atlantic salmon in these rivers varied prior to liming, from being entirely lost in six highly acidified rivers and in different stages of decline in seven less acidified rivers. Four of the rivers are heavily affected by hydropower development. The abundance and prevalence of European eel increased significantly during the study period. The best model for predicting eel abundance was that with four explanatory variables: time after liming, time after liming squared, status of salmon stocks and hydropower regulation. The eel density was expected to increase by a factor of almost 5 after 10 years of liming. The model also predicts that a river with a formerly reduced Atlantic salmon stock has a 2.8 times higher density of eel than rivers with formerly lost salmon stocks. Before liming, European eel were on average recorded at 15 and 41% of the sampling stations in rivers with formerly lost and reduced Atlantic salmon populations, respectively, increasing to 49 and 68% in individual rivers, respectively, after 10 years of liming. The recovery of European eel in these formerly acidified rivers by means of liming took place during the same period as their abundance declined in other parts of their distribution area in Norway and elsewhere in Europe.     

A genetic tool for evaluating male‐mediated stock introgression in Atlantic salmon

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A Review of Factors Influencing Maturation of Atlantic Salmon,Salmo salar,with Focus on Water Recirculation Aquaculture System Environments

Sexual maturation of Atlantic salmon, Salmo salar, is a complex process, with many variables having the capacity to influence the timing and prevalence of maturation and acting as promoters and/or inhibitors of sexual development. Precocious maturation has the capacity to seriously impact production in commercial aquaculture settings, and in response there has been a significant amount of research devoted to understanding this issue in order to develop remedial strategies. Very little research has been conducted specifically examining salmon maturation in land‐based, closed containment water recirculation aquaculture systems, which have recently received attention as an alternative technology for the sustainable production of market‐size Atlantic salmon. Unfortunately, the nascent closed containment salmon industry has thus far experienced high levels of precocious maturation, for reasons that are presently unclear. Given the economic challenges facing the closed containment industry's expansion, it is imperative that best management practices be developed to reduce economic losses from early maturation, in order to assist the sustainable growth of farmed Atlantic salmon production. This review provides a brief summary of published research on factors associated with early salmonid maturation, as well as information from research examining maturation and growout performance of Atlantic salmon in closed containment aquaculture systems.     

Atlantic salmon in the North Pacific

The first catches of Atlantic salmon, Salmo salar L., in British Columbia (BC) waters occurred in 1987. The first reported escape of Atlantic salmon (2000 individuals) occurred in 1988. From 1988 to 1995, 97 799 Atlantic salmon were reported escaped from net pens in BC but the true number was higher as not all escapes are reported. Since 1987 a total of 9096 Atlantic salmon was caught in the coastal marine waters of BC, Washington and Alaska, and 188 were caught in fresh water. Most catches occurred in the Johnstone Strait area, where the abundance of salmon farms is highest. The most distant recovery occurred in 1994 when an Atlantic salmon was caught near the western end of the Alaska Peninsula. There have been no reports of successful reproduction of Atlantic salmon in the wild and no feral juveniles have been found. Atlantic salmon caught in the ocean in BC have substantial amounts of adipose tissue and they are heavier at length than fish caught in Alaska. The proportion of fish with prey items in their stomachs is generally low but higher in Alaska (13.1%) than in BC (5.8%). Most fish caught in fresh water are either maturing or mature.     

Impact of stocked Atlantic salmon (Salmo salar L.) on habitat use by the wild population

Laffaille P. Impact of stocked Atlantic salmon (Salmo salar L.) on habitat use by the wild population.
Ecology of Freshwater Fish 2011: 20: 67–73. © 2010 John Wiley & Sons A/S Abstract – We investigated the summer habitat occupied by populations of young‐of‐the‐year wild and stocked (farmed populations released into the native range) Atlantic salmon under allopatric and sympatric conditions. Under allopatric conditions, farmed and wild salmon occupied habitats with the same characteristics. The salmon preferentially occupied the riffle areas. However, under sympatric conditions, the fish occupied meso‐ and micro‐habitats with different characteristics. Wild salmon avoided habitats used by farmed salmon and preferred glide areas with considerable vegetation cover. This study suggests that differences in the pattern of habitats used by young Atlantic salmon were both size‐ and origin‐dependent and may result from intra‐species competition between farmed and wild populations. Given that stocking with farmed Atlantic salmon is carried out intensively to enhance recreational angling or to conserve salmon populations, this study warns that this can have a negative impact on the extant wild Atlantic salmon population.     

Presence and genetic variability of Piscine orthoreovirus genotype 1 (PRV‐1) in wild salmonids in Northern Europe and North Atlantic Ocean

Piscine orthoreovirus genotype 1 (PRV‐1) is widespread in farmed Atlantic salmon (Salmo salar L.) populations in northern Europe, Canada and Chile. PRV‐1 occurs in wild fish in Norway and Canada; however, little information of its geographical distribution in wild populations is currently available, and the effect of PRV‐1 infection in wild populations is currently unknown. In this study, we present the findings of a survey conducted on 1,130 wild salmonids sampled in Denmark, Sweden, Ireland, Faroe Islands, France, Belgium and Greenland between 2008 and 2017. PRV‐1 is reported for the first time in wild salmonids in Denmark, Sweden, Faroe Island and Ireland. The annual PRV‐1 prevalence ranged from 0% in France, Belgium and Greenland to 43% in Faroe Islands. In total, 66 samples tested positive for PRV‐1, including Atlantic salmon broodfish returning to spawn and Atlantic salmon collected at the feeding ground north of Faroe Islands. The phylogenetic analysis of S1 sequences of the PRV‐1 isolates obtained in this survey did not show systematic geographical distribution. This study sheds light on the spread and genetic diversity of the virus identified in populations of free‐living fish and provides rationale for screening wild broodfish used in restocking programmes.     

Aeromonas salmonicida infectivity studies in goldsinny wrasse, Ctenolabrus rupestris (L.)

Goldsinny wrasse, Ctenolabrus rupestris (L.). were experimentally and naturally infected with Aeromonas salmonicida. Goldsinny wrasse were found to be susceptible to infection with A. salmonicida but significantly more resistant to infection than Atlantic salmon, Salmo salar L. The pathology of the acute infection is described. Following infection significantly higher levels of agglutinating antibody were detected in the sera of recovered wrasse than those observed in the Atlantic salmon controls. However, a large proportion of the recovered wrasse were culture positive for A. salmonicida and appeared to have entered a chronic stage of infection quite distinct from the carrier status that can develop in Atlantic salmon. This study indicates that, although goldsinny wrasse are susceptible to A. salmonicida, these fish are unlikely to become primarily infected, but contract furunculosis from infected Atlantic salmon. However, goldsinny wrasse may act as a reservoir for subsequent infections of cultivated Atlantic salmon because of the development of a chronic form of the disease. The potential for the vaccination of goldsinny wrasse against furunculosis is discussed.     

Survival of migrating sea trout (Salmo trutta) and Atlantic salmon (Salmo salar) smolts negotiating weirs in small Danish rivers

Abstract – The survival of brown trout and Atlantic salmon smolts during passage over small weirs was estimated in two small Danish rivers during the spring of 1998. Parallel groups of smolts were released upstream and downstream of the weirs and recaptured in traps further downstream. The results showed a smolt loss varying from 18 to 71% for trout and 53% for salmon. Furthermore, the surviving smolts from the upstream groups were delayed for up to 9 days compared to downstream groups. The study demonstrated that an increased proportion of total river discharge allocated to fish passage increased the smolt survival. Losses may be because of fish penetrating grids erected at fish farm inlets, predation and delays, which may lead to desmoltification. The low survival may seriously threat both the long-term viability of wild populations of anadromous salmonids and the outcome of the intensive stocking programme in Denmark.     

Direct and indirect effects of riparian canopy on juvenile Atlantic salmon,Salmo salar,and brown trout,Salmo trutta,in south‐west Ireland

Abstract Dense riparian tree canopy is generally found to have a negative effect on salmonid populations. Canopy can affect fish both directly via trophic impacts and its effects as cover, and indirectly via its effects on the distribution of instream vegetation. This study examined the impact of riparian canopy on the ecology of juvenile Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in south‐west Ireland. Riparian canopy reduced the density, length and gut contents of juvenile salmon, but not brown trout. The negative relationship between canopy cover and fish size and feeding was strongly influenced by the abundance of instream macrophytes, which in turn varied as a function of catchment water chemistry. As a management strategy, the reduction of dense riparian canopy is unlikely to have the same effect on juvenile salmonids on all streams within an ecoregion because of differences in catchment‐wide factors.     

A survey of salmon gill poxvirus (SGPV) in wild salmonids in Norway

In 2016, the Norwegian health monitoring programme for wild salmonids conducted a real‐time PCR‐based screening for salmon gill poxvirus (SGPV) in anadromous Arctic char (Salvelinus alpinus L.), anadromous and non‐anadromous Atlantic salmon (Salmo salar L.) and trout (Salmo trutta L.). SGPV was widely distributed in wild Atlantic salmon returning from marine migration. In addition, characteristic gill lesions, including apoptosis, were detected in this species. A low amount of SGPV DNA, as indicated by high Ct‐values, was detected in anadromous trout, but only in fish cohabiting with SGPV‐positive salmon. SGPV was not detected in trout and salmon from non‐anadromous water courses, and thus seems to be primarily linked to the marine environment. This could indicate that trout are not a natural host for the virus. SGPV was not detected in Arctic char but, due to a low sample size, these results are inconclusive. The use of freshwater from anadromous water sources may constitute a risk of introducing SGPV to aquaculture facilities. Moreover, SGPV‐infected Atlantic salmon farms will hold considerable potential for virus propagation and spillback to wild populations. This interaction should therefore be further investigated.     

Movements of two strains of radio tagged Altlantic salmon, Salmo salar L., smolts through a reservoir

Smolt migration through a shallow and turbid hydro-reservoir in a major Danish river system was investigated using radiotelemetry. Hatchery-reared 1+-year-old Atlantic salmon, Salmo salar L., smolts of equal size from two different non-native strains were radio-tagged and followed during their downstream migration through the 12-km-long reservoir. A total of 50 salmon smolts, 25 of Swedish (Øtran River) and 25 of Irish (Burrishoole River) origin, were surgically implanted with miniature radiotransmitters. The tagged smolts were tracked daily over a 3-week period in May 1996. The Øtran smolts initiated migration first ( P  < 0.001), moved faster ( P  < 0.01), were delayed less when passing a culvert ( P  < 0.001) and were more successful in moving through the reservoir than the Burrishoole smolts. The observed differences in migratory behaviour are interpreted as evidence of a genetic component influencing smolt migration.     

Straying intensity and genetic differentiation in salmon populations

This paper summarizes world literature and the authors' results on straying intensity and genetic differentiation in salmon populations. The following points are discussed: straying intensity in salmonid species; the concept of effective population size and its estimates for different salmon species; relation between the N_em parameter of population structure and spatial genetic differentiation at allozyme loci; possible genetic consequences of homing distortion. We conclude that homing is a historically established species-specific trait responsible for the equilibrium between population differentiation and integration processes which regulate the ratio of intra- and interpopulation gene diversity levels. The distortion of this ratio results in negative genetic effects for rational fishery and successful management of populations.     

Cardiomyopathy syndrome in Atlantic salmon Salmo salar L.: A review of the current state of knowledge

Cardiomyopathy syndrome (CMS) is a severe cardiac disease affecting Atlantic salmon Salmo salar L. The disease was first recognized in farmed Atlantic salmon in Norway in 1985 and subsequently in farmed salmon in the Faroe Islands, Scotland and Ireland. CMS has also been described in wild Atlantic salmon in Norway. The demonstration of CMS as a transmissible disease in 2009, and the subsequent detection and initial characterization of piscine myocarditis virus (PMCV) in 2010 and 2011 were significant discoveries that gave new impetus to the CMS research. In Norway, CMS usually causes mortality in large salmon in ongrowing and broodfish farms, resulting in reduced fish welfare, significant management‐related challenges and substantial economic losses. The disease thus has a significant impact on the Atlantic salmon farming industry. There is a need to gain further basic knowledge about the virus, the disease and its epidemiology, but also applied knowledge from the industry to enable the generation and implementation of effective prevention and control measures. This review summarizes the currently available, scientific information on CMS and PMCV with special focus on epidemiology and factors influencing the development of CMS.