Arne Johan Jensen

Arne Johan Jensen
Norwegian Institute for Nature Research | NINA · Department of Aquatic Ecology

Dr. philos.

About

157
Publications
30,962
Reads
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5,296
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Introduction
Arne Johan Jensen currently works at the Department of Aquatic Ecology, Norwegian Institute for Nature Research. Arne does research in Ecology, Marine Biology and Zoology.
Additional affiliations
September 1988 - present
Norwegian Institute for Nature Research
Position
  • Senior Researcher
March 1978 - August 1988
Norwegian Directorate for Nature Management
Norwegian Directorate for Nature Management
Position
  • Researcher
June 1976 - March 1978
SINTEF
Position
  • Research Associate

Publications

Publications (157)
Article
Full-text available
Ecological regime shifts are abrupt changes in the structure and function of ecosystems that persist over time, but evidence of contemporary regime shifts are rare. Historical scale data from 52,384 individual wild Atlantic salmon caught in 180 rivers from 1989 to 2017 reveal that growth of Atlantic salmon across the Northeast Atlantic Ocean abrupt...
Article
Full-text available
The timing of seaward migration is a key life‐history trait for many anadromous fish species, with growth and survival at sea depending on a match/mismatch scenario between the timing of the sea entry and optimal conditions. Based on a 25‐year study with 15 226 individually tagged brown trout (Salmo trutta) in a Norwegian river, we analyzed how the...
Chapter
Full-text available
Arctic rivers are among the most pristine ecosystems worldwide but are under increasing threat from global and regional anthropogenic impacts, including long-range transport of pollutants, overfishing, exotic species, hydropower development, and climate change. Snow and ice are a particular feature of Arctic rivers and discharge is typically low or...
Chapter
Rivers of the Boreal Uplands vary greatly in size and hydrological regime. The most typical feature of all rivers is their importance in valleys as landscape elements and as key economic centers. To reduce perturbations and maintain catchments for coming generations, 388 parts of or entire catchments are protected through a special Protection Plan...
Article
Full-text available
After a half a century of salmon farming, we have yet to understand how the influx of genes from farmed escapees affects the full life history of Atlantic salmon (Salmo salar L.) in the wild. Using scale samples of over 6900 wild adult salmon from 105 rivers, we document that increased farmed genetic ancestry is associated with increased growth thr...
Article
Full-text available
Aim Accurate predictions about transition timing of salmon smolts between freshwater and marine environments are key to effective management. We aimed to use available data on Atlantic salmon smolt migration to predict the emigration timing in rivers throughout Norway. Location In this study, we used outmigration timing data of Atlantic salmon (Sa...
Article
Full-text available
The survival of Atlantic salmon (Salmo salar), an increasingly rare anadromous species, has declined dramatically during its marine phase, with disproportionate impacts on the poorly understood early post‐smolt period. Logistical constraints on collecting oceanic data to inform this issue pose a formidable obstacle. To advance understanding of post...
Article
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Salmon lice Lepeophtheirus salmonis infestation of sea trout Salmo trutta results in both additional marine mortality and behavioral changes which may contribute to sea trout population decline. For effective management of activities that increase exposure to salmon lice, such as salmon aquaculture, it is necessary to have a full understanding of h...
Article
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Many salmonid populations are of conservation concern, and the release of hatchery-produced juveniles is a frequently used measure to alleviate declines and increase harvest opportunities. While such releases may be of conservation value for some populations, stocking may also decrease the effective population size and subsequently impose additiona...
Article
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For successful evaluation of the overall effects of salmon louse infestation on brown trout population dynamics, it is crucial to have a realistic understanding of how lice infestation distributions are generated and how they should be interpreted. Here, we simulated the potential effects of spatio-temporal variance in lice larvae densities, tempor...
Article
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Consistent individual differences in behaviour has been demonstrated for many animals, but there are few studies of consequences of such repeated behaviour in the wild. We tested consistency in migration timing to and from the sea among anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta), using data from a study period of abo...
Article
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It is hypothesized that in diadromous fish, migrations may occur because of differences in the availability of food in marine and freshwater habitats. The benefits of migration to sea may be increased growth opportunities and reproductive output, while the costs may be increased mortality and increased energy use. Here we examine mortality rates of...
Article
Full-text available
Stocking of hatchery produced fish is common practice to mitigate declines in natural populations and may have unwanted genetic consequences. Here we describe a novel phenomenon arising where broodstock used for stocking may be introgressed with farmed individuals. We test how stocking affects introgression in a wild population of Atlantic salmon (...
Article
The return migration of adult Atlantic salmon was investigated by analysing recaptures of individuals tagged and released as smolts in the River Altaelva and the River Halselva using a catch per unit effort approach. Although the salmon were recaptured over a large area along the coastline (from >1100 km south to > 500 km northeast of their home ri...
Article
Full-text available
Background Selection acts strongly on individuals that colonise a habitat and have phenotypic traits that deviate from the local optima. Our objective was to investigate the evolutionary rates in Atlantic salmon (Salmo salar) in a river system (the Vefsna watershed in Norway), fewer than 15 generations after colonisation of two new branches of the...
Article
Full-text available
Data from a 25-year study of anadromous Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in the River Halselva provided evidence that survival during winter was linked to marine growth during the previous summer. The study supported the “critical size and critical period” hypothesis, which postulates that regulation of the abundance...
Article
Full-text available
This study found empirical evidence supporting the “growth–survival” paradigm in the marine phase of Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta). The paradigm postulates that larger or faster-growing individuals are more likely to survive than smaller or slower-growing conspecifics. The study employed long-term (25 year) capture...
Article
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Interbreeding between domesticated and wild animals occurs in several species. This gene flow has long been anticipated to induce genetic changes in life-history traits of wild populations, thereby influencing population dynamics and viability. Here, we show that individuals with high levels of introgression (domesticated ancestry) have altered age...
Article
Full-text available
The rapid growth of aquaculture raises questions about the welfare status of mass-produced species. Sagittal otoliths are primary hearing structures in the inner ear of all teleost (bony) fishes and are normally composed of aragonite, though abnormal vaterite replacement is sometimes seen in the wild. We provide the first widespread evaluation of t...
Article
Full-text available
Despite satisfactory reactions to seawater challenge tests indicative of appropriate physiological state, hatchery-reared Atlantic salmon Salmo salar smolts stocked in the Eira River in Norway between 2001 and 2011 performed less well at sea in terms of growth, age at maturity and survival than smolts of natural origin. The mean rates of return to...
Article
Parasites can, in theory, have large impacts on the survival of fish populations. One method to evaluate such impacts on anadromous species is to apply manipulative field experiments in which parallel groups of antiparasitically treated and non-treated fish are simultaneously released and then subsequently recaptured as returning adults. A systemat...
Article
Full-text available
Males and females share many traits that have a common genetic basis, however selection on these traits often differs between the sexes leading to sexual conflict. Under such sexual antagonism, theory predicts the evolution of genetic architectures that resolve this sexual conflict. Yet, despite intense theoretical and empirical interest, the speci...
Preprint
Full-text available
Males and females share many traits that have a common genetic basis, however selection on these traits often differs between the sexes leading to sexual conflict. Under such sexual antagonism, theory predicts the evolution of genetic architectures that resolve this sexual conflict. Yet, despite intense theoretical and empirical interest, the speci...
Article
Full-text available
A long-term study in the River Halselva in the Arctic region of Norway demonstrated that movements between watersheds were considerably higher in anadromous brown trout (Salmo trutta) than anadromous Arctic char (Salvelinus alpinus). Fourteen smolt year classes of both species were captured in a fish trap, individually tagged, and thereafter regist...
Article
A model that explains 48% of the annual variation in Atlantic salmon Salmo salar smolt production in the River Orkla, Norway, has been established. This variation could be explained by egg deposition, minimum daily discharge during the previous winter and minimum weekly discharge during the summer 3 years before smolt migration. All coefficients in...
Article
Full-text available
138 Atlantic salmon (Salmo salar) captured in the Advent Fjord off Svalbard were genetically assigned to two main clusters of European salmon. Two-thirds were assigned to salmon rivers in Finnmark (the northernmost county in Norway) and the rest to salmon rivers further south in Norway. The genetic assignment was based on genetic profiles from 60 N...
Article
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ABSTRACT: Tagging or marking of fishes enables the collection of population-based information for ecological research, yet few techniques enable 100% mark detection success. We tested a new mass-marking technique: otolith marking with enriched stable isotopes delivered during vaccination. Atlantic salmon (Salmo salar) parr were injected in either t...
Article
Full-text available
Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo...
Article
Full-text available
This paper describes the first observations of escaped farmed Atlantic salmon Salmo salar in the Arctic Ocean. Among 138 individuals of Atlantic salmon captured at the west coast of the Spitsbergen Island at Svalbard in the period 2008−2010, 11 individuals (8%) were classified as escaped farmed salmon based on genetic analysis and scale characters....
Article
Full-text available
Atlantic salmon populations are reported to be declining throughout its range, raising major management concerns. Variation in adult fish abundance may be due to variation in survival, growth, and timing of life history decisions. Given the complex life history, utilizing highly divergent habitats, the reasons for declines may be multiple and diffi...
Article
Full-text available
Mork, K. A., Gilbey, J., Hansen, L. P., Jensen, A. J., Jacobsen, J. A., Holm, M., Holst, J. C., Ó Maoiléidigh, N., Vikebø, F., McGinnity, P., Melle, W., Thomas, K., Verspoor, E., and Wennevik, V. 2012. Modelling the migration of post-smolt Atlantic salmon (Salmo salar) in the Northeast Atlantic. – ICES Journal of Marine Science, 69: 1616–1624. The...
Article
Full-text available
Jensen, A. J., Ó Maoiléidigh, N., Thomas, K., Einarsson, S. M., Haugland, M., Erkinaro, J., Fiske, P., Friedland, K. D., Gudmundsdottir, A. K., Haantie, J., Holm, M., Holst, J. C., Jacobsen, J. A., Jensås, J. G., Kuusela, J., Melle, W., Mork, K. A., Wennevik, V., and Østborg, G. M. 2012. Age and fine-scale marine growth of Atlantic salmon post-smol...
Article
Full-text available
A study over a 22-year period of first-time migrants (smolts) of three sympatric salmonids (Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and Arctic char (Salvelinus alpinus)) in a watercourse in northern Norway demonstrated that although there was considerable overlap in smolt migration timing among the species, Atlantic salmon migrat...
Article
Full-text available
Interspecific hybridization between Atlantic salmon and brown trout is well documented, but why it should vary so much among populations is not clear. Determining the maternal origin of hybrids can provide insights into the mechanisms underlying interspecific hybridization, but this information is lacking in many studies. Here we present a species-...
Article
Full-text available
We tested the importance of thermal adaptations and energy efficiency in relation to the geographical distribution of two competing freshwater salmonid fish species. Presence–absence data for Arctic char and brown trout were obtained from 1502 Norwegian lakes embracing both temperature and productivity gradients. The distributions were contrasted w...
Article
Full-text available
Hedger, R. D., Uglem, I., Thorstad, E. B., Finstad, B., Chittenden, C. M., Arechavala-Lopez, P., Jensen, A. J., Nilsen, R., and Økland, F. 2011. Behaviour of Atlantic cod, a marine fish predator, during Atlantic salmon post-smolt migration. – ICES Journal of Marine Science, 68: 2152–2162. Acoustic telemetry was used to determine the behavioural str...
Data
Partial Autocorrelation Function of the normalized residuals for each river. Numbers correspond to ‘ID’ column in Table S1. (TIF)
Data
Spatial similarities. Mantel correlogram computed for 12 geographical distance classes on the 60 normalized residual time series. Positive values of the Mantel correlation indicate that similarity within that class of distance is higher than average, whereas, it is negative when the similarity is lower. Filled dots indicate significant results (P<0...
Data
Full-text available
Summary of the variables used in this large-scale analysis ( n = 60 one-sea-winter Atlantic salmon time series). (PDF)
Data
Time series of Atlantic salmon grilse caught in the 60 rivers analyzed. Numbers correspond to ‘ID’ column in Table S1. Red dots highlight interpolated values for those time series with missing data. Note also that y-axis values differ among plots. (TIF)
Data
Rivers' characteristics. Box plots showing the variation in: (A) natural log-transformed catchment areas, (B) natural log-transformed mean water flow during upstream migration, (C) coastal migration distance (distance from river mouth to the coastal shelf), and (D) natural log-transformed steepness (ratio between altitude and river length) for the...
Data
Normalized residuals versus fitted values by river. Numbers correspond to ‘ID’ column in Table S1. (TIF)
Data
Pairwise Spearman correlations between river's normalized residuals and geographical distance (i.e. 1770 possible combinations). Open black circles indicate non-significant correlations; blue dots show significant correlations (301), and red dots show the significant pair correlations after Bonferroni correction (8; the corresponding rivers' number...
Data
Water temperature and runoff. Plot of water temperature (°C) against runoff (m3 s–1) during upstream migration months (June–August) measured in six Norwegian rivers (Tovdalselva, Audna, Vosso, Gaula, Jølstra and Vefsna) from 1992 to 2007. The fitted curve from a biexponential model is also shown. (TIF)
Data
Full-text available
List of the rivers which interannual grilse catches were analyzed in this study. Latitude (N) and longitude (E) give the geographical position of each river mouth. Overall mean ±SD (kg), and number of observations (years), with the number of missing years between parentheses, are also shown. The last column indicates the first year (yy) in the time...
Data
Median dates as well as earliest and latest dates of smolt run of Atlantic salmon in some Norwegian watersheds over several years. The descent date is defined as the day each year when 50% of the smolts have passed the gauging station. (PDF)
Data
Full-text available
Further details on catch data and model robustness. (PDF)
Data
Model validation. Normality of the within-group normalized residuals (A), and scatterplot of the normalized residuals versus the fitted values (B). In addition, no significant patterns were found when plotting the residuals versus each explanatory variable (not shown). Normal plot (C) and scatterplot (D) of estimated random effects. YearC indicates...
Data
Full-text available
Comparison of different models showing the number of parameters, Bayesian Information Criteria (BIC) and the difference in BIC values between each model and the model with the optimal random structure. First, we selected the appropriate random effects (Models 1 to 5) where the fixed component contained all explanatory variables and reasonable inter...
Article
Full-text available
Many Atlantic salmon, Salmo salar, populations are decreasing throughout the species' distributional range probably due to several factors acting in concert. A number of studies have documented the influence of freshwater and ocean conditions, climate variability and human impacts resulting from impoundment and aquaculture. However, most previous r...
Article
Full-text available
Some of the salmon rivers on the western and northern coasts of Norway are very cold, and the sea temperature outside these rivers is almost always higher than that in the river. Growth rates of Atlantic salmon (Salmo salar) parr and smolt ages and sizes have been examined in three such cold rivers. We found indications that the lower temperature l...
Article
Full-text available
Development time at different temperatures from hatching to 50% feeding was studied in Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) alevins. Live animals were used as food. In both species the development time decreased with increasing temperature, and these relationships were described by power curves. The results were compared wit...
Article
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Scales in Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) from two cold Norwegian rivers first appeared when the salmon were 33–34 mm long (total length) and the trout were 35–38 mm long. A considerable proportion of the yearlings did not form scales in years with a low water temperature (less than 1000–1100 degree-days from May to Oct...
Article
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More synchronous growth was observed between close, than more distantly separated populations of At