leifcst

• Peri, Marcos Llope; Blenckner, Thorsten; Vasilakopoulos, Paraskevas; McGinty, Niall; Lynam, Christopher P. & Hélaouët, Pierre [Vis alle 11 forfattere av denne artikkelen] (2026). Stress and resilience in northern European marine ecosystems. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 123(8), s. 1–7. doi: 10.1073/pnas.2527939123. Fulltekst i vitenarkiv Vis sammendrag

  Marine ecosystems are facing multiple pressures from human activities, such as fishing and nutrient inputs from farming and agriculture, compounded by the global effects of climate change. As a result, the ecosystem services that societies depend on are at risk from the cumulative impact of these pressures. To better understand how different ecosystems respond, it is essential to assess their resilience. While predicting ecosystem resilience remains challenging, significant progress has been made in developing methods to measure it. In this study, we assessed resilience in four northern European marine ecosystems: the Icelandic Waters, the Barents Sea, the Baltic Sea, and the North Sea, spanning 3 to 5 decades. “Folded stability landscapes” were constructed for the Baltic and North Sea. This region provides a unique setting, with a south-north gradient from temperate to subarctic environments and a southeast-northwest gradient from open to semienclosed topographies. The Icelandic Waters and Barents Sea evolved relatively continuously, while the Baltic Sea and North Sea underwent more drastic changes. By comparing results across these gradients, we explore the role of isolation, level of pressures, and food web complexity in shaping resilience patterns and discuss the implications for managing resilient marine ecosystems in the future.

• Helgesen, Kari Marie Olli; Aaen, Stian Mørch; Stige, Leif Christian; Horsberg, Tor Einar & Krutto, Annika (2026). Azamethiphos resistance in salmon lice (Lepeophtheirus salmonis) in Norway 2014–2022: A study of farm level resistance and treatment intensity. Aquaculture. ISSN 0044-8486. 612, s. 743273–743273. doi: 10.1016/j.aquaculture.2025.743273. Fulltekst i vitenarkiv Vis sammendrag

  Organophosphates have been used as bath treatment against salmon lice in aquaculture since the 1970s. Resistance to organophosphates was first suspected in salmon lice in the 1990s, while the exact resistance mechanism was described in 2015. Genetic testing of lice for this mechanism is commercially available in Norway and provides information used to make treatment choices. This study describes the resistance development in salmon lice against organophosphates in Norway 2014–2022, using a dataset from commercial testing. It includes a farm-level regression analysis to gain deeper insight into the relationship between treatments and resistance level. The main findings from this study are that the resistance level on a farm is associated with the geographic area the farm belongs to and that increased treatment frequency on the same farm and on neighbouring farms are associated with more resistance. The findings in the current study can be used for better resistance management, both for medicines where resistance is established and for medicines that are novel and where resistance is not established. They can, for example, be incorporated into models for resistance development used to simulate the effect of management practices on resistance development.

• Stige, Leif Christian; Aldrin, Magne Tommy; Engebretsen, Solveig; Rafoss, Trond & Jansen, Peder A (2026). The efficacy of lumpfish in controlling salmon lice in fish farms. Aquaculture. ISSN 0044-8486. 612(1). doi: 10.1016/j.aquaculture.2025.743137. Fulltekst i vitenarkiv Vis sammendrag

  Lumpfish (Cyclopterus lumpus) are frequently used as “cleaner fish” to control parasitic sea lice in salmonid fish farms, but it has been questioned whether the benefits in terms of sea louse control outweigh the economic and lumpfish-welfare costs involved. Here we estimated the efficacy of lumpfish in controlling salmon lice (Lepeophtheirus salmonis) in salmonid farms by combining analyses of occurrence of salmon lice in stomach contents of lumpfish and experimental results on digestion time. We then conducted scenario simulations of salmon louse dynamics in salmonid fish farms, by combining the lumpfish feeding model with a lumpfish growth model and a salmon louse population model. Results showed that at a mean lumpfish weight of 50 g and typical conditions for other factors (9 °C, 2 kg salmonids, and 0.8 pre-adult and adult salmon lice per salmonid), the estimated feeding rate was 0.17 salmon lice per lumpfish per day (95 % confidence interval: 0.12–0.22). This rate increased with salmon louse concentration, temperature and salmonid weight and decreased with lumpfish weight. Scenario simulations of salmon louse dynamics under conditions representative for salmonid farms in Norway suggested that stocking lumpfish from the start of the production cycle with a 1:10 lumpfish per salmon ratio on average postponed the first salmon louse treatment by 43 days. The longest postponement was at intermediate external infestation pressure. Scenario simulations for a network of farms suggested that coordinated and strategic use of lumpfish after a spring treatment may succeed in supressing salmon louse outbreaks through spring and summer.

• Olsen, Tora; Stige, Leif Christian; Dupont, Nicolas; Durant, Joël M & Langangen, Øystein Ole Gahr (2025). Reply to Bogstad et al. (2025) ‘Comment on “Repeated large declines in the Barents Sea capelin populations are associated with different ecosystem conditions” by Olsen et al. (2024)’. ICES Journal of Marine Science. ISSN 1054-3139. 82(4). doi: 10.1093/icesjms/fsaf054. Fulltekst i vitenarkiv Vis sammendrag

  Herring predates on young capelin in the Barents Sea (BS), which affects the recruitment of BS capelin. However, our modelling study does not support the hypothesis that Bogstad et al. advocated that herring predation is necessary for the observed large declines (collapses) of the BS capelin population. What Bogstad et al. do not consider is the magnitude of the herring predation effect compared to other influences on the population dynamics of capelin. Our results suggest that while herring significantly reduced age-0 abundance of capelin at the start of the collapses, these reductions were probably not the main cause of the subsequent large population declines. All models have limitations, but we do not agree with Bogstad et al. that model limitations were the reason for our findings on the importance of herring predation for capelin biomass collapses.

• Stige, Leif Christian; Fall, Johanna Jennifer Elisabeth & Langangen, Øystein Ole Gahr (2025). The Roles of Environmental Change and Fishing in Norwegian Coastal Cod Stock Dynamics. Fisheries Oceanography. ISSN 1054-6006. 34(4). doi: 10.1111/fog.12728. Fulltekst i vitenarkiv Vis sammendrag

  Disentangling the roles of fishing and environmental factors in fish stock dynamics is fundamental for sustainable fisheries management. The stock biomass of Norwegian coastal cod north of 67°N has varied between periods of increase and decline in recent decades, with declining biomass since 2014. Here we developed a population model for the dynamics of this stock. The model was statistically fitted to survey indices of abundance- and length-at-age and environmental covariates from 1995 to 2022. The final model included a negative effect of saithe biomass on survival to age 1, positive temperature effects on growth to ages 2 and 3, density dependence in survival and growth, size-dependent maturation, and negative fishery effects on adult survival. Hindcast scenario simulations, where environmental influences or mortality from fishing were fixed, were used to disentangle the roles of recruitment, growth and adult survival for stock fluctuations in recent decades. The changes in stock biomass appear mainly to be driven by adult survival and hence fishing. The fishery effects on stock biomass were mostly the direct effects of biomass removal, with no indication of fishery-caused recruitment failure at the spatial scale represented by the model.

• Stige, Leif Christian; Qviller, Lars; Viljugrein, Hildegunn & Tavornpanich, Saraya (2025). A salmon lice prediction model. Preventive Veterinary Medicine. ISSN 0167-5877. 235. doi: 10.1016/j.prevetmed.2024.106405. Fulltekst i vitenarkiv
• Stige, Leif Christian; Colquhoun, Duncan John & Oliveira, Victor Henrique Silva de (2025). Associations Between Delousing Practices and Pasteurellosis in Farmed Atlantic Salmon. Journal of Fish Diseases. ISSN 0140-7775. 48(5), s. 1–6. doi: 10.1111/jfd.14085. Fulltekst i vitenarkiv
• Olsen, Tora; Stige, Leif Christian; Dupont, Nicolas; Durant, Joël & Langangen, Øystein Ole Gahr (2024). Repeated large declines in the Barents Sea capelin population are associated with different ecosystem conditions. ICES Journal of Marine Science. ISSN 1054-3139. 81(8), s. 1584–1593. doi: 10.1093/icesjms/fsae101. Fulltekst i vitenarkiv Vis sammendrag

  Although fluctuations in the biomass of small pelagic fish are strong and rapid, they are largely investigated as individual events or generalized to what is common across several species and populations. The Barents Sea capelin population, which experienced four large decreases in biomass between 1980 and 2016, can be used to compare the similarity of causes and sequence of events leading up to large biomass decline in the same population. Here, we used an age-structured state-space model to investigate the possible contributions from somatic growth, food availability, temperature, predation by Atlantic cod, herring interactions, and/or fisheries on the capelin biomass declines. We recalculated total biomass while perturbing these effects and assessed the change in total biomass. We did not find a single, common cause for the dramatic biomass declines. Although median biomass increased in several of the scenarios, a large decline in total biomass was mostly retained. Atlantic cod predation and food availability influenced adult capelin biomass. Food availability mainly impacted the first period, while the importance of Atlantic cod predation increased from the first period to the third period. Reducing larval mortality from herring interactions or temperature did not suppress the biomass declines. Recruitment failures were maintained due to a combination of process errors and uncertainty in the effect of spawning biomass, and thus fisheries, on age 0 abundance. The impact of each perturbation depended on the specific ecosystem context at the time of the biomass decline.

• Stige, Leif Christian; Jansen, Peder A & Helgesen, Kari Marie Olli (2024). Effects of regional coordination of salmon louse control in reducing negative impacts of salmonid aquaculture on wild salmonids. International Journal for Parasitology. ISSN 0020-7519. 54(8-9), s. 463–474. doi: 10.1016/j.ijpara.2024.04.003. Fulltekst i vitenarkiv Vis sammendrag

  Parasitic salmon lice (Lepeophtheirus salmonis) are a constraint to the sustainable growth of salmonids in open net pens, and this issue has caused production to level off in recent years in the most aquaculture-intensive areas of Norway. The maximum allowed biomass at a regional level is regulated by using the so-called “traffic light” system, where salmon louse-induced mortality of migrating wild salmon post-smolts is evaluated against set targets. As a case study, we have investigated how a specific aquaculture-intensive area can reduce its louse levels sufficiently to achieve a low impact on wild salmon. Analyses of the output from a virtual post-smolt model that uses data on the reported number of salmon lice in fish farms as key input data and estimates the salmon louse-induced mortality of wild out-migrating Atlantic salmon post-smolts, suggested that female louse abundance on the local farms must be halved in spring to reach the goal implied by the traffic light system. The outcome of a modelling scenario simulating a proposed new plan for coordinated production and fallowing proved beneficial, with an overall reduction in louse infestations and treatment efforts. The interannual variability in louse abundance in spring, however, increased for this scenario, implying unacceptably high louse abundance when many farms were in their second production year. We then combined the scenario with coordinated production with other louse control measures. Only measures that reduced the density of farmed salmonids in open cages in the study area resulted in reductions in salmon louse infestations to acceptable levels. This could be achieved either by stocking with larger fish to reduce exposure time or by reducing fish numbers, e.g. by producing in closed units.

• Engebretsen, Solveig; Aldrin, Magne Tommy; Staven, Fredrik Ribsskog; Bendiksen, Eskil; Stige, Leif Christian & Jansen, Peder Andreas (2024). Heterogeneous Weight Development of Lumpfish (Cyclopterus lumpus) Used as Cleaner Fish in Atlantic Salmon (Salmo salar) Farming. Fishes. 9(9). doi: 10.3390/fishes9090336. Fulltekst i vitenarkiv Vis sammendrag

  Lumpfish (Cyclopterus lumpus) are used as cleaner fish in Atlantic salmon (Salmo salar) aquaculture as one of multiple control measures against salmon lice (Lepeophtheirus salmonis). Numerous studies have documented weight as an important factor for characterising the cleaning efficacy of individual lumpfish. Hence, the efficacy of lumpfish in fish farms depends on the size at stocking and the weight development over time. Here, we aimed to quantify how weight developed over time for lumpfish deployed in salmon farming sea cages in Norway through modelling the daily growth rate. We found that the coefficient of variation for lumpfish weight increased over time, implying that the standard deviation increased more than the expected weight. The data thus showed heterogeneous growth for lumpfish in salmon farming cages, where some individuals exhibited no apparent growth, and others significant proliferation. We found that the daily growth rate was best described as bell-shaped functions of weight and temperature, consistent with a sigmoid-shaped growth curve and an optimal temperature around 10 °C. These results allow for more realistic modelling of the efficacy of lumpfish in controlling salmon lice in fish farms, as one can combine estimates of weight-dependent cleaning efficacy with weight development over time.

• Dupont, Nicolas; Durant, Joël; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2024). Changes in prey-predator interactions in an Arctic food web under climate change. Progress in Oceanography. ISSN 0079-6611. 229, s. 1–16. doi: 10.1016/j.pocean.2024.103380. Fulltekst i vitenarkiv Vis sammendrag

  Global warming affects marine ecosystems by changing environmental conditions, ecosystem structure, and ecosystem functioning. In parts of the Arctic, increased sea temperature and decreased sea ice have led to a poleward expansion of boreal species and increased their interactions with native Arctic species. To investigate and quantify the changing interactions in an Arctic marine food web under new environmental conditions, we studied the interactions between key prey fish species in the seasonally ice-covered parts of the Barents Sea: adult polar cod (Boreogadus saida) and capelin (Mallotus villosus) and one of the major predators in the system: Atlantic cod (Gadus morhua). For this, we compared the predictive performance of threshold models predicting the abundance of adult polar cod as a function of Atlantic cod. Each model was associated with a hypothesis describing prey-predator interactions in different environmental conditions defined by threshold values of summer sea-ice or capelin stock biomass. The best predictive model showed that the predation effect of Atlantic cod on polar cod was strongest in years of low summer sea ice cover and low capelin stock biomass. Our results exemplified that Arctic species such as polar cod may experience increased predation pressure under climate change from boreal species such as Atlantic cod. These effects depend, however, not only on changes in abiotic drivers of species distributions, but also on food-web interactions involving mid-trophic level species such as capelin.

• Stige, Leif Christian; Huseby, Ragnar Bang; Helgesen, Kari Marie Olli; Aldrin, Magne Tommy & Qviller, Lars (2024). Consequences of reduced effectiveness of salmon lice treatments for lice control. Preventive Veterinary Medicine. ISSN 0167-5877. 224. doi: 10.1016/j.prevetmed.2024.106134. Fulltekst i vitenarkiv Vis sammendrag

  The effective control of ectoparasitic salmon lice, Lepeophtheirus salmonis, in fish farms is challenged by the salmon lice having developed resistance towards several antiparasitic drugs and by the effectiveness of non-medicinal treatments being limited by considerations of fish welfare. When new antiparasitics are introduced to the market, these should be used sparingly to slow resistance development. Using a population model for salmon lice parameterised for salmonid fish farms in Norway, we quantified how reduced treatment effectiveness influences treatment frequency and lice abundance. Furthermore, we investigated when in the production cycle a highly effective lice treatment leads to the largest reduction in the total number of treatments, mean lice abundance and lice larvae production. Results showed that reductions in treatment effectiveness to lower than 50% led to the steepest increases in treatment frequency and mean lice abundance, as well as to increased risk that lice abundance increased beyond control. The timing of the most effective treatment had only moderate effects on the total treatment need and the mean number of adult female lice through the production cycle, but large effect on the production of lice larvae in spring. These findings imply that farmers can optimise the timing of the most effective treatment to reduce the release of lice larvae in the period of year when wild salmonids are in coastal waters, without compromising total treatment need or mean lice levels.

• Aldrin, Magne Tommy; Huseby, Ragnar Bang; Stige, Leif Christian & Helgesen, Kari Marie Olli (2023). Estimated effectiveness of treatments against salmon lice in marine salmonid farming. Aquaculture. ISSN 0044-8486. 575. doi: 10.1016/j.aquaculture.2023.739749. Fulltekst i vitenarkiv Vis sammendrag

  We here estimate the effectiveness of ten types of salmon lice treatments currently used in the salmonid industry by analysing daily and cage-wise data from 90 full production cycles from farms spread along the Norwegian coast. The calculations are based on a stage-structured population model for salmon lice and accounts for the structure of the data, including the uncertainties that arise from the weekly counting of lice on a subset of the fish. Results suggest that the most commonly used treatment methods in the data set, i.e. thermal, mechanical and freshwater treatments, kill 70–80% of the lice in average, but with high variability. Feed treatments with emamectin benzoate are also commonly used, but are only estimated to kill around 35% of the lice in average. Bath treatments with hydrogen peroxide are estimated to kill around 74% and pyrethroids 50% of the lice in average. The other medicinal treatments were infrequently used in the data set and the estimates are therefore more uncertain. Of note is that the recently licenced bath treatment with imidacloprid is estimated to kill more than 99% of sessile and 98% of pre-adult and adult lice in average. The estimated effects of hydrogen peroxide, pyrethroids and azamethiphos, here based on data from 2017–2020, are lower than estimates from a previous analysis of production data from 2011–2014, possibly because of resistance development. In contrast, there is no indication of reduced effects of thermal, mechanical or freshwater treatments compared to previous analyses of production data from 2013–2018. These results allow comparing the effectiveness of the different treatment methods in a consistent and comprehensive way, hence enabling fish farmers and authorities to better balance the expected benefits of the treatments in terms of lice control against the economic costs, fish welfare and risk of resistance development.

• Gerland, Sebastian; Ingvaldsen, Randi Brunvær; Reigstad, Marit; Sundfjord, Arild; Bogstad, Bjarte & Chierici, Melissa [Vis alle 41 forfattere av denne artikkelen] (2023). Still Arctic? — The changing Barents Sea. Elementa: Science of the Anthropocene. 11(1), s. 1–62. doi: 10.1525/elementa.2022.00088. Fulltekst i vitenarkiv Vis sammendrag

  The Barents Sea is one of the Polar regions where current climate and ecosystem change is most pronounced. Here we review the current state of knowledge of the physical, chemical and biological systems in the Barents Sea. Physical conditions in this area are characterized by large seasonal contrasts between partial sea-ice cover in winter and spring versus predominantly open water in summer and autumn. Observations over recent decades show that surface air and ocean temperatures have increased, sea-ice extent has decreased, ocean stratification has weakened, and water chemistry and ecosystem components have changed, the latter in a direction often described as “Atlantification” or “borealisation,” with a less “Arctic” appearance. Temporal and spatial changes in the Barents Sea have a wider relevance, both in the context of large-scale climatic (air, water mass and sea-ice) transport processes and in comparison to other Arctic regions. These observed changes also have socioeconomic consequences, including for fisheries and other human activities. While several of the ongoing changes are monitored and quantified, observation and knowledge gaps remain, especially for winter months when field observations and sample collections are still sparse. Knowledge of the interplay of physical and biogeochemical drivers and ecosystem responses, including complex feedback processes, needs further development.

• Endo, Clarissa Akemi Kajiya; Skogen, Morten D.; Stige, Leif Christian; Hjøllo, Solfrid Sætre & Vikebø, Frode Bendiksen (2023). The effects of spatial and temporal variations in spawning on offspring survival in Northeast Arctic cod. ICES Journal of Marine Science. ISSN 1054-3139. 81(3), s. 616–626. doi: 10.1093/icesjms/fsad034. Fulltekst i vitenarkiv Vis sammendrag

  Climate change and harvesting result in temporal and spatial changes and variability in spawning, and thus in offspring ambient drift conditions. As a result, variable survival of offspring and thereby in recruitment are expected. This is especially true for species with long reproduction migration as is the case for some Atlantic cod stocks. We utilize biophysical model simulations to analyze survival from spawning until age 1 resulting from different scenarios of spatial and temporal changes in spawning. We find that survival is 1.5–2 times higher when spawning is shifted southwards as compared to northerly shifts. In general, survival is more sensitive to shifts in spawning location than in spawning time. Early spawning is only favourable if spawning is concurrently shifted farther north. A future spawning scenario with a northward shift in spawning grounds beyond what has been observed historically suggests reduced offspring survival and increased sensitivity to the timing of spawning.

• Yaragina, Natalia A.; Stige, Leif Christian & Langangen, Øystein Ole Gahr (2022). Bycatch data from ichthyoplankton surveys reveal long-term trends in gelatinous zooplankton in the Norwegian and Barents Seas. ICES Journal of Marine Science. ISSN 1054-3139. 79(3), s. 868–881. doi: 10.1093/icesjms/fsab225. Fulltekst i vitenarkiv
• Ohlberger, Jan; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2022). Age structure affects population productivity in an exploited fish species. Ecological Applications. ISSN 1051-0761. 32(5). doi: 10.1002/eap.2614. Fulltekst i vitenarkiv Vis sammendrag

  Long-term changes in the age and size structure of animal populations are well documented, yet their impacts on population productivity are poorly understood. Fishery exploitation can be a major driver of changes in population age–size structure because fisheries significantly increase mortality and often selectively remove larger and older fish. Climate change is another potential driver of shifts in the demographic structure of fish populations. Northeast Arctic (NEA) cod is the largest population of Atlantic cod (Gadus morhua) and one of the world's most important commercial fish stocks. This population has experienced considerable changes in population age–size structure over the past century, largely in response to fishing. In this study, we investigate whether changes in spawner age structure have affected population productivity in NEA cod, measured as recruits per spawning stock biomass, over the past 75 years. We find evidence that shifts in age structure toward younger spawners negatively affect population productivity, implying higher recruitment success when the spawning stock is composed of older individuals. The positive effect of an older spawning stock is likely linked to maternal effects and higher reproductive output of larger females. Our results indicate a threefold difference in productivity between the youngest and oldest spawning stock that has been observed since the 1950s. Further, our results suggest a positive effect of environmental temperature and a negative effect of intraspecific cannibalism by older juveniles on population productivity, which partly masked the effect of spawner age structure unless accounted for in the model. Collectively, these findings emphasize the importance of population age structure for the productivity of fish populations and suggest that harvest-induced demographic changes can have negative feedbacks for fisheries that lead to a younger spawning stock. Incorporating demographic data into harvest strategies could thus facilitate sustainable fishery management.

• Engebretsen, Solveig; Aldrin, Magne Tommy; Qviller, Lars; Stige, Leif Christian; Rafoss, Trond & Danielsen, Ole Roald [Vis alle 8 forfattere av denne artikkelen] (2022). Salmon lice (Lepeophtheirus salmonis) in the stomach contents of lumpfish (Cyclopterus lumpus) sampled from Norwegian fish farms: Relationship between lice grazing and operational conditions. Aquaculture. ISSN 0044-8486. 563(2). doi: 10.1016/j.aquaculture.2022.738967. Fulltekst i vitenarkiv Vis sammendrag

  Cleaner fish are commonly used as a control measure against salmon lice infestations in salmonid farms. Lumpfish (Cyclopterus lumpus) is the most common cleaner fish species used in Norwegian farms. However, little is known about how different operational, including environmental, conditions affect the salmon lice grazing efficacy by lumpfish. In this paper, we analyse salmon lice (Lepeophtheirus salmonis) in the stomach contents of a large sample of more than 20,000 lumpfish from 80 different Norwegian farms. We investigate the proportion of lumpfish with salmon lice and the mean number of salmon lice in the stomach contents of the lumpfish. We further explore how the salmon lice contents vary with different factors like lumpfish weight, weight of salmonids, salmon lice abundance in the cage, cloud cover, and sea temperature. We find that 3.1% of the 24,693 lumpfish contained salmon lice. Most of the lumpfish with salmon lice in their stomach contents contained few (one or two) lice, while there were a few lumpfish which contained many salmon lice. We find more salmon lice in the stomach contents with increasing abundance of salmon lice in the sea cage, lower weight of the salmonids, and in clear weather. Interestingly, for the relationship between lumpfish weight and salmon lice in the stomach contents, we find increased salmon lice grazing from ca. 5 g up to an optimal weight of ca. 40 g, and then a decrease from 40 g. Surprisingly, we find no relationship between sea temperature and salmon lice per lumpfish. We find more salmon lice in the stomach contents of the lumpfish with comparatively high condition. By studying the factors associated with most efficient salmon lice grazing, our paper contributes to understanding how different operational factors affect salmon lice grazing by lumpfish. For controllable factors, the results thus contribute to guiding the best practice for use of lumpfish as a salmon lice control measure.

• Dunse, Thorben; Dong, Kaixing; Aas, Kjetil Schanke & Stige, Leif Christian (2022). Regional-scale phytoplankton dynamics and their association with glacier meltwater runoff in Svalbard. Biogeosciences. ISSN 1726-4170. 19(2), s. 271–294. doi: 10.5194/bg-19-271-2022. Fulltekst i vitenarkiv Vis sammendrag

  Arctic amplification of global warming has accelerated mass loss of Arctic land ice over the past decades and led to increased freshwater discharge into glacier fjords and adjacent seas. Glacier freshwater discharge is typically associated with high sediment load which limits the euphotic depth but may also aid to provide surface waters with essential nutrients, thus having counteracting effects on marine productivity. In situ observations from a few measured fjords across the Arctic indicate that glacier fjords dominated by marine-terminating glaciers are typically more productive than those with only land-terminating glaciers. Here we combine chlorophyll a from satellite ocean color, an indicator of phytoplankton biomass, with glacier meltwater runoff from climatic mass-balance modeling to establish a statistical model of summertime phytoplankton dynamics in Svalbard (mid-June to September). Statistical analysis reveals significant and positive spatiotemporal associations of chlorophyll a with glacier runoff for 7 out of 14 primary hydrological regions but only within 10 km distance from the shore. These seven regions consist predominantly of the major fjord systems of Svalbard. The adjacent land areas are characterized by a wide range of total glacier coverage (35.5%to 81.2 %) and fraction of marine-terminating glacier area (40.2% to 87.4 %). We find that an increase in specific glacier-runoff rate of 10mm water equivalent per 8 d period raises summertime chlorophyll a concentrations by 5.2% to 20.0%, depending on the region. During the annual peak discharge we estimate that glacier runoff increases chlorophyll a by 13.1% to 50.2% compared to situations with no runoff. This suggests that glacier runoff is an important factor sustaining summertime phytoplankton production in Svalbard fjords, in line with findings from several fjords in Greenland. In contrast, for regions bordering open coasts, and beyond 10 km distance from the shore, we do not find significant associations of chlorophyll a with runoff. In these regions, physical ocean and sea-ice variables control chlorophyll a, pointing at the importance of a late sea-ice breakup in northern Svalbard, as well as the advection of Atlantic water masses along the West Spitsbergen Current for summertime phytoplankton dynamics. Our method allows for the investigation and monitoring of glacier-runoff effects on primary production throughout the summer season and is applicable on a pan-Arctic scale, thus complementing valuable but scarce in situ measurements in both space and time.

• Planque, Benjamin; Aarflot, Johanna Myrseth; Buttay, Lucie; Carroll, JoLynn; Fransner, Sara Filippa Krusmynta & Hansen, Cecilie [Vis alle 17 forfattere av denne artikkelen] (2022). A standard protocol for describing the evaluation of ecological models. Ecological Modelling. ISSN 0304-3800. 471. doi: 10.1016/j.ecolmodel.2022.110059. Fulltekst i vitenarkiv Vis sammendrag

  Numerical models of ecological systems are increasingly used to address complex environmental and resource management questions. One challenge for scientists, managers, and stakeholders is to appraise how well suited these models are to answer questions of scientific or societal relevance, that is, to perform, communicate, or access transparent evaluations of ecological models. While there have been substantial developments to support standardised descriptions of ecological models, less has been done to standardise and to report model evaluation practices. We present here a general protocol designed to guide the reporting of model evaluation. The protocol is organised in three major parts: the objective(s) of the modelling application, the ecological patterns o relevance and the evaluation methodology proper, and is termed the OPE (objectives, patterns, evaluation) protocol. We present the 25 questions of the OPE protocol which address the many aspects of the evaluation process and then apply them to six case studies based on a diversity of ecological models. In addition to standardising and increasing the transparency of the model evaluation process, we find that going through the OPE protocol helps modelers to think more deeply about the evaluation of their models. From this last point, we suggest that it would be highly beneficial for modelers to consider the OPE early in the modelling process, in addition to using it as a reporting tool and as a reviewing tool. Standardisation Best practice Ecological patterns Skill assessment Transparency

• Langangen, Øystein Ole Gahr; Ohlberger, Jan Philipp; Stige, Leif Christian; Patin, Rémi; Buttay, Lucie & Stenseth, Nils Christian [Vis alle 8 forfattere av denne artikkelen] (2022). Effects of early life mass mortality events on fish populations. Fish and Fisheries. ISSN 1467-2960. 24(1), s. 176–186. doi: 10.1111/faf.12718. Fulltekst i vitenarkiv Vis sammendrag

  Mass mortality events are ubiquitous in nature and can be caused by, for example, diseases, extreme weather and human perturbations such as contamination. Despite being prevalent and rising globally, how mass mortality in early life causes population-level effects such as reduced total population biomass, is not fully explored. In particular for fish, mass mortality affecting early life may be dampened by compensatory density-dependent processes. However, due to large variations in year-class strength, potentially caused by density-independent variability in survival, the impact at the population level may be high in certain years. We quantify population-level impacts at two levels of mass mortality (50% and 99% additional mortality) during early life across 40 fish species using age-structured population dynamics models. The findings from these species-specific models are further supported by an analysis of detailed stock-specific models for three of the species. We find that population impacts are highly variable between years and species. Short-lived species that exhibit a low degree of compensatory density dependence and high interannual variation in survival experience the strongest impacts at the population level. These quantitative and general relationships allow predicting the range of potential impacts of mass mortality events on species based on their life history. This is critical considering that the frequency and severity of mass mortality events are increasing worldwide.

• Stige, Leif Christian; Helgesen, Kari Marie Olli; Viljugrein, Hildegunn & Qviller, Lars (2022). Modelling salmon lice-induced mortality of wild salmon post-smolts is highly sensitive to calibration data. Aquaculture Environment Interactions. ISSN 1869-215X. 14, s. 263–277. doi: 10.3354/aei00443. Fulltekst i vitenarkiv
• Lundsør, Elisabeth; Eikrem, Wenche; Stige, Leif Christian; Engesmo, Anette; Gran-Stadniczeñko, Sandra & Edvardsen, Bente (2022). Changes in phytoplankton community structure over a century in relation to environmental factors. Journal of Plankton Research. ISSN 0142-7873. 44(6), s. 854–871. doi: 10.1093/plankt/fbac055. Fulltekst i vitenarkiv Vis sammendrag

  Changes in phytoplankton abundance and biomass during the period 1933–2020 were examined by statistical modeling using data from the Inner Oslofjorden phytoplankton database. The phytoplankton abundances increased with eutrophication from 1930s to 1970s, but with the implementation of sewage cleaning measures and a resulting reduction in nutrient releases, the phytoplankton abundance has since then decreased significantly. The onset of the seasonal blooms has started progressively later during the last 15 years, especially the spring bloom. The delayed spring bloom co-occurred with increasing temperature in winter and spring. The diatom biomass decreased more than that of dinoflagellates and other microeukaryotes. The diatom genus Skeletonema dominated the spring bloom and was found to be the key taxa in explaining these changes in abundance and phenology. Extensive summer blooms of the coccolithophore Emiliania huxleyi, which has been characteristic for the inner Oslofjorden, has also gradually decreased during the last decades, along with reducing eutrophication. Dinoflagellates have not had the same reduction in abundance as the other groups. Despite an increasing proportion of dinoflagellates compared with other taxa, there are no clear indications of increased occurrence of toxic algal blooms in inner Oslofjorden. However, the introduction of new “toxin-producing” species may cause concern.

• Endo, Clarissa Akemi Kajiya; Stige, Leif Christian; Skogen, Morten D.; Ciannelli, Lorenzo & Vikebø, Frode Bendiksen (2022). Two decades of match-mismatch in Northeast Arctic cod – Feeding conditions and survival. Frontiers in Marine Science. 9, s. 1–14. doi: 10.3389/fmars.2022.767290. Fulltekst i vitenarkiv Vis sammendrag

  The successful recruitment of Northeast Arctic (NEA) cod is thought to depend on sufficient and suitable prey for the newly hatched larvae, in particular the nauplii stages of the lipid-rich calanoid copepod species Calanus finmarchicus. The role of spatial and temporal variations in prey availability in combination with temperature and other factors in influencing growth and survival of cod larvae is, however, incompletely understood. By combining an individual based model for NEA cod larvae at the Norwegian coast with a high-resolution ocean model and a nutrient-phytoplankton-zooplankton-detritus model providing 18 years of daily environmental conditions and prey availability we assessed larval growth and survival until they settle in their feeding habitat in the Barents Sea in early fall. We find on average a two-week delay from the peak timing of first-feeding cod larvae to the peak in prey availability. In warm years, more larvae experience food limitation than in normal years. The positive effects of high temperature on growth, survival and ultimately recruitment are nonetheless larger than the negative effects of food limitation. Food limitation mainly affects larvae spawned in southern areas or late in the spawning season as these larvae experience the highest temperatures and have the highest energy requirements. Our findings highlight the spatial and temporal differences in mechanisms that regulate growth and survival of early life stages of NEA cod and suggest that spatially resolved data may be essential for understanding match-mismatch dynamics.

• Dong, Kaixing; Kvile, Kristina Øie; Stenseth, Nils C. & Stige, Leif C. (2021). Associations between timing and magnitude of spring blooms and zooplankton dynamics in the southwestern Barents Sea. Marine Ecology Progress Series. ISSN 0171-8630. 668, s. 57–72. doi: 10.3354/meps13740. Fulltekst i vitenarkiv Vis sammendrag

  During the past decades, many high-latitude marine systems have experienced a strong warming trend with poorly understood consequences for trophic coupling and ecosystem functioning. A key knowledge gap is how timing and magnitude of phytoplankton blooms influence higher trophic levels. We investigated associations between timing and magnitude of phytoplankton blooms and dynamics of 3 size fractions of mesozooplankton from 1998 to 2019. The study focused on the southwestern Barents Sea, an Arctic shelf sea area that is dominated by relatively warm Atlantic waters and which remains ice-free year-round. Results showed that an early spring bloom (late April to early May) was associated with high biomass of medium-sized (1-2 mm) zooplankton in areas ‘downstream’ of the phytoplankton bloom, along the prevailing currents. Conversely, a late spring bloom was associated with high biomass of small-sized (0.180-1 mm) zooplankton, with no spatial shift. High peak magnitude of the bloom (>5 mg chl a m-3) was associated with low zooplankton biomass, suggesting either top-down control or that the zooplankton utilized intense and presumably short blooms inefficiently. For small- and large-sized (>2 mm) zooplankton, the relationship was nonlinear, as zooplankton biomass was also low when bloom peak magnitude was very low (<4 mg chl a m-3). Our findings imply that if phytoplankton blooms in the region occur earlier, this will increase the biomass of medium-sized zooplankton that are important prey for planktivorous fishes. Moreover, our study highlights that increased biomass of phytoplankton does not necessarily translate into increased zooplankton biomass.

• Stige, Leif Christian; Helgesen, Kari Marie Olli; Viljugrein, Hildegunn & Qviller, Lars (2021). A statistical mechanistic approach including temperature and salinity effects to improve salmon lice modelling of infestation pressure. Aquaculture Environment Interactions. ISSN 1869-215X. 13, s. 339–361. doi: 10.3354/aei00410. Fulltekst i vitenarkiv
• Kvile, Kristina Øie; Prokopchuk, Irina P. & Stige, Leif Christian (2021). Environmental effects on Calanus finmarchicus abundance and depth distribution in the Barents Sea. ICES Journal of Marine Science. ISSN 1054-3139. 79(3), s. 815–828. doi: 10.1093/icesjms/fsab133. Fulltekst i vitenarkiv Vis sammendrag

  The vertical migrations performed by zooplankton at daily and seasonal scales are important for marine ecosystem dynamics and biogeochemical cycles. We analysed associations between seasonal variation in abundance and depth distribution of the copepod Calanus finmarchicus and temperature and predation pressure from visual (capelin and herring) and non-visual (ctenophores) predators, using data from a > 30-year survey in the southwestern Barents Sea. Calanus finmarchicus abundances were significantly reduced in upper waters with increased capelin biomass, possibly due to a combination of predation mortality and active avoidance of the upper layer. The weighted mean depth of Calanus finmarchicus tended to become shallower, and abundances in deeper layers lower, with a high probability of ctenophore occurrence, possibly due to a predation effect at depth. Temperature influenced the seasonal timing of Calanus finmarchicus, but appeared less important for depth distribution. This study illustrates how climate-driven changes in the physical and biological environment can influence the seasonal and vertical distribution of zooplankton, which has major implications for the flow of energy and nutrients in marine ecosystems.

• Durant, Joël M; Yaragina, Natalia & Stige, Leif Christian (2021). The role of spatial distribution for growth and survival of juvenile cod Gadus morhua in the Barents Sea. ICES Journal of Marine Science. ISSN 1054-3139. 78(8), s. 2700–2708. doi: 10.1093/icesjms/fsab143. Fulltekst i vitenarkiv Vis sammendrag

  While the importance of early life survival and growth variations for population dynamics is well documented, there is still a relatively limited understanding of how survival and growth is affected by the species’ spatial distribution. Using Barents Sea spatial bottom survey data (1994–2018), we study the spatiotemporal variability of the juvenile Atlantic cod (Gadus morhua) growth and survival. We used indices of the spatial distribution of juvenile cod at age-1 to study the role of distribution for the change in abundance and mean body size through their second winter of life (from age-1 to age-2). Over the 24 years analysed, we found that the location where the age-1 cod are in the Barents Sea matters for their growth and survival. We found that year-classes growing up in the western Barents Sea have higher mortality but faster growth than year-classes distributed farther east. Our results indicate that the biotic and abiotic conditions encountered at the settlement location may influence the spatial survival and growth of age-1 cod and subsequently the population dynamics. Our results underscore the importance of distribution for survival and growth early in life and by providing this essential information has implications for stock assessment and spatial fisheries management.

• Dunse, Thorben; Dong, Kaixing; Aas, Kjetil Schanke & Stige, Leif Christian (2021). Regional-scale phytoplankton dynamics and their association with glacier meltwater runoff in Svalbard. Biogeosciences Discussions (BGD). ISSN 1810-6285. doi: 10.5194/bg-2021-181. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joël; Gjøsæter, Harald; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2021). Effects of sea ice cover, temperature and predation on the stock dynamics of the key Arctic fish species polar cod Boreogadus saida. Marine Ecology Progress Series. ISSN 0171-8630. 677, s. 141–159. doi: 10.3354/meps13878. Fulltekst i vitenarkiv Vis sammendrag

  Climate change has large effects on population dynamics of fish species in high latitude ecosystems. Arctic fish stocks experience multiple pressures with changing abiotic living conditions and increased competition and predation from boreal species. However, there are many unknowns regarding how environmental change influences the dynamics of those populations. Here, we focused on the Barents Sea polar cod, a pan-Arctic zooplanktivorous key fish species physiologically and ecologically adapted to the presence of sea ice. We developed an age-resolved Bayesian state-space model of the dynamics of polar cod based on 30 yr of survey data (1986-2015). Using this model, we quantified how inter-annual changes in abundance were associated with abiotic variables (temperature and sea ice cover) and biotic variables (prey biomasses and a predation index). Using the model output, we used a hindcast scenario approach to investigate to which degree the observed variations in total population size were related to the abiotic or biotic variables. Our results showed that variation in abundance of young polar cod (ages 0 and 1) was best explained by abiotic variables while variation in the older age groups (ages 3 and 4) was best explained by predation. Hindcast scenarios showed that the abiotic variables had a more evident effect than predation on population dynamics, but none of the variables we considered could explain the drastic population decline observed in recent years. Our work shows the advantages of studying age-specific responses as a stepping stone to understand changes at the population level.

• Feng, Jianfeng; Stige, Leif Christian; Hessen, Dag Olav; Zuo, Zhiling; Zhu, Lin & Stenseth, Nils Christian (2021). A Threshold Sea-Surface Temperature at 14°C for Phytoplankton Nonlinear Responses to Ocean Warming. Global Biogeochemical Cycles. ISSN 0886-6236. 35(5), s. 1–13. doi: 10.1029/2020GB006808. Fulltekst i vitenarkiv Vis sammendrag

  Marine phytoplankton play a central role in supporting life in the oceans and profoundly affect global biogeochemical cycles. Previous studies have revealed positive effects of sea-surface temperature (SST) on phytoplankton in terms of chlorophyll a concentrations (Chla) in high latitude oceans, while negative effects prevail in tropical and midlatitude oceans as well as under stratified summer conditions at higher latitudes. Based on a global analysis of 20 years of ocean Chla and SST data, we first investigated how interannual variability in SST is associated with Chla for each month of the season for every ocean province. We then quantified how the SST-Chla relationships varied with the long-term average (baseline) SST. We found significant season-dependent SST effects on Chla in most ocean provinces. The signs and magnitudes of these effects were consistently associated with the baseline SST, with a shift from positive to negative effects of SST on Chla around 14°C. Based on field observations and literature data, we also estimated the interaction between nitrate limitation and temperature on the SST-Chla relationship. Our findings suggest that the ocean warming effects on Chla depend consistently on the baseline temperature, both with regard to seasonal effects within regions and regional effects between high and low latitude provinces. Our analysis further suggests that the monthly 14°C isotherms can be used as a first approximation to separate areas and seasons where warming has opposite signed effects.

• Ciannelli, Lorenzo; Neuheimer, Anna B.; Stige, Leif Christian; Frank, Kenneth T.; Durant, Joël & Hunsicker, Mary E. [Vis alle 10 forfattere av denne artikkelen] (2021). Ontogenetic spatial constraints of sub-arctic marine fish species. Fish and Fisheries. ISSN 1467-2960. s. 1–16. doi: 10.1111/faf.12619. Fulltekst i vitenarkiv Vis sammendrag

  Climate change influences ecological processes and biogeochemical cycles of marine environments. Species may respond and adapt to these changes through shifting spatial distributions, but options may be limited by the required occupancy of essential habitats which are anchored in space. Marine fish species typically have complex life cycles composed of multiple life stages with different degrees of habitat preferences. Limited knowledge of when spatial constraints are most likely to occur in marine fish life cycles has impeded the development of realistic distribution forecasts. In this study, we develop and implement analytical techniques to identify spatial constraints, defined by both the consistency through which a particular geographic area is used year after year, and by the extent of such area with respect to the entire population range. This approach is applied to ten case studies including six groundfish species from the Eastern Bering Sea, three from the Scotian Shelf, and one from the Barents Sea. Our analyses illustrate that the early phase of the species’ life cycle is more spatially constrained than older life stages, and that adult stages are more closely associated with particular temperatures or climate velocities. We detected significant species-specific variability in both the degree to which species are anchored in space throughout their life cycle, and the ontogenetic changes of the geographic association. Some of this variability can be explained by the species life history strategy and this provides promising avenues to extend similar analyses to data poor species. The presence of life history spatial constraints, particularly during early life stages, indicates restrictions exist to changes of spatial distribution and thus questions the assertion that global warming will uniformly result in an increase of harvest at higher latitudes and decreases at lower latitudes. Species distribution models are often parameterized from data based on life stages that are highly variable in space, such as the adult stages during summer months which may result in unrealistic forecasts of distribution. Our study develops ecological and analytical insights that are critical for developing accurate projections of species distributions under different climate change scenarios.

• Langangen, Øystein & Stige, Leif Christian (2021). Shedding light on the link between the spatial distribution of eggs and survival in Northeast Arctic cod. Fisheries Oceanography. ISSN 1054-6006. 30, s. 429–436. doi: 10.1111/fog.12528. Fulltekst i vitenarkiv Vis sammendrag

  Spreading the offspring in space and time may offer bet-hedging benefits by buffering environmental influences on parts of the offspring distribution. It has previously been shown that high mean age and size of spawners in the Northeast Arctic stock of Atlantic cod (Gadus morhua) is positively associated with high abundance and wide spatiotemporal distribution of eggs. However, little support has been found for a wide egg distribution acting as a buffer against environmental influences by leading to higher mean or less variable recruitment. The lacking relation between egg distribution and recruitment can be due to data limitation or alternatively that wide egg distributions may be of limited relevance for survival in later stages. To investigate these two alternatives, we analysed the output from a mechanistic coupled physical–biological drift model that projected the abundance of juvenile cod on the nursing grounds in the Barents Sea from empirically estimated egg distributions. The projections were performed with initial egg distributions reflecting the expected distributions at high and low mean weight of the spawners. We found that the extended distribution at the fringes only marginally contributed to recruitment, as a large proportion of the extra eggs at high mean age and size of spawners did not reach suitable nursing areas or failed to grow to a suitable size by the end of the season. In conclusion, our results suggest that the buffering effect of a geographically wide distribution of spawning products is insignificant compared to other effects on recruitment.

• Dupont, Nicolas; Durant, Joel Marcel; Langangen, Øystein; Gjøsæter, Harald & Stige, Leif Christian (2020). Sea ice, temperature, and prey effects on annual variations in mean lengths of a key Arctic fish, Boreogadus saida, in the Barents Sea. ICES Journal of Marine Science. ISSN 1054-3139. 77(5), s. 1796–1805. doi: 10.1093/icesjms/fsaa040. Fulltekst i vitenarkiv Vis sammendrag

  Oceanographic conditions in the Arctic are changing, with sea ice cover decreasing and sea temperatures increasing. Our understanding of the effects on marine populations in the area is, however, limited. Here, we focus on the Barents Sea stock of polar cod (Boreogadus saida). Polar cod is a key fish species for the transfer of energy from zooplankton to higher trophic levels in the Arctic food web. We analyse the relationships between 30-year data series on the length-at-age of polar cod cohorts (ages 0–4) and sea surface temperature, sea ice concentration, prey biomasses, predator indices, and length-at-age the previous year using multiple linear regression. Results for several ages showed that high length-at-age is significantly associated with low sea ice concentration and high length-at-age the previous year. Only length-at-age for age 1 shows a positive significant relationship with prey biomass. Our results suggest that retreating sea ice has positive effects on the growth of polar cod in the Barents Sea despite previous observations of a stagnating stock biomass and decreasing stock abundance. Our results contribute to identifying mechanisms by which climate variability affects the polar cod population, with implications for our understanding of how future climate change may affect Arctic ecosystems.

• Dong, Kaixing; Kvile, Kristina Øie; Stenseth, Nils Christian & Stige, Leif Christian (2020). Associations among temperature, sea ice and phytoplankton bloom dynamics in the Barents Sea. Marine Ecology Progress Series. ISSN 0171-8630. 635, s. 25–36. doi: 10.3354/meps13218. Fulltekst i vitenarkiv
• Ferreira, Ana Sofia De Araújo; Stige, Leif Christian; Neuheimer, Anna B.; Bogstad, Bjarte; Yaragina, Natalia A. & Prokopchuk, Irina [Vis alle 7 forfattere av denne artikkelen] (2020). Match-mismatch dynamics in the Norwegian-Barents Sea system. Marine Ecology Progress Series. ISSN 0171-8630. 650, s. 81–94. doi: 10.3354/MEPS13276. Fulltekst i vitenarkiv Vis sammendrag

  A key process affecting variation in the recruitment of fish into fisheries is the spatio-temporal overlap between prey and predator (match-mismatch hypothesis, MMH). The Northeast Arctic cod Gadus morhua and its dominant prey, the copepod Calanus finmarchicus, have long been studied in the Norwegian-Barents Sea system. However, the mechanistic explanation of how cod survival is affected by MMH dynamics remains unclear. Most MMH studies have focused on either the time synchrony or the spatial overlap between trophic levels. Here, we used G. morhua larvae and C. finmarchicus data collected in the Norwegian-Barents Sea via ichthyoplankton surveys from 1959-1992 to assess the effect of the predator-prey relationship on predator recruitment to the fisheries at age 3 (as a measure of survival) and to develop a metric of predator-prey overlap using spatio-temporal statistical models. We then compared the interannual variability of the predator-prey overlap with the predator’s abundance at recruitment to assess how MMH dynamics explain the survival of cod during its early life stages. We found that the amount of overlap between cod larvae (length: 11-15 mm) and their prey explained 29% of cod recruitment variability. Positive correlations between predator-prey overlap and subsequent recruitment were also found for predators of 6-10 and 16-20 mm, but not for 21+ mm. This improved predator-prey overlap metric is thus (1) useful to better understand how predator-prey dynamics at early life stages of fish impact the survival of later stages; and (2) a valuable tool for assessing the state of an ecosystem.

• Lundsør, Elisabeth; Stige, Leif Christian; Sørensen, Kai & Edvardsen, Bente (2020). Long-term coastal monitoring data show nutrient-driven reduction in chlorophyll. Journal of Sea Research. ISSN 1385-1101. 164. doi: 10.1016/j.seares.2020.101925. Fulltekst i vitenarkiv Vis sammendrag

  In this study we have compiled a long-term monitoring dataset from the inner Oslofjorden and supplemented it with short-term research data from the same station. Using generalized additive models analysing the data from this time series, we have examined how chlorophyll-a, hydrography, and various nutrient concentrations have changed during 1973–2017 and how they correlate. We describe the seasonality in chlorophyll-a, nitrogen, phosphorus, Secchi-depth, temperature and salinity and how the levels of each variable have changed the last forty years. The results show specifically how levels of chlorophyll-a have decreased significantly and how this correlates with decrease in nitrogen and phosphorus levels. Our results show a significantly positive correlation between chlorophyll-a and phosphorus during spring bloom and between chlorophyll-a and nitrogen during autumn bloom. However, phosphorus levels have increased again during the last 20 years, but chlorophyll-a levels are still low, indicating that the chlorophyll-a level currently may be controlled by the continuous decreasing trend in nitrogen. If nitrogen increase again, the chlorophyll-a level may also begin to increase. The impact of increasing temperature and possible change in starting point for the growing season should be studied further.

• Endo, Clarissa; Vikebø, Frode Bendiksen; Yaragina, Natalia A.; Hjøllo, Solfrid Sætre & Stige, Leif Christian (2020). Effects of climate and spawning stock structure on the spatial distribution of Northeast Arctic cod larvae. ICES Journal of Marine Science. ISSN 1054-3139. 78, s. 666–679. doi: 10.1093/icesjms/fsaa057. Fulltekst i vitenarkiv Vis sammendrag

  The spatial distribution of fish early life stages can impact recruitment at later stages and affect population size and resilience. Northeast Arctic (NEA) cod spawning occurs along the Norwegian coast. Eggs, larvae, and pelagic juveniles drift near-surface towards the Barents Sea nursery area. In this study, a 35-year long time series of NEA cod larvae data was analysed in combination with factors that potentially may affect the distribution of eggs and larvae. These factors included biological aspects of the spawning stock, and environmental variables, such as water temperature, wind, ocean current, and prey abundance. Our aim was to shed light on how these factors influence larval abundance and distribution and how larval abundance and distribution influenced recruitment at age 3. We found that biomass and mean weight of the spawners were positively associated with larval abundance and that a high liver condition index of the spawners was associated with a north-easterly distribution of the larvae. The environmental variables showed generally weak or no correlations with abundance or distribution of larvae. Lastly, we found significant association between larval abundance and year-class abundance at age 3, while the spatial distribution metrics of the larvae, i.e. distribution extent, mean longitude, and mean latitude, showed no significant association with future year-class abundance.

• Xu, Lei; Stige, Leif Christian; Leirs, Herwig; Neerinckx, Simon; Gage, Kenneth L. & Yang, Ruifu [Vis alle 13 forfattere av denne artikkelen] (2019). Historical and genomic data reveal the influencing factors on global transmission velocity of plague during the Third Pandemic. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 116(24), s. 11833–11838. doi: 10.1073/pnas.1901366116. Fulltekst i vitenarkiv Vis sammendrag

  Quantitative knowledge about which natural and anthropogenic factors influence the global spread of plague remains sparse. We estimated the worldwide spreading velocity of plague during the Third Pandemic, using more than 200 years of extensive human plague case records and genomic data, and analyzed the association of spatiotemporal environmental factors with spreading velocity. Here, we show that two lineages, 2.MED and 1.ORI3, spread significantly faster than others, possibly reflecting differences among strains in transmission mechanisms and virulence. Plague spread fastest in regions with low population density and high proportion of pasture- or forestland, findings that should be taken into account for effective plague monitoring and control. Temperature exhibited a nonlinear, U-shaped association with spread speed, with a minimum around 20 °C, while precipitation showed a positive association. Our results suggest that global warming may accelerate plague spread in warm, tropical regions and that the projected increased precipitation in the Northern Hemisphere may increase plague spread in relevant regions.

• Durant, Joel Marcel; Molinero, Juan Carlos; Ottersen, Geir; Reygondeau, Gabriel; Stige, Leif Christian & Langangen, Øystein (2019). Contrasting effects of rising temperatures on trophic interactions in marine ecosystems. Scientific Reports. 9:15213, s. 1–9. doi: 10.1038/s41598-019-51607-w. Fulltekst i vitenarkiv Vis sammendrag

  In high-latitude marine environments, primary producers and their consumers show seasonal peaks of abundance in response to annual light cycle, water column stability and nutrient availability. Predatory species have adapted to this pattern by synchronising life-history events such as reproduction with prey availability. However, changing temperatures may pose unprecedented challenges by decoupling the predator-prey interactions. Here we build a predator-prey model accounting for the full life-cycle of fish and zooplankton including their phenology. The model assumes that fish production is bottom-up controlled by zooplankton prey abundance and match or mismatch between predator and prey phenology, and is parameterised based on empirical findings of how climate influences phenology and prey abundance. With this model, we project possible climate-warming effects on match-mismatch dynamics in Arcto-boreal and temperate biomes. We find a strong dependence on synchrony with zooplankton prey in the Arcto-boreal fish population, pointing towards a possible pronounced population decline with warming because of frequent desynchronization with its zooplankton prey. In contrast, the temperate fish population appears better able to track changes in prey timing and hence avoid strong population decline. These results underline that climate change may enhance the risks of predator-prey seasonal asynchrony and fish population declines at higher latitudes.

• Stige, Leif Christian; Rogers, Lauren; Neuheimer, Anna B.; Hunsicker, Mary E.; Yaragina, Natalia A. & Ottersen, Geir [Vis alle 9 forfattere av denne artikkelen] (2019). Density‐ and size‐dependent mortality in fish early life stages. Fish and Fisheries. ISSN 1467-2960. 20(5), s. 962–976. doi: 10.1111/faf.12391. Fulltekst i vitenarkiv Vis sammendrag

  The importance of survival and growth variations early in life for population dynamics depends on the degrees of compensatory density dependence and size dependence in survival at later life stages. Quantifying density‐ and size‐dependent mortality at different juvenile stages is therefore important to understand and potentially predict the recruitment to the population. We applied a statistical state‐space modelling approach to analyse time series of abundance and mean body size of larval and juvenile fish. The focus was to identify the importance of abundance and body size for growth and survival through successive larval and juvenile age intervals, and to quantify how the dynamics propagate through the early life to influence recruitment. We thus identified both relevant ages and mechanisms (i.e. density dependence and size dependence in survival and growth) linking recruitment variability to early life dynamics. The analysis was conducted on six economically and ecologically important fish populations from cold temperate and sub‐arctic marine ecosystems. Our results underscore the importance of size for survival early in life. The comparative analysis suggests that size‐dependent mortality and density‐dependent growth frequently occur at a transition from pelagic to demersal habitats, which may be linked to competition for suitable habitat. The generality of this hypothesis warrants testing in future research.

• Stige, Leif Christian; Eriksen, Elena; Dalpadado, Padmini & Ono, Kotaro (2019). Direct and indirect effects of sea ice cover on major zooplankton groups and planktivorous fishes in the Barents Sea. ICES Journal of Marine Science. ISSN 1054-3139. 76(Supplement_1), s. i24–i36. doi: 10.1093/icesjms/fsz063. Fulltekst i vitenarkiv Vis sammendrag

  Reductions in Arctic sea ice affect marine food webs through a multitude of direct and indirect effects. We here analysed direct, indirect, and delayed associations between winter sea ice cover and year-to-year changes in biomasses of the main zooplankton groups (copepods, krill, amphipods) and planktivorous fishes (capelin, polar cod) in the central and northern Barents Sea from 1980 to 2015. Climate effects and species interactions were estimated jointly in a Bayesian state-space model framework. We found that population biomass of capelin increased in years with low sea ice cover, while biomasses of copepods and amphipods decreased. Furthermore, results suggested strong bottom-up effects by krill on capelin and by copepods on amphipods and top-down effects by polar cod on amphipods and by capelin on krill and copepods. Sea ice effects thereby cascaded through the food web through indirect and delayed effects. The indirect and delayed effects amplified the effects of sea ice cover on capelin, copepods and amphipods. For krill, low sea ice cover most likely increased biomass in the short-term but reduced biomass in longer terms because of increased predation pressure. These findings suggest that both bottom-up and top-down processes need to be considered when projecting effects of future climate change on ecosystems.

• Niiranen, S.; Richter, Andries Peter; Blenckner, Thorstein; Stige, Leif Christian; Valman, Matilda & Eikeset, Anne Maria (2018). Global connectivity and cross-scale interactions create uncertainty for Blue Growth of Arctic fisheries. Marine Policy. ISSN 0308-597X. 87, s. 321–330. doi: 10.1016/j.marpol.2017.10.024. Fulltekst i vitenarkiv Vis sammendrag

  The Arctic faces high expectations of Blue Growth due to future projections of easier access and increased biological productivity. These expectations are, however, often based on global and regional climate change projections and largely ignore the complexity of social-ecological interactions taking place across different temporal and spatial scales. This paper illustrates how such cross-scale interactions at, and across, different dimensions (e.g., ecological, socioeconomic and governance) can affect the development of Arctic fisheries; and potentially create uncertainties for future Blue Growth projections. Two Arctic marine systems, The Barents Sea and the Central Arctic Ocean (CAO), are used as focus areas. The former hosts productive fisheries and is mostly covered by the EEZs of Norway and Russia, while the latter is still mainly covered by sea-ice and is a high seas area with no multilevel governance system in place. The examples show that, both systems are affected by a number of processes, beyond the environmental change, spanning a wide range of dimensions, as well as spatial and temporal scales. To address the complexity of the Arctic marine systems calls for an increase in holistic scientific understanding together with adaptive management practices. This is particularly important in the CAO, where no robust regional management structures are in place. Recognizing how cross-scale dynamics can cause uncertainties to the current fisheries projections and implementing well-functioning adaptive management structures across different Arctic sub-systems can play a key role in whether the Blue Growth potential in Arctic fisheries is realized or lost.

• Langangen, Øystein; Färber, Leonie Anette; Stige, Leif Christian; Diekert, Florian Klaus; Barth, Julia Maria Isis & Matschiner, Michael [Vis alle 11 forfattere av denne artikkelen] (2018). Ticket to spawn: Combining economic and genetic data to evaluate the effect of climate and demographic structure on spawning distribution in Atlantic cod. Global Change Biology. ISSN 1354-1013. 25(1), s. 134–143. doi: 10.1111/gcb.14474. Fulltekst i vitenarkiv Vis sammendrag

  Climate warming and harvesting affect the dynamics of species across the globe through a multitude of mechanisms, including distribution changes. In fish, migrations to and distribution on spawning grounds are likely influenced by both climate warming and harvesting. The Northeast Arctic (NEA) cod (Gadus morhua) performs seasonal migrations from its feeding grounds in the Barents Sea to spawning grounds along the Norwegian coast. The distribution of cod between the spawning grounds has historically changed at decadal scales, mainly due to variable use of the northern and southern margins of the spawning area. Based on historical landing records, two major hypotheses have been put forward to explain these changes: climate and harvesting. Climate could affect the distribution through, for example, spatial habitat shifts. Harvesting could affect the distribution through impacting the demographic structure. If demographic structure is important, theory predicts increasing spawner size with migration distance. Here, we evaluate these hypotheses with modern data from a period (2000–2016) of increasing temperature and recovering stock structure. We first analyze economic data from the Norwegian fisheries to investigate geographical differences in size of spawning fish among spawning grounds, as well as interannual differences in mean latitude of spawning in relation to changes in temperature and demographic parameters. Second, we analyze genetically determined fish sampled at the spawning grounds to unambiguously separate between migratory NEA cod and potentially smaller sized coastal cod of local origin. Our results indicate smaller spawners farther away from the feeding grounds, hence not supporting the hypothesis that harvesting is a main driver for the contemporary spawning ground distribution. We find a positive correlation between annual mean spawning latitude and temperature. In conclusion, based on contemporary data, there is more support for climate compared to harvesting in shaping spawning ground distribution in this major fish stock in the North Atlantic Ocean.

• Langangen, Øystein; Stige, Leif Christian; Kvile, Kristina Øie; Yaragina, Natalia A.; Skjæraasen, Jon Egil & Vikebø, Frode Bendiksen [Vis alle 7 forfattere av denne artikkelen] (2018). Multi-decadal variations in spawning ground use in Northeast Arctic haddock (Melanogrammus aeglefinus). Fisheries Oceanography. ISSN 1054-6006. 27(5), s. 435–444. doi: 10.1111/fog.12264. Fulltekst i vitenarkiv
• Stige, Leif Christian; Kvile, Kristina Øie; Bogstad, Bjarte & Langangen, Øystein (2018). Predator-prey interactions cause apparent competition between marine zooplankton groups. Ecology. ISSN 0012-9658. 99(3), s. 632–641. doi: 10.1002/ecy.2126. Fulltekst i vitenarkiv Vis sammendrag

  Predator‐mediated apparent competition is an indirect negative interaction between two prey species mediated by a shared predator. Quantifying such indirect ecosystem effects is methodologically challenging but important for understanding ecosystem functioning. Still, there are few examples of apparent competition from pelagic marine environments. Using state‐space statistical modeling, we here provide evidence for apparent competition between two dominant zooplankton groups in a large marine ecosystem, i.e., krill and copepods in the Barents Sea. This effect is mediated by a positive association between krill biomass and survival of the main planktivorous fish in the Barents Sea, capelin Mallotus villosus, and a negative association between capelin and copepod biomasses. The biomass of Atlantic krill species is expected to increase in the Barents Sea due to ongoing climate change, thereby potentially negatively affecting copepods through apparent competition. By demonstrating and quantifying apparent competition in a large marine ecosystem, our study paves the way for more realistic projections of indirect ecosystem effects of climate change and harvesting.

• Stige, Leif Christian; Ottersen, Geir; Yaragina, Nathalia A.; Vikebø, Frode Bendiksen; Stenseth, Nils Christian & Langangen, Øystein (2018). Combined effects of fishing and oil spills on marine fish: Role of stock demographic structure for offspring overlap with oil. Marine Pollution Bulletin. ISSN 0025-326X. 129(1), s. 336–342. doi: 10.1016/j.marpolbul.2018.02.056. Fulltekst i vitenarkiv Vis sammendrag

  It has been proposed that the multiple pressures of fishing and petroleum activities impact fish stocks in synergy, as fishing-induced demographic changes in a stock may lead to increased sensitivity to detrimental effects of acute oil spills. High fishing pressure may erode the demographic structure of fish stocks, lead to less diverse spawning strategies, and more concentrated distributions of offspring in space and time. Hence an oil spill may potentially hit a larger fraction of a year-class of offspring. Such a link between demographic structure and egg distribution was recently demonstrated for the Northeast Arctic stock of Atlantic cod for years 1959–1993. We here estimate that this variation translates into a two-fold variation in the maximal proportion of cod eggs potentially exposed to a large oil spill. With this information it is possible to quantitatively account for demographic structure in prospective studies of population effects of possible oil spills.

Se alle arbeider i NVA

• Gismervik, Kristine; Bjørklund, Kristin; Nielsen, Kristoffer Vale; Harasimczuk, Ewa; Qviller, Lars & Stige, Leif Christian [Vis alle 7 forfattere av denne artikkelen] (2025). Fiskehelserapporten 2024, kapittel 5 Fiskevelferd. doi: https:/www.vetinst.no/rapporter-og-publikasjoner/rapporter/2025/fiskehelserapporten-2024. Fulltekst i vitenarkiv Vis sammendrag

  Fiskehelserapporten 2024 belyser noen av de viktigste helseutfordringene i norsk oppdrettsnæring i 2024. Ifølge månedlige rapporteringer døde 45,8 millioner laks og 3,4 millioner regnbueørret over 3 gram fra settefiskproduksjon på land i 2024. I tillegg døde 57,8 millioner laks og 2,4 millioner regnbueørret i sjøfasen. Skader etter avlusning, kompleks gjellesykdom og vintersår rangeres som tidligere år blant de viktigste helseproblemene for laks i sjø i spørreundersøkelsen som er sendt til fiskehelsepersonell og inspektører og rådgivere i Mattilsynet. Skader forårsaket av maneter har imidlertid rykket opp og ligger på en tredjeplass. Samlet sett er sår, uansett etiologi, trolig det største helseproblemet for laks. Når det gjelder alvorlige, smittsomme sykdommer, ble i ILA stadfestet på 13 lokaliteter i 2024, mens det var mistanke på ytterligere ni lokaliteter. Med 48 nye PD-¬tilfeller var antallet det laveste siden 2005, og det ble ikke påvist PD utenfor endemisk sone. BKD ble påvist på åtte lokaliteter i PO5 og PO6 i fjor. Pasteurellose ble påvist på omtrent like mange lokaliteter som i 2023, men det er bekymringsfullt at pasteurellose ble påvist lenger nord enn tidligere. Piscirickettsiose er kun påvist sporadisk siden 2003, men ble påvist på flere lokaliteter i Nord-¬Norge i fjor høst. Både CMS og HSMB ble påvist på færre lokaliteter i 2024 enn foregående år, men virusene som forårsaker sykdommene ble påvist på flere lokaliteter enn foregående år. De siste årene har det vært relativt få IPN-utbrudd, men IPN-virus påvises på flere anlegg enn tidligere år. Det er rapportert om en ny variant av IPN-virus hos QTL-¬fisk.

• Bornø, Geir; Hansen, Haakon; Qviller, Lars; Stige, Leif Christian & Helgesen, Kari Marie Olli (2025). Fiskehelserapporten 2024, kapittel 9 Parasittsykdommer hos laksefisk i oppdrett. doi: https:/www.vetinst.no/rapporter-og-publikasjoner/rapporter/2025/fiskehelserapporten-2024. Fulltekst i vitenarkiv Vis sammendrag

  Fiskehelserapporten 2024 belyser noen av de viktigste helseutfordringene i norsk oppdrettsnæring i 2024. Ifølge månedlige rapporteringer døde 45,8 millioner laks og 3,4 millioner regnbueørret over 3 gram fra settefiskproduksjon på land i 2024. I tillegg døde 57,8 millioner laks og 2,4 millioner regnbueørret i sjøfasen. Skader etter avlusning, kompleks gjellesykdom og vintersår rangeres som tidligere år blant de viktigste helseproblemene for laks i sjø i spørreundersøkelsen som er sendt til fiskehelsepersonell og inspektører og rådgivere i Mattilsynet. Skader forårsaket av maneter har imidlertid rykket opp og ligger på en tredjeplass. Samlet sett er sår, uansett etiologi, trolig det største helseproblemet for laks. Når det gjelder alvorlige, smittsomme sykdommer, ble i ILA stadfestet på 13 lokaliteter i 2024, mens det var mistanke på ytterligere ni lokaliteter. Med 48 nye PD-¬tilfeller var antallet det laveste siden 2005, og det ble ikke påvist PD utenfor endemisk sone. BKD ble påvist på åtte lokaliteter i PO5 og PO6 i fjor. Pasteurellose ble påvist på omtrent like mange lokaliteter som i 2023, men det er bekymringsfullt at pasteurellose ble påvist lenger nord enn tidligere. Piscirickettsiose er kun påvist sporadisk siden 2003, men ble påvist på flere lokaliteter i Nord-¬Norge i fjor høst. Både CMS og HSMB ble påvist på færre lokaliteter i 2024 enn foregående år, men virusene som forårsaker sykdommene ble påvist på flere lokaliteter enn foregående år. De siste årene har det vært relativt få IPN-utbrudd, men IPN-virus påvises på flere anlegg enn tidligere år. Det er rapportert om en ny variant av IPN-virus hos QTL-¬fisk.

• Stige, Leif Christian; Vollset, Knut; Diserud, Ola Håvard; Karlsen, Ørjan; Knutsen, Øyvind & Nilsen, Frank [Vis alle 9 forfattere av denne artikkelen] (2025). Comment on “Salmon Lice Biology, Environmental Factors, and Smolt Behaviour With Implications for the Norwegian Salmon Farming Management System: A Critical Review”. Reviews in Aquaculture. ISSN 1753-5123. 17(3). doi: 10.1111/raq.70040. Fulltekst i vitenarkiv
• Nilsen, Hanne Katrine; Colquhoun, Duncan John; Stige, Leif Christian; Olsen, Anne Berit & Gulla, Snorre (2024). Pasteurellosis in Fish. Technical report An overview of emerging diseases in the salmonid farming industry. Fulltekst i vitenarkiv
• Gismervik, Kristine; Nielsen, Kristoffer Vale; Bjørklund, Kristin; Osnes, Magnus Nygård; Gåsnes, Siri Kristine Sollien & Stige, Leif Christian [Vis alle 9 forfattere av denne artikkelen] (2024). Kapittel 5 Fiskevelferd. I Sommerset, Ingunn; Wiik-Nielsen, Jannicke; Moldal, Torfinn; Oliveira, Victor Henrique Silva de; Svendsen, Julie; Haukaas, Asle & Brun, Edgar (Red.), Fiskehelserapporten 2023. Veterinærinstituttet. s. 55–105. Fulltekst i vitenarkiv Vis sammendrag

  I sammendraget belyser vi noen av de viktigste helseutfordringene vi ser i norsk oppdrettsnæring og hos vill laksefisk i 2023. I følge månedlige rapporteringer døde 37,7 millioner laks og 2,4 millioner regnbueørret over 3 gram fra settefiskproduksjon på land i 2023. I tillegg døde 62,8 millioner laks (16,7 prosent) og 2,5 millioner regnbueørret (14 prosent) i sjøfasen av produksjonen. For laks i sjøfasen er dødelighetstallene i 2023, både i antall og prosentvis, de høyeste registrert så langt. Samlet sett, er det de samme tre helseproblemene som utmerker seg i 2023 som i 2022: Skader ved avlusningsoperasjoner, kompleks gjellesykdom og vintersår. En vesentlig endring i 2023 er at skader forårsaket av maneter rangeres blant de ti viktigste helseutfordringene. Blant lokaliteter som deler data på dødsårsakskategorier, utgjorde kategorien «maneter» 1,7 prosent av dødeligheten i 2023. Av alvorlige, smittsomme sykdommer har det i 2023 vært en bekymringsfull økning i påvisninger av bakteriell nyresyke (BKD) og fire tilfeller med pankreassykdom (PD) nord for endemisk PD-sone. Disse sykdommene har ikke forårsaket spesielt høy dødelighet på anleggsnivå, men er alvorlige grunnet smitterisikoen. På et overordnet nivå, ser de ulike virussykdommene til å ha stabilisert seg, mens det fortsatt er en negativ utvikling for flere bakterielle infeksjonssykdommer, spesielt vintersår og yersiniose. En positiv utvikling er at nedgangen i antall PD-tilfeller på nasjonalt plan fortsetter i 2023, noe som sammenfaller med økt vaksinasjonsgrad, spesielt i Midt-Norge.

• Hoff, Siv Nam Khang; Tørresen, Ole Kristian; Maurstad, Marius Filomeno; Ravinet, Mark; Godiksen, Jane Aanestad & Stige, Leif Christian [Vis alle 10 forfattere av denne artikkelen] (2024). Delineate the population structure of a keystone marine fish species in the Northern Atlantic region using whole genome sequencing data. Fulltekst i vitenarkiv
• Hansen, Haakon; Bornø, Geir; Qviller, Lars; Stige, Leif Christian; Helgesen, Kari Marie Olli & Øines, Øivind [Vis alle 8 forfattere av denne artikkelen] (2024). Kapittel 9 Parasittsykdommer hos laksefisk i oppdrett. I Sommerset, Ingunn; Wiik-Nielsen, Jannicke; Moldal, Torfinn; Oliveira, Victor Henrique Silva de; Svendsen, Julie; Haukaas, Asle & Brun, Edgar (Red.), Fiskehelserapporten 2023. Veterinærinstituttet. Fulltekst i vitenarkiv Vis sammendrag

  I sammendraget belyser vi noen av de viktigste helseutfordringene vi ser i norsk oppdrettsnæring og hos vill laksefisk i 2023. I følge månedlige rapporteringer døde 37,7 millioner laks og 2,4 millioner regnbueørret over 3 gram fra settefiskproduksjon på land i 2023. I tillegg døde 62,8 millioner laks (16,7 prosent) og 2,5 millioner regnbueørret (14 prosent) i sjøfasen av produksjonen. For laks i sjøfasen er dødelighetstallene i 2023, både i antall og prosentvis, de høyeste registrert så langt. Samlet sett, er det de samme tre helseproblemene som utmerker seg i 2023 som i 2022: Skader ved avlusningsoperasjoner, kompleks gjellesykdom og vintersår. En vesentlig endring i 2023 er at skader forårsaket av maneter rangeres blant de ti viktigste helseutfordringene. Blant lokaliteter som deler data på dødsårsakskategorier, utgjorde kategorien «maneter» 1,7 prosent av dødeligheten i 2023. Av alvorlige, smittsomme sykdommer har det i 2023 vært en bekymringsfull økning i påvisninger av bakteriell nyresyke (BKD) og fire tilfeller med pankreassykdom (PD) nord for endemisk PD-sone. Disse sykdommene har ikke forårsaket spesielt høy dødelighet på anleggsnivå, men er alvorlige grunnet smitterisikoen. På et overordnet nivå, ser de ulike virussykdommene til å ha stabilisert seg, mens det fortsatt er en negativ utvikling for flere bakterielle infeksjonssykdommer, spesielt vintersår og yersiniose. En positiv utvikling er at nedgangen i antall PD-tilfeller på nasjonalt plan fortsetter i 2023, noe som sammenfaller med økt vaksinasjonsgrad, spesielt i Midt-Norge.

• Gerland, Sebastian; Ingvaldsen, Randi Brunvær; Reigstad, Marit; Sundfjord, Arild; Bogstad, Bjarte & Chierici, Melissa [Vis alle 12 forfattere av denne artikkelen] (2024). Still Arctic? - The changing Barents Sea. Fulltekst i vitenarkiv
• Planque, Benjamin; Aarflot, Johanna Myrseth; Buttay, Lucie; Carroll, JoLynn; Fransner, Sara Filippa Krusmynta & Eide, Cecilie Hansen [Vis alle 17 forfattere av denne artikkelen] (2023). A standard protocol for describing the evaluation of ecological models. Fulltekst i vitenarkiv
• Gismervik, Kristine; Harasimczuk, Ewa; nielsen, Kristoffer vale; Stige, Leif Christian; Qviller, Lars & Tørud, Brit [Vis alle 7 forfattere av denne artikkelen] (2023). Kapittel 4 Fiskevelferd. I Wiik-Nielsen, Jannicke; Oliveira, Victor Henrique Silva de; Moldal, Torfinn; Bornø, Geir; Haukaas, Asle & Brun, Edgar (Red.), Fiskehelserapporten 2022. Veterinærinstituttet. s. 33–69. Fulltekst i vitenarkiv
• Brun, Edgar; Colquhoun, Duncan John; Garseth, Åse Helen; Grave, Kari; Gulla, Snorre & Hansen, Haakon [Vis alle 10 forfattere av denne artikkelen] (2023). Kapittel 3 Endringer i smitterisiko. I Wiik-Nielsen, Jannicke; Oliveira, Victor Henrique Silva de; Moldal, Torfinn; Bornø, Geir; Haukaas, Asle & Brun, Edgar (Red.), Fiskehelserapporten 2022. Veterinærinstituttet. s. 24–32. Fulltekst i vitenarkiv
• Hansen, Haakon; Bornø, Geir; Qviller, Lars; Stige, Leif Christian; Helgesen, Kari Marie Olli & Olsen, Anne Berit [Vis alle 9 forfattere av denne artikkelen] (2023). Kapittel 8 Parasittsykdommer hos laksefisk i oppdrett. I Wiik-Nielsen, Jannicke; Oliveira, Victor Henrique Silva de; Moldal, Torfinn; Bornø, Geir; Haukaas, Asle & Brun, Edgar (Red.), Fiskehelserapporten 2022. Veterinærinstituttet. s. 128–152. Fulltekst i vitenarkiv
• Hoff, Siv Nam Khang; Maurstad, Marius Filomeno; Alan, Le Moan; Ravinet, Mark; Durant, Joël & Tørresen, Ole K. [Vis alle 18 forfattere av denne artikkelen] (2023). Identification of multiple chromosomal inversions and fusions in a keystone Arctic species with high gene flow. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joël; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2023). Survival of adult polar cod (Boreogadus saida) in the context of “borealization” of the Barents Sea. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joël; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2023). Effects of abrupt ecological change on the Barents Sea Arctic food-web: predictions from a food-web state-space model. Fulltekst i vitenarkiv
• Helgesen, Kari Marie Olli & Stige, Leif Christian (2023). Er dagens bruk av emamektinbenzoat mot lakselus riktig? Norsk Fiskeoppdrett. ISSN 0332-7132. s. 58–60. Fulltekst i vitenarkiv
• Hoff, Siv Nam Khang; Maurstad, Marius Filomeno; Moan, Alan Le; Ravinet, Mark; Durant, Joël & Tørresen, Ole Kristian [Vis alle 18 forfattere av denne artikkelen] (2023). Identification of multiple chromosomal inversions and fusions in a keystone Arctic species with high gene flow. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joël; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2022). Change in the Barents Sea Arctic food-web dynamic based on biotic and abiotic environmental factors. Fulltekst i vitenarkiv
• Langangen, Øystein Ole Gahr & Stige, Leif Christian (2022). The role of large spawners for population productivity in Northeast Arctic cod. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joël; Gjøsæter, Harald; Langangen, Øystein Ole Gahr & Stige, Leif Christian (2021). Using time series to predict the future: quantifying the effects of borealization on polar cod (Boreogadus saida). Fulltekst i vitenarkiv
• Endo, Clarissa Akemi Kajiya; Vikebø, Frode Bendiksen; Yaragina, Natalia A.; Hjøllo, Solfrid Sætre & Stige, Leif Christian (2021). Cod's journey back home – from birth to nursery. Frontiers for Young Minds. 9. doi: 10.3389/frym.2021.622088. Fulltekst i vitenarkiv
• Vogt, Yngve & Stige, Leif Christian (2020). Klimaendringene forstyrrer økobalansen i Barentshavet. [Journal]. Apollon : Forskningsmagasin for Universitetet i Oslo. Fulltekst i vitenarkiv
• Endo, Clarissa; Vikebø, Frode Bendiksen; Yaragina, Natalia A.; Hjøllo, Solfrid Sætre & Stige, Leif Christian (2020). Effects of the environment and the spawning stock structure on the distribution of Northeast Arctic cod larvae. Fulltekst i vitenarkiv
• Müller, Malte; Stige, Leif Christian; Gabrielsen, Geir W.; Rinaldo, Øyvind; Knudsen, Stig Morten & Rødven, Rolf [Vis alle 8 forfattere av denne artikkelen] (2020). Arctic Frontiers side event FROM NANSEN LEGACY SCIENCE TO USEFUL KNOWLEDGE FOR SOCIETY. Fulltekst i vitenarkiv
• Stige, Leif Christian (2020). Ecosystem and management of a changing Arctic Ocean. Fulltekst i vitenarkiv
• Stige, Leif Christian (2020). The Polar Sea Ice Melts: What Happens to the Fish Under the Ice? Frontiers for Young Minds. 8. doi: 10.3389/frym.2020.00091. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joel Marcel; Langangen, Øystein; Gjøsæter, Harald & Stige, Leif Christian (2019). Environmental effects on population annual mean length of polar cod (Boreogadus saida) in the Barents Sea. Fulltekst i vitenarkiv
• Dupont, Nicolas; Durant, Joel Marcel; Langangen, Øystein; Gjøsæter, Harald & Stige, Leif Christian (2019). Environmental effects on population annual mean length of polar cod (Boreogadus saida) in the Barents Sea. Fulltekst i vitenarkiv
• Endo, Clarissa Akemi Kajiya; Yaragina, Natalia A.; Vikebø, Frode Bendiksen; Skogen, Morten D.; Hjøllo, Solfrid Sætre & Stige, Leif Christian (2019). Long-term ichthyoplankton survey reveal effects of climate and spawning stock structure on the spatial distribution of Northeast Arctic cod larvae. Fulltekst i vitenarkiv
• Stige, Leif Christian; Kløver, Geir Olav; Dupont, Nicolas; Borgå, Katrine; Stenseth, Nils Christian & Isachsen, Pål Erik [Vis alle 7 forfattere av denne artikkelen] (2019). Kunnskap fra isødet. Fulltekst i vitenarkiv Vis sammendrag

  Åpent arrangement med disse foredragene: "Kunnskapsinnhøsting i Arktis ombord i Fram 1893-1896" (Kløver); "Arven etter Nansen" (Stige); "Hva skjer med økosystemet når sjøisen forsvinner?" (Dupont); "Miljøgifter i Arktis" (Borgå); "Havstrømmene i Arktis – hvorfor er de spesielle?" (Isachsen); "En djerv polarforsker: Hanna Resvoll-Holmsen (1873-1943)" (Sandberg). Ordstyrere: Stige og Stenseth.

• Stige, Leif Christian; Rogers, Lauren; Neuheimer, Anna B.; Hunsicker, Mary E.; Yaragina, Natalia A. & Ottersen, Geir [Vis alle 9 forfattere av denne artikkelen] (2019). Density- and size-dependent mortality in fish early life stages. Fulltekst i vitenarkiv
• Stige, Leif Christian (2019). Arven etter Nansen. Fulltekst i vitenarkiv
• Stige, Leif Christian; Durant, Joel Marcel & Langangen, Øystein (2019). Effects of climate change, fishing and oil on marine ecosystems. Fulltekst i vitenarkiv
• Dunse, Thorben; Dong, Kaixing; Aas, Kjetil Schanke & Stige, Leif Christian (2019). Glacier meltwater runoff as a potential driver of phytoplankton dynamics around Svalbard. Fulltekst i vitenarkiv
• Stige, Leif Christian; Langangen, Øystein; Durant, Joel Marcel; Knutsen, Halvor; Olsen, Esben Moland & Ottersen, Geir (2019). Forskning på torsk. Biolog. ISSN 0801-0722. 37(2), s. 46–49. Fulltekst i vitenarkiv
• Stenseth, Nils Christian; Stige, Leif Christian & Langangen, Øystein (2018). Kunnskapsbasert forvaltning i et varmere klima. Aftenposten (morgenutg. : trykt utg.). ISSN 0804-3116. s. 16–16. Fulltekst i vitenarkiv
• Stige, Leif Christian; Langangen, Øystein & Stenseth, Nils Christian (2018). Skreien ikke utenfor livsfare. Dagens næringsliv. ISSN 0803-9372. s. 32–32. Fulltekst i vitenarkiv
• Llope, Marcos; Blenckner, Thorsten; Vasilakopoulos, Paris; McGinty, Niall; Lynam, Christopher Philip & Helaouët, Pierre [Vis alle 10 forfattere av denne artikkelen] (2018). Resilience of northeast Atlantic marine ecosystems. Fulltekst i vitenarkiv
• Stige, Leif Christian; Eriksen, Elena & Dalpadado, Padmini (2018). Climate effects on zooplankton species composition in the Barents Sea. Fulltekst i vitenarkiv
• Llope, Marcos; Blenckner, Thorsten; Vasilakopoulos, Paris; McGinty, Niall; Lynam, Christopher Philip & Helaouët, Pierre [Vis alle 10 forfattere av denne artikkelen] (2018). Continuous and abrupt changes in the resilience of northeast Atlantic marine ecosystems. Fulltekst i vitenarkiv
• Myksvoll, Mari Skuggedal; Bøhn, Thomas; Dalvin, Sussie Trine; Bolstad, Geir Hysing; Diserud, Ola Håvard & Folkedal, Ole [Vis alle 24 forfattere av denne artikkelen] (2026). Råd om akseptabelt utslippsnivå av lakselus | Havforskningsinstituttet. Havforskningsinstituttet. doi: https:/www.hi.no/templates/reporteditor/report-pdf?id=116501&nc=53481641062. Fulltekst i vitenarkiv Vis sammendrag

  Rapporten gir et samlet naturfaglig råd om hva som kan anses som et akseptabelt utslippsnivå av lakselus fra oppdrettsnæringen, med utgangspunkt i en bestilling fra Nærings- og fiskeridepartementet (NFD). Målet er å finne et akseptabelt lusenivå i oppdrett som sikrer at påvirkningen på vill laksefisk ikke overstiger det fastsatte miljømålet, definert som maksimalt 10 % dødelighet i populasjoner av ville laksefisk grunnet lakselus alene. Rådet er utarbeidet i samarbeid med flere forskningsmiljøer og bygger på flere ulike modeller. Felles for modellene er at de simulerer hvordan lakselus som produseres i oppdrettsanleggene spres og fester seg på villfisk, og medfører dermed økt dødelighet på utvandrende laksesmolt og redusert fitness (evne til å overleve og reprodusere) for sjøørret. Utslippsnivået som beregnes i rapporten blir oppgitt som totalt antall voksne hunnlus i oppdrettsanleggene, og ikke antall luselarver. Et akseptabelt utslippsnivå basert på totalt antall hunnlus gir større forutsigbarhet for oppdretterne og er enklere å håndheve enn et utslippsnivå basert på antall luselarver. Resultatene viser tydelig at det akseptable lusenivået varierer betydelig mellom ulike geografiske områder og mellom år. Denne variasjonen skyldes både biologiske forhold, som utvandringstidspunkt, og fysiske forhold som temperatur og strøm. For laks ligger medianverdiene for akseptabelt lusenivå i ulike produksjonsområder på omtrent 0,9 til 4 millioner voksne hunnlus til enhver tid, mens tilsvarende nivå for sjøørret er betydelig lavere, fra rundt 0,08 til 1,25 millioner hunnlus. Forskjellen skyldes i hovedsak artsspesifikke ulikheter i eksponering: laks oppholder seg relativt kort tid i kystsonen, mens sjøørret (og sjørøye) kan oppholde seg i fjorder og kystnære områder i lange perioder og dermed utsettes for lakselus over lengre tid. Rapporten viser at hvis reguleringen av lakselus baseres på akseptabelt lusenivå for laksen alene, vil det i mange tilfeller gi for høye lusenivåer for sjøørret. Beregninger indikerer at en slik praksis kan føre til betydelig økt negativ påvirkning på sjøørretbestandene, i noen tilfeller godt over miljømålet. Derfor konkluderes det med at hensynet til sjøørret i praksis vil være dimensjonerende for hvor lave lusenivåene må settes dersom man skal beskytte begge arter. Rapporten peker også på at det er betydelig usikkerhet knyttet til beregningene. Viktige kilder til usikkerhet er kvaliteten på lusetellinger og antallsberegninger av fisk i oppdrettsanlegg, variasjon i modellforutsetninger (for eksempel tålegrenser for lus), geografisk fordeling av oppdrettsanlegg og naturlige variasjoner mellom år. Resultatene er også oppgitt som intervaller, ikke absolutte grenser, for å tydeliggjøre at det akseptable lusenivået i oppdrett vil variere mellom år. For høy sannsynlighet for oppnåelse av miljømålet alle år så bør man sikte på de laveste verdiene innen intervallet. Rapporten legger også fram et forslag til nye reguleringsområder. Dagens 13 produksjonsområder er foreslått oppdelt i 28 mindre reguleringsområder, kun basert på naturfaglige hensyn. Bakgrunnen er at dagens områder er for heterogene, slik at samme totale lusenivå kan gi svært ulik påvirkning avhengig av hvor i området utslippene skjer. Mindre og mer homogene områder vil gi bedre samsvar mellom regulering og faktisk miljøeffekt, selv om det innebærer en økt betydning av smitte mellom områder. Rapporten påpeker at kunnskapsgrunnlaget for sjørøye er utilstrekkelig til å inkludere arten i de kvantitative beregningene. Likevel tyder eksisterende kunnskap på at også denne arten er svært sårbar for lakselus, noe som tilsier at fremtidig forvaltning er avhengig av mer kunnskap om denne arten.

• Stige, Leif Christian; Vollset, Knut; Diserud, Ola Håvard; Karlsen, Ørjan; Knutsen, Øyvind & Nilsen, Frank [Vis alle 10 forfattere av denne artikkelen] (2025). Oppdaterte resultater og vurderinger for 2024. Ekspertgruppe for vurdering av lusepåvirkning. Fulltekst i vitenarkiv Vis sammendrag

  Dette dokumentet inneholder oppdaterte resultater og vurderinger av lakseluspåvirkning i produksjonsområdene for 2024. Som beskrevet i kapittel 3.5.5 i ekspertgrupperapporten for 2025 og vedlegg III-V til denne rapporten, har de virtuelle postsmoltmodellene blitt oppdatert etter publiseringen av ekspertgrupperapporten for 2024. Det har også tilkommet noe ny informasjon om utvandringstid i PO10. Ekspertgruppen har derfor gjort en forenklet ny SHELF-vurdering av påvirkningen for hvert produksjonsområde. Utgangspunktet for vurderingene er vurderingene gjort i 2024, begrunnelsen for vurderingene som beskrevet i 2024-rapporten og årets modellberegninger for 2024. Oppdaterte vurderinger og begrunnelser for lakseluspåvirkning, og vurderinger av heterogenitet i lakseluspåvirkning, presenteres i det følgende for alle produksjonsområdene.

• Stige, Leif Christian; Vollset, Knut; Diserud, Ola Håvard; Karlsen, Ørjan; Knutsen, Øyvind & Nilsen, Frank [Vis alle 10 forfattere av denne artikkelen] (2025). Produksjonsområdebasert vurdering av lakselusindusert villaksdødelighet 2025. Ekspertgruppe for vurdering av lusepåvirkning. ISSN 9788293932185. Fulltekst i vitenarkiv Vis sammendrag

  I produksjonsområdeforskriften fra 2017 er kysten delt inn i 13 produksjonsområder (POer), hvor bærekraftsindikatorer skal bestemme hvor stor produksjon man skal tillate i oppdrettsanlegg. I forskriften står følgende: «Produksjonskapasiteten i produksjonsområder for akvakultur reguleres i samsvar med områdets miljømessige bærekraft. Påvirkningen fra akvakultur på miljøet overvåkes etter de til enhver tid gjeldende miljøindikatorene […]». Gjeldende og eneste miljøindikator er i 2025, som tidligere år, effekten lakselus har på vill laksefisk. Nærings- og fiskeridepartementet (NFD) har derfor oppnevnt en styringsgruppe som igjen har oppnevnt en ekspertgruppe bestående av ni forskere som skal vurdere lakselusindusert villfiskdødelighet per produksjonsområde. Mandatet til ekspertgruppen er: «Ekspertgruppen skal hvert år utarbeide en statusrapport for lakseluspåvirkning i produksjonsområdene. Rapporten skal legge vekt på tilstanden knyttet til årets overvåkning, og sammenligne resultatene med de foregående år. Usikkerheten i vurderingene må komme tydelig fram. ... Rapportene som leveres skal legge hovedvekt på påvirkningen av villaks inntil sjøørret og/eller sjørøye er fullt inkludert i trafikklyssystemet.» I årets rapport følges den samme framgangsmåten som i 2024 for å vurdere hvor store andeler av laksepostsmolten som dør på grunn av lakseluspåvirkning. Effekter på sjøørret eller sjørøye blir ikke vurdert, men det vises til rapport fra Norsk institutt for naturforskning om effekter på sjøørret. I tillegg til vurderinger for 2025, inneholder årets ekspertgrupperapport oppdaterte vurderinger for 2024 basert på ny kunnskap, bl.a. som resultat av utvikling av modellene som brukes av Ekspertgruppen. Oppdateringen innebærer at påvirkningen i PO9 i 2024 blir vurdert til moderat, mens den i fjorårets rapport ble vurdert til å være helt på grensen mellom lav og moderat. For andre POer påvirker oppdateringen kun konklusjoner om usikkerhet (gjelder PO7 og PO10) og hvilke kategorier av sårbare og viktige vassdrag der resultater indikerer at enkeltbestander hadde lakselusindusert dødelighet i en høyere kategori enn POet som helhet (gjelder PO7). Oppsummert er kategoriene for lakselusindusert dødelighet for vill laksepostsmolt i 2024 og 2025 som følger: (1) Høy (over 30 % dødelighet) i PO3 i både 2024 og 2025 (2) Moderat (mellom 10 og 30 % dødelighet) i PO2, PO4, PO5, PO6, PO7, PO8, PO10 og PO11 i både 2024 og 2025 (3) Lav (under 10 % dødelighet) i PO1, PO12 og PO13 i både 2024 og 2025 (4) Moderat i PO9 i 2024 og lav til moderat i 2025. Dette innebærer at dødeligheten vurderes til å være helt på grensen mellom lav og moderat og at informasjonsgrunnlaget ikke er tilstrekkelig til å avgjøre hvilken av disse kategoriene som har sannsynlighetsovervekt i dette POet i 2025. Mandatet krever videre at usikkerheten ved vurderingene skal komme tydelig fram. Vurderingene av påvirkning og usikkerhet gjøres gjennom SHELF-metoden, forklart i Kapittel 5.1. Usikkerheten i vurderingene beskrives som sannsynligheten for at dødeligheten er over 10 eller 30 %, ved bruk av åtte kategorier av sannsynlighet fra svært usannsynlig til svært sannsynlig, definert i Tabell 5.1. Tabell 0.1 oppsummerer vurderingene av usikkerhet. Videre er det vurdert om heterogenitet i lakseluspåvirkning gjør at deler av et PO har lakselusindusert dødelighet i en høyere kategori enn konkludert med for POet som helhet. Det vurderes som mer sannsynlig enn ikke at lakselusindusert dødelighet i deler av POet var i en høyere kategori enn POet som helhet for PO5, PO6, PO7 og PO12 i 2024 og for PO2, PO4, PO6 og PO7 i 2025. Det vil si at det er sannsynlighetsovervekt for at dødeligheten var over 30 % for enkeltbestander i PO5, PO6 og PO7 i 2024 og PO2, PO4, PO6 og PO7 i 2025 og over 10 % for enkeltbestander i PO12 i 2024. Det er også sannsynlighetsovervekt for at enkeltbestander i PO9 hadde dødelighet over 10 % i 2025. I disse POene ble det undersøkt hvordan heterogeniteten påvirker bestander kategorisert som sårbare og viktige. Konklusjonene om gjennomsnittlig dødelighet for sårbare og viktige bestander er: • Lakselusindusert dødelighet var mer sannsynlig enn ikke over 30 % i gjennomsnitt for bestander under reetablering i PO6 i både 2024 og 2025 og for den ene bestanden som er under reetablering i PO4 i 2025. • Lakselusindusert dødelighet var mer sannsynlig enn ikke over 10 % i gjennomsnitt for bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen og for små og sårbare bestander i PO9 i 2025. Resultater fra én eller flere virtuelle postsmoltmodeller indikerer at enkeltbestander i de følgende kategoriene av sårbare og viktige bestander hadde lakselusindusert dødelighet i en høyere kategori enn POet som helhet (over 30 % i PO5, PO6 og PO7 i 2024 og PO2, PO4, PO6 og PO7 i 2025 eller over 10 % i PO12 i 2024 og PO9 i 2025): • Nasjonale laksevassdrag, bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen, små og sårbare bestander og bestander under reetablering i PO5 i 2024. • Nasjonale laksevassdrag, bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen, små og sårbare bestander og bestander under reetablering i PO6 i både 2024 og 2025. • Nasjonale laksevassdrag, bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen og små og sårbare bestander i PO7 i 2024. • Nasjonale laksevassdrag og små og sårbare bestander i PO12 i 2024. • Nasjonale laksevassdrag og små og sårbare bestander i PO2 i 2025. • Nasjonale laksevassdrag, bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen, små og sårbare bestander og bestander under reetablering i PO4 i 2025. • Bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen og små og sårbare bestander i PO7 i 2025. • Bestander med dårlig eller svært dårlig tilstand etter delnormen “Gytebestandsmål og høstingspotensial” i kvalitetsnormen og små og sårbare bestander i PO9 i 2025. I de resterende POene er det ingen deler av området der lakselusindusert dødelighet med sannsynlighetsovervekt er vurdert til en høyere kategori enn POet som helhet. Mandatet ber om at Ekspertgruppen skal sammenligne resultatene med de foregående år. Et generelt mønster er at områder med høyt utslipp av lakselus fra oppdrett med jevne mellomrom har kommet i høy kategori, men at vurderingen av lakselusindusert villaksdødelighet kan variere mye fra år til år avhengig av biologiske, fysiske og produksjonsmessige forhold. Disse forholdene bidrar til usikkerheten i vurderingene av lakselusindusert dødelighet for enkeltår. Usikkerheten er imidlertid lavere når det gjelder påvirkningen sett over to eller flere år. Ekspertgruppen påpeker at det er økende smittepress i de nordlige områdene samtidig som det er flere POer (PO8, PO9 og PO11) som har svært lite observasjonsdata av luseforekomster på villfisk. For andre år på rad vurderes nå påvirkningen til å være moderat eller helt på grensen til moderat i alle POer fra PO8 til PO11 – POer som med kun to unntak har hatt lav påvirkning alle år fra 2016 til 2023. Denne økningen de siste to årene har sammenheng med økt antall oppdrettsfisk i sjø og høy sjøtemperatur, men det er ennå usikkert i hvilken grad andre forhold også har spilt inn. På grunn av toårige sykluser i oppdrettsproduksjonen kan det være hensiktsmessig å se på smittepress i to-årsperioder. I PO2 har totalantall hunnlus om våren økt betydelig i to-årsperiodene fra 2012–2013 til 2024–2025 på grunn av høyere antall rapporterte lus per fisk og økt antall fisk, men økningen har avtatt de siste årene. I PO3 har derimot totalantall hunnlus om våren blitt redusert i to-årsperiodene fra 2014–2015 til 2024–2025, hovedsakelig på grunn av lavere antall rapporterte lus per fisk. Antall lus per kvadratkilometer i PO3 er likevel blant de høyeste i landet. Også i PO4 er det en nedgang i totalantall hunnlus om våren fra 2016–2017 til 2024–2025. Denne nedgangen skyldes utelukkende lavere antall rapportert lus per fisk. I PO5 til PO12 er det generelt økende totalantall hunnlus om våren gjennom de siste to-årsperiodene i tråd med generelt økende antall oppdrettsfisk, men med variasjoner som skyldes forskjeller i antall rapporterte lus per fisk. Ekspertgruppen er samstemt i sine konklusjoner.

• Skår, Ketil; Løkslett, Hege; Misund, Bård; Sandvik, Anne Dagrun; Stige, Leif Christian & Taranger, Geir Lasse [Vis alle 7 forfattere av denne artikkelen] (2024). Sluttrapport: Fra rød til grønn kyst - Kunnskapsinnhenting for bærekraftig omstilling av havbruksaktiviteten i Vestland - Veterinærinstituttet. Veterinærinstituttet. Fulltekst i vitenarkiv Vis sammendrag

  I denne rapporten er det skissert noen mulige løsningsforslag og anbefalinger for tiltak i forbindelse med hva som skal til for å oppnå grønn status i sjøbasert lakseoppdrett i Vestland fylke. Produksjonsområde 3 og produksjonsområde 4 (PO3 og PO4) i Vestland har fått rødt trafikklys i 2018/2019 (PO4) og 2020/2021 (PO3 og PO4). Havbruksnæringen i regionen har også over tid hatt høyest dødelighet, mest sykdom og mest lus. Dette har også tidvis gitt svakere økonomiske resultater sammenlignet med landet som helhet.

• Helgesen, Kari Marie Olli; Horsberg, Tor Einar; Stige, Leif Christian; Tarpai, Attila & Norheim, Kari (2024). The surveillance programme for resistance to chemotherapeutants in L. salmonis in Norway 2023. Veterinærinstituttet. Fulltekst i vitenarkiv
• Jansen, Peder A; Lindhom, Andreas; Danielsen, Ole Roald; Rafoss, Trond; Engebretsen, Solveig & Aldrin, Magne Tommy [Vis alle 7 forfattere av denne artikkelen] (2024). Rensefiskbetingelser: Betingelser som fremmer lusespising hos rensefisk Faglig sluttrapport for FHF-prosjekt Rensefiskbetingelser (P.nr.: 901766). Norsk Regnesentral. Fulltekst i vitenarkiv
• Helgesen, Kari Marie Olli; Horsberg, Tor Einar; Stige, Leif Christian; Tarpai, Attila & Norheim, Kari (2023). The surveillance programme for resistance to chemotherapeutants in L. salmonis in Norway 2022. Veterinærinstituttet. Fulltekst i vitenarkiv
• Thorstad, Eva Bonsak; Bergh, Øivind; Bøhn, Thomas; Fiske, Peder; Forseth, Torbjørn & Stige, Leif Christian [Vis alle 7 forfattere av denne artikkelen] (2022). Vurdering av kriterier for å vekte laksebestander i Trafikklyssystemet. Styringsgruppen for vurdering av lakseluspåvirkning.. ISSN 9788293932055. Fulltekst i vitenarkiv Vis sammendrag

  Trafikklyssystemet Nærings- og fiskeridepartementet Styringsgruppen Lakselus Vekting av laksebestander Produksjonsområder

• Reigstad, Marit; Gabrielsen, Tove M.; Amargant-Arumi, Marti; Amundsen, Rita; Bluhm, Bodil & Bodur, Yasemin V. [Vis alle 37 forfattere av denne artikkelen] (2022). Seasonal Cruise Q3: Cruise Report. Septentrio Academic Publishing. Fulltekst i vitenarkiv Vis sammendrag

  The Nansen Legacy Q3 cruise, 5-27 August 2019, initiated the seasonal investigations of the Nansen Legacy transect. The transect represent an environmental gradient going through the northern Barents Sea, and included 7 process stations (P1-P7) lasting 6-53 hrs. CTD stations were taken to increase the hydrographic resolution on the transect. The program included measurements and sampling from the atmosphere, sea ice, ocean and sea floor. Data collected ranged from physical observations, chemical, biological and geological data collection, and the aim was to link observations and measurements to improve our understanding of the systems involving both climate, human impacts and the ecosystems. Deployment of moorings and gliders extended the observational capacity in time and space, outside the cruise period.

• Stige, Leif Christian; Ellingsen, Ingrid Helene; Finstad, Bengt; Karlsen, Ørjan; Lien, Vidar Surén & Myksvoll, Mari Skuggedal [Vis alle 12 forfattere av denne artikkelen] (2022). Vurdering av heterogenitet i lakselusindusert villfiskdødelighet innen produksjonsområder i 2020 og 2021. Ekspertgruppe for vurdering av lusepåvirkning. ISSN 9788293932079. Fulltekst i vitenarkiv Vis sammendrag

  Trafikklyssystemet Nærings- og fiskeridepartementet Lakselus Dødelighet laksesmolt Vekting av bestander Produksjonsområder

• Vollset, Knut; Nilsen, Frank; Ellingsen, Ingrid Helene; Karlsen, Ørjan; Paterson, Rachel & Qviller, Lars [Vis alle 11 forfattere av denne artikkelen] (2022). Produksjonsområdebasert vurdering av lakselusindusert villfiskdødelighet i 2022. Ekspertgruppe for vurdering av lusepåvirkning. ISSN 9788293932031. Fulltekst i vitenarkiv Vis sammendrag

  Trafikklyssystemet Nærings- og fiskeridepartementet Ekspertgruppen Lakselus Dødelighet laksesmolt Produksjonsområder

• Planque, Benjamin; Carroll, JoLynn; Fransner, Filippa; Hansen, Cecilie; Husson, Berengere & Keenlyside, Noel [Vis alle 13 forfattere av denne artikkelen] (2020). Best practices for ecological model evaluation I : Workshop Report. Septentrio Academic Publishing. Fulltekst i vitenarkiv
• Ingvaldsen, Randi Brunvær; Bluhm, Bodil; Aberle-Malzahn, Nicole; Amundsen, Rita; Ardelan, Murat Van & Bagøien, Espen [Vis alle 33 forfattere av denne artikkelen] (2020). Joint Cruise 1-2 2018: Cruise Report. Septentrio Academic Publishing. Fulltekst i vitenarkiv

Se alle arbeider i NVA