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• Durant, Joël M.; Langangen, Øystein Ole Gahr; Dolgov, Andrey V.; Lindstrøm, Ulf Ove; Krasnov, Yuri & Nikolaeva, Natalia G. [Show all 7 contributors for this article] (2026). Importance of capelin in the diet of Barents Sea predators relative to alternative prey. Marine Ecology Progress Series. ISSN 0171-8630. 781. doi: 10.3354/meps15078. Full text in Research Archive Show summary

  The Arcto-boreal Barents Sea is significantly impacted by temperature warming, with potential effects on trophic interactions and population dynamics. Capelin, a small pelagic fish species, dominates the Barents Sea’s relatively simple food web. Capelin are an essential link between lower trophic levels and top predators, like in many Arcto-boreal systems. This study investigates the factors controlling capelin consumption by Barents Sea predators. We analysed changes in capelin presence in the diet of predators and related it to capelin and krill abundances, using 8 unique diet data sets from major Barents Sea predators (3 fish, 2 seabird, and 2 marine mammal species) spanning 10-36 yr. Only 2 fish species showed a positive relationship between the percentage of capelin in the stomach and capelin abundance, while all fish species exhibited a negative correlation with krill abundance. This finding suggests that these species replace capelin with krill in their diet based on prey availability. Our results confirm the central role of capelin in the Barents Sea ecosystem, with most predators’ diets being influenced by that species’ abundance. Krill plays a more significant role in the Southern Barents Sea, particularly for central place foragers. Although diet data can have limitations, our study shows that diet analysis remains a valuable method to study predator-prey relationships. This information is essential for understanding predator-prey dynamics of key species in the Barents Sea, supporting ecosystem-based and multi-species fisheries management efforts under current and future climate conditions.

• Bardon, Gaël; Barracho, Téo; Durant, Joël M.; Lecomte, Nicolas; Maho, Yvon Le & Stenseth, Nils Christian [Show all 8 contributors for this article] (2026). Multiannual environmental forcing shapes breeding phenology and success in a sub-Antarctic seabird. Science Advances. 12(11). doi: 10.1126/sciadv.aea6342. Full text in Research Archive Show summary

  Climate-driven phenological mismatches threaten avian reproduction by disrupting food availability during critical breeding stages. In marine ecosystems, time lags between environmental changes and their effects on food webs are challenging to model, yet they can have a profound impact on reproduction at higher trophic levels. We disentangle how oceanic and climatic variability influence the breeding phenology and success of a major predator species in the Southern Ocean, drawing on 24 years of data from 17,000 marked king penguins. We document a 19-day advancement in breeding phenology, alongside increased breeding success (44% in 2000 and 62% in 2023). A sliding-window analysis reveals that sea temperature and primary production in key foraging zones predict both phenology and breeding success, with lags up to several weeks and 2 years, respectively. The amplitude of their recent response, as well as their dependence on multiyear environmental conditions, underscores a potential vulnerability in a context of decreasing environment predictability. However, so far, king penguins appear to be keeping pace with environmental changes and demonstrate a remarkable resilience and important flexibility in the face of variable oceanographic conditions.

• Langangen, Øystein Ole Gahr; Kaartvedt, Stein; Hylland, Ketil & Durant, Joël (2026). The collapse of Atlantic cod in the Oslofjord. Frontiers in Marine Science. 13. doi: 10.3389/fmars.2026.1746235. Full text in Research Archive Show summary

  Coastal fish populations in temperate regions increasingly experience environmental pressures and dramatic decreases in stock size. Currently, there are serious concerns about the status of the Atlantic cod ( Gadus morhua ) in the Oslofjord region, a 120-km inlet in southeastern Norway. Given the recent political debate, the large public interest, and the recent decision to close large areas in the Oslofjord to all fishing, the scarcity of quantitative estimates on cod biomass in the region presents an acute challenge. Typically, the state of the cod in the Oslofjord has been assessed by the analysis of juvenile fish datasets. However, scientific surveys targeting adult life stages are limited, and abundance and biomass estimates are based on relatively short time series and with limited spatial coverage. Here, we demonstrate how commercial landings data can be used to describe a recent decline in catch per unit effort in the region, a proxy related to biomass. These results are highly topical and can serve as a baseline for further investigations on the reasons for the collapse of the cod population. While our results demonstrate the value of the large commercial dataset, the introduction of conservation actions calls for alternative and more comprehensive monitoring in the area for documenting a potential future recovery. Our results highlight research and data needs associated with current efforts to improve the status of fish stocks in general, and the Atlantic cod in the Oslofjord in particular.

• Peri, Marcos Llope; Blenckner, Thorsten; Vasilakopoulos, Paraskevas; McGinty, Niall; Lynam, Christopher P. & Hélaouët, Pierre [Show all 11 contributors for this article] (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), p. 1–7. doi: 10.1073/pnas.2527939123. Full text in Research Archive Show summary

  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.

• 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. Full text in Research Archive Show summary

  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.

• Langangen, Øystein Ole Gahr; Olsen, Tora; Ottersen, Geir; Eriksen, Elena & Durant, Joël M. (2025). Consequences of climate-related poleward shifts in cod spawning. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 82, p. 1–11. doi: 10.1139/cjfas-2024-0380. Full text in Research Archive Show summary

  With climate change, many species alter their distribution according to local climate velocities. For marine fish, suitable areas for spawning in a warming climate may be less favorable for the resulting offspring, e.g., the sensitive larval and juvenile phases. The size of the young-of-the-year before their first winter is an important factor for subsequent survival, year class formation, and population dynamics of many fish species and populations. Here, we investigate how the change in spawning location of the Barents Sea population of Atlantic cod ( Gadus morhua) may affect the mean individual size of the offspring in their first fall. We demonstrate how the observed climate warming-related northerly shift in spawning location may lead to smaller sizes of young-of-the-year cod. Our analysis reveals a positive effect of sea temperature on offspring size and a nonlinear effect of spawning stock biomass (SSB) with smaller offspring size at both the high and low end of SSB. Decreased offspring size is likely to affect population dynamics through reduced recruitment success, and we hypothesize that it may have been part of the reason for this population's recent reduction in biomass.

• Helmerson, Cecilia; Durant, Joël; Hoff, Siv Nam Khang; Brieuc, Marine Servane Ono; Berg, Paul Ragnar & Jorde, Per Erik [Show all 14 contributors for this article] (2025). A century of anthropogenic perturbations impact genomic signatures of the iconic migratory Atlantic cod. Science Advances. 11(31). doi: 10.1126/sciadv.adp3342. Full text in Research Archive Show summary

  Anthropogenic stressors have led to marked ecosystem perturbations, including population declines and shifts in habitat range for key marine fish species. Understanding how these changes affect genome-wide characteristics, causing long-term evolutionary responses, is still in its infancy. Genome-wide retrospective assessment of the iconic migratory Atlantic cod ( Gadus morhua ) from the Barents Sea, unraveled varying degree of admixture with the nonmigratory coastal ecotype throughout the 20th century, and intriguingly more intensified during recent decades. These genomic changes were supported by an increased number of individuals displaying the heterozygous state of the chromosomal inversion coupled to migratory behavior in Atlantic cod. Ecological models and genome-wide scans identified that some of the observed frequency shifts, coupled to neural development, metabolic, and growth regulation, covaried with intensified fisheries, reduced generation time, and ocean warming. Our results demonstrate how anthropogenic perturbations impact the dynamics between two well-known ecotypes of Atlantic cod and thus, their genomic signatures, with potential implications for future management programs.

• Durant, Joël; Dupont, Nicolas; Ono, Kotaro & Langangen, Øystein Ole Gahr (2024). Interaction between three key species in the sea ice-reduced Arctic Barents Sea system. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 291(2032). doi: 10.1098/rspb.2024.1408. Full text in Research Archive Show summary

  Population dynamics depend on trophic interactions that are affected by climate change. The rise in sea temperature is associated with the disappearance of sea ice in the Arctic. In the Arctic part of the Barents Sea, Atlantic cod, capelin and polar cod are three fish populations that interact and are confronted with climate-induced sea ice reductions. The first is a major predator in the system, while the last two are key species in Arctic and sub-Arctic ecosystems, respectively. There are still many unknowns regarding how predicted environmental change may influence the joint dynamics of these populations. Using time series from a 32 yearlong survey, we developed a state-space model that jointly modelled the dynamics of cod, capelin and polar cod. Using a hindcast scenario approach, we projected the effect of reduced sea ice on these populations. We show that the impact of sea ice reduction and concomitant sea temperature increase may lead to a decrease of polar cod abundance at the benefit of capelin but n

• 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), p. 1584–1593. doi: 10.1093/icesjms/fsae101. Full text in Research Archive Show summary

  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.

• Olsen, Tora; Frøysa, Håvard Guldbrandsen; Yaragina, Natalya; Titelman, Josefin; Durant, Joël & Langangen, Øystein Ole Gahr (2024). Predator biomass affects west–east shifts in Barents Sea capelin (Mallotus villosus) spawning ground use. Fisheries Oceanography. ISSN 1054-6006. 33(6). doi: 10.1111/fog.12685. Full text in Research Archive Show summary

  Spawning locations of migratory fish influence the environmental and oceanographic fate of eggs and larvae. However, we have an incomplete understanding of how and why realized spawning locations vary. We quantified the yearly variation in spawning location for Barents Sea capelin (Mallotus villosus) within the recognized spawning areas along the coast of northern Norway and Murman. Furthermore, we tested whether water temperature, sea ice cover, predation and capelin fisheries are associated with spawning locations. Estimated spatial variation in spawning longitude used data from Soviet-Russian ichthyoplankton surveys from 1959 to 1993 and a bootstrap procedure. The mean spawning area along the coast was then calculated by combining larvae observations with backtracking a larvae drift model from potential spawning areas. We fitted a generalized additive model (GAM) to assess the effects of environmental conditions on these drift-corrected spawning longitudes. Capelin's mean yearly spawning location varied substantially across the study period. An increase in immature cod biomass, a major predator of capelin, during the spawning migration period in winter and early spring corresponds to more eastward capelin spawning. The eastward shift in mean spawning longitude seems to reach an eastern limit at high immature cod biomass. Sea temperature, sea ice cover and capelin fisheries were not associated with mean capelin spawning longitude. We show that the realized spawning areas for capelin are related to cod biomass, potentially through cod predation depleting and/or acting as a migration barrier for mature capelin.

• Ferreira, Ana Sofia de Araújo; Langangen, Øystein Ole Gahr; Yaragina, Nathalia A.; Prokopchuk, Irina P. & Durant, Joël (2024). How the spatio-temporal overlap of cod, haddock, and capelin larvae affects their recruitment in the Norwegian–Barents Sea system. Marine Ecology Progress Series. ISSN 0171-8630. 734, p. 79–90. doi: 10.3354/meps14564. Full text in Research Archive Show summary

  The Norwegian-Barents Sea (NBS) system is very productive; however, the extent to which this productivity varies remains uncertain for many species. Cod Gadus morhua , haddock Melanogrammus aeglefinus , and capelin Mallotus villosus are 3 key species that overlap in a large portion of the NBS ecosystem. In this hypothesis-driven study, we investigated the interaction of these 3 species during their pelagic larval stage and assessed the impact of their spatio-temporal overlap on survival. We hypothesised that the spatio-temporal overlap between the larvae of the 3 species, as they likely drift together, influences their survival at later stages. We calculated the spatio-temporal overlap of each pair of the 3 studied species and tested it against their recruitment. We utilised a multiple linear regression model with temperature, spawning stock biomass, and spatio-temporal overlap among larvae, their food, and competitors as explanatory variables; this model explained ∼43, ∼24, and ∼73% of the variability in cod, haddock, and capelin recruitment, respectively. The overlaps between larval cod and competing species and/or food have a negative influence on cod recruitment, whereas the sign of the relationships pertaining to haddock and capelin varies. These results improve our understanding of how these fish species use their critical habitats to face emerging environmental stressors.

• Durant, Joël; Holt, Rebecca Emma & Langangen, Øystein Ole Gahr (2024). Large biomass reduction effect on the relative role of climate, fishing, and recruitment on fish population dynamics. Scientific Reports. 14(1). doi: 10.1038/s41598-024-59569-4. Full text in Research Archive Show summary

  Many species around the world have collapsed, yet only some have recovered. A key question is what happens to populations post collapse. Traditionally, marine fish collapses are linked to overfishing, poor climate, and recruitment. We test whether the effect on biomass change from these drivers remains the same after a collapse. We used a regression model to analyse the effect of harvesting, recruitment, and climate variability on biomass change before and after a collapse across 54 marine fish populations around the world. The most salient result was the change in fishing effect that became weaker after a collapse. The change in sea temperature and recruitment effects were more variable across systems. The strongest changes were in the pelagic habitats. The resultant change in the sensitivity to external drivers indicates that whilst biomass may be rebuilt, the responses to variables known to affect stocks may have changed after a collapse. Our results show that a general model applied to many stocks provides useful insights, but that not all stocks respond similarly to a collapse calling for stock-specific models. Stocks respond to environmental drivers differently after a collapse, so caution is needed when using pre-collapse knowledge to advise on population dynamics and management.

• 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, p. 1–16. doi: 10.1016/j.pocean.2024.103380. Full text in Research Archive Show summary

  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.

• Langangen, Øystein Ole Gahr & Durant, Joël (2024). Persistence of fish populations to longer, more intense, and more frequent mass mortality events. Global Change Biology. ISSN 1354-1013. 30(3), p. 1–10. doi: 10.1111/gcb.17251. Full text in Research Archive Show summary

  Abstract Over the last decades, mass mortality events have become increasingly common across taxa with sometimes devastating effects on population biomass. In the aquatic environment, fish are sensitive to mass mortality events, particularly at the early life stages that are crucial for population dynamics. However, it has recently been shown for fish, that a single mass mortality event in early life typically does not lead to population collapse. Moreover, the frequency and intensity of extreme events that can cause mass mortality, such as marine heatwaves, are increasing. Here, we show that increasing frequency and intensity of mass mortality events may lead to population collapse. Since the drivers of mass mortality events are diverse, and often linked to climate change, it is challenging to predict the frequency and severity of future mass mortality events. As an alternative, we quantify the probability of population collapse depending on the frequency and intensity as well as the duration of mass mortality events. Based on 39 fish species, we show that the probability of collapse typically increases with increasing frequency, intensity, and duration of the mortality events. In addition, we show that the collapse depends on key traits such as natural mortality, recruitment variation, and density dependence. The presented framework provides quantitative estimates of the sensitivity of fish species to these increasingly common extreme events, which paves the way for potential mitigation actions to alleviate adverse impacts on harvested fish populations across the globe.

• Ferreira, Ana Sofia de Araújo; Neuheimer, Anna B. & Durant, Joël (2023). Impacts of the match-mismatch hypothesis across three trophic levels – a case study in the North Sea. ICES Journal of Marine Science. ISSN 1054-3139. 80(2), p. 308–316. doi: 10.1093/icesjms/fsac237. Full text in Research Archive Show summary

  Abstract Sustainable fishery practices require accurate predictions of fish recruitment—the abundance of a new year class entering a fishery. A key driver of recruitment is the impact predator-prey dynamics experienced during early life stages has on their survival at later stages, as in the Match-Mismatch Hypothesis (MMH). MMH states that predator survival depends on the match (or mismatch) between the timing of predator feeding and that of prey availability. This study aims to understand how predator-prey spatio-temporal overlap explains the variation in a pelagic fish population. We explore the predator-prey overlap between each pair of three trophic levels in the North Sea (NS) from 1982–2017: herring (Clupea harengus) larvae, zooplankton (Temora longicornis, Oithona sp.,Pseudocalanus spp., and Acartia spp.), and a phytoplankton index. We found that MMH explained 23% of recruitment (1-year-old) of NS autumn-spawning (NSAS) herring, performed similarly (21–26%) when using different trophic levels, and that there was a spatial pattern in both the overlap and the negative relationship between the overlap and recruitment, similar to the variation of habitat use of NS herring. Our results characterize how the MMH, including spatial variability, plays in controlling herring recruitment, while also considering unexplained variation for future study.

• Durant, Joël; Holt, Rebecca Emma; Ono, Kotaro & Langangen, Øystein Ole Gahr (2023). Predatory walls may impair climate warming-associated population expansion. Ecology. ISSN 0012-9658. 104(9), p. 1–8. doi: 10.1002/ecy.4130. Full text in Research Archive Show summary

  Climate change has a profound impact on species distribution and abundanceglobally, as well as local diversity, which affects ecosystem functioning. In par-ticular, changes in population distribution and abundance may lead tochanges in trophic interactions. Although species can often shift their spatialdistribution when suitable habitats are available, it has been suggested thatpredator presence can be a constraint on climate-related distribution shifts.We test this using two well-studied and data-rich marine environments.Focusing on a pair of sympatric fishes, Atlantic haddock Melanogrammus aeglefinus and cod Gadus morhua, we study the effect of the presence andabundance of the latter on the former distribution. We found that the distribu-tion of cod and increased abundance may limit the expansion of haddock tonew areas and could consequently buffer ecosystem changes due to climatechange. Though marine species may track the rate and direction of climateshifts, our results demonstrate that the presence of predators may limit theirexpansion to thermally suitable habitats. By integrating climatic and ecologicaldata at scales that can resolve predator–prey relationships, this analysis dem-onstrates the usefulness of considering trophic interactions to gain a morecomprehensive understanding and to mitigate the effects of climate change onspecies distributions.

• Geoffroy, Maxime; Bouchard, Caroline; Flores, Hauke; Robert, Dominique; Gjøsæter, Harald & Hoover, Carie [Show all 40 contributors for this article] (2023). The circumpolar impacts of climate change and anthropogenic stressors on Arctic cod (Boreogadus saida) and its ecosystem. Elementa: Science of the Anthropocene. 11(1). doi: 10.1525/elementa.2022.00097. Full text in Research Archive Show summary

  Arctic cod biomass are predicted. In most Arctic seas, the relative abundance of Arctic cod within the fish community will likely fluctuate in accordance with cold and warm periods. A reduced abundance of Arctic cod will negatively affect the abundance, distribution, and physiological condition of certain predators, whereas some predators will successfully adapt to a more boreal diet. Regional management measures that recognize thecritical roleof Arcticcod arerequiredtoensure that increased anthropogenic activities do not exacerbate the impacts of climate change on Arctic marine ecosystems. Ultimately, the mitigation of habitat loss for Arctic cod will only be achieved through a global reduction in carbon emissions.

• Durant, Joël; Ono, Kotaro & Langangen, Øystein Ole Gahr (2022). Empirical evidence of nonlinearity in bottom up effect in a marine predator-prey system. Biology Letters. ISSN 1744-9561. 18(11). doi: 10.1098/rsbl.2022.0309. Full text in Research Archive Show summary

  Strength of species interaction may have profound effects on population dynamics. Empirical estimates of interaction strength is often based on the assumption that the interaction strengths are constant. Barents Sea cod and capelin are two fish populations for which such interaction has been acknowledged and used, under the assumption of constant interaction strength, when studying their population dynamics. However, species interaction can often be non-linear in marine ecosystems and might profoundly change our understanding of food chains. Analysing 37 years long survey time series in the Arcto-Boreal Barents Sea with a state-space modelling framework, we demonstrate that the effect of capelin on cod is not linear but shifts depending on capelin abundance: while capelin is beneficial for cod population at high abundance, below the threshold, it becomes less important for cod. Our analysis therefore shows the importance of investigating non-linearity in species interaction and may contribute to an improved understanding on species assemblages.

• Langangen, Øystein Ole Gahr; Ohlberger, Jan Philipp; Stige, Leif Christian; Patin, Rémi; Buttay, Lucie & Stenseth, Nils Christian [Show all 8 contributors for this article] (2022). Effects of early life mass mortality events on fish populations. Fish and Fisheries. ISSN 1467-2960. 24(1), p. 176–186. doi: 10.1111/faf.12718. Full text in Research Archive Show summary

  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.

• Walseng, Bjørn; Durant, Joël; Hessen, Dag Olav; Jerstad, Kurt; Nilsson, Anna & Røstad, Ole Wiggo [Show all 7 contributors for this article] (2022). Long-term annual and spatial variation of polygyny in the white-throated dipper (Cinclus cinclus). Ecology and Evolution. 12(10). doi: 10.1002/ece3.9416. Full text in Research Archive Show summary

  Mating strategies are key components in the fitness of organisms, and notably in birds the occurrence of monogamy versus polygyny has attracted wide interest. We address this by a very comprehensive dataset (2899 breeding events spanning the years 1978–2019) of the white-throated dipper Cinclus cinclus. Though the mating system of this species has been regarded as generally monogamous, we find that 7% of all breeding events were performed by polygynous males (approximately 15% of all pairs). The fraction of polygyny has been stable over the entire study period irrespective of population size. The assumption that polygyny is most common at low population density was not supported. Surprisingly, there was no difference between polygynous and monogamous males with regard to the quality of the territories they inhabited, ranked according to their overall frequency of use. The most common age group, first-year breeders, dominated among monogamous males, while among polygynous males second-year breeders were most common, followed by third and first-year breeders. The primary females were in general older than females mated to monogamous males, also when controlled for their general frequency in the population. The majority of the two females mated to a polygynous male, bred in the vicinity of each other. The probability for a male to be involved in polygyny more than once, was significantly higher than by chance, suggesting phenotypic quality differences among males.

• Finne, Eirik Aasmo; Varpe, Øystein; Durant, Joël; Gabrielsen, Geir W. & Poste, Amanda (2022). Nutrient fluxes from an Arctic seabird colony to the adjacent coastal marine ecosystem. Polar Biology. ISSN 0722-4060. doi: 10.1007/s00300-022-03024-5. Full text in Research Archive Show summary

  Seabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes (Rissa tridactyla) and Brünnich’s Guillemots (Uria lomvia) on stream nutrient concentrations and fuxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ13C and δ15N) was used to assess whether seabird derived nitrogen (N) could be traced into flamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO3−) and nitrite (NO2) peaked in July at 9200 µg N L−1 in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO4 3−) in seabird-impacted streams were 21.9 µg P L−1, tenfold higher than in controls. Areal fuxes from seabird-impacted study catchments of NO3− + NO2− and PO4 3− had estimated ranges of 400–2100 kg N km−2 and 15–70 kg P km−2, respectively. Higher δ15N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ15N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers. Cross-ecosystem fuxes · Runof · Svalbard · Seabird guano · Rissa tridactyla · Uria lomvia · Macroalgae

• Townhill, Bryony; Holt, Rebecca Emma; Bogstad, Bjarte; Durant, Joël; Pinnegar, John K. & Dolgov, Andrey V. [Show all 9 contributors for this article] (2021). Diets of the Barents Sea cod (Gadus morhua) from the 1930s to 2018. Earth System Science Data. ISSN 1866-3508. 13(3), p. 1361–1370. doi: 10.5194/essd-13-1361-2021. Full text in Research Archive Show summary

  A new dataset on the diet of Atlantic cod in the Barents Sea from the 1930s to the present day has been compiled to produce one of the largest fish diet datasets available globally. Atlantic cod is one of the most ecologically and commercially important fish species in the North Atlantic. The stock in the Barents Sea is by far the largest, as a result of both successful management and favourable environmental conditions since the early 2000s. As a top predator, cod plays a key role in the Barents Sea ecosystem. The species has a broad diet consisting mainly of crustaceans and teleost fish, and both the amount and type of prey vary in space and time. The data – from Russia, Norway and the United Kingdom – represent quantitative stomach content records from more than 400 000 fish and qualitative data from 2.5 million fish. Many of the data are from joint collaborative surveys between Norway and Russia. The sampling was conducted throughout each year, allowing for seasonal, annual and decadal comparisons to be made. Visual analysis shows cod diets have changed considerably from the start of the dataset in the 1930s to the present day. There was a large proportion of herring in the diets in the 1930s, whereas in more recent decades capelin, invertebrates and other fish dominate. There are also significant interannual asynchronous fluctuations in prey, particularly capelin and euphausiids. Combining these datasets can help us understand how the environment and ecosystems are responding to climatic changes, and what influences the diet and prey switching of cod. Trends in temperature and variability indices can be tested against the occurrence of different prey items, and the effects of fishing pressure on cod and prey stocks on diet composition could be investigated. The dataset will also enable us to improve parametrization of food web models and to forecast how Barents Sea fisheries may respond in the future to management and to climate change. The Russian data are available through joint projects with the Polar Branch of the Russian Federal Research Institute of Fisheries and Oceanography (VNIRO).

• 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), p. 2700–2708. doi: 10.1093/icesjms/fsab143. Full text in Research Archive Show summary

  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.

• Durant, Joël; Aarvold, Leana & Langangen, Øystein Ole Gahr (2021). Stock collapse and its effect on species interactions: Cod and herring in the Norwegian-Barents Seas system as an example. Ecology and Evolution. 11, p. 16993–17004. doi: 10.1002/ece3.8336. Full text in Research Archive Show summary

  Both the Norwegian Spring Spawning herring (Clupea harengus) and the Northeast Arctic (NEA) cod (Gadus morhua) are examples of strong stock reduction and decline of the associated fisheries due to overfishing followed by a recovery. Cod and herring are both part of the Barents Sea ecosystem, which has experienced major warming events in the early (1920–1940) and late 20th century. While the collapse or near collapse of these stocks seems to be linked to an instability created by overfishing and climate, the difference of population dynamics before and after is not fully understood. In particular, it is unclear how the changes in population dynamics before and after the collapses are associated with biotic interactions. The combination of the availability of unique long-term time series for herring and cod makes it a well-suited study system to investigate the effects of collapse. We examine how species interactions may differently affect the herring and cod population dynamic before and after a collapse. Particularly we explore, using a GAM modeling approach, how herring could affect cod and vice versa. We found that the effect of cod biomass on herring that was generally positive (i.e., covariation) became negative after the collapse (i.e., predation or competition). Likewise a change occurred for the cod, the juvenile herring biomass that had no effect before the collapse had a negative effect after. Our results indicate that the population collapses may alter the inter-specific interactions and response to abiotic environmental changes. While the stocks are at similar abundance levels before and after the collapses, the system is potentially different in its functioning and may require different management action.

• 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, p. 141–159. doi: 10.3354/meps13878. Full text in Research Archive Show summary

  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.

• Ciannelli, Lorenzo; Neuheimer, Anna B.; Stige, Leif Christian; Frank, Kenneth T.; Durant, Joël & Hunsicker, Mary E. [Show all 10 contributors for this article] (2021). Ontogenetic spatial constraints of sub-arctic marine fish species. Fish and Fisheries. ISSN 1467-2960. p. 1–16. doi: 10.1111/faf.12619. Full text in Research Archive Show summary

  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.

• Färber, Leonie Anette; Gemert, Rob van; Langangen, Øystein; Durant, Joel Marcel & Andersen, Ken Hasle (2020). Population variability under stressors is dependent on body mass growth and asymptotic body size. Royal Society Open Science. 7(2), p. 1–11. doi: 10.1098/rsos.192011. Full text in Research Archive Show summary

  The recruitment and biomass of a fish stock are influenced by their environmental conditions and anthropogenic pressures such as fishing. The variability in the environment often translates into fluctuations in recruitment, which then propagate throughout the stock biomass. In order to manage fish stocks sustainably, it is necessary to understand their dynamics. Here, we systematically explore the dynamics and sensitivity of fish stock recruitment and biomass to environmental noise. Using an age-structured and trait-based model, we explore random noise (white noise) and autocorrelated noise (red noise) in combination with low to high levels of harvesting. We determine the vital rates of stocks covering a wide range of possible body mass (size) growth rates and asymptotic size parameter combinations. Our study indicates that the variability of stock recruitment and biomass are probably correlated with the stock's asymptotic size and growth rate. We find that fast-growing and large-sized fish stocks are likely to be less vulnerable to disturbances than slow-growing and small-sized fish stocks. We show how the natural variability in fish stocks is amplified by fishing, not just for one stock but for a broad range of fish life histories.

• 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), p. 1796–1805. doi: 10.1093/icesjms/fsaa040. Full text in Research Archive Show summary

  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.

• Durant, Joel Marcel; Ono, Kotaro; Stenseth, Nils Christian & Langangen, Øystein (2020). Nonlinearity in interspecific interactions in response to climate change: Cod and haddock as an example. Global Change Biology. ISSN 1354-1013. 26(10), p. 5554–5563. doi: 10.1111/gcb.15264. Full text in Research Archive Show summary

  Climate change has profound ecological effects, yet our understanding of how trophic interactions among species are affected by climate change is still patchy. The sympatric Atlantic haddock and cod are co‐occurring across the North Atlantic. They compete for food at younger stages and thereafter the former is preyed by the latter. Climate change might affect the interaction and coexistence of these two species. Particularly, the increase in sea temperature (ST) has been shown to affect distribution, population growth and trophic interactions in marine systems. We used 33‐year long time series of haddock and cod abundances estimates from two data sources (acoustic and trawl survey) to analyse the dynamic effect of climate on the coexistence of these two sympatric species in the Arcto‐Boreal Barents Sea. Using a Bayesian state‐space threshold model, we demonstrated that long‐term climate variation, as expressed by changes of ST, affected species demography through different influences on density‐independent processes. The interaction between cod and haddock has shifted in the last two decades due to an increase in ST, altering the equilibrium abundances and the dynamics of the system. During warm years (ST over ca. 4°C), the increase in the cod abundance negatively affected haddock abundance while it did not during cold years. This change in interactions therefore changed the equilibrium population size with a higher population size during warm years. Our analyses show that long‐term climate change in the Arcto‐Boreal system can generate differences in the equilibrium conditions of species assemblages.

• Ferreira, Ana Sofia De Araújo; Stige, Leif Christian; Neuheimer, Anna B.; Bogstad, Bjarte; Yaragina, Natalia A. & Prokopchuk, Irina [Show all 7 contributors for this article] (2020). Match-mismatch dynamics in the Norwegian-Barents Sea system. Marine Ecology Progress Series. ISSN 0171-8630. 650, p. 81–94. doi: 10.3354/MEPS13276. Full text in Research Archive Show summary

  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.

• Stenseth, Nils Christian; Payne, Mark R.; Bonsdorff, Erik; Dankel, Dorothy Jane; Durant, Joel Marcel & Anderson, Leif G. [Show all 17 contributors for this article] (2020). Attuning to a changing ocean. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 117(34), p. 20363–20371. doi: 10.1073/pnas.1915352117. Full text in Research Archive Show summary

  The ocean is a lifeline for human existence, but current practices risk severely undermining ocean sustainability. Present and future social−ecological challenges necessitate the maintenance and development of knowledge and action by stimulating collaboration among scientists and between science, policy, and practice. Here we explore not only how such collaborations have developed in the Nordic countries and adjacent seas but also how knowledge from these regions contributes to an understanding of how to obtain a sustainable ocean. Our collective experience may be summarized in three points: 1) In the absence of long-term observations, decision-making is subject to high risk arising from natural variability; 2) in the absence of established scientific organizations, advice to stakeholders often relies on a few advisors, making them prone to biased perceptions; and 3) in the absence of trust between policy makers and the science community, attuning to a changing ocean will be subject to arbitrary decision-making with unforeseen and negative ramifications. Underpinning these observations, we show that collaboration across scientific disciplines and stakeholders and between nations is a necessary condition for appropriate actions.

• Sguotti, Camilla; Otto, Saskia A; Frelat, Romain; Langbehn, Tom; Ryberg, M Plambech & Lindegren, Martin [Show all 9 contributors for this article] (2019). Catastrophic dynamics limit Atlantic cod recovery. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 286(1898). doi: 10.1098/rspb.2018.2877. Full text in Research Archive Show summary

  Collapses and regime changes are pervasive in complex systems (such as marine ecosystems) governed by multiple stressors. The demise of Atlantic cod (Gadus morhua) stocks constitutes a text book example of the consequences of overexploiting marine living resources, yet the drivers of these nearly synchronous collapses are still debated. Moreover, it is still unclear why rebuilding of collapsed fish stocks such as cod is often slow or absent. Here, we apply the stochastic cusp model, based on catastrophe theory, and show that collapse and recovery of cod stocks are potentially driven by the specific interaction between exploitation pressure and environmental drivers. Our statistical modelling study demonstrates that for most of the cod stocks, ocean warming could induce a nonlinear discontinuous relationship between fishing pressure and stock size, which would explain hysteresis in their response to reduced exploitation pressure. Our study suggests further that a continuing increase in ocean temperatures will probably limit productivity and hence future fishing opportunities for most cod stocks of the Atlantic Ocean. Moreover, our study contributes to the ongoing discussion on the importance of climate and fishing effects on commercially exploited fish stocks, highlighting the importance of considering discontinuous dynamics in holistic ecosystem-based management approaches, particularly under climate change.

• Brosset, Pablo; Durant, Joel Marcel; Beveren, Elisabeth Van & Plourde, Stéphane (2019). Fish population growth in the Gulf of St Lawrence: effects of climate, fishing and predator abundance. Marine Ecology Progress Series. ISSN 0171-8630. 624, p. 167–181. doi: 10.3354/meps13029. Full text in Research Archive Show summary

  Climate variability, fishing and predation are the main factors affecting fish population dynamics. In this study, the drivers of population growth variability were investigated for 7 fish stocks (2 cod, 4 herring and 1 mackerel stock) in the Gulf of St. Lawrence (NW Atlantic). The annual population growth sensitivity to both recruitment and survival (i.e. how much population growth depends on recruitment and survival) was estimated through elasticity analyses before being linked to harvesting history as well as environmental conditions (climate and predation). Stock-specific generalized additive models showed that population growth was most sensitive to recruitment variability with decreasing fish generation time, increasing water temperature and, in some cases, with predation. The dependence of population growth on recruitment, however, was generally close to 0, albeit higher for pelagic stocks than for demersal ones. This indicates that adult survival was more important than recruitment in shaping population growth and thus population size. As climate mainly acts on recruitment while fishing affects adult survival, management efforts seem more important than climate variability in regulating population growth, especially for long-lived cod. Nevertheless, population growth may become increasingly dependent on recruitment variability with warming waters; therefore, more flexible management strategies should be developed to cope with these oscillations.

• 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, p. 1–9. doi: 10.1038/s41598-019-51607-w. Full text in Research Archive Show summary

  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.

• Holt, Rebecca Emma; Bogstad, Bjarte; Durant, Joel Marcel; Dolgov, Andrey & Ottersen, Geir (2019). Barents Sea cod (Gadus morhua) diet composition: long-term interannual, seasonal, and ontogenetic patterns. ICES Journal of Marine Science. ISSN 1054-3139. 76(6), p. 1641–1652. doi: 10.1093/icesjms/fsz082. Full text in Research Archive Show summary

  Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year time-series of stomach-content data from 1984 to 2016. We assessed patterns in diet (prey) composition across years, between seasons, as well as ontogenetic trends in diet, including predator–prey size relationships. Ontogenetic shifts in diet were observed, with fish becoming more important prey with increasing cod size. A very early onset of piscivory was found in <20 cm cod. Cannibalism was found in cod > 20 cm and increased with size. Juvenile cod exhibit a tendency towards consuming prey up to 33% of their body length, whereas larger cod feed on all prey sizes, resulting in asymmetric predator–prey size distributions. Diet varied significantly during 1984–2016, consistent with changes in both prey, cod abundance, and distribution. Seasonal differences were observed; capelin dominated the winter diet, whereas cod, polar cod, and other fish species were prevalent in summer/autumn months. This work represents an important step towards understanding trophic linkages that determine BS ecosystem dynamics.

• Stige, Leif Christian; Rogers, Lauren; Neuheimer, Anna B.; Hunsicker, Mary E.; Yaragina, Natalia A. & Ottersen, Geir [Show all 9 contributors for this article] (2019). Density‐ and size‐dependent mortality in fish early life stages. Fish and Fisheries. ISSN 1467-2960. 20(5), p. 962–976. doi: 10.1111/faf.12391. Full text in Research Archive Show summary

  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.

• Färber, Leonie Anette; Durant, Joel Marcel; Vindenes, Yngvild & Langangen, Øystein (2018). Increased early offspring growth can offset the costs of long-distance spawning migration in fish. Marine Ecology Progress Series. ISSN 0171-8630. 600, p. 141–150. doi: 10.3354/meps12662. Full text in Research Archive Show summary

  For long-distance migrations to pay off for individual fish, the energetic costs must be counterbalanced by benefits. Understanding the fitness trade-offs associated with migration is essential for our ability to sustainably manage migratory species. Here, we investigated such trade-offs associated with the spawning migration of Northeast Arctic cod Gadus morhua, a stock of high historical and commercial value known to be able to migrate more than 1000 km southward to reach suitable spawning grounds. Reaching the more distant spawning grounds requires more energy and hence leaves less energy available for processes such as egg production. Previous studies have indicated that increased larval survival (e.g. from rapid early development in warmer southern waters) may offset the parental costs of migration. However, it was suggested that spatial variability in survival of early life stages might cancel out this survival benefit. As an alternative, we ask if the fitness benefit of long-distance migration may reside in increased offspring growth. Using an integral projection model incorporating effects of body length and migration distance, we quantified the increase in offspring growth needed to offset parental costs of long-distance migration on fitness. Our results suggest that a 12.5% length in crease of juvenile cod is required to offset parental costs of long-distance migration. This is within the estimated growth benefit of 20% suggested by drift models of early life stages of cod. These results highlight the potential importance of offspring growth as another factor explaining the benefit of long distance migration, broadening our knowledge on spawning migration.

• Langangen, Øystein; Färber, Leonie Anette; Stige, Leif Christian; Diekert, Florian Klaus; Barth, Julia Maria Isis & Matschiner, Michael [Show all 11 contributors for this article] (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), p. 134–143. doi: 10.1111/gcb.14474. Full text in Research Archive Show summary

  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.

• Durant, Joel M & Hjermann, Dag Ø (2017). Age-structure, harvesting and climate effects on population growth of Arcto-boreal fish stocks. Marine Ecology Progress Series. ISSN 0171-8630. 577, p. 177–188. doi: 10.3354/meps12210. Full text in Research Archive Show summary

  We used a comparative approach investigating commercially fished species with contrasting life histories and trophic positions in an Arcto-boreal system, the Barents Sea. Our objective was to address the ecological consequences of harvesting on stock properties (stochastic growth rate; a property related to intrinsic growth rate) in relation to different external conditions (fishing pressure and climate). We used age-structured population matrices to calculate the transient elasticity of population growth with respect to recruitment (how much population growth depends on recruitment) over time. Using a generalized additive model (GAM) analysis, we found that the transient elasticity of population growth to recruitment overall depends mostly on age structure (which in turn is affected by fishing) but also on climate (temperature change or winter North Atlantic Oscillation). Our results indicate that under warmer conditions, population growth of high latitude stocks becomes increasingly dependent on recruitment, which makes the stocks more difficult to manage. In general, there was no effect of ongoing fishing pressure on elasticity after age structure had been taken into account, supporting the view that long-term fishing pressure affects the susceptibility of the population to climate indirectly, by changing the age structure of the stock. However, for most of the stocks we have studied here, populations have low elasticity to recruitment due to their life history, meaning that the health of the stock mainly depends on survival after the recruitment stage; i.e. fisheries management is more important than climate.

• Langangen, Øystein; Ohlberger, Jan; Stige, Leif C.; Durant, Joel M.; Ravagnan, Elisa & Stenseth, Nils C. [Show all 7 contributors for this article] (2017). Cascading effects of mass mortality events in Arctic marine communities. Global Change Biology. ISSN 1354-1013. 23(1), p. 283–292. doi: 10.1111/gcb.13344. Full text in Research Archive Show summary

  Mass mortality events caused by pulse anthropogenic or environmental perturbations (e.g., extreme weather, toxic spills or epizootics) severely reduce the abundance of a population in a short time. The frequency and impact of these events are likely to increase across the globe. Studies on how such events may affect ecological communities of inter-acting species are scarce. By combining a multispecies Gompertz model with a Bayesian state-space framework, we quantify community-level effects of a mass mortality event in a single species. We present a case study on a community of fish and zooplankton in the Barents Sea to illustrate how a mass mortality event of different intensities affecting the lower trophic level (krill) may propagate to higher trophic levels (capelin and cod). This approach is especially valuable for assessing community-level effects of potential anthropogenic-driven mass mortality events, owing to the ability to account for uncertainty in the assessed impact due to uncertainty about the ecological dynamics. We hence quantify how the assessed impact of a mass mortality event depends on the degree of precaution considered. We suggest that this approach can be useful for assessing the possible detrimental outcomes of toxic spills, for example oil spills, in relatively simple communities such as often found in the Arctic, a region under increasing influence of human activities due to increased land and sea use.

• Paasche, Øyvind; Österblom, Henrik; Neuenfeldt, Stefan; Bonsdorff, Erik; Brander, Keith M. & Conley, Daniel [Show all 13 contributors for this article] (2015). Connecting the seas of Norden. Nature Climate Change. ISSN 1758-678X. 5(2), p. 89–92. doi: 10.1038/nclimate2471. Full text in Research Archive
• Feng, Jianfeng; Durant, Joel Marcel; Stige, Leif Christian; Hessen, Dag Olav; Hjermann, Dag Øystein & Zhu, Lin [Show all 8 contributors for this article] (2015). Contrasting correlation patterns between environmental factors and chlorophyll levels in the global ocean. Global Biogeochemical Cycles. ISSN 0886-6236. 29(12), p. 2095–2107. doi: 10.1002/2015GB005216. Full text in Research Archive
• Stenseth, Nils Christian; Durant, Joel Marcel; Fowler, Mike; Matthysen, Erik; Adriaensen, Frank & Jonzén, Niclas [Show all 12 contributors for this article] (2015). Testing for effects of climate change on competitive relationships and coexistence between two bird species. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 282, p. 1–9. doi: 10.1098/rspb.2014.1958. Full text in Research Archive
• Durant, Joel Marcel; Skern-Mauritzen, Mette; Krasnov, Yuri V.; Nikolaeva, Natalia G.; Lindstrøm, Ulf & Dolgov, Andrey V. (2014). Temporal dynamics of top predators interactions in the Barents Sea. PLOS ONE. 9(11). doi: 10.1371/journal.pone.0110933. Full text in Research Archive Show summary

  The Barents Sea system is often depicted as a simple food web in terms of number of dominant feeding links. The most conspicuous feeding link is between the Northeast Arctic cod Gadus morhua, the world's largest cod stock which is presently at a historical high level, and capelin Mallotus villosus. The system also holds diverse seabird and marine mammal communities. Previous diet studies may suggest that these top predators (cod, bird and sea mammals) compete for food particularly with respect to pelagic fish such as capelin and juvenile herring (Clupea harengus), and krill. In this paper we explored the diet of some Barents Sea top predators (cod, Black-legged kittiwake Rissa tridactyla, Common guillemot Uria aalge, and Minke whale Balaenoptera acutorostrata). We developed a GAM modelling approach to analyse the temporal variation diet composition within and between predators, to explore intra- and inter-specific interactions. The GAM models demonstrated that the seabird diet is temperature dependent while the diet of Minke whale and cod is prey dependent; Minke whale and cod diets depend on the abundance of herring and capelin, respectively. There was significant diet overlap between cod and Minke whale, and between kittiwake and guillemot. In general, the diet overlap between predators increased with changes in herring and krill abundances. The diet overlap models developed in this study may help to identify inter-specific interactions and their dynamics that potentially affect the stocks targeted by fisheries.

• Stige, Leif Christian; Dalpadado, Padmini; Orlova, Emma L.; Boulay, Ann-Cecilie; Durant, Joel Marcel & Ottersen, Geir [Show all 7 contributors for this article] (2014). Spatiotemporal statistical analyses reveal predator-driven zooplankton fluctuations in the Barents Sea. Progress in Oceanography. ISSN 0079-6611. 120, p. 243–253. doi: 10.1016/j.pocean.2013.09.006. Full text in Research Archive
• Feng, Jianfeng; Stige, Leif Christian; Durant, Joel Marcel; Hessen, Dag Olav; Zhu, Lin & Hjermann, Dag Øystein [Show all 8 contributors for this article] (2014). Large-scale season-dependent effects of temperature and zooplankton on phytoplankton in the North Atlantic. Marine Ecology Progress Series. ISSN 0171-8630. 502, p. 25–37. doi: 10.3354/meps10724. Full text in Research Archive
• Ottersen, Geir; Stige, Leif Christian; Durant, Joel Marcel; Chan, Kung-Sik; Rouyer, Tristan Alexander & Drinkwater, Kennneth F. [Show all 7 contributors for this article] (2013). Temporal shifts in recruitment dynamics of North Atlantic fish stocks: effects of spawning stock and temperature. Marine Ecology Progress Series. ISSN 0171-8630. 480, p. 205–225. doi: 10.3354/meps10249. Full text in Research Archive
• Durant, Joel Marcel; Hjermann, Dag Øystein & Handrich, Yves (2013). Diel feeding strategy during breeding in male Barn Owls (Tyto alba). Journal of Ornithology = Journal fur Ornithologie. ISSN 0021-8375. 154(3), p. 863–869. doi: 10.1007/s10336-013-0956-1. Full text in Research Archive Show summary

  During reproduction, birds are confronted with two requirements: building up their energetic reserves during the activity period, and provisioning the nest. Storing reserves imposes a higher flight cost and a lower hunting efficiency. This conflict is accentuated in species such as the Barn Owl (Tyto alba), where the nest food supply is entirely taken in charge by the male during a long period (ca. 37 days). We tested the prediction that Barn Owl males were postponing their meal to the end of the night in order to fly with a low body mass. Nocturnal changes in body mass (i.e., estimates of feeding events) were monitored remotely on six free-ranging Barn Owl pairs nesting in eastern France using an automated weighing system. Male Barn Owls were gaining the more weight at the end of the night, supporting the prediction that they make their biggest meal after the nest provisioning activities hunting period that is taking place at the beginning of the night. This is a preprint version of the article. The final publication is available at link.springer.com

• Durant, Joel Marcel; Hidalgo, Manuel; Rouyer, Tristan Alexander; Hjermann, Dag Øystein; Ciannelli, Lorenzo & Eikeset, Anne Marie [Show all 8 contributors for this article] (2013). Population growth across heterogeneous environments: effects of harvesting and age structure. Marine Ecology Progress Series. ISSN 0171-8630. 480, p. 277–287. doi: 10.3354/meps10308. Full text in Research Archive Show summary

  Population growth is affected by several factors such as climate, species interaction and harvesting pressure. However, additional complexity can arise if fishing increases the sensitivity to environmental variability. To predict the effects of fisheries and climate on marine populations, there is a need for improved understanding of how they affect key ecological processes such as population growth. In this study, we used a comparative approach investigating commercially fished species across different ecosystems: the Norwegian Sea-Barents Sea (Northeast Arctic cod), the North Sea (North Sea cod), the Atlantic Ocean (European hake), the Mediterranean Sea (European hake), and the Gulf of Alaska and Bering Sea (walleye pollock). Our objective was to compare the effects of commercial fisheries, age structure and environmental variability on population growth rate. We show that although all stocks experienced a decline in abundance, only 3 of them showed a concomitant decreasing trend in generation time (South Atlantic hake, North Atlantic hake and Northeast Arctic cod), suggesting a fishing-induced erosion in their age structure. Intra-specific analysis shows that changes in generation time triggered an increase in the relative contribution of recruitment to population growth. Furthermore, the contribution from recruitment to population growth changes due to large-scale climate indices or regional-scale environmental covariates, such as sea temperature. This study illustrates how and where the interaction between large-scale ecological patterns and regional/short-scale processes are important for designing management regulations. This in a MEPS Free Access Article. IR retains copyright.

• Durant, Joel Marcel; Hjermann, Dag Øystein; Falkenhaug, Tone; Gifford, Dian; Naustvoll, Lars Johan & Sullivan, Barbara [Show all 8 contributors for this article] (2013). Extension of the match-mismatch hypothesis to predator-controlled systems. Marine Ecology Progress Series. ISSN 0171-8630. 474, p. 43–52. doi: 10.3354/meps10089. Full text in Research Archive Show summary

  Differential change in the phenology of predators and prey is a potentially important climate-mediated mechanism influencing populations. The match-mismatch hypothesis describes the effect of predator-prey population synchrony on predator development and survival and is used to describe climate effects on ecological patterns and processes in prey-controlled terrestrial and marine ecosystems. We evaluated the hypothesis by considering the broader effects of predator-prey synchrony on prey standing stock and survival in addition to its well documented effects on the predator. Specifically, we suggest that an increase in asynchrony between predator and prey peak abundance can lead to increased survival and potentially increased recruitment of the prey in some systems. Using generalized additive models, we demonstrated that the matchmismatch hypothesis can be used not only for prey-controlled systems, but also for predatorcontrolled systems.

• Chambers, Lynda E.; Altwegg, Res; Barbraud, Christophe; Barnard, Phoebe; Beaumont, Linda J. & Crawford, Robert J. M. [Show all 16 contributors for this article] (2013). Phenological Changes in the Southern Hemisphere. PLOS ONE. 8(10). doi: 10.1371/journal.pone.0075514. Full text in Research Archive Show summary

  Current evidence of phenological responses to recent climate change is substantially biased towards northern hemisphere temperate regions. Given regional differences in climate change, shifts in phenology will not be uniform across the globe, and conclusions drawn from temperate systems in the northern hemisphere might not be applicable to other regions on the planet. We conduct the largest meta-analysis to date of phenological drivers and trends among southern hemisphere species, assessing 1208 long-term datasets from 89 studies on 347 species. Data were mostly from Australasia (Australia and New Zealand), South America and the Antarctic/subantarctic, and focused primarily on plants and birds. This meta-analysis shows an advance in the timing of spring events (with a strong Australian data bias), although substantial differences in trends were apparent among taxonomic groups and regions. When only statistically significant trends were considered, 82% of terrestrial datasets and 42% of marine datasets demonstrated an advance in phenology. Temperature was most frequently identified as the primary driver of phenological changes; however, in many studies it was the only climate variable considered. When precipitation was examined, it often played a key role but, in contrast with temperature, the direction of phenological shifts in response to precipitation variation was difficult to predict a priori. We discuss how phenological information can inform the adaptive capacity of species, their resilience, and constraints on autonomous adaptation. We also highlight serious weaknesses in past and current data collection and analyses at large regional scales (with very few studies in the tropics or from Africa) and dramatic taxonomic biases. If accurate predictions regarding the general effects of climate change on the biology of organisms are to be made, data collection policies focussing on targeting data-deficient regions and taxa need to be financially and logistically supported. Copyright: 2013 Chambers et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

• Hidalgo, Manuel; Rouyer, Tristan Alexander; Bartolino, Valerio; Cerviño, Santiago; Ciannelli, Lorenzo & Massuti, Enric [Show all 12 contributors for this article] (2012). Context-dependent interplays between truncated demographies and climate variation shape the population growth rate of a harvested species. Ecography. ISSN 0906-7590. 35(7), p. 637–649. doi: 10.1111/j.1600-0587.2011.07314.x. Full text in Research Archive
• Durant, Joel Marcel; Krasnov, Yuri V.; Nikolaeva, Natalia G. & Stenseth, Nils Christian (2012). Within and between species competition in a seabird community: statistical exploration and modeling of time-series data. Oecologia. ISSN 0029-8549. 169(3), p. 685–694. doi: 10.1007/s00442-011-2226-3. Full text in Research Archive
• Sabarros, Philippe Sunil; Durant, Joel Marcel; Grémillet, David; Crawford, Robert J. M. & Stenseth, Nils Christian (2012). Differential responses of three sympatric seabirds to spatio-temporal variability in shared resources. Marine Ecology Progress Series. ISSN 0171-8630. 468, p. 291–301. doi: 10.3354/meps09972. Full text in Research Archive Show summary

  Environmental change linked to climate and human activities may affect top predators via the food chain in marine systems. Understanding the functional link between resources and predator responses (e.g. foraging effort, reproductive success, population growth) is of crucial importance in the context of an ecosystem-based approach to fisheries. In the Benguela upwelling ecosystem located off the South African coast, both climate and overfishing may have modified the spatio-temporal availability of sardines and anchovies over the past 2 decades. These fish are prevalent prey items for 3 seabirds: the African penguin Spheniscus demersus, Cape gannet Morus capensis and Cape cormorant Phalacrocorax capensis. Species-specific responses of these 3 sympatric seabirds to the fluctuations in their shared prey are poorly understood. Here we used generalized additive modelling to examine the ‘local population response’ (i.e. number of breeders) of the 3 seabirds to spatio-temporal variations in prey availability from 1987 to 2007. We showed that prey fluctuations influence seabird local population responses, presumably by modulating recruitment, breeding decision and breeding performance. We also identified speciesspecific population responses to prey availability: positive in African penguins and Cape gannets, and null in Cape cormorants. These patterns could be explained by seabirds partitioning prey in time via separated breeding periods, and space via accessing different foraging grounds due to specific feeding techniques. These responses also suggest different degrees of dependency upon pelagic resources among predators, which are likely due to contrasting foraging ecologies (e.g. dietary plasticity, foraging techniques, foraging ranges).

• Saraux, Claire; Bohec, Céline Le; Durant, Joel Marcel; Viblanc, Vincent A.; Gauthier-Clerc, Michel & Beaune, David [Show all 10 contributors for this article] (2011). Reliability of flipper-banded penguins as indicators of climate change. Nature. ISSN 0028-0836. 469(7329), p. 203–208. doi: 10.1038/nature09630. Full text in Research Archive
• Rouyer, Tristan Alexander; Ottersen, Geir; Durant, Joel Marcel; Hidalgo, Manuel; Hjermann, Dag Øystein & Persson, Jonas [Show all 8 contributors for this article] (2011). Shifting dynamic forces in fish stock fluctuations triggered by age truncation? Global Change Biology. ISSN 1354-1013. 17(10), p. 3046–3057. doi: 10.1111/j.1365-2486.2011.02443.x. Full text in Research Archive

View all works in NVA

• Langangen, Øystein Ole Gahr; Olsen, Tora; Durant, Joël; Ottersen, Geir & Eriksen, Elena (2024). Poleward shift in spawning leads to smaller Atlantic cod offspring. Full text in Research Archive
• Langangen, Øystein Ole Gahr; Olsen, Tora; Durant, Joël; Ottersen, Geir & Eriksen, Elena (2024). Poleward shift in spawning leads to smaller Atlantic cod offspring. Full text in Research Archive
• Hoff, Siv Nam Khang; Maurstad, Marius Filomeno; Alan, Le Moan; Ravinet, Mark; Durant, Joël & Tørresen, Ole K. [Show all 18 contributors for this article] (2023). Identification of multiple chromosomal inversions and fusions in a keystone Arctic species with high gene flow. Full text in Research Archive
• Langangen, Øystein Ole Gahr & Durant, Joël (2023). Mass mortality and population dynamics of fish. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• Durant, Joël; Ono, Kotaro & Langangen, Øystein Ole Gahr (2023). Empirical evidence of non-linearity in the interaction between fish stocks in the Barents Sea. Full text in Research Archive Show summary

  The strength of species interactions can have a significant impact on population dynamics. Empirical estimates of interaction strength are often based on the assumption that the interaction strength is constant. Several fish species interact in the Barents Sea and their population dynamics are typically modelled under the assumption of constant interaction strength. However, interactions between species are often non-linear in marine ecosystems and this could fundamentally change our understanding of food webs’ functioning. Here, we present two examples of such nonlinear interactions in the Barents Sea, between cod Gadus morhua and capelin Mallotus villosus, and between cod and haddock Melanogrammus aeglefinus. Analysis of long survey time series in the Arcto-boreal Barents Sea within a state-space modelling framework showed that the effect of capelin on cod is not linear but varies with capelin abundance. Similarly, interactions between cod and haddock have changed over the past two decades due to rising ocean temperatures, altering the equilibrium abundances and the dynamics of the system. Our analyses demonstrate that long-term climate change in the Arcto-boreal system leads to differences in equilibrium conditions for species communities and demonstrates the importance of investigating nonlinearities in species interactions, leading to a better understanding of species communities and species assemblages.

• Hoff, Siv Nam Khang; Maurstad, Marius Filomeno; Moan, Alan Le; Ravinet, Mark; Durant, Joël & Tørresen, Ole Kristian [Show all 18 contributors for this article] (2023). Identification of multiple chromosomal inversions and fusions in a keystone Arctic species with high gene flow. Full text in Research Archive
• 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. Full text in Research Archive
• Durant, Joël (2022). Non-linearity in interspecific interactions between Barents Sea cod and haddock in response to climate change. Full text in Research Archive Show summary

  Climate change is affecting many fish populations globally. For instance, sea temperature warming has been shown to affect distribution, population growth and trophic interactions in marine systems. This is particularly true in high-latitude marine ecosystems where the sea warming effect is projected to be strongest. In the cold Barents Sea, increase of sea temperature is beneficial for the productivity of many commercially important fish species, such as the haddock Melanogrammus aeglefinus and the Atlantic cod Gadus morhua. These sympatric fish compete for food at younger stages and thereafter the former is preyed by the latter but Climate change might affect the interaction and coexistence of these two species. We used 33-year long time series of haddock and cod abundances estimates from two data sources (acoustic and trawl survey) to analyse the dynamic effect of climate on the coexistence of these two sympatric species in the Arcto-Boreal Barents Sea. Using a Bayesian state-space threshold model, we demonstrated that long-term climate variation, as expressed by changes of sea temperature, affected species demography through different influences on density-independent processes. The interaction between cod and haddock has shifted in the last two decades due to an increase in sea temperature, altering the equilibrium abundances and the dynamics of the system. During warm years (sea temperature over ca 4°C), the increase of the cod abundance negatively affected haddock abundance while it did not during cold years. This change in interactions therefore changed the equilibrium population size with a higher population size during warm years. Our analyses show that long-term climate change in the Arcto-boreal system can generate differences in the equilibrium conditions of species assemblages.

• Durant, Joël (2022). Match-mismatch, trophic interactions and climate change. Full text in Research Archive Show summary

  Climate change is affecting the trophic interactions on which we base our understanding of marine systems. The consequence is that we must get used to a world where our hard acquired knowledge on ecosystem and trophic interactions is no longer accurate, or at least not reliably so. In other words, the models we have developed based on long-term time series may not be reliable. We know that the physiology and the mechanisms it is driving are changing at the slower pace than climate. Building mechanistic models could thus be useful to explore the future consequences of climate change. In fish, the major driver of population dynamics is the recruitment of individuals through the reproduction process (i.e., production and survival through the early life stages). Several mechanistic hypotheses have been set forth to explain changes in fish production in relation to phenology, which is well documented to be strongly affected by climate change. One of the most well-known is the “match-mismatch” hypothesis (MMH) elaborated by David Cushing. A question is if the MMH is a useful tool to understand animal recruitment in the context of global climate change. I will present some of the latest development from my group on match-mismatch models (role of abundance and spatial distribution…) and the role of MMH for population dynamics. Finally, I will address the value of the MMH to make projection and I will highlight some of the limitation of our current understanding of MMH.

• 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). Full text in Research Archive
• Jentoft, Sissel & Durant, Joël (2021). A not so icy relationship: The Polar cod in the Barents Sea. Full text in Research Archive
• 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. Full text in Research Archive
• 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. Full text in Research Archive
• Holt, Rebecca Emma; Bogstad, Bjarte; Durant, Joël; Dolgov, Andrey V. & Ottersen, Geir (2019). Erratum: Barents Sea cod (Gadus morhua) diet composition: Long-term interannual, seasonal, and ontogenetic patterns (ICES Journal of Marine Science (2019) DOI: 10.1093/icesjms/fsz082). ICES Journal of Marine Science. ISSN 1054-3139. 76(6), p. 1936–1936. doi: 10.1093/icesjms/fsz117. Full text in Research Archive
• Fauchald, Per & Durant, Joel Marcel (2019). Hvorfor fluktuerer de store marine fiskebestandene? Naturen. ISSN 0028-0887. 143(3), p. 124–132. doi: 10.18261/issn.1504-3118-2019-03-06. Full text in Research Archive Show summary

  Fluktuasjoner i de store fiskebestandene har store konsekvenser for fiskeriavhengige kystsamfunn, men også for de marine økosystemene. Overfiske og klimaendringer, sammen med økologiske interaksjoner som predasjon og konkurranse, er de viktigste driverne bak dynamikken. Kollaps og vekst i de store fiskebestandene har store konsekvenser for økosystemene, og resultatet kan være vedvarende bestandskollaps og uforutsette skift i økosystemet. Vi gir her en kort og selektiv oversikt over dette omfattende temaet, med eksempler fra nordlige marine økosystemer.

• Stige, Leif Christian; Rogers, Lauren; Neuheimer, Anna B.; Hunsicker, Mary E.; Yaragina, Natalia A. & Ottersen, Geir [Show all 9 contributors for this article] (2019). Density- and size-dependent mortality in fish early life stages. Full text in Research Archive
• Stige, Leif Christian; Durant, Joel Marcel & Langangen, Øystein (2019). Effects of climate change, fishing and oil on marine ecosystems. Full text in Research Archive
• 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), p. 46–49. Full text in Research Archive
• Llope, Marcos; Blenckner, Thorsten; Vasilakopoulos, Paris; McGinty, Niall; Lynam, Christopher Philip & Helaouët, Pierre [Show all 10 contributors for this article] (2018). Resilience of northeast Atlantic marine ecosystems. Full text in Research Archive
• Färber, Leonie Anette; Camilla, Sguotti; Durant, Joel Marcel; Langangen, Øystein; Otto, Saskia A & Möllmann, Christian (2018). Detecting catastrophic transitions – the case of North Atlantic herring. Full text in Research Archive
• Deris, Leana; Langangen, Øystein & Durant, Joel Marcel (2018). Effect of cod (Gadus morhua) predation on juvenile herring (Clupea harengus) in the Barents Sea. Full text in Research Archive Show summary

  The Barents Sea is a shelf sea sustaining a highly productive ecosystem including several commercially important fish stocks among which the Northeast Arctic (NEA) cod (Gadus morhua), Norwegian Spring Spawning (NSS) herring (Clupea harengus) and the Barents Sea (BS) capelin (Mallotus villosus) are key fish species in this ecosytem. NSS herring is currently one of the largest herring stocks in the world, and it is both an important prey (for e.g. cod and marine mammals) and predator species (for e.g. planktonic early life stages of fish and zooplankton). It spawns in the Norwegian Sea in February-March and deposits eggs on the sea bottom. After hatching, larvae and 0-group appear in the upper water layer and drift by the coastal current to enter the Barents Sea where they spend their first 3 to 4 years of life before migrating to the north Atlantic as adult. It is during its juvenile life stage that the herring is susceptible to predation by the large stock of NEA cod. Here, we develop a state-space model to estimate the effect of cod predation on young herring mortality. We used the obtained estimates to quantify at the population level the joint effect of fishing and cod predation on young herring. Our results indicate a significant effect of cod and illustrate how management of NSS herring benefits from jointly considering cod and fishing.

• Llope, Marcos; Blenckner, Thorsten; Vasilakopoulos, Paris; McGinty, Niall; Lynam, Christopher Philip & Helaouët, Pierre [Show all 10 contributors for this article] (2018). Continuous and abrupt changes in the resilience of northeast Atlantic marine ecosystems. Full text in Research Archive
• Färber, Leonie Anette; Sguotti, Camilla; Durant, Joel Marcel; Langangen, Øystein; Otto, Saskia A & Möllmann, Christian (2018). Detecting catastrophic transitions – the case of North Atlantic herring. Full text in Research Archive
• Deris, Leana; Langangen, Øystein & Durant, Joel Marcel (2018). Effect of stock collapse on predator prey relationships. Full text in Research Archive
• Holt, Rebecca Emma; Durant, Joel Marcel; Ottersen, Geir & Bogstad, Bjarte (2017). Cod diet and food web dynamics: What can we learn from the past? Full text in Research Archive
• Durant, Joel Marcel; Langangen, Øystein & Dupont, Nicolas (2017). Barents Sea cod larvae survival and match-mismatch. Full text in Research Archive
• Färber, Leonie Anette; Durant, Joel Marcel; Vindenes, Yngvild & Langangen, Øystein (2017). Benefit of long distance migration for Barents Sea cod. Full text in Research Archive
• Diekert, Florian Klaus; Langangen, Øystein; Färber, Leonie Anette; Stige, Leif Christian & Durant, Joel Marcel (2016). Ticket to Spawn – Using economic data to shed light on biological hypothesis. Full text in Research Archive
• Färber, Leonie Anette; Stige, Leif Christian; Durant, Joel Marcel; Diekert, Florian Klaus & Langangen, Øystein (2016). Ticket to Spawn – Using economic data to shed light on biological hypothesis. Full text in Research Archive
• Durant, Joel Marcel (2016). MARmaED: MARine MAnagement and Ecosystem Dynamics under climate change. Full text in Research Archive
• Durant, Joel Marcel & Ottersen, Geir (2016). Effect of juvenile distribution and environment on the Northeast Arctic haddock. Full text in Research Archive
• Walle, Eirik & Durant, Joel Marcel (2015). Investigating the effect of changes in the timing of fishing on the breeding success of a South African seabird. Full text in Research Archive
• Durant, Joel Marcel; Krasnov, Yuri V.; Nikolaeva, Natalia G. & Hjermann, Dag Øystein (2015). Prey abundance and Competition with fish as drivers for kittiwake population in the subarctic. Full text in Research Archive
• Dankel, Dorothy Jane; Durant, Joel Marcel; Ottersen, Geir; Kjesbu, Olav Sigurd & Stenseth, Nils Christian (2014). "Eco-Harvest Control Rules". Full text in Research Archive
• Durant, Joel Marcel & Ottersen, Geir (2014). Match-mismatch and climate warming, what can we expect? Full text in Research Archive
• Durant, Joel Marcel (2014). Harvesting and Population Structure Effect on Population Growth. Full text in Research Archive
• Durant, Joel Marcel; Ottersen, Geir & Stenseth, Nils Christian (2013). Impact of climate and fisheries on sub-Arctic stocks - INTRODUCTION. Marine Ecology Progress Series. ISSN 0171-8630. 480, p. 199–203. Full text in Research Archive
• Durant, Joel Marcel; Skern-Mauritzen, Mette; Krasnov, Yuri V.; Nikolaeva, Natalia G. & Lindstrøm, Ulf (2013). Temporal dynamics of the major predator interaction in the Barents Sea. Full text in Research Archive
• Saraux, Claire; Bohec, Céline Le; Durant, Joel Marcel & Stenseth, Nils Christian (2011). Terres Australes : les bagues pénalisent les manchots royaux. [Internet]. Ecolorama.fr. Full text in Research Archive
• Moan, Andre Grande; Solvang, Hiroko Kato; Skaug, Hans Julius; Henden, John-Andre; Nilssen, Kjell Tormod & Ryeng, Kathrine [Show all 16 contributors for this article] (2024). Sjøpattedyrutvalget 2024 - Tilrådning om forskning og forvaltning. Havforskningsinstituttet. Full text in Research Archive Show summary

  Sjøpattedyrutvalget hadde sitt årlige møte i Tromsø 18.-19. november 2024. Utvalgets oppgave er å utarbeide anbefalinger og tilrådninger om forskning og forvaltning av sjøpattedyr i Norge. Dette inkluderer kvoteråd for arter som fangstes eller jaktes. I denne rapporten oppsummeres sakene som ble behandlet på årets møte.

• Arneberg, Per; Husson, Berengere; Siwertsson, Anna; Albretsen, Jon; Børsheim, Knut Yngve & Denechaud, Côme [Show all 24 contributors for this article] (2023). Panel-based Assessment of Ecosystem Condition of the North Sea Shelf Ecosystem - Appendices. Havforskningsinstituttet. Full text in Research Archive
• Arneberg, Per; Husson, Berengere; Siwertsson, Anna; Albretsen, Jon; Børsheim, Knut Yngve & Denechaud, Côme [Show all 24 contributors for this article] (2023). Panel-based Assessment of Ecosystem Condition of the North Sea Shelf Ecosystem. Havforskningsinstituttet. Full text in Research Archive Show summary

  The System for Assessment of Ecological Condition, coordinated by the Norwegian Environment Agency, is intended to form the foundation for evidence-based assessments of the ecological condition of Norwegian terrestrial and marine ecosystems not covered by the EU Water Framework Directive. The reference condition is defined as “intact ecosystems”, i.e., a condition that is largely unimpacted by modern industrial anthropogenic activities. An ecosystem in good ecological condition does not deviate substantially from this reference condition in structure, functions or productivity. This report describes the first operational assessment of the ecological condition of the marine shelf ecosystem in the Norwegian sector of the North Sea and Skagerrak. The assessment method employed is the Panel-based Assessment of Ecosystem Condition (PAEC1) and the current assessment has considered to what extent the North Sea and Skagerrak shelf ecosystem deviates from the reference condition2 by evaluating change trajectories.

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