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• Perryman, Holly Ann; Hansen, Cecilie; Howell, Daniel; Stenevik, Erling Kåre; Nilsen, Ina & Pitcher, T J [Show all 7 contributors for this article] (2025). An ecosystem-based management strategy evaluation of harvest control rules for Norwegian spring-spawning herring (Clupea harengus L.). ICES Journal of Marine Science. ISSN 1054-3139. 82(9). doi: 10.1093/icesjms/fsaf159. Full text in Research Archive Show summary

  Norwegian spring-spawning herring (Clupea harengus L.) play a vital ecological and socio-economic role in the Northeast Atlantic and Arctic Oceans, with several coastal states and fishing nations participating in the fishery. The stock collapsed in the 1960s due to environmental changes and overfishing, prompting changes in management. A harvest control rule was introduced in a long-term management plan agreed upon by the coastal states in 1999, aiding stock recovery. In 2018, the International Council for the Exploration of the Sea (ICES) conducted a benchmark and management strategy evaluation, leading to a revised long-term management plan implemented in 2019. Although Norwegian spring-spawning herring, as forage fish, are prime candidates for ecosystem-based fisheries management, the current ICES management strategy evaluation omitted ecosystem interactions. Our study employed an ecosystem-based operating model (Atlantis) to test and evaluate four threshold harvest control rules for Norwegian spring-spawning herring, considering uncertainty in recruitment and zooplankton biomass. The candidate harvest control rules included the previous long-term management plan (1999–2018), the current long-term management plan (2019–present), and two harvest control rules that varied the target fishing mortality and spawning stock biomass reference thresholds. In our results, the previous long-term management plan often led to greater long-term Norwegian spring-spawning herring biomass and catch with less catch variation, outperforming the current long-term management strategy. We discuss our findings in the context of balancing the parameterizations of harvest control rule reference points to support long-term catch and stock biomass under an ecosystem context. Incorporating ecosystem models into management strategy evaluation, alongside the more commonly used single-species models, offers a more comprehensive and nuanced understanding of the impacts of alternative fishery strategies when evaluating Norwegian spring-spawning herring harvest control rules. This aligns with ICES objectives for sustainable seafood provision and marine ecosystem understanding.

• Årthun, Marius; Dinh, van Khuong; Dörr, Jakob Simon; Dupont, Nicolas; Fransner, Filippa & Nilsen, Ina [Show all 18 contributors for this article] (2025). The future Barents Sea- A synthesis of physical, biogeochemical, and ecological changes toward 2050 and 2100. Elementa: Science of the Anthropocene. 13(1), p. 1–17. doi: 10.1525/elementa.2024.00046. Full text in Research Archive Show summary

  Barentshavet er preget av sterke klimaendringene, som manifesterer seg i en rask oppvarming av havet og atmosfæren og en sterk nedgang i havisdekket om vinteren. Disse endringene i det fysiske miljøet har store konsekvenser for de marine økosystemene, inkludert de kommersielle fiskebestandene. I et varmere klima i fremtiden forventes både de fysiske og økologiske endringene å forsterkes. Her gir vi en første omfattende oversikt over framtidige klimaendringer i Barentshavet og de tilhørende fysiske, biogeokjemiske og økologiske konsekvensene basert på klimamodeller og helhetlige økosystemmodeller. Vi diskuterer også potensielle fremtidige endringer i menneskelige aktiviteter og konsekvensene av disse, inkludert endringer i skipsaktivitet og forurensing. Vi analyserer resultatene for to tidshorisonter - nær fremtid (2040-2050) og fjern fremtid (2090-2100) - og for to ulike utslippsscenarioer: ett med moderate fremtidige klimagassutslipp (SSP2-4,5) og ett med høye utslipp (SSP5-8,5). Resultatene viser at fremtidens Barentshavet vil bli varmere, mindre isdekket, surere og mer produktivt, og at fiskebestander og gyteområder vil flytte seg nordover. Det er små forskjeller i de gjennomsnittlige fysiske og biogeokjemiske projeksjonene fra flere modeller mellom de to utslippsscenariene innen 2050, mens det er store forskjeller mellom scenariene mot slutten av århundret. Disse resultatene har vidtrekkende konsekvenser, blant annet ved at de kan identifisere økosystemenes følsomhet for fremtidige utslipp, gi informasjon om regionale forvaltningsstrategier og potensielt identifisere behov for tilpasning til endringer som sannsynligvis allerede vil inntreffe.

• Nilsen, Ina; Hansen, Cecilie & Kaplan, Isaac C (2025). A shifting chessboard: Projections of prawn, capelin, mesopelagic fish, zooplankton, and their Nordic and Barents Seas food web under climate change. Progress in Oceanography. ISSN 0079-6611. 231. doi: 10.1016/j.pocean.2024.103387. Full text in Research Archive Show summary

  As climate change is already altering ocean temperatures, there is an urgent need to understand how environmental changes will affect marine ecosystems. Although great efforts have been made to understand the impacts of ocean warming, there are still uncertainties regarding effects on lower trophic levels and how these may propagate to higher trophic levels. In this study, physics from three different climate projections (SPP1-2.6, SSP2-4.5 and SSP5-8.5) were applied to study the impact of rising temperatures in the Nordic and Barents Seas Atlantis ecosystem model (NoBa Atlantis). We also included variation in phyto- and zooplankton levels to account for the uncertainty regarding how lower trophic levels might respond to climate change. This approach by us is the first study where three different sets of physics have been applied to an end-to-end ecosystem model representing the Nordic and Barents Seas. We therefore treat the projected results with caution, and focus on the underlying mechanisms that drive the changes, to inform future ecosystem studies. The spatial nature of the model (a “shifting chessboard”) allowed us to study how local changes in temperature and prey could affect entire populations. For instance, the thermal niches of mesopelagic fish allowed for an increase in abundance in northern areas, benefiting predators such as blue whiting. On the other hand, thermal limits of capelin together with zooplankton overlap resulted in declines, which subsequently led to reduction in cod growth. This study demonstrates how ecosystem studies could benefit from both modeling and empirical studies that consider not only broad-brush impacts on primary production and trophic transfer, but also spatial considerations of local predator–prey interactions, thermal habitat and spawning-area suitability.

• Nilsen, Ina; Fransner, Sara Filippa Krusmynta; Olsen, Are; Tjiputra, Jerry; Hordoir, Robinson & Hansen, Cecilie (2023). Trivial gain of downscaling in future projections of higher trophic levels in the Nordic and Barents Seas. Fisheries Oceanography. ISSN 1054-6006. 32(5), p. 479–493. doi: 10.1111/fog.12641. Full text in Research Archive Show summary

  Downscaling physical forcing from global climate models is both time consuming and labor demanding and can delay or limit the physical forcing available for regional marine ecosystem modelers. Earlier studies have shown that downscaled physics is necessary for capturing the dynamics of primary production and lower trophic levels; however, it is not clear how higher trophic levels respond to the coarse resolution physics of global models. Here, we apply the Nordic and Barents Seas Atlantis ecosystem model (NoBa) to study the consequences of using physical forcing from global climate models versus using that from regional models. The study is therefore (i) a comparison between a regional model and its driving global model to investigate the extent to which a global climate model can be used for regional ecosystem predictions and (ii) a study of the impact of future climate change in the Nordic and Barents Seas. We found that few higher trophic level species were affected by using forcing from a global versus a regional model, and there was a general agreement in future biomass trends and distribution patterns. However, the slight difference in temperature between the models dramatically impacted Northeast Arctic cod (Gadus morhua), which highlights how species projection uncertainty could arise from poor physical representation of the physical forcing, in addition to uncertainty in the ecosystem model parameterization.

• Nilsen, Ina; Hansen, Cecilie; Kaplan, Isaac; Holmes, Elizabeth & Langangen, Øystein Ole Gahr (2022). Exploring the role of Northeast Atlantic cod in the Barents Sea food web using a multi-model approach. Fish and Fisheries. ISSN 1467-2960. 23(5), p. 1083–1098. doi: 10.1111/faf.12671. Full text in Research Archive Show summary

  It is commonly accepted that no ecosystem model is the ‘best’, but rather that ecosystem models should be used in ensembles. This is also the case for the Barents Sea ecosystem, where we have used two different ecosystem models to explore the role of the top-predator Northeast Arctic (NEA) stock of Atlantic cod (Gadus morhua, Gadidae) in the food web. The two models differ in complexity; Gompertz being less complex in terms of food web (7 components) and processes compared to the complex Nordic and Barents Seas Atlantis model (53 components). On the other hand, Gompertz provides thousands of stochastic realizations for each scenario, whereas Atlantis provides only one deterministic simulation. To compare the response to changes in NEA cod on two key prey species, capelin (Mallotus villosus, Osmeridae) and polar cod (Boreogadus saida, Gadidae), we perturbed the historical fishing pressure by ±50% and used the same NEA cod biomass in both models. Even though the links between NEA cod and the prey species are similar in the two models, the results from the study reveal that indirect effects through other food-web components might be as important as direct predator–prey interactions. Differences in spatial structure and overlap between species also influence the species response to the perturbations. In this study, we focus on the mechanisms that drives the changes in the models, and advise on potential consequences for fisheries management. The two models can complement each other, and the differences between them point to areas where more knowledge is needed.

• Nilsen, Ina; Kolding, Jeppe; Eide, Cecilie Hansen & Howell, Daniel (2020). Exploring balanced harvesting by using an Atlantis ecosystem model for the Nordic and Barents seas. Frontiers in Marine Science. 7. doi: 10.3389/fmars.2020.00070. Full text in Research Archive Show summary

  “Balanced Harvesting” (BH) has been suggested as a possible strategy to meet the objectives of the Ecosystem Approach to Fisheries, ensuring a high sustainable yield while maintaining ecosystem structure and function. BH proposes a moderate fishing mortality in proportion to productivity spread across the widest possible range of species, stocks, and sizes in an ecosystem producing a sustainable and overall non-selective harvest. The Norwegian and Barents Seas have been subjected to moderate fishing pressure on commercial species, and elements of an ecosystem-based approach to management for many years, but not the fishing pattern proposed by BH. By using an Atlantis ecosystem model of the Nordic and Barents Seas, we investigated the effects of applying a BH regime to a region with existing successful fisheries management. This was done by running simulations with combinations of historic fishing pressure and fishing mortality rates proportional to 25% of the productivity of most species and sizes. The simulations were then compared to a control run where the historical fisheries were applied. The model results showed that implementing a BH regime in the Norwegian and Barents Seas would only produce marginal increases in total yields of currently commercially exploited stocks, likely because the Norwegian fisheries are already mostly well-managed. However, expanding the fishery to include species that are not commercially exploited today did produce higher yields, especially on lower trophic levels. This study represents the first attempted examination of implementing BH based on productivity using an Atlantis ecosystem model, as well as the first investigation of BH in the Norwegian and Barents Seas. We use this model as a case study to identify the gains that species-based BH can be expected to give over well-implemented traditional fisheries management rather than simply comparing to an over-exploited system.

• Olsen, Erik Joel Steinar; Hansen, Cecilie; Nilsen, Ina; Perryman, Holly Ann & Vikebø, Frode Bendiksen (2019). Ecological Effects and Ecosystem Shifts Caused by Mass Mortality Events on Early Life Stages of Fish. Frontiers in Marine Science. 6. doi: 10.3389/fmars.2019.00669. Full text in Research Archive Show summary

  Mass mortality events (MMEs) are a key concern for the management of marine ecosystems. Specific stages and species are at risk and the causes may be single or cumulative pressure from a range of sources including pollutants, anthropogenic climate change or natural variability. Identifying risk and quantifying effects of plausible scenarios including MMEs are key to stakeholders and a quest for scientists. MMEs affect the whole ecosystem, but are traditionally only studied in relation to specific species, disregarding ecological feedbacks. Here we use an end-to-end ecosystem model adapted to the Nordic and Barents seas to evaluate the species-specific and ecological impacts for 50 years following an MME. MMEs were modeled as 10, 50, or 90% reduced recruitment for cod, herring and haddock, individually or in combination. The MME scenarios were compared to a base case model run that includes the current fishing mortality. All species showed declines in population biomass following an MME, increasing in duration and severity with increasing mortality. Cod biomass rebounded to the base case level within 3–13 years post the MME independent of scenario, while neither haddock nor herring fully rebounded to base case levels within the considered time horizon. Haddock responded much more variably to the mortality scenarios than cod or herring, with some scenarios yielding much higher levels of biomass than the base case. Herring responded negatively to all scenarios, leading to lower herring biomass and a steeper decline of the species than seen in the base case due to persistent harvest pressure. Corresponding responses showed that the demersal guild biomass increased substantially, while the pelagic guild biomass declined. Few effects were observed on the other guilds, including the top predators. Ecosystem effects as measured by ecological indicators were greatest after 5 years, but persisted through the entire model run. Fishery indicators showed the same features, but the responses were stronger than for the ecosystem indicators. Taken together this indicates long-term, ecological response to MMEs that can be described as regime shifts, highlighting the importance of using ecosystem models when evaluating effects of MMEs.

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• Ottersen, Geir; Hansen, Cecilie; Hjøllo, Solfrid Sætre; Hordoir, Robinson; Koseki, Mariko & Nilsen, Ina [Show all 8 contributors for this article] (2026). Cod and climate change – projecting the future of the Barents Sea cod stock towards the end of the 21st century. Full text in Research Archive Show summary

  The Barents Sea (BS), is one of the areas where strongest impacts of climate change is expected. Change from ice to open will affect the ecosystem. Climate change will have particular strong impact in the Arctic due to the amplified temperature increase there resulting in a fundamental change from a seasonally ice-covered to a permanently open ocean system. The northern and eastern parts of the Barents Sea (BS), north of Norway and NW Russia, are essentially of arctic nature. The southwestern part of the BS is boreal and heavily influenced by Atlantic water masses, the boundary between the two regimes shifts with the water masses. The Northeast Arctic population of Atlantic cod (Gadus Morhua) is a key player in the BS ecosystem. It is the largest stock of Atlantic cod and of commercial and cultural value to man. It has been monitored for well over 100 years and is likely one of the fish populations with mos accumulated knowledge on response to climate variability. Higher temperature historically been favourable, mainly acting through enhanced recruitment and arger distribution area. In this talk we summarise the main results from several recent studies that explore the state of the BS cod towards the end of the century. More precisely, by means of recent dynamical physical modelling, ecosystem modelling and expert assessments, the responses of cod to a range of downscaled IPCC CMIP6 climate scenarios are given. IPCC has defined a set of scenarios called Shared Socioeconomic Pathways, we explore SSP1–2.6 (low), SSP2–4.5 (intermediate), SSP5–8.5 (extremely high). One approach is by means of the Nemo-NAA10km ocean model, in climate downscaling mode, and the biogeochemical model NORWECOM.e2e (NORWegian ECOlogical Model system end-to-end). Based upon knowledge established form history, the projections of key physical variables (sea temperature, ice…) from Nemo-NAA10km and biogeochemistry (net primary production, gross secondary production) from NORWECOM.e2e, expert evaluations were conducted. BS cod is found to respons positively to climate change, especially the high co2 scenario. This result is supported by a regression analysis, which E2E suggest that increased ocean temperature and abundant zooplankton SSP5–8.5 may lead to a large cod stock. Alternative analyses has been conducted by means of the Nordic and Barents Seas Atlantis model (NoBa Atlantis). This is an end-to-end ecosystem model with 53 species and functional groups. Contrary to above, the NoBa Atlantis analyses concluded that the BS cod will respond negatively to climate warming, and more so under SSP5-8.5 then SSP2-4.5. The decrease in cod was strongly related to a decrease in capelin, their main food. Thus, while ther eis much knowledge on BS cod, the future is still open.

• Nilsen, Ina (2023). Ina fra Flekkefjord har fullført doktorgrad: Givende og utfordrende arbeid. [Journal]. Avisen Agder. Full text in Research Archive
• Ottersen, Geir; Arneborg, Lars; Maar, Marie; Almroth-Rosell, Elin; Fredriksson, Sam & Gonzalez, Silvana [Show all 16 contributors for this article] (2025). Effects of climate change on future environment and marine life in the Nordic sea areas. Nordic Council of Ministers. ISSN 9789289382403. doi: 10.6027/temanord2025-527. Full text in Research Archive Show summary

  The Nordic Council of Ministers sees a need to increase our understanding of the effects of future climate change specifically on the Nordic sea areas and has asked for regional analyses and assessments. NorScen aims to address the request and the results are presented in this report

• Nilsen, Ina; Eide, Cecilie Hansen; Olsen, Are; Langangen, Øystein Ole Gahr & Kaplan, Isaac (2023). Dealing with uncertainty in ecosystem models along three axes; resolution, forcing and projections. Universitetet i Bergen. ISSN 9788230843871. Full text in Research Archive Show summary

  With the imminent threat of climate change, there is an urgent need to understand how warmer temperatures will affect marine ecosystems. Models provide the best tools to study the future, but although great efforts have been made to understand the impacts of warming temperatures, there is still large uncertainties related to the model projections. The uncertainties can arise from structural uncertainty of the ecosystem model, uncertainties regarding climate projections, or uncertainties related to how species will respond to future climate changes. In this thesis, we therefore apply ecosystem models of varying complexity, climate models of varying resolution and climate projections under various emission scenarios to understand and quantify uncertainty. By assessing the uncertainty, we highlight consistent results that suggest higher confidence, and areas where differences in the results suggest that more research is needed. The results from this thesis are divided into three research papers. The first paper deals with structural uncertainty regarding model complexity, as we explore the role of Northeast Atlantic cod (Gadus Morhua) in the Barents Sea food web by using a multi-model approach. We apply two ecosystem models of different complexity; the minimalistic Gompertz model and the highly complex Atlantis model, to study how capelin and polar cod respond to changing levels of cod. We highlight consistent results across the models and identify diverging results due to differences in spatial structure and number of foodweb components, and conclude that for fishery management purposes, the two models can complement each other. The second paper deals with uncertainty regarding the resolution of climate projections used to force ecosystem models, where we apply physics (temperature, salinity, volume transport and sea ice) from a regional model (Nemo-NAA10km) and its driving global climate model (NorESM2) to the Nordic and Barents Seas Atlantis ecosystem model (NoBa). We found that few higher trophic level (TL>3) species were affected by using forcing from a global versus a regional model, and there was a general agreement in future biomass trends and distribution patterns. Yet, our results showed how a slight difference in temperature can have dramatic consequences for specific species and demonstrate that species projection uncertainty could arise from poor representation of the physical forcing, as well as due to uncertainty in the ecosystem model parameterization. In the third and final paper, we deal with the uncertainty regarding ecosystem responses to future climate changes. We apply physics from three different climate projections (SPP1-2.6, SSP2-4.5 and SSP5-8.5) to study the impact of rising temperatures in the Nordic and Barents Seas using NoBa. To account for uncertainty in the response of phytoplankton and zooplankton to future climate change, we included variation in phyto- and zooplankton growth levels. We identify potential winners and losers in a warming climate and focus on the underlying mechanisms that drives the changes in the model, including spatial differences, thermal tolerance, and species interactions. Through our work we have demonstrated the value of using ecosystem models of varying complexity, climate models of varying resolution and climate projections under various emission scenarios to quantify uncertainty regarding model projections. By investigating uncertainty along these three axes, we learn more about the models and the mechanisms that drives the changes and provide valuable insight for management and future ecosystem studies.

• Planque, Benjamin; Aarflot, Johanna Myrseth; Buttay, Luice; Fransner, Filippa; Hansen, Cecilie & Husson, Berengere [Show all 15 contributors for this article] (2020). Best practices for ecological model evaluation II: Workshop Report. Septentrio Academic Publishing. Full text in Research Archive

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