Back to the Future for Cod

• Johannesen, Edda; Ottersen, Geir; Berg, Florian; Bogstad, Bjarte; Dalpadado, Padmini & Denechaud, Côme [Show all 17 contributors for this article] (2026). The Abrupt and Persistent Decline in Recruitment Success in Northeast Arctic Cod: A Review of Probable Causes. Fish and Fisheries. ISSN 1467-2960. doi: 10.1111/faf.70074. Full text in Research Archive Show summary

  Most of the previously large cod stocks in the North Atlantic are depleted to very low levels. A notable exception has been the Northeast Arctic cod inhabiting the Barents Sea. This cod stock reached a record high level around 2013, but since then has declined sharply, with older fish being fished out and few new recruits entering the stock. More specifically, since 2006 the average recruitment at age 3 per unit spawning stock biomass has dropped to a very low level. Here we review recent literature and data to evaluate potential causes of poor recruitment. We find that in most years the large spawning stock was successful in producing offspring up to the 0-group stage, but the survival thereafter was reduced—leading to few recruits into the fishable stock. Evidence points to consequences of northwards shifts of spawning locations, reduced inflow of Calanus and density dependent factors influencing pre-recruit survival at times when the spawning stock was at a record high level. However, large uncertainties in the causes of recruitment failure remain at a time when the Barents Sea ecosystem is experiencing unprecedented warming. A precautionary measure to avoid further decline and potential stock collapse in the current situation is to lower fishing pressure and improve management by setting reference points based on the recent period with low productivity. Including demographic characteristics like age diversity as explicit management targets to ensure spatial and temporal spread in spawning should be a goal for future method development.

• 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.

• 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.

• 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

• 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.

• 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.

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