kotaroo

• Kotwicki, Stan; O’Driscoll, Richard L.; Bacheler, Nathan M.; Baetscher, Diana; Barnett, Lewis A.K. & Bolser, Derek G. [Show all 23 contributors for this article] (2026). Pathways toward modernizing fisheries-independent surveys. ICES Journal of Marine Science. ISSN 1054-3139. 83(7). doi: 10.1093/icesjms/fsag134. Full text in Research Archive
• Rodriguez, Hector Antonio Andrade; Vihtakari, Mikko Juhani; Hansen, Hege Øverbø; Helle, Kristin & Ono, Kotaro (2026). Growth, maturity, and length-based spawning potential of tusk in the Norwegian and Barents Seas. ICES Journal of Marine Science. ISSN 1054-3139. 83(6). doi: 10.1093/icesjms/fsag113. Full text in Research Archive
• Ma, Shuyang; Bogstad, Bjarte; Dalpadado, Padmini; Strand, Espen; Schmidt, Thassya Christina dos Santos & Bagøien, Espen [Show all 12 contributors for this article] (2026). Leveraging the Highly Data-Rich Northeast Arctic Cod (Gadus morhua, Gadidae) to Identify Key Biophysical Factors Behind Recruitment Success. Fish and Fisheries. ISSN 1467-2960. doi: 10.1111/faf.70098. Full text in Research Archive Show summary

  Forecasting the number of individuals entering a fishery is critical for sustainable harvest and thereby management actions, but it remains challenging due to the considerable inter-annual variability and the complex nature of causal factors. This long-standing ‘recruitment problem’ has become even more urgent under ongoing climate change and the associated regime shifts overturning traditional predictive models. Leveraging the highly data-rich Northeast Arctic cod (Gadus morhua, Gadidae), this study proceeds beyond traditional data and method limitations. Such an initiative appears most timely because its recruitment (R), measured as number of 3-year-olds, is currently low and raising socio-economic concerns. We hypothesize a causal map and then apply Dynamic Structural Equation Model with sensitivity analyses to explore complex response patterns. The higher temperature exhibited a dual role: positive for spawning stock biomass (SSB) but negative for abundance of 1-year-olds (Age1) and R. Predation on postlarvae by northward-migrating Northeast Atlantic mackerel (Scomber scombrus, Scombridae), but not by herring (Clupea harengus, Clupeidae), appeared to influence Age1 negatively. As expected, fishing reduced SSB, whereas prey availability, represented by mesozooplankton biomass and stomach fullness, exerted a positive effect on Age1 and R. These suite of links remained robust, but shorter time series (< 30 years) may blur underlying patterns. Essentially, the low recruitment success (R/SSB) seen since 2010 (from the 2007 year class onwards) seems related to an overall poor situation for the 1-year-olds. Predictions give a less optimistic outlook and underline the high importance of maintaining today's advanced precautionary management strategies for this world's largest cod stock.

• Ward, Eric J.; Head, Melissa A.; Ono, Kotaro; Johnson, Kelli F. & Marshall, Kristin N. (2026). Applying information theory to increase the efficiency of life-history sampling in fisheries data. Fisheries Research. ISSN 0165-7836. 293. doi: 10.1016/j.fishres.2025.107641. Full text in Research Archive Show summary

  Effective monitoring of fish populations is critical for understanding life-history traits such as maturation or growth, which directly impact population dynamics and fisheries management. Long-term monitoring efforts around the world are faced with rising survey costs and a more uncertain future, as environmental variability is projected to increase. Together, these pressures necessitate more efficient sampling designs. In this study, we use information theory (Fisher Information) to evaluate and optimize life-history sampling, focusing on how variation in fish growth or maturation can guide more informed sampling decisions. Fisher Information is closely related to variance, in that samples with higher information result in greater precision. Using life-history parameters from eight commercially important groundfish species assessed on the U.S. West Coast, we develop three case studies illustrating how sampling strategies can be improved using Fisher Information. The first example focuses on estimating maturity ogives in the absence of spatial and temporal variability; our second case study incorporates spatial and temporal variation; and the third adds a second life-history trait (growth) to jointly optimize sampling for maturity. Our results indicate that for informing maturity ogives, Fisher Information is maximized at lengths near the inflection point, and that the range of most informative lengths can shift across space and time due to habitat or environmental variation. When both growth and maturation are considered, optimal sampling windows broaden for some species but remain narrow for others. Our simulation results also show that sampling fish in proportion to Fisher Information, rather than random sampling, can reduce sampling effort by more than 50 % while maintaining or improving the precision of parameter estimates. While the benefits of using Fisher Information are species specific, these findings suggest that adaptive sampling based on Fisher Information can substantially increase the efficiency and effectiveness of monitoring programs, especially under budgetary or logistical constraints.

• Ma, Shuyang; Huse, Geir; Ono, Kotaro; Alix, Maud; Tian, Yongjun & Hart, Paul J. B. [Show all 7 contributors for this article] (2026). Global Marine Fishery Stock Productivity Under Climate Change. Global Change Biology. ISSN 1354-1013. 32(3). doi: 10.1111/gcb.70784. Full text in Research Archive Show summary

  ABSTRACT Marine capture fisheries play crucial roles in global aquatic protein supply and livelihoods of millions of people. Anthropogenic climate change comes as an overlying threat, potentially necessitating substantial adjustments of harvest control rules or rebuilding plans, especially for species (stocks) that are naturally adapted to restricted environmental fluctuations. Stock productivity, defined as surplus production provided by per unit of stock biomass, offers an informative yet underutilized metric for assessing these impacts. With the help of global fishery‐related databases and earth system models, stock productivity estimates were related to key biophysical drivers by state‐of‐the‐art statistical methods. The ultimate goal thereby is to clarify how climate change has affected and will continue to affect this harvest potential. Results show that the hindcasted global stock productivity (710 stocks) exhibited pronounced stock‐specific and regional heterogeneity, with signs of an overall decline (1980–2022). Variations in sea temperature and chlorophyll concentration significantly affected the productivity of about half of the assessed stocks (1993–2020). The subsequent productivity projections indicated relatively moderate reductions in the global mean productivity proxy (2021–2100), though these projections were characterized by uncertainty and with different data availability depending on the regions. However, the important finding of a general balanced prevalence of stock ‘winners’ and ‘losers’ lessened this regional quantification problem. As inferred, by the end of the century, global productivity (also applied to fishery landings) is projected to decline by 3.0% (−6.3% to +0.4%) under a ‘business‐as‐usual’ scenario and 1.0% (−1.6% to −0.3%) under a ‘sustainability’ scenario. Thus, our research indicates relatively moderate effects of climate change on the global fisheries productivity, though with the above‐mentioned existence of clear winners and losers. This finding contrasts with previous investigations that depict remarkable declines in future fishery landings.

• Conner, Jason; Kotwicki, Stan; Ono, Kotaro & Barnett, Lewis A.K. (2025). The sensitivity of fisheries-independent survey indices to decisions of sampling design and intensity and the mitigation of biased precision estimators for systematic sampling. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 82. doi: 10.1139/cjfas-2024-0405. Full text in Research Archive Show summary

  Fisheries-independent surveys are used to track trends in fish stocks globally. Survey alterations occur for a myriad of reasons (e.g., vessel availability, changes in fish distribution, funding shortfalls). Understanding the sensitivity of survey estimates to changes in sampling is pivotal to sustainable management. We present a case-study of an annual multispecies survey. Simulating distributions for four species with a spatiotemporal model, we evaluated simple random, stratified random, and systematic grid sampling designs across four sampling intensities. The systematic design yielded higher-precision estimates at all sampling intensities. However, the commonly used standard error estimator thereof resulted in mean biases from 24% to 63%. We evaluated two alternative standard error estimators that successfully mitigated these biases. Our results indicate that estimates from systematic survey designs may be robust to decreases in sampling intensity, and that analyses such as integrated stock assessments which use these estimates may mitigate model misspecification by applying alternative variance estimators.

• Skjoldal, Hein Rune; Eriksen, Elena; Ono, Kotaro & Dolgov, Andrey (2025). Diet and trophic structure of fishes in the Barents Sea: between empty and full stomachs – large individual variability follows a common pattern. Journal of Fish Biology. ISSN 0022-1112. 106(6), p. 1734–1751. doi: 10.1111/jfb.16058. Full text in Research Archive Show summary

  More than 27,000 stomachs from 70 species of fish were collected from the Barents Sea in 2015. Quantitative stomach content expressed relative to the body weight of the predator fish (g g−1 as %) varied by four to five orders of magnitude for six species with the largest sample size (Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, Greenland halibut Reinhardtius hippoglossoides, long rough dab Hippoglossoides platessoides, polar cod Boreogadus saida, and Atlantic capelin Mallotus villosus). The quantitative stomach contents of individual fish followed a common and strict statistical relationship for predator species or groups of species (by families), and for prey categories across predator species. The common pattern was log-normal-like and was modelled with good fit by different types of right-skewed distributions, that is, variants of the Box–Cox, generalized inverse Gaussian, inverse gamma, or gamma distributions. The long tail in the high end reflects high variation with no clear sign of a plateau, as could be expected from the concept of a “full stomach”. This is interpreted to reflect that high stomach contents are rare events that are sampled at low frequencies. The maximum recorded stomach content varied from 1% to 34% of body weight for 55 species of fish, being positively correlated (R2 = 0.45) with sample size. About a third of the stomachs were empty, and the low tail of the log-normal-like distribution represents the transition to empty stomachs. The amount of food in the stomachs was overall low compared to maximum values, with mean and median of 2.0% and 1.1%, respectively, for the 17,873 stomachs containing food. Supported by bioenergetic considerations, this suggests relatively low feeding rates of the various fish predators but sufficient to meet their energy demands.

• Aarflot, Johanna Myrseth; Bjørdal, Vilde Regine; Dunlop, Katherine Mary; Espinasse, Marina; Husson, Berengere & Lindstrøm, Ulf Ove [Show all 10 contributors for this article] (2024). Ecosystem risk from human use of ocean space and resources: A case study from the Norwegian coast. Ocean and Coastal Management. ISSN 0964-5691. 256. doi: 10.1016/j.ocecoaman.2024.107299. Full text in Research Archive Show summary

  Coastal and adjacent shelf waters are generally highly productive ecosystems harboring important ecological processes and exposed to a range of anthropogenic pressures from land-based and marine sectors. Ensuring that the cumulative pressures from human activities do not cause unacceptable, permanent harm to the ecosystem is challenging but crucial for sustainable management of these regions. Linkage frameworks and ecological risk assessments have proven to be useful tools for holistic evaluations of cumulative human pressures as a guide to managers and policy makers for prioritization of risk factors. Here, we present the first holistic assessment of ecosystem risk from human activities along the Norwegian coast. Pressures from coastal sectors are identified and weighted by the exposure to and potential impact on ecosystem components following the ODEMM (Options for Delivering Ecosystem-based Marine Management) framework. We focus on four coastal regions with contrasting scales of human activities. Two southern regions with multiple anthropogenic activities are associated with higher cumulative risk of negative impacts compared to northern areas where less extensive activities have a lower potential of harming the coastal ecosystems. Despite latitudinal differences in human use of the coastline, the pressures and ecosystem components associated with the greatest risk of cumulative impacts are relatively similar between the regions. Contaminants and underwater noise stand out as high-risk pressures, associated with multiple sectors with a high spatiotemporal footprint and with the potential to negatively impact a range of ecosystem components. Nevertheless, a confidence assessment also highlights the need for more in-depth analysis on the input, spread and effect of these pressures on coastal ecosystems. We discuss strengths and weaknesses of the risk assessment framework and suggest new directions which may enhance the utility and uptake of such assessments for sustainable management of coastal ecosystems.

• Breivik, Olav Nikolai Risdal; Zimmermann, Fabian; Johannesen, Edda; Ono, Kotaro; Fall, Johanna Jennifer Elisabeth & Howell, Daniel [Show all 7 contributors for this article] (2024). Incorporation of observation uncertainty in stock assessment using spatio-temporal modeling of catch-at-length and age-at-length survey data. ICES Journal of Marine Science. ISSN 1054-3139. 81(7), p. 1195–1208. doi: 10.1093/icesjms/fsae079. Full text in Research Archive Show summary

  Spatio-temporal models are essential tools for estimating abundance indices and quantifying the associated uncertainty. Time series of index uncertainties can be used to objectively determine the influence each index has on the assessment. This can involve reducing the influence of indices in years with limited data. However, incorporating uncertainty in age-length conversion into assessment models has remained a challenge. In this research, we propose an index estimation approach that combines an abundance-at-length model with a model for age-at-length to generate age-specific abundance indices. By jointly modeling abundance-at-length and age-at-length, we address uncertainties in both components of the index-at-age. Using North East Arctic haddock (Melanogrammus aeglefinus) as a case study, we validate the uncertainty of the indices by integrating them into the state space assessment model SAM. The results indicate that the uncertainty estimates are realistic, and we further demonstrate that incorporating uncertainty in age conversion has effects on the assessment results. Our case study demonstrates that incorporating the uncertainty in age-at-length data improves the characterization of uncertainty in stock assessment, and hence better accounts for risk in precautionary management.

• 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

• Dalpadado, Padmini; Prokopchuk, Irina P.; Bogstad, Bjarte; Skaret, Georg; Ingvaldsen, Randi Brunvær & Dolgov, Andreyv V. [Show all 11 contributors for this article] (2024). Zooplankton link climate to capelin and polar cod in the Barents Sea. Progress in Oceanography. ISSN 0079-6611. 226. doi: 10.1016/j.pocean.2024.103302. Full text in Research Archive Show summary

  Capelin (Mallotus villosus) and polar cod (Boreogadus saida) hold a fundamental position in the Barents Sea ecosystem as consumers of zooplankton while serving as forage fish for the commercial and ecological key species Atlantic cod (Gadus morhua). The ongoing warming and Atlantification of the Barents Sea, along with increasing net primary production, makes previously inaccessible northern areas available as feeding grounds for capelin. The opposite effect is anticipated for the ice-dependent polar cod. The transport of Atlantic water with boreal plankton from the Norwegian Sea is important for sustaining biodiversity and production in the Barents Sea. A decline of the medium-sized mesozooplankton biomass to a low level during 2016 to 2022 coincided with a strongly decreasing summer volume transport with the Atlantic Current. The low biomass of medium-sized zooplankton observed in later years raises concern about the feeding conditions now experienced by the higher trophic levels. Both capelin and polar cod feed predominantly on lipid rich sub-Arctic and Arctic zooplankton species. We found a significant inverse relationship between capelin and mesozooplankton biomass and a clear dietary shift from smaller to larger predator size. Smaller capelin (<12 cm) contained a comparatively higher proportion of copepods, dominated by Calanus glacialis, followed by C. finmarchicus and Metridia longa (copepodite stages IV-VI). As the capelin grow, their diet switches towards larger zooplankton, primarily euphausiids (mainly Thysanoessa inermis). All age groups of polar cod fed heavily on pelagic amphipods (mostly Themisto libellula) in addition to copepods and euphausiids, and to some degree also on fish, thus displaying a higher trophic position than capelin. Capelin growth from age 1 to 2 was negatively associated with their abundance at age 2, but positively related to stomach fullness for 2-year-old fish, indicating density-dependent growth. While our study reveals interactions between capelin and zooplankton, such signals between polar cod and their prey were not evident.

• Eriksen, Elena; Skjoldal, Hein Rune; Ono, Kotaro & Dolgov, Andrey (2024). Diet and trophic structure of fishes in the Barents Sea: Effects of size within (ontogenetic) and between species. Progress in Oceanography. ISSN 0079-6611. 227. doi: 10.1016/j.pocean.2024.103299. Full text in Research Archive Show summary

  A large data set on stomach content (over 27,000 individual fish) – collected in the Barents Sea in 2015 – was used to examine ontogenetic and interspecific changes in diet with size for 35 fish species. The analysis combined the use of hierarchical clustering and random forest. Two different diet metrics were used (% weight of prey types per weight of stomach content or per weight of fish, the latter reflecting also feeding intensity), and data were analysed based on average diet of predator groups (species and size groups) across the entire sample series (from the whole Barents Sea in different seasons), or for data broken down by geographical areas and seasons. Similar trophic groups (clusters) were identified for the various data sets suggesting that the results on trophic structure were robust. The trophic groups including size information were broadly similar to groups found earlier with data averaged at species level. Hierarchical clustering produces a hierarchy of trophic groups (or trophic guilds) at various levels of diet dissimilarity. With 12 clusters identified, one cluster had fish as dominant prey, and 5–6 others had either plankton or benthos as dominant prey. The clusters tended to be distinct and homogenous with one dominant prey category in average diet (often > 60 %). This was especially the case for the plankton clusters, with copepods, euphausiids, hyperiid amphipods, or gelatinous zooplankton as dominant prey in each of 4 trophic groups. The benthos clusters tended to be less dissimilar with more overlap in diet composition, with predominance of either hard-shelled forms (echinoderms and molluscs) or softer prey (polychaetes and crustaceans) for groups of clusters. There were clear patterns of ontogenetic shifts in fish diet. Fish that clustered as piscivores at larger size tended to grow from being planktivores when smaller. Smaller species of planktivores or benthivores shifted position among trophic groups but remained within the categories of planktivores or benthivores, respectively. Taxonomy (species) tended to be more important than size for explaining the diet composition of the different clusters of fish predators.

• Ono, Kotaro; Katara, Isidora; Eliasen, Sólvá Káradóttir; Broms, Cecilie Thorsen; Campbell, Andy & Schmidt, Thassya Christina dos Santos [Show all 20 contributors for this article] (2024). Effect of environmental drivers on the spatiotemporal distribution of mackerel at age in the Nordic Seas during 2010−20. ICES Journal of Marine Science. ISSN 1054-3139. 81(7), p. 1282–1294. doi: 10.1093/icesjms/fsae087. Full text in Research Archive Show summary

  A joint spatio–temporal distribution model of mackerel (ages 3–10) was developed to investigate the age-based responses of mackerel to three environmental drivers: sea surface temperature (SST), mixed layer depth, and chlorophyll-a concentration during the summer months 2010–20 in the Nordic Seas. The study showed that SST was the most important variable amongst the ones tested and had the strongest impact on the distribution of the younger age classes (3–5), which had a narrower range of favourable SST and a stronger aversion to cold temperatures than older individuals. Consequently, the impact of SST differed regionally; in the polar front regions, SST explained up to 61% of the variability in the observed density of young individuals, where Arctic water masses likely acted as a barrier to these young individuals. That said, part of it could be confounded with the limited migration capability of young mackerels, which could not reach the furthest frontal regions. In warmer southern waters, the same environmental variables had less explanatory power for mackerel of all ages. Individuals in the south were likely not constrained by temperature and perhaps more influenced by other variables, such as food availability or ocean current (throughout their migration path), for which appropriate data are lacking. Moreover, the model showed that older mackerel were distributed more to the north and west, and their migration pattern changed when the 2013 year-class no longer migrated to the west compared to previous year-classes. Additionally, all-year classes started migrating more eastward from summer 2018.

• Szalay, Paul G. von; Laman, Edward A.; Kotwicki, Stan; Barnett, Lewis A. K. & Ono, Kotaro (2024). Quantifying the effects of sample size and species distribution on the precision and accuracy of abundance estimates from bottom-trawl surveys in the Gulf of Alaska. Fishery Bulletin. ISSN 0090-0656. 122(4), p. 143–161. doi: 10.7755/FB.122.4.2. Full text in Research Archive Show summary

  We assessed the effect of survey effort reduction on the accuracy and precision of estimates of abundance for 4 commercially or ecologically important species with differing distributions observed in a bottom-trawl survey conducted in the Gulf of Alaska. Simulations from a spatiotemporal generalized linear mixed model based on historical observations of catch densities were used to evaluate the statistical robustness, measured in terms of coefficient of variation, relative bias, and relative root mean square error, of the abundance estimates and their variances. These metrics were used to compare estimates between the traditional design-based estimator and the alternative estimator, based on a vector autoregressive spatiotemporal model, at 4 different sampling densities, representing 2 historical and 2 theoretical sampling effort levels on either side of the historical range. The recent reduction in the density of survey sampling from 820 to 550 stations had only a modest effect on the performance metrics for both estimators for arrowtooth flounder (Atheresthes stomias), Pacific cod (Gadus macrocephalus), and Pacific ocean perch (Sebastes alutus). However, the effect on the abundance estimates for sablefish (Anoplopoma fimbria) was substantial. We attribute this difference in results to the wider depth range utilized by sablefish, which preferentially occupy the relatively under-sampled deep strata (>500 m), and to the truncated survey area at the reduced sampling levels where the deepest strata (>700 m) have been eliminated.

• Ma, Shuyang; Huse, Geir; Ono, Kotaro; Nash, Richard David Marriott; Vølstad, Jon Helge & Kjesbu, Olav Sigurd (2024). Northeast Atlantic fish stock productivity hindcasts and forecasts from a Bayesian framework reveal pronounced climate-induced dynamics. Fish and Fisheries. ISSN 1467-2960. 25(4), p. 686–710. doi: 10.1111/faf.12833. Full text in Research Archive Show summary

  Climate change continues to exert pressure on ocean ecosystems. The fisheries-related responses, such as altered body growth, recruitment and spatial distribution of the targeted stock(s), have generally been reasonably well investigated. Nevertheless, there are still important knowledge gaps in how biophysical drivers impact stock productivity and thereby sustainable harvest levels. Considering this, we investigated 26 fish stocks in the Northeast Atlantic, a region characterized by accelerated climate change effects and a diverse set of fisheries. A novel, stepwise, Bayesian framework to quantify stock productivity was established to identify shared trends and project future patterns, aiming at determining essential baselines for adaptive fishery management in the face of climate change. Despite variation among large marine ecosystems and stocks, an overall declining trend in productivity over the past four decades was observed, especially in high-latitude areas. These hindcast results were mainly attributed to higher temperatures posing negative effects on productivity, which was dependent on the stock's thermal preference. Contrastingly, the proxy for food availability – gross secondary production – exhibited less consistent impacts. In the forecast, the applied Shared Socio-economic Pathways (SSPs) indicated that most stocks are likely to encounter adverse effects, with the worst cases expected to occur under SSP2-4.5 in the 2050s, and under SSP5-8.5 in the 2090s. Thus, this study generally not only supports earlier climate vulnerability assessments (‘scorings’) of experts but also provides evidence for revised directional effects under climate change, underlining the complexity of processes affecting stock productivity.

• Schmidt, Thassya Christina dos Santos; Slotte, Aril; Olafsdottir, Anna H.; Nøttestad, Leif; Jansen, Teunis & Jacobsen, Jan Arge [Show all 13 contributors for this article] (2023). Poleward spawning of Atlantic mackerel (Scomber scombrus) is facilitated by ocean warming but triggered by energetic constraints. ICES Journal of Marine Science. ISSN 1054-3139. 81(3), p. 600–615. doi: 10.1093/icesjms/fsad098. Full text in Research Archive Show summary

  The Northeast Atlantic mackerel is an income breeder with indeterminate fecundity, spawning in multiple batches at optimal temperatures around 11°C in the upper water column during February–July along the continental shelf from 36–62°N. Based on macroscopic staging of gonads (N ∼62000) collected in 2004–2021, we detected an on-going extension of spawning activities into the Norwegian Sea feeding area (62–75°N), reaching stable levels around 2012 onwards. This poleward expansion increased as more fish entered the area, whilst the maximum proportions of spawners concurrently dropped from about 75 to 15% from May to July. Detailed histological examinations in 2018 confirmed the macroscopic results but clarified that 38% of the spawning-capable females in July terminated their spawning by atresia. We suggest that increased access to suitable spawning areas (≥10°C), following ocean warming from 2002 onwards, functions as a proximate cause behind the noticed expansion, whereas the ultimate trigger was the historic drop in body growth and condition about 10 years later. Driven by these energetic constraints, mackerel likely spawn in the direction of high prey concentrations to rebuild body resources and secure the future rather than current reproduction success. The ambient temperature that far north is considered suboptimal for egg and larval survival.

• 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.

• Clegg, Thomas L; Fuglebakk, Edvin & Ono, Kotaro (2023). Evaluating assumptions behind design-based estimators for unreported catches. Fisheries Research. ISSN 0165-7836. 263. doi: 10.1016/j.fishres.2023.106686. Full text in Research Archive Show summary

  Understanding a fishery’s impact on the marine ecosystem requires a quantification of total catches, which include unreported catches. For recent years in Norwegian waters, unreported catches have been estimated using data collected by the Norwegian Reference Fleet, a fisher self-sampling programme that regularly gathers data on catches of all species (including unwanted bycatches and discards). In this study, we focused on the use of design-based estimators for total catches in offshore fisheries, which have previously been used to estimate discards in the Norwegian coastal gillnet fisheries. After adapting the current methodology to the data available in offshore fisheries, we explored the assumptions behind both unit- and ratio-based estimators, and the effect of ignoring the cluster sampling design. Using a jack-knife resampling method to estimate the true bias in estimates of total catches and associated variability, we found that ignoring the cluster sampling design tended to underestimate the variability, which lead to occurrences where unreported catches were statistically detected when in fact there was too much uncertainty to make such a conclusion. Further validations suggested the cluster unit estimator is not unbiased as theoretically expected due to the sampling design favouring the selection of more active vessels. We therefore concluded that the unit and ratio cluster estimators are applied and compared, as per best practices.

• Anderson, Sean C.; Bacheler, Nate; Barnett, Lewis; Berg, Casper Willestofte; Blackhart, Kristan & Bolser, Derek [Show all 47 contributors for this article] (2023). WORKSHOP ON UNAVOIDABLE SURVEY EFFORT REDUCTION 2 (WKUSER2). ICES Scientific Reports. 5(13). doi: 10.17895/ices.pub.22086845. Full text in Research Archive
• Ma, Shuyang; Huse, Geir; Ono, Kotaro; Nash, Richard David Marriott; Sandø, Anne Britt & Nedreaas, Kjell Harald [Show all 11 contributors for this article] (2023). Recruitment regime shifts and nonstationarity are widespread phenomena in harvestable stocks experiencing pronounced climate fluctuations. Fish and Fisheries. ISSN 1467-2960. doi: 10.1111/faf.12810. Full text in Research Archive Show summary

  Methods to reliably identify jump discontinuities in biological time series and to assess the specific contribution of various covariates are rapidly progressing. Here, we took advantage of these statistical improvements as well as those seen in complementary, down-scaled climate and biogeochemical models to investigate causes of the substantial interannual variability observed in recruitment strength in hindcast analyses. This systematic meta-analysis included 23 data-rich, commercially valuable, warm- and cold-temperate stocks in the North, Norwegian and Barents Seas. Since this study focuses on recruitment strength variability, we have used the term “recruitment regime shift” to distinguish from the concept of ecosystem regime shift. The breakpoint analysis revealed that the former criterion applied to more than half of the time series, mainly with respect to North Sea stocks but also to those in the Norwegian Sea. The exploratory analysis using vcGAM indicated that 1–3 shifts per stock were real, when using five drivers spanning spawning stock biomass to large-scale climatic processes. Thus, non-stationary relationships were extensively prevalent, indicating that each stock is uniquely adapted to its locally varying conditions. Outputs from the stationary GAM resembled those from the vcGAM but not after the threshold year. In-depth case studies showed that the proxy of a given driver for the process which was to be included should be critically considered in a spatiotemporal context. Furthermore, the stock-specific uncertainty associated with the given recruitment figures as such should also be an in-built component of the model construct and thereby in the evaluation of the output.

• 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.

• Ono, Kotaro; Slotte, Aril; Hølleland, Sondre Nedreås; Mackinson, Steven; Jónsson, Sigurður Þór & Jacobsen, Jan Arge [Show all 7 contributors for this article] (2022). Space-time recapture dynamics of PIT-tagged Northeast Atlantic mackerel (Scomber scombrus) reveal size-dependent migratory behaviour. Frontiers in Marine Science. 9. doi: 10.3389/fmars.2022.983962. Full text in Research Archive Show summary

  Based on GIS-mapping and semi-parametric modelling of recaptures from PIT-tag experiments in the North Sea nursery area (September 2011), the Celtic Seas spawning area (May-June 2014-2021) and the Icelandic Waters feeding area (August 2015-2019), we argue that the distribution of Northeast Atlantic (NEA) mackerel is influenced by a size-dependent migratory behaviour. The time-space recapture dynamics revealed that larger mackerel tended to migrate a longer distance between spawning and feeding areas, either through a western route from the Celtic Seas into the Icelandic Waters and the Greenland Sea or by following the main route northwards through the Faroe-Shetland Channel into the Norwegian Sea. This long-distance travel resulted in turn in delayed arrival in the North Sea wintering area. During the return spawning migration into the Celtic Seas, larger individuals remained in the front, likely heading to spawning grounds farther south than smaller conspecifics. Migration patterns also evolved with time at liberty as the mackerel grew older and larger, while possibly covering a progressively wider area over its annual migration cycle as suggested from the tagging data. However, the study also showed large inter-annual variability in the recapture patterns which likely reflect changes in environmental condition (prey availability and ocean current), NEA mackerel population demographics, and the spatial fishery dynamics.

• Berg, Hilde Sofie Fantoft; Clegg, Tom; Blom, Geir; Kolding, Jeppe; Ono, Kotaro & Nedreaas, Kjell Harald (2022). Discards of cod (Gadus morhua) in the Norwegian coastal fisheries: Improving past and future estimates. ICES Journal of Marine Science. ISSN 1054-3139. 79(5), p. 1548–1560. doi: 10.1093/icesjms/fsac081. Full text in Research Archive Show summary

  Discarding can be an unknown source of biases and uncertainties in stock assessments. Discarding patterns and quantities vary so a routine methodology for estimating discards is important to give a better picture of total catches, and potentially mortality, in fisheries. Using data from the Norwegian Reference Fleet between 2012 and 2018, this study presents a revised methodology for estimating discards of cod (Gadus morhua) in the Norwegian coastal gillnet fisheries, which accounts for variations in discarding between vessels and uncertainties in the conversion of numbers to weight discarded. The estimated average discard rate of cod (weight of cod discarded as percentage of total weight caught) is 0.55% (95% confidence interval: 0.45–0.70%), although discard rates in southern areas were an order of magnitude higher than in northern areas. We also present an exploratory analysis of the drivers behind discarding using a random forest regression model. Spatial variations and fishing intensity were identified as the most important drivers of discarding. Results from this study suggest ways in which self-sampled data can be used to estimate discards in Norwegian coastal fisheries, and where the accuracy of future estimates can be improved when a higher resolution data collection programme is established.

• 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.

• Kleiven, Alf Ring; Espeland, Sigurd Heiberg; Stiansen, Stian; Ono, Kotaro; Zimmermann, Fabian & Olsen, Esben Moland (2022). Technological creep masks continued decline in a lobster (Homarus gammarus) fishery over a century. Scientific Reports. 12. doi: 10.1038/s41598-022-07293-2. Full text in Research Archive Show summary

  Fishery-dependent data are frequently used to inform management decisions. However, inferences about stock development based on commercial data such as Catch-Per-Unit-Effort (CPUE) can be severely biased due to a phenomenon known as technological creep, where fishing technology improves over time. Here we show how trap improvement over nine decades has driven technological creep in a European lobster (Homarus gammarus) fishery. We combined fishing data, experimental fishing with contemporary and older trap types, and information on depletion effects during fishing seasons. The resulting standardized CPUE time series indicates a 92% decline in lobster abundance between 1928 and 2019 compared to 70% if technological creep is not corrected for. Differences are most pronounced within the last 40 years when the most substantial shift in gear technology occurred: an uncorrected CPUE index suggests an 8% increase in lobster abundance during this period, while the corrected CPUE index declined by 57%. We conclude that technological creep has masked a continuous stock decline, particularly in recent decades and largely driven by the shift from one- to two-chambered traps, as well as the ability of newer trap designs to capture larger lobsters. Our study confirms the importance of adequate standardization, including technological development, when using fishery dependent CPUE for monitoring and management of data-limited fisheries.

• Berg, Casper Willestofte; Beukhof, Esther; Börjesson, Patrik; Costas, Gersom; Cunningham, Curry & Jaworski, Andrzj [Show all 16 contributors for this article] (2021). . Working group on improving survey data for analysis and advice (WGISDAA; outputs from 2020 meeting). ICES Scientific Reports. doi: 10.17895/ices.pub.8250. Full text in Research Archive
• Ono, Kotaro; Gundersen, Sofie & Nedreaas, Kjell Harald (2021). Estimating the status of anglerfish (Lophius piscatorius) in the north of 62˚N management unit (ICES Subareas 1 and 2) using life-history ratios, length compositions, and CPUE data. In Howell, Daniel (Eds.), Arctic Fisheries Working Group (AFWG). ICES Scientific Reports 3:58.. ICES. p. 753–775. Full text in Research Archive
• Ono, Kotaro; Gundersen, Sofie; Reecht, Yves & Nedreaas, Kjell Harald (2021). Estimating the status of coastal cod (Gadus morhua) north of 62˚N (ICES Subarea 2) using CPUE data from the Norwegian coastal reference fleet. In Howell, Daniel (Eds.), Arctic Fisheries Working Group (AFWG). ICES Scientific Reports 3:58.. ICES. p. 637–649. Full text in Research Archive
• Lu, Yonglong; Wang, Pei; Wang, Chenchen; Zhang, Meng; Cao, Xianghui & Chen, Chunci [Show all 34 contributors for this article] (2021). Multiple pollutants stress the coastal ecosystem with climate and anthropogenic drivers. Journal of Hazardous Materials. ISSN 0304-3894. p. 1–10. doi: 10.1016/j.jhazmat.2021.127570. Full text in Research Archive
• Deininger, Anne; Martin, Angela Helen; Pardo, Juan; Berg, Paul Ragnar; Bhardwaj, Jyotirmoy & Catarino, Diana Sofia de Oliveira [Show all 15 contributors for this article] (2021). Coastal Research Seen Through an Early Career Lens—A Perspective on Barriers to Interdisciplinarity in Norway. Frontiers in Marine Science. 8. doi: 10.3389/fmars.2021.634999. Full text in Research Archive Show summary

  The value of interdisciplinarity for solving complex coastal problems is widely recognized. Many early career researchers (ECRs) therefore actively seek this type of collaboration through choice or necessity, for professional development or project funding. However, establishing and conducting interdisciplinary research collaborations as an ECR has many challenges. Here, we identify these challenges through the lens of ECRs working in different disciplines on a common ecosystem, the Norwegian Skagerrak coast. The most densely populated coastline in Norway, the Skagerrak coast, is experiencing a multitude of anthropogenic stressors including fishing, aquaculture, eutrophication, climate change, land runoff, development, and invasive species. The Skagerrak coastline has also been the focus of environmental science research for decades, much of which aims to inform management of these stressors. The region provides a fantastic opportunity for interdisciplinary collaboration, both within and beyond the environmental sciences. This perspective article identifies the barriers ECRs in Norway face in establishing interdisciplinary and collaborative research to inform management of coastal ecosystems, along with their root causes. We believe our discussion will be of broad interest to all research institutions who employ or educate ECRs (in Norway and worldwide), and to those who develop funding mechanisms for ECRs and interdisciplinary research.

• Clegg, Tom; Fuglebakk, Edvin; Ono, Kotaro; Vølstad, Jon Helge & Nedreaas, Kjell Harald (2021). A simulation approach to assessing bias in a fisheries self-sampling programme. ICES Journal of Marine Science. ISSN 1054-3139. 79(1), p. 76–87. doi: 10.1093/icesjms/fsab242. Full text in Research Archive Show summary

  The hierarchical structure and non-probabilistic sampling in fisher self-sampling programmes makes it difficult to evaluate biases in total catch estimates. While so, it is possible to evaluate bias in the reported component of catches, which can then be used to infer likely bias in total catches. We assessed bias in the reported component of catches for 18 species in the Barents Sea trawl and longline fisheries by simulating 2000 realizations of the Norwegian Reference Fleet sampling programme using the mandatory catch reporting system, then for each realization we estimated fleet-wide catches using simple design-based estimators and quantified bias. We then inserted variations (e.g. simple random and systematic sampling) at different levels of the sampling design (sampling frame, vessel, and operation) to identify important factors and trends affecting bias in reported catches. We found that whilst current sampling procedures for fishing operations were not biased, non-probabilistic vessel sampling resulted in bias for some species. However, we concluded this was typically within the bounds of expected variation from probabilistic sampling. Our results highlight the risk of applying these simple estimators to all species. We recommend that future estimates of total catches consider alternative estimators and more conservative estimates of uncertainty where necessary.

• Goto, Daisuke; Devine, Jennifer Ann; Umar, Ibrahim; Fischer, Simon; Oliveira, Jose & Howell, Daniel [Show all 9 contributors for this article] (2021). Shaping sustainable harvest boundaries for marine populations despite estimation bias. Ecosphere. 13(2). doi: 10.1002/ecs2.3923. Full text in Research Archive Show summary

  Biased estimates of population status are a pervasive conservation problem. This problem has plagued assessments of commercial exploitation of marine species and can threaten the sustainability of both populations and fisheries. We develop a computer-intensive approach to minimize adverse effects of persistent estimation bias in assessments by optimizing operational harvest measures (harvest control rules) with closed-loop simulation of resource–management feedback systems: management strategy evaluation. Using saithe (Pollachius virens), a bottom-water, apex predator in the North Sea, as a real-world case study, we illustrate the approach by first diagnosing robustness of the existing harvest control rule and then optimizing it through propagation of biases (overestimated stock abundance and underestimated fishing pressure) along with select process and observation uncertainties. Analyses showed that severe biases lead to overly optimistic catch limits and then progressively magnify the amplitude of catch fluctuation, thereby posing unacceptably high overharvest risks. Consistent performance of management strategies to conserve the resource can be achieved by developing more robust control rules. These rules explicitly account for estimation bias through a computational grid search for a set of control parameters (threshold abundance that triggers management action, Btrigger, and target exploitation rate, Ftarget) that maximize yield while keeping stock abundance above a precautionary level. When the biases become too severe, optimized control parameters– for saithe, raising Btrigger and lowering Ftarget–would safeguard against overharvest risk (<3.5% probability of stock depletion) and provide short-term stability in catch limit (<20% year-to-year variation), thereby minimizing disruption to fishing communities. The precautionary approach to fine-tuning adaptive risk management through management strategy evaluation offers a powerful tool to better shape sustainable harvest boundaries for exploited resource populations when estimation bias persists. By explicitly accounting for emergent sources of uncertainty our proposed approach ensures effective conservation and sustainable exploitation of living marine resources even under profound uncertainty.

• 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.

• Ono, Kotaro; Langangen, Øystein & Stenseth, Nils Christian (2019). Improving risk assessments in conservation ecology. Nature Communications. 10, p. 1–7. doi: 10.1038/s41467-019-10700-4. Full text in Research Archive Show summary

  Conservation efforts and management decisions on the living environment of our planet often rely on the results from statistical models. Yet, these models are imperfect and quantification of risk associated with the estimate of management-relevant quantities becomes crucial in providing robust advice. Here we demonstrate that estimates of risk themselves could be substantially biased but by combining data fitting with an extensive simulation–estimation procedure, one can back-calculate the correct values. We apply the method to 627 time series of population abundance across four taxa using the Gompertz state-space model as an example. We find that the risk of large bias in population status estimate increases with the species’ growth rate, population variability, weaker density dependence, and shorter time series, across taxa. We urge scientists dealing with conservation and management to adopt a similar approach to ensure a more accurate estimate of risk measures and contribute towards a precautionary approach to management.

• Ono, Kotaro; Knutsen, Halvor; Olsen, Esben M; Ruus, Anders; Hjermann, Dag Ø & Stenseth, Nils Chr (2019). Possible adverse impact of contaminants on Atlantic cod population dynamics in coastal ecosystems. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 286(1908), p. 1–9. doi: 10.1098/rspb.2019.1167. Full text in Research Archive Show summary

  While many in-laboratory ecotoxicological studies have shown the adverse impact of pollutants to the fitness of an individual, direct evidence from the field on the population dynamics of wildlife animals has been lacking. Here, we provide empirical support for a negative effect of pollution on Atlantic cod (Gadus morhua) population dynamics in coastal waters of Norway by combining unique time series of juvenile cod abundance, body size, environmental concentration of toxic contaminants and a spatially structured population dynamics model. The study shows that mercury concentration might have decreased the reproductive potential of cod in the region despite the general decline in the environmental concentration of mercury, cadmium and hexachlorobenzene since the implementation of national environmental laws. However, some cod populations appeared to be more resistant to mercury pollution than others, and the strength and shape of mercury effect on cod reproductive potential was fjord-specific. Additionally, cod growth rate changed at scales smaller than fjords with a gradient related to the exposure to the open ocean and offshore cod. These spatial differences in life-history traits emphasize the importance of local adaptation in shaping the dynamics of local wildlife populations. Finally, this study highlights the possibility to mitigate pollution effects on natural populations by reducing the overall pollution level, but also reveals that pollution reduction alone is not enough to rebuild local cod populations. Cod population recovery probably requires complementary efforts on fishing regulation and habitat restoration.

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

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

• Kotwicki, Stan & Ono, Kotaro (2019). The effect of random and density-dependent variation in sampling efficiency on variance of abundance estimates from fishery surveys. Fish and Fisheries. ISSN 1467-2960. 20, p. 760–774. doi: 10.1111/faf.12375. Full text in Research Archive
• Ono, Kotaro; Kotwicki, Stan; Dingsør, Gjert Endre & Johnsen, Espen (2018). Multispecies acoustic dead-zone correction and bias ratio estimates between acoustic and bottom-trawl data. ICES Journal of Marine Science. ISSN 1054-3139. 75(1), p. 361–373. doi: 10.1093/icesjms/fsx115. Full text in Research Archive Show summary

  In this study, we extended the original work of Kotwicki et al. (2013. Combining bottom trawl and acoustic data to model acoustic dead zone correction and bottom trawl efficiency parameters for semipelagic species. Canadian Journal of Fisheries and Aquatic Sciences 70: 208–219) to jointly estimate the acoustic dead-zone correction, the bias ratio, and the gear efficiency for multiple species by using simultaneously collected acoustic and bottom-trawl data. The model was applied to cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in the Barents Sea and demonstrated a better or similar performance compared with a single species approach. The vertical distribution of cod and haddock was highly variable and was influenced by light level, water temperature, salinity, and depth. Temperature and sunlight were the most influential factors in this study. Increase in temperature resulted in decreasing catch and fish density in the acoustic dead zone (ADZ), while increasing sun altitude (surrogate for light level) increased the catch and fish density in the ADZ. The catch and density of haddock in the ADZ also increased at the lowest sun altitude level (shortly after midnight). Generally, the density of cod and haddock changed more rapidly in the ADZ than in the catch (from bottom to the effective fishing height) indicating the importance of modelling fish density in the ADZ. Finally, the uncorrelated variability in the annual residual variance of cod and haddock further strengthen the conclusion that species vertical distribution changes frequently and that there are probably many other unobserved environmental variables that affect them independently.

• Ono, Kotaro; Haynie, Alan C.; Hollowed, Anne Babcock; Ianelli, James N; McGilliard, Carey R & Punt, André E. (2018). Management strategy analysis for multispecies fisheries including technical interactions and human behavior in modeling management decisions and fishing. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 75(8), p. 1185–1202. doi: 10.1139/cjfas-2017-0135. Full text in Research Archive Show summary

  A multispecies fishery management strategy evaluation (MSE) framework based on the example of the groundfish fishery in the Bering Sea and Aleutian Islands region of Alaska was used to examine the interplay between a bycatch species and three groundfish species. The study introduces a framework for a realistic multispecies fishery MSE by accounting for fleet dynamics, multispecies fishery quota allocation, and the temporal dynamics of technical interactions. The quota allocation and the fleet dynamics models were implemented using linear programming, and regression approaches were used to realistically project future users’ behavioral response to changes in the fishery. Models were calibrated and then validated using historical and out-of-sample data, respectively. The results highlight the importance of accounting for technical interactions and their inter-annual dynamics for both quota allocation and fleet dynamics to design a realistic multispecies fishery MSE (without them, the amount of lost yield increased). Particular attention should therefore be paid to understanding human behavior as well as its uncertainty and to refining approaches to incorporate this information into a multispecies fishery management strategy analysis

• Ono, Kotaro; Ianelli, James N; McGilliard, Carey R & Punt, André E. (2017). Integrating data from multiple surveys and accounting for spatio-temporal correlation to index the abundance of juvenile Pacific halibut in Alaska. ICES Journal of Marine Science. ISSN 1054-3139. 75(2), p. 572–584. doi: 10.1093/icesjms/fsx174. Full text in Research Archive Show summary

  Survey indices of abundance are one of the main sources of information used in fish stock assessment. Many regions around the world, including the United States and Europe, develop survey protocols to aid in creating these indices. As ecosystems function as a continuum across borders, there is a need to develop a standardized framework for combining information across surveys. Such methods could help resolve differences in timing, spatial coverage, catchability, and selectivity among surveys. We present a method that uses survey data by length class. These data come from several regional surveys each with differing sampling designs, spatial and temporal coverage, and sampling gear. The method accounts for the spatio-temporal correlation structure in length-specific catch rates and occurrence, and allows for differences in catchability and selectivity among regions. The approach was applied to Pacific halibut (Hippoglossus stenolepis) in Alaska, a broadly distributed species for which there is considerable uncertainty in recent recruitment estimates. Results confirm the major recruitment event of 1987 recorded in the most recent stock assessment and also detected recruitment peaks in more recent years (1998 and 2004–2005). The signal seems to be mostly related to the Eastern Bering Sea shelf survey data. The approach introduced in this study is general and could be expanded to other regions and species where standardized survey data are collected that include extensive length and/or age measurements.

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• Ma, Shuyang; Huse, Geir; Clegg, Tom; Sandø, Anne Britt; Hjøllo, Solfrid Sætre & Ono, Kotaro [Show all 10 contributors for this article] (2023). Bridging climate, biophysical and statistical models to identify key drivers of recruitment variability of fish stocks inhabiting different North-East Atlantic ecoregions. 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.

• Homrum, Eydna í; Óskarsson, Guðmundur J.; Ono, Kotaro; Hølleland, Sondre Nedreås & Slotte, Aril (2022). Changes towards stable good somatic condition and increased gonad investment of Norwegian spring-spawning herring (Clupea harengus) after 2005 are linked to extended feeding period. Frontiers in Marine Science. 9. doi: 10.3389/fmars.2022.803171. Full text in Research Archive
• Christensen-Dalsgaard, Signe; Layton-Matthews, Kate; Ono, Kotaro; Strøm, Hallvard; Tarroux, Arnaud & Bærum, Kim Magnus (2022). Toward a sustainable fishery in the North: The impacts of seabird bycatch on the population dynamics of threatened seabirds. Full text in Research Archive
• Berg, Casper; Kotwicki, Stan; Ono, Kotaro; Barnett, Lewis; Berg, Casper & Beyer, Sabrina [Show all 54 contributors for this article] (2026). Workshop on Unavoidable Survey Effort Reduction 3 (WKUSER3). International Council for the Exploration of the Sea (ICES). doi: 10.17895/ICES.PUB.31833745. Full text in Research Archive Show summary

  The Workshop on Unavoidable Survey Effort Reduction 3 (WKUSER3) focused on identifying and evaluating the best available approaches for addressing unavoidable changes in survey effort. The workshop reviewed current research, existing practices, and future needs across four key themes: i) Preparedness for change – how to anticipate and plan for potential modifications to survey effort. ii) Methods for testing and evaluating impacts – approaches for assessing the consequences of survey changes. iii) Transitioning between time series – considerations when moving from an established survey design to a revised one. iv) New technologies and sampling methods – evaluating emerging tools and approaches that can complement existing survey programs. A roadmap was developed to help scientists, survey coordinators, and other stakeholders follow essential steps for preparing for changes and assessing their impacts. Evaluations should rely on sensitivity analyses and/or simulation testing, grounded in clearly defined objectives and performance criteria. Proper accounting of total uncertainty (e.g. time series calibration uncertainty) was also found crucial for assessing impacts to assessment outputs. Although many tools already exist, further development is needed to ensure they remain accessible, reproducible, and easy to use, particularly in light of emerging technologies that can enhance or support traditional survey methods. Echoing conclusions from WKUSER2, the group emphasized the ongoing need to establish clear survey objectives and priorities. Such clarity is fundamental for properly evaluating the consequences and risks associated with any changes to survey design or implementation.

• Ono, Kotaro; Gundersen, Sofie; Nedreaas, Kjell Harald & Søvik, Guldborg (2025). HI kvoteråd 2026 - Breiflabb nord for 62°N. Havforskningsinstituttet. Full text in Research Archive Show summary

  Resultatene som presenteres i dette dokumentet er basert på en oppdatering av bestandsmodellen, som inkluderer alle data frem til midten av oktober 2025, og med en estimert fangst på 4 000 tonn for 2025. Disse resultatene er kvalitativt konsistente med resultatene som ble presentert under AFWG i 2025, som baserte seg på data frem til og med 2024. Offisiell landingsstatistikk og fiskerirelaterte data fra Kystreferanseflåten brukes i bestandsvurderingen. Bestandsstørrelsen avtok i perioden 1992-2014, særlig etter 2000, men har økt noe siden 2015, med en liten nedgang i 2025. Fiskedødeligheten i 2025 er beregnet til å være litt over FMSY (med 66% sjanse for å være over FMSY), og bestanden vil trolig være over BMSY (med 78 % sannsynlighet) ved inngangen til 2026. Basert på MSY tilnærming anbefales det at fangsten i 2026 ikke overstiger 2 402 tonn.

• Hjelset, Ann Merete; Zimmermann, Fabian; Ono, Kotaro; Marcussen, Johanna Bjånes; Casla, Alex Rosa & Jenssen, Maria [Show all 7 contributors for this article] (2025). Kongekrabbe i norsk sone— Status og rådgivning for 2026. Havforskningsinstituttet. Full text in Research Archive Show summary

  Bestandsvurderingen viser en nedgang i den høstbare kongekrabbebestanden. Det ser ut til at en økning i kvoten for 2024 har ført til en høyere fiskeridødelighet i bestanden.

• Stock, Brian; Korsbrekke, Knut; Howell, Daniel; Johannesen, Edda; Bogstad, Bjarte & Ono, Kotaro [Show all 8 contributors for this article] (2025). Rammeverk for rådgivning om minstemål. Havforskningsinstituttet. Full text in Research Archive Show summary

  Establishing a minimum size limit, the length at which fish change from "unwanted bycatch" to "desired catch", is a useful management tool to avoid growth and recruitment overfishing and improve sustainable yield. We review and recommend methods for giving advice on how to set minimum size limits across a range of data and model complexity. The simplest methods are based on maturity or growth data and can be used for data-limited stocks without assessments. More complex methods are recommended for stocks with age-based assessment models. We also provide comments on practicality, caveats, and examples.

• Sivle, Lise Doksæter; Forland, Tonje Nesse; McQueen, Kate; Utne-Palm, Anne Christine; Ono, Kotaro & Strømme, Marte Louise [Show all 13 contributors for this article] (2025). Effekter av seismikk-undersøkelser på fiskeriene — FiskeriSeis prosjektrapport. Havforskningsinstituttet. Full text in Research Archive Show summary

  Petroleumsvirksomhet og fiskeri er to av de viktigste næringene i Norge. Petroleumsvirksomheter avhengig av seismikk-undersøkelser for å lokalisere olje og gass i havbunnen, og slike undersøkelser kan komme i konflikt med fiskeriaktivitet. Seismikk-undersøkelser kan påvirke fiskeri hovedsakelig på to ulike måter; ved arealkonflikt – altså at undersøkelsen beslaglegger et område og fysisk forhindrer et aktivt fiskeri, eller at lyden fra den seismiske luftkanonen påvirker fiskens adferd på en måte som gjør den vanskeligere å fange. I dette prosjektet har vi gjennom en rekke ulike metoder hatt som målsetning å a) kartlegge eksisterende kunnskap om hvordan seismikk påvirker fiskeriene, b) identifisere de viktigste utfordringene som forhindrer god sameksistens og komme med forslag til løsninger c) kartlegge fiskernes erfaringer med seismikk, d) undersøke om fangsten endrer seg som følge av seismikk og e) modellere lydutbredelse for å bedre forstå hvilke avstander en kan forvente påvirkning.

• Fall, Johanna Jennifer Elisabeth; Nedreaas, Kjell Harald; Ono, Kotaro; Otterå, Håkon Magne & Gundersen, Sofie (2024). Kartlegging av menneskelig aktivitet på utvalgte gytefelt for kysttorsk nord for 62°N. Havforskningsinstituttet. Full text in Research Archive Show summary

  Formålet med denne rapporten er kartlegging av fiskeriaktivitet og annen menneskelig aktivitet på og rundt høyt verdisatte gytefelt for kysttorsk for å identifisere områder som kan egne seg som verneområder. Rapporten svarer delvis opp bestillinger vedrørende kysttorsk i tildelingsbrevet 2023 til Havforskningsinstitutet, og vil fungere som kunnskapsgrunnlag i videre arbeid med gytefeltvern i samarbeid med Fiskeridirektoratet. Hovedfokus i rapporten er kartlegging av kommersiell fiskeriaktivitet i tid og rom på lokasjonsnivå og innenfor gytefeltene, samt akvakultur og turistfiskebedrifter. Landingsdata fra kommersielle fiskerier har blitt koblet til sporingsdata så langt mulig for å kartlegge fiskeriaktivitet på selve gytefeltene. Vi gir råd om reduksjon av fiske og/eller begrensning av annen menneskelig aktivitet på selve gytefeltet og/eller på lokasjonsnivå, der datagrunnlaget tilsier dette. I de fleste lokasjoner som omtales er torskefisket konsentrert i gytetiden, og mesteparten av torsken fiskes med garn fra fartøy < 11m. Områder med størst torskefangst i gyteområdene er Kvænangen, Smørfjorden (Porsanger), Sør-Vikna, Grytøya-Vikafjorden (Vandve-Dønna), samt Revsbotn og Repparfjorden i Finnmark. Områder med størst andel torskefangst på gytfeltet (i forhold til lokasjonen som helhelt) er Borgundfjorden, Revsbotn og Repparfjorden, Kvænangen, Baljsfjorden, og Vandve-Dønna. Det er stor oppdrettsaktivitet i flere av de utvalgte områdene, og noen områder har i lang tid vært utsatt for utslipp fra industrivirksomhet (f.eks. gytefeltet Hemnes i Ranfjorden). Ved eventuelt vern av gytefelt er det viktig å vurdere tidsperiode og areal i forhold til gytevandring og gyteperiode, for å unngå at torsken fiskes på vei inn til gytefeltet.

• Glemarec, Gildas; Bærum, Kim Magnus; Kingston, Allen; Campbell, Neil; Clark, Bethany L. & Hornborg, Sara [Show all 12 contributors for this article] (2024). Workshop on seabird bycatch monitoring in the NEAFC regulatory areas (WKBB). International Council for the Exploration of the Sea (ICES). Full text in Research Archive Show summary

  In 2021, ICES received a special request for advice from the North-East Atlantic Fisheries Commission (NEAFC) on seabird bycatch in the NEAFC regulatory areas (RAs). Data scoping exercises conducted in 2021, 2022, and 2023 on the availability of bycatch data in the region on the one hand and on the availability of fisheries data on the other hand concluded of important shortages both in terms of quality and quantity that prevented in-depth analyses of the magnitude and the scale of the seabird bycatch problem in the NEAFC RAs. The Workshop on seabird Bycatch monitoring in the NEAFC regulatory areas (WKBB) was the next step in the NEAFC special request. This report describes the work undertaken at the WKBB workshop that took place in Copenhagen and online in May 2023, presents a synthesis of the analytical outputs (including conclusions), and provides some recommendations for the scope and implementation of a pilot monitoring programme which will significantly improve the evidence base related to the incidental bycatch of seabirds in commercial fisheries operating in the NEAFC RAs. The data at hand for the workshop – fisheries effort and two complementary seabird tracking datasets – were used to estimate the spatiotemporal overlap between seabirds and fishing activities in the period 2018-2022. Following this, a bycatch risk assessment method originally developed for marine mammal bycatch (called ByRA) was adapted to estimate risk scores and to map high-risk areas for 20 seabird species susceptible to bycatch in the NEAFC RAs. The results are discussed, including the uncertainty in the data used during the workshop. Based on the results from the ByRA, the last part of the report presents recommendations for a pilot monitoring study to increase the understanding of the scale and of the magnitude of seabirds fisheries interactions in the NEAFC RAs.

• Howell, Daniel; Nielsen, Anders; Stock, Brian; Ono, Kotaro; Clain, Laura & Fossheim, Maria [Show all 45 contributors for this article] (2024). Advice on fishing opportunities for Northeast Arctic haddock in 2025 in ICES subareas 1 and 2. Havforskningsinstituttet. Full text in Research Archive
• Howell, Daniel; Nielsen, Anders; Stock, Brian; Ono, Kotaro; Clain, Laura & Fossheim, Maria [Show all 45 contributors for this article] (2024). Advice on fishing opportunities for beaked redfish in 2025 and 2026 in ICES subareas 1 and 2. Havforskningsinstituttet. Full text in Research Archive
• Howell, Daniel; Nielsen, Anders; Stock, Brian; Ono, Kotaro; Clain, Laura & Fossheim, Maria [Show all 45 contributors for this article] (2023). Advice on fishing opportunities for Barents Sea capelin in 2024 — ICES subareas 1 and 2 excluding Division 2.a west of 5°W. Havforskningsinstituttet. Full text in Research Archive
• Olafsdottir, Anna H.; Planque, Benjamin; Anker-Nilssen, Tycho; Arneberg, Per; Bas, Lucas Johannes & Berset, Are [Show all 40 contributors for this article] (2023). Working group on the integrated assessments of the Norwegian Sea (WGINOR, outputs from 2022 meeting). International Council for the Exploration of the Sea (ICES). Full text in Research Archive
• Howell, Daniel; Berg, Erik; Bernreuther, Matthias; Bogstad, Bjarte; Breivik, Olav Nikolai & Chetyrkin, Anatoly [Show all 24 contributors for this article] (2021). Benchmark workshop for Barents Sea and Faroese stocks (WKBARFAR 2021). International Council for the Exploration of the Sea (ICES). doi: 10.17895/ices.pub.7920. Full text in Research Archive Show summary

  WKBARFAR 2021 met online to revise the advice basis of three stocks: Northeast Arctic (NEA) cod, Norwegian coastal cod north of 62 degrees, and Faroese ling. During the course of the meeting, it was decided to split the Norwegian coastal cod into two separate stocks: a data-rich stock north of 67 degrees north, and a data-poor stock between 62 and 67 degrees north. The NEA cod received a revision to the existing Category 1 SAM (State-space Assessment Model) model, Norwegian coastal cod south will receive advice based on the “3-over-2” rule, while both Norwegian coastal cod north and Faroese ling move from Category 3 to Category 1 stocks with SAM assessments. NEA cod: A revised version of the Category 1 SAM assessment was approved for the advice basis for NEA cod. Given the use of density-dependence in estimating reference points, the benchmark was not able to revise these estimates. Tests were conducted indicating the biomass limit (Blim) remained appropriate, that the existing Harvest Control Rule (HCR) remained precautionary, and that the performance of the HCR is not expected to be substantially impacted by the revision in the assessment model. Reference points will be fully re-evaluated at a forthcoming HCR evaluation, likely in 2022. Faroese Ling: This stock will now be assessed with a Category 1 SAM model, previously the stock was Category 3 with no analytic assessment. Full reference points are estimated, although the actual management is currently based on days at sea controls. Norwegian coastal cod north of 67°N: Category 1 SAM model, the first accepted analytic assessment for this stock. Evaluation of the Spawning–stock biomass (SSB) to recruit plot indicated a continued increase in recruitment across the range of SSBs observed during the model period. Consequently, Blim is provisionally set to the highest observed SSB, with a strong recommendation to conduct further investigations and put in place a recovery plan for this stock. Without evidence of recruitment performance above Blim, no reliable estimates could be provided for F reference points. Norwegian coastal cod between 62 and 67°N: Advice for this stock will be using Category 3, with a “3-over-2” rule based on the Catch Per Unit of Effort (CPUE) index from the reference fleet, with a Length-Based Spawners Per Recruit (LBSPR) model used to indicate if a precautionary buffer is required. It is likely that a SPiCT (Production model in Continuous Time) model may be a viable future assessment method, once the reference fleet CPUE time-series has been extended sufficiently.

• Clegg, Thomas L; Blom, Geir; Ono, Kotaro & Nedreaas, Kjell Harald (2021). Estimating the size distribution of reported catches on-board factory vessels – Issues with using data from the production process. Fiskeridirektoratet. ISSN 9788292075098. Full text in Research Archive Show summary

  High-grading is the practice of discarding lower value catches to make space for catches with higher value. It is necessary to understand the extent and variation in these unreported discards to improve stock assessments and management decisions. Where discards are not directly observed, a proposed methodology for estimating high-grading involves comparing size distributions of total catches (before sorting) and landed catches (after sorting), but we have yet to identify a suitable data source for the landed portion. This report presents data from two pilot studies exploring the suitability of data gathered during the onboard factory production process for describing the size distribution of reported catches. We received these data in a summarised report, where individual fish weights are aggregated into coarse, overlapping size grades. This summarised form results in a large loss of information. Applying the necessary statistical procedures to get a more detailed picture of fish size distributions would introduce even more uncertainty into an already uncertain estimation, potentially leading to non-signficant results, and can introduce unknown biases. We conclude that it is necessary to use the raw data behind summarised reports which provide data on individual fish. To this end, we address the logistical and statistical issues posed by production data including individual fish observations.

• Olsen, Erik Joel Steinar; Aanes, Sondre; Aldrin, Magne Tommy; Breivik, Olav Nikolai; Fuglebakk, Edvin & Goto, Daisuke [Show all 21 contributors for this article] (2021). Final report for the REDUS project - Reduced Uncertainty in Stock Assessment. Havforskningsinstituttet. Full text in Research Archive Show summary

  The REDUS project (2016-2020) has been a strategic project at the Institute of Marine Research (IMR) aimed at quantifying and reducing the uncertainty in data-rich and age-structured stock assessments (e.g., cod, herring, haddock, capelin). Work was organized in four topical work-packages: Fisheries-dependent (catch) surveys and assessment modeling (WP1), Fishery-independent (scientific) surveys (WP2), Evaluating and testing of long-term management strategies (WP3), and Communication of uncertainty, dissemination of project results and capacity building (WP4). The Norwegian Computing Center (NR) was contracted in as a strategic partner in statistical modeling and analysis, contributing mainly to WP1 and WP2, but found the research of fundamental interest therefore also allocating internal (NR) funding to develop the statistical science base of several of the methods.

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