Greenland Halibut Research Articles

The diet and diving behaviour of the ringed seal (Pusa hispida) in Kangia (Ilulissat Icefjord), Greenland

AbstractThis study uses telemetry and stomach content analysis to describe the ringed seals’ dive pattern and prey selection within Kangia (Ilulissat Icefjord), Greenland, where the ringed seals are known to be exceptionally large and genetically distinct. Data from twenty-four ringed seals (Pusa hispida) tagged in Kangia, with satellite relay data loggers from 2012 to 2020, were used to describe the dive patterns. The transmitters were active between 28 and 270 days and showed that subadults most frequently dove to around 150 m. Adult males frequently dove to this depth, but they also had a second frequently visited depth at around 400 m, some adults significantly deeper. Adult males generally dove deeper than females and adult seals showed deeper dives during the winter, a feature that was less prominent in subadults. The stomach content from ringed seals (n = 108) harvested in Kangia by subsistence hunters revealed that polar cod (Boreogadus saida), capelin (Mallotus villosus), mysids (Mysis oculata, M. littoralis, M. Polaris) and shrimps (mainly Pandalus borealis) were the dominant prey. Shrimps were observed more often in adults, likely due to the frequently visited dive depth of around 400 m, whereas mysids were more observed in small subadult seals. The stomach content from harp seals (Pagophilus groenlandicus) and Greenland halibut (Reinhardtius hippoglossoides) caught in Kangia also showed a strong niche overlap with the ringed seals. These findings outline the unique ecological adaptations and the importance of Kangia as a critical habitat of ringed seals.

Community perspectives inform coastal marine ecosystem research in northwestern Greenland

The Arctic is warming faster than the rest of the world, affecting the natural environment ecosystem and society. Because human society utilizes coastal areas and relies on marine resources for living, research is needed to study human impacts on the coastal marine ecosystem as well as the influence of the changing ecosystem on society. To better understand the changing coastal environments and the impact on society, we performed multidisciplinary research in Qaanaaq, northwestern Greenland. To share and discuss our research results, we organized workshops with residents in Qaanaaq from 2016 to 2019, and in 2022 and 2023. One workshop topic of intense discussion was the summer distribution of Greenland halibut (Reinhardtius hippoglossoides), because of its socio-economic importance in the region. Another point of interest for the residents was the potential presence of pollution on the beach, as a result of the nearby village. Residents voiced concern about the accumulation of heavy metals in Mytilus spp. (blue mussel) because residents catch mussels near the dump site. Close collaboration with residents as well as co-design and direction of the research is increasingly important for researchers to contribute to a sustainable future for populations living in the Arctic.

Climate change, community well-being, and consumption: Reconsidering human-environment relationships in Greenland under global change

We reassess the research on the impact of climate change on society and propose examining the social dimensions of climate change from a perspective of community well-being. We argue that to better understand community dynamics in the Arctic, it is helpful to shift the research focus from the environment and view the environment and climate change as a backdrop to social phenomena. Specifically, we consider the increasing living standards and expanding basic needs that fall under consumption, one of the three domains of economic activity. This represents a shift from the conventional anthropological perspective, which focuses solely on production (food procurement, subsistence) and distribution, to a more balanced consideration of the three economic domains and their intricate relations. This shift also involves moving away from the conventional anthropological theory, which posits that the relationship to the environment influences, organizes, and shapes people's lives, to the reverse: people's increasing needs reshape, rearrange, or alter the human–environment relationship. The perspective of community well-being considers the interplay between the environment, social (local assets), and economic domains (consumption and increasing needs) of community dynamics. To illustrate this perspective in Arctic studies, we draw on two examples from our experience in Greenland: sheep farming in South Greenland and Greenland halibut fisheries in North Greenland.

Exploring capelin (Mallotus villosus) population dynamics using Empirical Dynamic Modelling (EDM)

Capelin (Mallotus villosus) populations on the Newfoundland shelf collapsed in the early 1990s, coinciding with a regime shift and greatly reduced capelin and groundfish biomasses which both persist to this day. The biphasic nature of this stock’s history suggest it may experience nonlinear dynamics, which are difficult to predict using linear models. This study explores the application of Empirical Dynamic Modelling (EDM) nonlinear, nonparametric time series forecasting tools to capelin biomass data, seeking to detect nonlinear dynamics, compare performance of linear and nonlinear multivariate predictive models, identify drivers of capelin biomass using convergent cross-mapping, and measure the sign and strength of capelin species interactions. We found capelin dynamics were nonlinear, and multivariate EDM predictive models returned equal or improved model diagnostics to linear models in most situations. We identified long-term climate dynamics and timing of sea ice retreat as the primary drivers of capelin dynamics, but some indications of potential top-down effects from Greenland halibut were also detected. Atlantic cod biomass, and capelin catch were investigated as potential drivers of capelin dynamics, but both were found more likely to be driven by capelin dynamics. Overall, our results support the idea that capelin dynamics are mostly bottom-up driven, and that capelin itself is a driver of its predators, suggesting that the overall ecosystem may be largely bottom-up driven. This study also clearly identifies the utilities of EDM as a complementary tool for stock assessments by detecting and forecasting nonlinear stock dynamics, and identifying and characterizing relationships between stock biomass and the factors which drive it.

Ongoing borealization of Siberian Arctic marine ichthyofauna: Further evidence

The occurrence, abundance, biomass and size composition of six boreal fish species (walleye pollock Gadus chalcogrammus, Pacific cod G. macrocephalus, northern wolffish Anarhichas denticulatus, beaked redfish Sebastes mentella, Greenland halibut Reinhardtius hippoglossoides, glacier lanternfish Benthosema glaciale) in the Siberian and Pacific Arctic are presented based on the analysis of open databases (OBIS, GBIF and FishBase) and the results of scientific surveys of TINRO 1977–2020. In open databases, information on the records of these species is available mainly for the eastern Chukchi Sea and the Beaufort Sea and is practically absent for the seas of the Siberian Arctic, which is due to technical reasons. Data from long–term surveys of TINRO indicate the extension of the ranges of North Atlantic species eastward and North Pacific species westward indicating the ongoing borealization of the Siberian Arctic due to a changing climate. At the species level, it can lead to the overlap of the ranges of the “western” and “eastern” populations of Greenland halibut, as well as the ranges of Pacific and Greenland cods, which will make it possible to exchange genetic material between these populations/species and will contribute to the disappearance of genetic differences between them.

Modelling seasonal and geographical n-3 polyunsaturated fatty acid contents in marine fish from the Northeast Atlantic Ocean

Demand for n-3 polyunsaturated fatty acids (n-3 PUFAs) exceeds supply. Large-scale studies on effects of season and geography of n-3 PUFAs in marine fish from the Northeast Atlantic Ocean (NEAO) may be used to optimize utilization and improve nutrition security. Using a sinusoid model, seasonal cycles of n-3 PUFAs were determined and found to be species-specific and clearly pronounced for the pelagic zooplankton feeding species. The Greenland halibut showed very little seasonal variation. The n-3 PUFA content in North Sea autumn-spawning (NSAS) herring peaked in summer, while Norwegian spring-spawning (NSS) herring and mackerel had their peak in autumn. A time shift of peaks in n-3 PUFAs between the two herring stocks was detected, likely due to different spawning strategies in addition to a delay of n-3 PUFAs flux in the northern regions of the NEAO. This study demonstrates that consideration of nutrient contents, such as n-3 PUFAs, when organizing and structuring fishery approaches may improve overall nutritional yield. Based on total annual Norwegian fish landings and seasonal variation in n-3 PUFA contents, n-3 PUFAs yield could theoretically be increased from 13.79 kilo ton per year from the current fishing tactics, to 15.54 if the pelagic species were only caught during the time of their seasonal n-3 PUFA peaks. Pelagic fish is a good source for dietary n-3 PUFAs, but harvest timing will also influence n-3 PUFAs intake by human consumers. One portion of fatty fish harvested during winter/spring may not meet the weekly intake reference nutritional guidelines for n-3 PUFAs. Marine n-3 PUFAs yields also varied geographically and decreased southwards, with the lowest values in Skagerrak. This study can serve as a model to understand patterns of reproductive cycles and geographical distribution of n-3 PUFAs in fatty fish from the NEAO and the novel approach may be useful to support sustainable, seasonal fishing programmes for optimization of n-3 PUFAs yields.

Arctic puzzle: Pioneering a northern shrimp (Pandalus borealis) habitat model in Disko Bay, West Greenland

Recent advancements in spatial modelling leverage remote sensing data and statistical species-environment relationships to forecast the distribution of a specific species. Our study focuses on Disko Bay in West Greenland, recognized as a significant marine biodiversity hotspot in the region. We conducted comprehensive analyses using multiple datasets spanning from 2010 to 2019, incorporating shrimp and fish surveys, commercial shrimp fishery catches, high-resolution (25 × 25 m) multibeam bathymetry and backscatter data along with a medium-resolution (200 × 200 m) bathymetric model, measured and modelled oceanographic data, and satellite chlorophyll data. Through multivariate regression analysis, we tested the significance of various physical factors (seafloor depth, sediment class, bottom water temperature, bottom water salinity, bottom current velocity, space, and time), biological factors (chlorophyll a, Greenland halibut (Reinhardtius hippoglossoides)), and anthropogenic impact (shrimp fishery; standardized catch per unit effort) on the density of northern shrimp in the area. Our results indicate a significant association between northern shrimp density, seafloor depth, and sediment class, explaining 36 % of the variation in shrimp density. Subsequently, we developed a high-resolution (optimized) spatial linear mixed–effect model to map the distribution of northern shrimp across Disko Bay, representing the first model of its kind developed for an Arctic area. The optimal habitat for northern shrimp is characterized by medium-deep waters (approximately 150–350 m), turbulent conditions, and mixed sediments, predominantly located in the northern and southern regions of Disko Bay. Notably, the northern region hosts a relatively diverse benthic community, with northern shrimp and sponges as the primary contributors of epibenthic biomass. This novel high-resolution model significantly enhances our understanding of the physical drivers and detailed spatial patterns influencing the distribution of northern shrimp in the Arctic.

Connectivity of Greenland halibut in the northwestern Atlantic Ocean inferred from otolith chemistry

Greenland Halibut (Reinhardtius hippoglossoides) is a deepwater flatfish having a circumpolar distribution. Understanding the spatial connectivity and migratory patterns of this commercially valuable species is essential for ensuring a sustainable fishery; nonetheless, this information remains relatively scarce for many Greenland Halibut populations. Here we evaluate the connectivity and the population structure of halibut along coastal Greenland and Canada to better characterize the contribution of each production zone to the various stocks found in the northwestern Atlantic Ocean. In 2014 and 2016, we sampled 411 large Greenland Halibut from coastal Nunavut, Labrador, and Greenland. We used the elemental fingerprint (magnesium, strontium, and barium) from the otolith core and margin of the sampled fish to determine spatial differentiation of the source areas of the collected halibut. From the 17 sample sites, margin elemental fingerprint delineated four “elemental sectors”, representing pooled adjacent sites having similar chemistry. Overall, 62% of Greenland Halibut were correctly assigned to their sampled coast. Elemental fingerprint of the otolith cores indicated three chemically distinct natal sources for the captured halibut. The chemical record in the otolith cores suggested a high connectivity of Greenland Halibut in the northwestern Atlantic and a main natal source located potentially along the west coast of Greenland. Given that our results suggest the presence of a large nursery around Disko Bay–Hellefiske Bank, protection measures should be considered for this area.

FishAgePredictioNet: A multi-stage fish age prediction framework based on segmentation, deep convolution network, and Gaussian process regression with otolith images

Fish ageing is a vital component of fisheries management as it enables the evaluation of fish population status and supports the development of sustainable management strategies. However, traditional methods of age determination through otolith analysis by experts are resource-intensive and time-consuming. Therefore, there is a growing demand for more cost-effective and automated techniques to accurately determine fish age. In accordance with this purpose, we proposed a multistage framework for fish age prediction using otolith images. First, otoliths in the images were detected using the Faster Region-based Convolutional Neural Networks (RCNN) model, which includes 8 convolution layers, and the detected otoliths were clipped. Subsequently, using a pre-trained neural network based on the transfer learning approach, deep features were extracted separately from the right and left otolith images, and all the obtained features were combined. Finally, these combined features are given as input to the Gaussian process regression model. To evaluate the performance of the proposed architecture, 4109 images of right and left otoliths belonging to Greenland halibut (flatfish, Reinhardtius hippoglossoides) were used. The proposed architecture produced 1.83 MSE, 0.98 R-squared, 1.35 RMSE, and 10.29 MAPE scores in the experimental studies. As a result, the proposed model achieved superior performance compared with previous studies. Our findings show that our FishAgePredictioNet system could help experts predict fish age based on otolith images.

Simultaneous Bayesian estimation of size-specific catchability and size spectrum parameters from trawl data

Abstract Fisheries-independent surveys are a critical tool for monitoring marine populations and communities. However, considerations must be made to account for variable-size-based catchability. The size-specific catchability function is therefore key for estimating size distributions, but often requires extensive data sets or specialized field experiments to determine. We develop a Bayesian model capable of simultaneously estimating both a size-based catchability curve and species-specific size spectrum parameters from trawl data by assuming that individual species size spectra follow a theoretically derived parametric size spectrum model. The resulting model provides a means of estimating catchability and size spectra within an adaptive framework capable of accommodating confounding factors such as vessel power and fish density, potentially allowing for improved biomass and productivity estimates. We demonstrate the application of this model using 15 years of Greenland Halibut (Reinhardtius hippoglossoides) survey data from Nunavut to determine size-specific catchabilities and assess whether the size spectrum of Greenland Halibut has changed across the time series. While size spectrum parameters for this stock were not found to vary, we did find evidence of time-varying catchability parameters across the study period.

A Comparative Analysis of Age Estimates for Greenland Halibut, Reinhardtius hippoglossoides matsuurae, from the Northwestern Pacific Ocean based on Different Methodological Approaches

A Comparative Analysis of Age Estimates for Greenland Halibut, Reinhardtius hippoglossoides matsuurae, from the Northwestern Pacific Ocean based on Different Methodological Approaches

Long-run management of Greenland's fishery on Greenland halibut (Reinhardtius hippoglossoides)

AbstractIn this paper, we consider four scenarios for economic optimal management of a fisheries resource by a high sea and coastal fleet segment. These scenarios differ with respect to whether a common or two separate fish stocks are considered and whether the profit from land-based processing is included. The model is parametrized using the Greenland halibut fishery on the west coast of Greenland as an empirical case. For this fishery, we show that the relative ranking of the optimal high sea industry harvest and profit compared to the coastal industry harvest and profit depends on the chosen scenario. When comparing the scenarios for optimal management and the actual situation, we find that the fish stock tends to be overexploited.

Fish assemblages at the Yermak Plateau and in northern Svalbard waters during the period 2012–2020

During several surveys covering the north-western and northern Svalbard waters, and the deeper Yermak Plateau north of Svalbard during the period 2012–2020, 291 standardized hauls with a demersal trawl were made. All fishes in the catches were identified to the lowest possible taxonomic level, mostly to species. In addition to the data generated from the trawl catches, bottom temperature, salinity, and depth were recorded at each trawl station. The eelpouts were the most species rich family, with 15 species, followed by codfishes and sculpins with six species each. The other 13 families were represented with one to four species each. Atlantic cod (Gadus morhua) dominated by weight in the catches, while polar cod (Boreogadus saida) dominated by numbers. In the deeper areas including the Yermak Plateau, Greenland halibut (Reinhardtius hippoglossoides) dominated by weight. Zoogeographically, 23 species were Arctic, 5 were Mainly Arctic, 4 Arctoboreal, 25 Mainly Boreal, 9 Boreal, and 2 Widely Distributed. The Arctic species dominated in the deeper areas (Yermak Plateau and slope > 500 m) and on the shallow eastern shelf, whereas the Mainly Boreal species dominated along the slope and on the western and northern shelves < 500 m. A hierarchical cluster analysis revealed three prominent station clusters consistent with the zoogeographical classifications which reflected the oceanographic conditions, water masses and sea ice. The hierarchical cluster analysis additionally separated the cold-water species into two groups consistent with the bathymetry of the region. Diet studies of Atlantic cod revealed that it mainly fed on hyperiids, and that its preferred food further south, capelin, was not prominent in the diet.Regional index terms: Northeast Atlantic, Fram Strait, Svalbard, Yermak Plateau.

Spatiotemporal variability in diet composition of Greenland halibut (Reinhardtius hippoglossoides) from the eastern Canadian Arctic.

Greenland halibut (Reinhardtius hippoglossoides) sustain one of the most lucrative fisheries in the eastern Canadian Arctic and Labrador Sea. This species also plays an important role in food web connectivity and benthic-pelagic coupling. Despite the relatively rich knowledge of this species, R. hippoglossoides ecology in these specific areas remains poorly understood. The main aim of this study was to characterize the diet of this deepwater fish in the Labrador Sea and Davis and Hudson Straits and characterize the predator-prey relationship with northern shrimp (Pandalus borealis), another commercially important species in the region. Stomach contents analyses were conducted on 1199 fish captured from 2018 to 2020. Small specimens (<20 cm) fed on invertebrates, whereas larger individuals (>60 cm) fed primarily on fish, indicative of size-related changes in diet composition. The relative abundance of Pandalus shrimp species in the environment was reflected in the diet. Location appeared to be the most influential variable on feeding patterns. Distinct oceanographic conditions among areas, resulting in differences in prey availability, could explain these results. Arctic cod (Boreogadus saida) and redfish (Sebastes sp.) were selected in locations where fish prey were the most abundant. These results shed light on the opportunistic nature of R. hippoglossoides and its preference for fish at large size. With the rapidly changing oceanographic conditions of Arctic waters, a distributional change in the biomass of shrimp is expected. Results suggest that an increase in abundance of predatory groundfish species in the system (e.g., Sebastes sp.) could lead to acute predation on shrimp and competition with R. hippoglossoides. By revealing key trophic links within the demersal ecosystem, this work provides valuable information on the development of ecosystem approaches to fisheries management for the region.

Sperm and northern bottlenose whale interactions with deep-water trawlers in the western North Atlantic.

Commercial fisheries have increased in all the world's oceans with diverse unintended impacts on marine ecosystems. As a result of resource overlap, interactions between cetaceans and fisheries are a common occurrence and, in many cases, can give rise to significant conservation issues. Research on the distribution and types of such interactions is important for efficient management. In this study, we describe the behaviors of two whale species: sperm whales (Physeter macrocephalus) and northern bottlenose whales (Hyperoodon ampullatus), interacting with benthic trawlers fishing off the eastern Grand Banks of the western North Atlantic in 2007. Whale interactions were only observed when vessels were targeting Greenland halibut (Reinhardtius hippoglossoides) in deep-water fishing areas and were most common during net hauling. Sperm whales and northern bottlenose whales appeared to engage in feeding behavior close to the surface during hauling, especially during the latter stages, suggesting they targeted fish escapees rather than discards. Using photo-identification methods, seven individual sperm whales were identified with multiple resights of six individuals being recorded over an almost two month period. The maximum distance between two resights was 234 km, suggesting individual sperm whales were repeatedly targeting and even following fishing vessels over multiple days and between fishing areas. By contrast, there were no photographic resights of individual northern bottlenose whales within this study, or with substantial photo-identification catalogues from other adjacent high density areas, suggesting that individuals of this species may be less likely to follow vessels or move between areas. This study documents the earliest confirmed records of northern bottlenose whales in this remote region. These interactions and high encounter rates may indicate that adjacent populations are recovering from the previous century of commercial whaling. Our study provides new insights and details on whale-fisheries interactions, which can inform future research and help managers understand the real and perceived impacts of depredation behaviour on fisheries and whales.

Deep‐sea sponge derived environmental DNA analysis reveals demersal fish biodiversity of a remote Arctic ecosystem

AbstractThe deep‐sea is vast, remote, and largely underexplored. However, methodological advances in environmental DNA (eDNA) surveys could aid in the exploration efforts, such as using sponges as natural eDNA filters for studying fish biodiversity. In this study, we analyzed the eDNA from 116 sponge tissue samples and compared these to 18 water eDNA samples and visual surveys obtained on an Arctic seamount. Across survey methods, we revealed approximately 30% of the species presumed to inhabit this area and 11 fish species were detected via sponge derived eDNA alone. These included commercially important fish such as the Greenland halibut and Atlantic mackerel. Fish eDNA detection was highly variable across sponge samples. Highest detection rates were found in sponges with low microbial activity such as those from the class Hexactinellida. The different survey methods also detected alternate fish communities, highlighted by only one species overlap between the visual surveys and the sponge eDNA samples. Therefore, we conclude that sponge eDNA can be a useful tool for surveying deep‐sea demersal fish communities and it synergises with visual surveys improving overall biodiversity assessments. Datasets such as this can form comprehensive baselines on fish biodiversity across seamounts, which in turn can inform marine management and conservation practices in the regions where such surveys are undertaken.

Greenland halibut stock state and fishery magement in the Barents Sea

The subject of this article is an assessment of reference points and the state of the black halibut stock in the Barents Sea. Despite the abundance of information accumulated over the years of fishing and research, the uncertainty of the dynamics of the stock remains quite high. The article describes and analyzes all currently known sources of information about the state of the stock –data from surveys, fishing statistics and the age structure of catches. Several types of models are being built – production models and age-structured model. The MSY value at the level of 28–32 thousand tons were obtained as a result of applying three different approaches to stock modeling: production models, combining cohort and production models and constructing a yield-recruit curve based on cohort models data. Despite the much greater uncertainty in the estimates of biomass, the current fishing intensity can be considered close to optimal based on the estimates obtained.

Spatiotemporal modelling of Greenland halibut maturation across the Northwest Atlantic

AbstractModelling life history trait variation at appropriate spatial and temporal scales is crucial for understanding population dynamics and developing effective fisheries management strategies. However, most efforts to model life history traits ignore spatial correlations and make a priori assumptions about the spatial structuring of populations, potentially clouding the ability to recognize true spatial structure. Here we develop spatiotemporal maturation models for Greenland halibut (Reinhardtius hippoglossoides) in the Northwest Atlantic, a species with large-scale movement patterns that can lead to uncertainty regarding effective stock boundaries. Our analysis using data from three Fisheries and Oceans Canada survey regions, Baffin Bay and Davis Strait in the eastern Canadian Arctic, Newfoundland and Labrador (NL), and the northern Gulf of St. Lawrence (GSL), is the first at such a large spatial scale. We also extend the traditional binary maturity status to a multinomial one that accounts for seasonal changes in maturation. Results show a decreasing temporal trend in size at maturity across the entire area. Spatial results regarding size at maturity provide new insight linking Greenland halibut south of Newfoundland (Northwest Atlantic Fisheries Organization Subdivision 3Ps) to the GSL stock rather than the NL stock. Results also highlight parts of the Davis Strait area, where size at maturity is smaller than in waters both north and south. Multinomial model results identify areas in GSL and Davis Strait that may be important for reproductive development in the summer and fall. Our analyses also reveal constraints on size at maturity that correspond with the well-known positive association between fish length and bottom depth. Broad-scale analyses of high resolution spatial patterns in life history traits, such as those performed here for Greenland halibut maturation, may identify recurrent patterns of association with environmental or habitat characteristics that might not otherwise be evident on a stock- or survey-specific basis.

Comparative analysis of the age estimates for greenland halibut &lt;i&gt;Reinhardtius hippoglossoides matsuurae&lt;/i&gt; in the North-West Pacific based on different methodological approaches

Significant decline in abundance of greenland halibut Reinhardtius hippoglossoides matsuurae in the North-West Pacific is one of the reasons for development the methods of this species age determination using different age-recording structures. The study is based on recommendations of the Northwest Atlantic Fisheries Organization (NAFO) and International Council for the Exploration of the Sea (ICES). Underestimation of age is found for the records on scales or whole otoliths, compared to records on the otolith slices through the tubercle. An exploitation strategy based on improper age determination can have a negative impact on the state of the greenland halibut stock, in combination with natural causes, or even be a major reason of this species depression.

Physiological effects of temperature on Greenland halibut Reinhardtius hippoglossoides shows high vulnerability of Arctic stenotherms to global warming.

Global warming affects the metabolism of ectothermic aquatic breathers forcing them to migrate and undergo high-latitudinal distribution shifts to circumvent the temperature-induced mismatch between increased metabolic demand and reduced water oxygen availability. Here the authors examined the effects of temperature on oxygen consumption rates in an Arctic stenotherm, the Greenland halibut Reinhardtius hippoglossoides, and calculated the optimal temperature for maximum aerobic scope, AS(Topt,AS ), which was found to be 2.44°C. They also investigated cardiac performance as limiting the oxygen transport chain at high temperatures by measuring maximum heart rate (fHmax ) over acute temperature increases and found various metrics related to fHmax to be at least 3.2°C higher than Topt,AS . The authors' measured Topt,AS closely reflected in situ temperature occurrences of Greenland halibut from long-term tagging studies, showing that AS of the species is adapted to its habitat temperature, and is thus a good proxy for the species' sensitivity to environmental warming. The authors did not find a close connection between fHmax and Topt,AS , suggesting that cardiac performance is not limiting for the oxygen transport chain at high temperatures in this particular Arctic stenotherm. The authors' estimate of the thermal envelope for AS of Greenland halibut was from -1.89 to 8.07°C, which is exceptionally narrow compared to most other species of fish. As ocean temperatures increase most rapidly in the Arctic in response to climate change, and species in these areas have limited possibility for further poleward-range shifts, these results suggest potential severe effects of global warming on Arctic stenotherms, such as the Greenland halibut. The considerable economic importance of the species raises concerns for future fisheries and species conservation of Arctic stenotherms in the Northern Hemisphere.