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Julius Nielsen - One of the best experts on this subject based on the ideXlab platform.
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Assessing the reproductive biology of the Greenland shark (Somniosus microcephalus).
PloS one, 2020Co-Authors: Julius Nielsen, R. B. Hedeholm, John F. Steffensen, Arve Lynghammar, Leon M. Mcclusky, Bjørn Berland, Jørgen S. ChristiansenAbstract:The Greenland shark (Somniosus microcephalus, Squaliformes: Somniosidae) is a long-lived Arctic top predator, which in combination with the high historical and modern fishing pressures, has made it subject to increased scientific focus in recent years. Key aspects of reproduction are not well known as exemplified by sparse and contradictory information e.g. on birth size and number of pups per pregnancy. This study represents the first comprehensive work on Greenland shark reproductive biology based on data from 312 specimens collected over the past 60 years. We provide guidelines quantifying reproductive parameters to assess specific maturation stages, as well as calculate body length-at-maturity (TL50) which was 2.84±0.06 m for males and 4.19±0.04 m for females. From the available information on the ovarian fecundity of Greenland sharks as well as a meta-analysis of Squaliform reproductive parameters, we estimate up to 200-324 pups per pregnancy (depending on maternal size) with a body length-at-birth of 35-45 cm. These estimates remain to be verified by future observations from gravid Greenland sharks.
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Table_1_Greenland Shark (Somniosus microcephalus) Stomach Contents and Stable Isotope Values Reveal an Ontogenetic Dietary Shift.pdf
2019Co-Authors: Julius Nielsen, Kim Præbel, Jorgen Schou Christiansen, Peter Grønkjær, Peter Bushnell, John Fleng Steffensen, Helene Overgaard Kiilerich, R. B. HedeholmAbstract:Current knowledge on the feeding ecology of the Greenland shark (Somniosus microcephalus), a potential top predator in arctic marine ecosystems, is based on small sample sizes as well as narrow size ranges of sharks. Therefore, potential size-related feeding patterns remain poorly documented. Using stomach content data (N = 88) and stable isotope values of white muscle tissue (N = 40), this study evaluates the diet of sharks ranging in size from 81 to 474 cm (total length). The importance of prey categories (“Fish,” “Mammal,” “Squid,” “Crustacean,” and “Other”) was evaluated based on the reconstructed prey biomass of the stomach contents. Stable isotope values of δ13C and δ15N ranged between -14.4 to -19.9‰ and 11.8 to 17.2‰, respectively. The importance of each prey category was estimated by the Index of Relative Importance (IRI). Our findings suggest that the smallest Greenland sharks (200 cm) mainly feed on higher trophic level prey such as seals, epibenthic and benthic fishes including gadoids (Gadidae), skates (Rajidae), righteye flounders (Pleuronectidae), lumpfish (Cyclopteridae), wolffish (Anarhichadidae), and redfish (Sebastidae). Redfish were, however, only found to be important in the largest sharks sampled (>400 cm). In addition to demonstrating ontogenetic shifts in their feeding preferences, this study supports that Greenland sharks are capable of active predation on fast swimming seals and large fishes.
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Greenland Shark (Somniosus microcephalus) Stomach Contents and Stable Isotope Values Reveal an Ontogenetic Dietary Shift
Frontiers Media S.A., 2019Co-Authors: Julius Nielsen, Jorgen Schou Christiansen, Peter Grønkjær, Peter Bushnell, John Fleng Steffensen, Helene Overgaard KiilerichAbstract:Current knowledge on the feeding ecology of the Greenland shark (Somniosus microcephalus), a potential top predator in arctic marine ecosystems, is based on small sample sizes as well as narrow size ranges of sharks. Therefore, potential size-related feeding patterns remain poorly documented. Using stomach content data (N = 88) and stable isotope values of white muscle tissue (N = 40), this study evaluates the diet of sharks ranging in size from 81 to 474 cm (total length). The importance of prey categories (“Fish,” “Mammal,” “Squid,” “Crustacean,” and “Other”) was evaluated based on the reconstructed prey biomass of the stomach contents. Stable isotope values of δ13C and δ15N ranged between -14.4 to -19.9‰ and 11.8 to 17.2‰, respectively. The importance of each prey category was estimated by the Index of Relative Importance (IRI). Our findings suggest that the smallest Greenland sharks (<200 cm) feed on lower trophic level prey, predominantly squids. Larger sharks (>200 cm) mainly feed on higher trophic level prey such as seals, epibenthic and benthic fishes including gadoids (Gadidae), skates (Rajidae), righteye flounders (Pleuronectidae), lumpfish (Cyclopteridae), wolffish (Anarhichadidae), and redfish (Sebastidae). Redfish were, however, only found to be important in the largest sharks sampled (>400 cm). In addition to demonstrating ontogenetic shifts in their feeding preferences, this study supports that Greenland sharks are capable of active predation on fast swimming seals and large fishes
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The complete mitochondrial genome of the long-lived Greenland shark (Somniosus microcephalus): characterization and phylogenetic position
Conservation Genetics Resources, 2017Co-Authors: Aintzane Santaquiteria, Julius Nielsen, Terje Klemetsen, Nils P. Willassen, Kim PræbelAbstract:The Greenland shark ( Somniosus microcephalus ) has recently been identified as the world’s longest-living vertebrate animal, which raises conservational concern in light of recently high bycatch. We report the complete mitochondrial genome of S. microcephalus to be 16,730 bp and composed by 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and a control region. The overall nucleotide composition was 30.8% A, 29.9% T, 14.5% G, and 24.9% C, with a total of 39.4% GC content. Phylogenetic analysis confirmed the position of S. microcephalus in the traditional tree of sharks. The availability of the S. microcephalus mitogenome will contribute to further conservational genetic studies of a unique species, listed as ‘data deficient’ on the Norwegian Red List and ‘near threatened’ on the IUCN Red list.
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anatomy of the olfactory bulb in greenland shark Somniosus microcephalus bloch schneider 1801
Journal of Applied Ichthyology, 2017Co-Authors: Sara Ferrando, Julius Nielsen, Js Christiansen, Lorenzo Gallus, Laura Ghigliotti, Marino Vacchi, Andrea Amaroli, Eva PisanoAbstract:Gross morphology and histology of the olfactory rosette of Greenland shark Somniosus microcephalus (Bloch & Schneider, 1801), suggest a well‐developed olfactory capability for this top predator and scavenger native to Arctic waters. In the present paper, observations on the olfactory rosette are reported together with the gross morphology and histology of the olfactory bulb whereby the histological analyses revealed some peculiar traits. The olfactory bulb is macroscopically divided into two sub‐bulbs and a central undivided part that contain the layers typical of olfactory bulb histology. The two visible sub‐bulbs are actually bundles of fila olfactoria. In addition, the olfactory lateral ventricle is peculiarly branched, which may increase the ependymal surface or, alternatively, decrease the distance between the tissues of the olfactory bulb and the ventricle itself. The ependymal surface is known to be a proliferative zone in the olfactory bulb of fishes. In Greenland shark, the olfactory epithelium showed frequent mitosis and apoptosis highlighting the importance of this site in cell renewal. This issue should be pursued further to gain a deeper understanding of the sensory biology of Greenland shark and of elasmobranchs in general.
John F. Steffensen - One of the best experts on this subject based on the ideXlab platform.
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Assessing the reproductive biology of the Greenland shark (Somniosus microcephalus).
PloS one, 2020Co-Authors: Julius Nielsen, R. B. Hedeholm, John F. Steffensen, Arve Lynghammar, Leon M. Mcclusky, Bjørn Berland, Jørgen S. ChristiansenAbstract:The Greenland shark (Somniosus microcephalus, Squaliformes: Somniosidae) is a long-lived Arctic top predator, which in combination with the high historical and modern fishing pressures, has made it subject to increased scientific focus in recent years. Key aspects of reproduction are not well known as exemplified by sparse and contradictory information e.g. on birth size and number of pups per pregnancy. This study represents the first comprehensive work on Greenland shark reproductive biology based on data from 312 specimens collected over the past 60 years. We provide guidelines quantifying reproductive parameters to assess specific maturation stages, as well as calculate body length-at-maturity (TL50) which was 2.84±0.06 m for males and 4.19±0.04 m for females. From the available information on the ovarian fecundity of Greenland sharks as well as a meta-analysis of Squaliform reproductive parameters, we estimate up to 200-324 pups per pregnancy (depending on maternal size) with a body length-at-birth of 35-45 cm. These estimates remain to be verified by future observations from gravid Greenland sharks.
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Blood pressure in the Greenland shark as estimated from ventral aortic elasticity
Journal of Experimental Biology, 2018Co-Authors: Robert E. Shadwick, Peter G Bushnell, Diego Bernal, John F. SteffensenAbstract:ABSTRACT We conducted in vitro inflations of freshly excised ventral aortas of the Greenland shark, Somniosus microcephalus , and used pressure–diameter data to estimate the point of transition from high to low compliance, which has been shown to occur at the mean blood pressure in other vertebrates including fishes. We also determined the pressure at which the modulus of elasticity of the aorta reached 0.4 MPa, as occurs at the compliance transition in other species. From these analyses, we predict the average ventral aortic blood pressure in S. microcephalus to be about 2.3–2.8 kPa, much lower than reported for other sharks. Our results support the idea that this species is slow moving and has a relatively low aerobic metabolism. Histological investigation of the ventral aorta shows that elastic fibres are present in relatively low abundance and loosely connected, consistent with this aorta having high compliance at a relatively low blood pressure.
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Blood O2 affinity of a large polar elasmobranch, the Greenland shark Somniosus microcephalus
Polar Biology, 2017Co-Authors: N.a. Herbert, Peter G Bushnell, Richard W Brill, Peter Vilhelm Skov, Bjørn Tirsgaard, C. Harvey Clark, John F. SteffensenAbstract:The Greenland shark (Somniosus microcephalus. Bloch & Schneider 1801) is a polar elasmobranch that is hypothesised to possess a unique metabolic physiology due to its extreme large size, the cold waters it inhabits and its slow swimming lifestyle. Our results therefore provide the first insight into the metabolic physiology of this unique shark, with a focus on blood O2 affinity. An evaluation of blood O2 affinity at 2 °C using tonometry revealed a P 50 of 11.7 mmHg at a PCO2 of 2.25 mmHg and a Bohr effect (binding sensitivity of blood to pH, ϕ = Δlog P 50/ΔpH) of −0.26. A comparative evaluation of blood O2 affinity across elasmobranch fishes suggests that S. microcephalus has a high blood O2 affinity (i.e., low P 50) and a small Bohr effect but these are common traits in sluggish elasmobranch fishes, with little evidence for any relationship of blood O2 affinity to the low metabolic rates, low environmental temperatures, or large body mass of S. microcephalus. After gathering this physiology data, a subsidiary aim attempted to understand whether a warming scenario would impose a negative effect on blood O2 binding. Incubating blood to a slightly elevated temperature of 7 °C resulted in a small but significant reduction of blood O2 affinity, but no significant change in the Bohr effect. The Hill’s cooperativity coefficient (n H) was also small (1.6–2.2) and unaffected by either PCO2 or temperature. The moderate sensitivity of Greenland shark blood O2 affinity to warming potentially implies little vulnerability of functional O2 supply to the temperature changes associated with the regular vertical movements of this species or warming of polar seas resulting from directional climate change.
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The Greenland shark: A new challenge for the oxidative stress theory of ageing? Part A Molecular & integrative physiology
Comparative Biochemistry and Physiology, 2017Co-Authors: David Costantini, Julius Nielsen, Shona Smith, Shaun S. Killen, John F. SteffensenAbstract:The free radical theory of ageing predicts that long-lived species should be more resistant to oxidative damage than short-lived species. Although many studies support this theory, recent studies found notable exceptions that challenge the generality of this theory. In this study, we have analysed the oxidative status of the Greenland shark (Somniosus microcephalus), which has recently been found as the longest living vertebrate animal known to science with a lifespan of at least 272years. As compared to other species, the Greenland shark had body mass-corrected values of muscle glutathione peroxidase and red blood cells protein carbonyls (metric of protein oxidative damage) above 75 percentile and below 25 percentile, respectively. None of the biochemical metrics of oxidative status measured in either skeletal muscle or red blood cells were correlated with maximum lifespan of species. We propose that the values of metrics of oxidative status we measured might be linked to ecological features (e.g., adaptation to cold waters and deep dives) of this shark species rather to its lifespan.
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The Greenland shark: A new challenge for the oxidative stress theory of ageing?
Comparative biochemistry and physiology. Part A Molecular & integrative physiology, 2016Co-Authors: David Costantini, Julius Nielsen, Shona Smith, Shaun S. Killen, John F. SteffensenAbstract:The free radical theory of ageing predicts that long-lived species should be more resistant to oxidative damage than short-lived species. Although many studies support this theory, recent studies found notable exceptions that challenge the generality of this theory. In this study, we have analysed the oxidative status of the Greenland shark (Somniosus microcephalus), which has recently been found as the longest living vertebrate animal known to science with a lifespan of at least 272 years. As compared to other species, the Greenland shark had body mass-corrected values of muscle glutathione peroxidase and red blood cells protein carbonyls (metric of protein oxidative damage) above 75 percentile and below 25 percentile, respectively. None of the biochemical metrics of oxidative status measured in either skeletal muscle or red blood cells were correlated with maximum lifespan of species. We propose that the values of metrics of oxidative status we measured might be linked to ecological features (e.g., adaptation to cold waters and deep dives) of this shark species rather to its lifespan.
Aaron T. Fisk - One of the best experts on this subject based on the ideXlab platform.
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Non-parametric analysis of the spatio-temporal variability in the fatty-acid profiles among Greenland sharks
Journal of the Marine Biological Association of the United Kingdom, 2016Co-Authors: Holly N. Steeves, Bailey C. Mcmeans, Aaron T. Fisk, Kit M. Kovacs, Christian Lydersen, Chris Field, Connie Stewart, Michael T. Arts, M. Aaron MacneilAbstract:Shifting prey distributions due to global warming are expected to generate dramatic ecosystem-wide changes in trophic structure within Arctic marine ecosystems. Yet a relatively poor understanding of contemporary Arctic food webs makes it difficult to predict the consequences of such changes for Arctic predators. Doing so requires quantitative approaches that can track contemporary changes in predator diets through time, using accurate, well-defined methods. Here we use fatty acids (FA) to quantify differences in consumer diet using permutational multivariate analysis of variance tests that characterize spatial and temporal changes in consumer FA signatures. Specifically we explore differences in Greenland shark (Somniosus microcephalus) FA to differentiate their potential trophic role between Svalbard, Norway and Cumberland Sound, Canada. Greenland shark FA signatures revealed significant inter-annual differences, probably driven by varying seal and Greenland halibut responses to environmental conditions such as the NAO, bottom temperature, and annual sea-ice extent. Uncommon FA were also found to play an important role in driving spatial and temporal differences in Greenland shark FA profiles. Our statistical approach should facilitate quantification of changing consumer diets across a range of marine ecosystems.
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A review of Greenland shark ( Somniosus microcephalus ) studies in the Kongsfjorden area, Svalbard Norway
Polar Biology, 2016Co-Authors: Christian Lydersen, Aaron T. Fisk, Kit M. KovacsAbstract:Herein, we review and synthesize results from a series of research projects that were conducted to evaluate the role of Greenland sharks (Somniosus microcephalus) in the marine ecosystem in Kongsfjorden, Svalbard, Norway. A total of 76 sharks were caught on baited lines during the summers of 2008 and 2009 for these investigations. All of these animals, including the largest shark, a female weighing 700 kg, were sexually immature. Approximately half of the gastrointestinal tracts (GITs, N = 33) examined contained seal tissue (42.3 %), and some also contained minke whale (Balaenoptera acutorostrata) tissue (18.2 %). Atlantic cod (Gadus morhua), Atlantic wolffish (Anarhichas lupus) and haddock (Melanogrammus aeglefinus) were the dominant fish species consumed by the sharks. These fish species were found in 39.4, 18.2 and 18.2 % of the GITs, respectively. Many of the fishes were swallowed whole, including an Atlantic wolffish weighing 8.6 kg. Satellite pop-up tags deployed on 20 of the sharks showed that they travelled in the water column from the surface to depths greater than 1500 m, encountering temperatures from −1.5° to 7.4°. Accelerometers deployed on six of the sharks showed that they swim extremely slowly, with average speeds of 0.34 m/s and burst speeds of only twice this value. Various types of circumstantial evidence, including the condition of the seals and fishes found in the sharks’ stomachs, indicate that they are not only scavengers, but also active predators of both fish and mammalian prey. Given the swim speed of these sharks, we suggest that the only way they could successfully capture a healthy seal is via cryptically approaching seals that are asleep in the water. Greenland sharks clearly play a significant role as large predators in the Kongsfjorden marine ecosystem, a fact that has been largely overlooked until recently.
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Juvenile Greenland sharks Somniosus microcephalus (Bloch & Schneider, 1801) in the Canadian Arctic
Polar Biology, 2015Co-Authors: Nigel E. Hussey, Ryan P. Walter, Steven T. Kessel, Aurelie Cosandey-godin, Kevin J. Hedges, Melanie Vangerwen-toyne, Amanda N. Barkley, Aaron T. FiskAbstract:Life-stage-based management of marine fishes requires information on juvenile habitat preferences to ensure sustainable population demographics. This is especially important in the Arctic region given very little is known about the life histories of many native species, yet exploitation by developing commercial and artisanal fisheries is increasing as the ice extent decreases. Through scientific surveys and bycatch data from gillnet fisheries, we document captures of rarely reported juvenile Greenland sharks ( Somniosus microcephalus ; ≤200 cm total length [TL]) during the ice-free period in the Canadian Arctic. A total of 22 juvenile animals (42 % of total catch; n = 54), including the smallest reliably measured individual of 117 cm TL, were caught on scientific longlines and bottom trawls in Scott Inlet and Sam Ford Trough over three consecutive years. Molecular genetic nuclear markers confirmed species identity for 44 of these sharks sampled; however, two sharks including a juvenile of 150 cm TL were identified as carrying a Pacific sleeper shark ( Somniosus pacificus ) mitochondrial cytochrome b (cyt b ) haplotype. This represents the first record of a Pacific sleeper shark genetic signature in Greenland sharks in Eastern Arctic waters. Juvenile sharks caught as bycatch in gillnet fisheries were only observed offshore in Baffin Bay surrounding a fishery closure area, while larger subadult and mature Greenland sharks (>200 cm TL) were caught in all fishing locations, including areas where juveniles were observed. The repeatable occurrence of juvenile Greenland sharks in a fjord and their presence at two offshore sites indicates that these smaller animals either reside in nurseries or have defined home ranges in both coastal and offshore regions or undertake large-scale inshore–offshore movements.
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juvenile greenland sharks Somniosus microcephalus bloch schneider 1801 in the canadian arctic
Polar Biology, 2015Co-Authors: Nigel E. Hussey, Ryan P. Walter, Steven T. Kessel, Kevin J. Hedges, Amanda N. Barkley, Aurelie Cosandeygodin, Melanie Vangerwentoyne, Aaron T. FiskAbstract:Life-stage-based management of marine fishes requires information on juvenile habitat preferences to ensure sustainable population demographics. This is especially important in the Arctic region given very little is known about the life histories of many native species, yet exploitation by developing commercial and artisanal fisheries is increasing as the ice extent decreases. Through scientific surveys and bycatch data from gillnet fisheries, we document captures of rarely reported juvenile Greenland sharks (Somniosus microcephalus; ≤200 cm total length [TL]) during the ice-free period in the Canadian Arctic. A total of 22 juvenile animals (42 % of total catch; n = 54), including the smallest reliably measured individual of 117 cm TL, were caught on scientific longlines and bottom trawls in Scott Inlet and Sam Ford Trough over three consecutive years. Molecular genetic nuclear markers confirmed species identity for 44 of these sharks sampled; however, two sharks including a juvenile of 150 cm TL were identified as carrying a Pacific sleeper shark (Somniosus pacificus) mitochondrial cytochrome b (cyt b) haplotype. This represents the first record of a Pacific sleeper shark genetic signature in Greenland sharks in Eastern Arctic waters. Juvenile sharks caught as bycatch in gillnet fisheries were only observed offshore in Baffin Bay surrounding a fishery closure area, while larger subadult and mature Greenland sharks (>200 cm TL) were caught in all fishing locations, including areas where juveniles were observed. The repeatable occurrence of juvenile Greenland sharks in a fjord and their presence at two offshore sites indicates that these smaller animals either reside in nurseries or have defined home ranges in both coastal and offshore regions or undertake large-scale inshore–offshore movements.
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Temporal and spatial variation in polychlorinated biphenyl chiral signatures of the Greenland shark (Somniosus microcephalus) and its arctic marine food web.
Environmental pollution (Barking Essex : 1987), 2014Co-Authors: Aaron T. Fisk, Bailey C. Mcmeans, Kit M. Kovacs, Christian Lydersen, Melissa A. Mckinney, Gregg T. Tomy, Bruno Rosenburg, Derek C. G. Muir, Charles S. WongAbstract:Polychlorinated biphenyls (PCBs) chiral signatures were measured in Greenland sharks (Somniosus microcephalus) and their potential prey in arctic marine food webs from Canada (Cumberland Sound) and Europe (Svalbard) to assess temporal and spatial variation in PCB contamination at the stereoisomer level. Marine mammals had species-specific enantiomer fractions (EFs), likely due to a combination of in vivo biotransformation and direct trophic transfer. Greenland sharks from Cumberland Sound in 2007e2008 had similar EFs to those sharks collected a decade ago in the same location (PCBs 91, 136 and 149) and also similar to their conspecifics from Svalbard for some PCB congeners (PCBs 95, 136 and 149). However, other PCB EFs in the sharks varied temporally (PCB 91) or spatially (PCB 95), suggesting a possible spatiotemporal variation in their diets, since biotransformation capacity was unlikely to have varied within this species from region to region or over the time frame studied.
Kit M. Kovacs - One of the best experts on this subject based on the ideXlab platform.
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Origins of the Greenland shark (Somniosus microcephalus): Impacts of ice-olation and introgression.
Ecology and evolution, 2017Co-Authors: Ryan P. Walter, Jörundur Svavarsson, Bailey C. Mcmeans, Nigel E. Hussey, Kit M. Kovacs, Christian Lydersen, Denis Roy, Björn Stelbrink, Steven T. Kessel, Sebastián Biton PorsmoguerAbstract:Herein, we use genetic data from 277 sleeper sharks to perform coalescent-based modeling to test the hypothesis of early Quaternary emergence of the Greenland shark (Somniosus microcephalus) from ancestral sleeper sharks in the Canadian Arctic-Subarctic region. Our results show that morphologically cryptic somniosids S. microcephalus and Somniosus pacificus can be genetically distinguished using combined mitochondrial and nuclear DNA markers. Our data confirm the presence of genetically admixed individuals in the Canadian Arctic and sub-Arctic, and temperate Eastern Atlantic regions, suggesting introgressive hybridization upon secondary contact following the initial species divergence. Conservative substitution rates fitted to an Isolation with Migration (IM) model indicate a likely species divergence time of 2.34 Ma, using the mitochondrial sequence DNA, which in conjunction with the geographic distribution of admixtures and Pacific signatures likely indicates speciation associated with processes other than the closing of the Isthmus of Panama. This time span coincides with further planetary cooling in the early Quaternary period followed by the onset of oscillating glacial-interglacial cycles. We propose that the initial S. microcephalus–S. pacificus split, and subsequent hybridization events, were likely associated with the onset of Pleistocene glacial oscillations, whereby fluctuating sea levels constrained connectivity among Arctic oceanic basins, Arctic marginal seas, and the North Atlantic Ocean. Our data demonstrates support for the evolutionary consequences of oscillatory vicariance via transient oceanic isolation with subsequent secondary contact associated with fluctuating sea levels throughout the Quaternary period—which may serve as a model for the origins of Arctic marine fauna on a broad taxonomic scale.
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Non-parametric analysis of the spatio-temporal variability in the fatty-acid profiles among Greenland sharks
Journal of the Marine Biological Association of the United Kingdom, 2016Co-Authors: Holly N. Steeves, Bailey C. Mcmeans, Aaron T. Fisk, Kit M. Kovacs, Christian Lydersen, Chris Field, Connie Stewart, Michael T. Arts, M. Aaron MacneilAbstract:Shifting prey distributions due to global warming are expected to generate dramatic ecosystem-wide changes in trophic structure within Arctic marine ecosystems. Yet a relatively poor understanding of contemporary Arctic food webs makes it difficult to predict the consequences of such changes for Arctic predators. Doing so requires quantitative approaches that can track contemporary changes in predator diets through time, using accurate, well-defined methods. Here we use fatty acids (FA) to quantify differences in consumer diet using permutational multivariate analysis of variance tests that characterize spatial and temporal changes in consumer FA signatures. Specifically we explore differences in Greenland shark (Somniosus microcephalus) FA to differentiate their potential trophic role between Svalbard, Norway and Cumberland Sound, Canada. Greenland shark FA signatures revealed significant inter-annual differences, probably driven by varying seal and Greenland halibut responses to environmental conditions such as the NAO, bottom temperature, and annual sea-ice extent. Uncommon FA were also found to play an important role in driving spatial and temporal differences in Greenland shark FA profiles. Our statistical approach should facilitate quantification of changing consumer diets across a range of marine ecosystems.
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A review of Greenland shark ( Somniosus microcephalus ) studies in the Kongsfjorden area, Svalbard Norway
Polar Biology, 2016Co-Authors: Christian Lydersen, Aaron T. Fisk, Kit M. KovacsAbstract:Herein, we review and synthesize results from a series of research projects that were conducted to evaluate the role of Greenland sharks (Somniosus microcephalus) in the marine ecosystem in Kongsfjorden, Svalbard, Norway. A total of 76 sharks were caught on baited lines during the summers of 2008 and 2009 for these investigations. All of these animals, including the largest shark, a female weighing 700 kg, were sexually immature. Approximately half of the gastrointestinal tracts (GITs, N = 33) examined contained seal tissue (42.3 %), and some also contained minke whale (Balaenoptera acutorostrata) tissue (18.2 %). Atlantic cod (Gadus morhua), Atlantic wolffish (Anarhichas lupus) and haddock (Melanogrammus aeglefinus) were the dominant fish species consumed by the sharks. These fish species were found in 39.4, 18.2 and 18.2 % of the GITs, respectively. Many of the fishes were swallowed whole, including an Atlantic wolffish weighing 8.6 kg. Satellite pop-up tags deployed on 20 of the sharks showed that they travelled in the water column from the surface to depths greater than 1500 m, encountering temperatures from −1.5° to 7.4°. Accelerometers deployed on six of the sharks showed that they swim extremely slowly, with average speeds of 0.34 m/s and burst speeds of only twice this value. Various types of circumstantial evidence, including the condition of the seals and fishes found in the sharks’ stomachs, indicate that they are not only scavengers, but also active predators of both fish and mammalian prey. Given the swim speed of these sharks, we suggest that the only way they could successfully capture a healthy seal is via cryptically approaching seals that are asleep in the water. Greenland sharks clearly play a significant role as large predators in the Kongsfjorden marine ecosystem, a fact that has been largely overlooked until recently.
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Temporal and spatial variation in polychlorinated biphenyl chiral signatures of the Greenland shark (Somniosus microcephalus) and its arctic marine food web.
Environmental pollution (Barking Essex : 1987), 2014Co-Authors: Aaron T. Fisk, Bailey C. Mcmeans, Kit M. Kovacs, Christian Lydersen, Melissa A. Mckinney, Gregg T. Tomy, Bruno Rosenburg, Derek C. G. Muir, Charles S. WongAbstract:Polychlorinated biphenyls (PCBs) chiral signatures were measured in Greenland sharks (Somniosus microcephalus) and their potential prey in arctic marine food webs from Canada (Cumberland Sound) and Europe (Svalbard) to assess temporal and spatial variation in PCB contamination at the stereoisomer level. Marine mammals had species-specific enantiomer fractions (EFs), likely due to a combination of in vivo biotransformation and direct trophic transfer. Greenland sharks from Cumberland Sound in 2007e2008 had similar EFs to those sharks collected a decade ago in the same location (PCBs 91, 136 and 149) and also similar to their conspecifics from Svalbard for some PCB congeners (PCBs 95, 136 and 149). However, other PCB EFs in the sharks varied temporally (PCB 91) or spatially (PCB 95), suggesting a possible spatiotemporal variation in their diets, since biotransformation capacity was unlikely to have varied within this species from region to region or over the time frame studied.
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Archival pop-off tag tracking of Greenland sharks Somniosus microcephalus in the High Arctic waters of Svalbard, Norway
Marine Ecology Progress Series, 2012Co-Authors: Aaron T. Fisk, Christian Lydersen, Kit M. KovacsAbstract:The Greenland shark Somniosus microcephalus is the largest fish in Arctic waters and a significant predator that is likely numerous, but little is known about its movement patterns or habitat preferences. In June 2008 and 2009, 20 archival pop-off tags were deployed on Green- land sharks in coastal waters in Svalbard, Norway (~80° N), to address this knowledge gap. Over the period June to December, 14 of the tags reported data. The swimming depth of the sharks was 111 ± 74 m (mean ± SD), but they occupied waters from the surface down to a depth of at least 1560 m (the depth limit of the tags), which is the deepest confirmed record for this species. The sharks displayed a wide range of depths within each 6 h time bin collected by the tags, with no obvious diel movement pattern. They experienced temperatures from �1.5 to 7.4°C (mean ± SD = 3.8 ± 1.4°C). The average depth of swimming increased and temperatures experienced by the sharks decreased from June through December. Most individuals moved north from the tagging area, and travelled a range of distances during their variable deployment times, but most tags popped off
Jörundur Svavarsson - One of the best experts on this subject based on the ideXlab platform.
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Origins of the Greenland shark (Somniosus microcephalus): Impacts of ice-olation and introgression.
Ecology and evolution, 2017Co-Authors: Ryan P. Walter, Jörundur Svavarsson, Bailey C. Mcmeans, Nigel E. Hussey, Kit M. Kovacs, Christian Lydersen, Denis Roy, Björn Stelbrink, Steven T. Kessel, Sebastián Biton PorsmoguerAbstract:Herein, we use genetic data from 277 sleeper sharks to perform coalescent-based modeling to test the hypothesis of early Quaternary emergence of the Greenland shark (Somniosus microcephalus) from ancestral sleeper sharks in the Canadian Arctic-Subarctic region. Our results show that morphologically cryptic somniosids S. microcephalus and Somniosus pacificus can be genetically distinguished using combined mitochondrial and nuclear DNA markers. Our data confirm the presence of genetically admixed individuals in the Canadian Arctic and sub-Arctic, and temperate Eastern Atlantic regions, suggesting introgressive hybridization upon secondary contact following the initial species divergence. Conservative substitution rates fitted to an Isolation with Migration (IM) model indicate a likely species divergence time of 2.34 Ma, using the mitochondrial sequence DNA, which in conjunction with the geographic distribution of admixtures and Pacific signatures likely indicates speciation associated with processes other than the closing of the Isthmus of Panama. This time span coincides with further planetary cooling in the early Quaternary period followed by the onset of oscillating glacial-interglacial cycles. We propose that the initial S. microcephalus–S. pacificus split, and subsequent hybridization events, were likely associated with the onset of Pleistocene glacial oscillations, whereby fluctuating sea levels constrained connectivity among Arctic oceanic basins, Arctic marginal seas, and the North Atlantic Ocean. Our data demonstrates support for the evolutionary consequences of oscillatory vicariance via transient oceanic isolation with subsequent secondary contact associated with fluctuating sea levels throughout the Quaternary period—which may serve as a model for the origins of Arctic marine fauna on a broad taxonomic scale.
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Biology of the Greenland shark Somniosus microcephalus.
Journal of fish biology, 2012Co-Authors: M. A. Macneil, Jörundur Svavarsson, Bailey C. Mcmeans, Nigel E. Hussey, P. Vecsei, Kit M. Kovacs, Christian Lydersen, Margaret A. Treble, Gregory B. Skomal, M. RamseyAbstract:Greenland shark Somniosus microcephalus is a potentially important yet poorly studied cold-water species inhabiting the North Atlantic and Arctic Oceans. Broad-scale changes in the Arctic ecosystem as a consequence of climate change have led to increased attention on trophic dynamics and the role of potential apex predators such as S. microcephalus in the structure of Arctic marine food webs. Although Nordic and Inuit populations have caught S. microcephalus for centuries, the species is of limited commercial interest among modern industrial fisheries. Here, the limited historical information available on S. microcephalus occurrence and ecology is reviewed and new catch, biological and life-history information from the Arctic and North Atlantic Ocean region is provided. Given the considerable by-catch rates in high North Atlantic Ocean latitudes it is suggested that S. microcephalus is an abundant predator that plays an important, yet unrecognized, role in Arctic marine ecosystems. Slow growth and large pup sizes, however, may make S. microcephalus vulnerable to increased fishing pressure in a warming Arctic environment.
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Neutral and phenolic brominated organic compounds of natural and anthropogenic origin in northeast Atlantic Greenland shark (Somniosus microcephalus)
Environmental toxicology and chemistry, 2010Co-Authors: Anna Strid, Jörundur Svavarsson, Maria Athanasiadou, Ioannis Athanassiadis, Olaf Päpke, Åke BergmanAbstract:In the present study, muscle and liver tissue from 10 female Greenland sharks (Somniosus microcephalus) collected in Icelandic waters were analyzed for neutral and phenolic brominated organic compo ...
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Diet and resource use among Greenland sharks (Somniosus microcephalus) and teleosts sampled in Icelandic waters, using δ13C, δ15N, and mercury
Canadian Journal of Fisheries and Aquatic Sciences, 2010Co-Authors: Bailey C. Mcmeans, Jörundur Svavarsson, Susan Dennards. Dennard, Aaron T. FiskAbstract:Stable carbon (δ13C) and nitrogen (δ15N) isotopes and total mercury (Hg) were used to investigate diet and resource use among Greenland sharks (Somniosus microcephalus) and 14 teleosts inhabiting I...
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Selected organochlorine pesticides, PCBs and their methyl sulfonyl metabolites in Greenland shark (Somniosus microcephalus)
2010Co-Authors: Anna Strid, Jörundur Svavarsson, Åke BergmanAbstract:The remote sub-Arctic/Arctic environment has due to human activities become a sink for organohalogen contaminants (OHCs). These OHC include traditional contaminants such as polychlorinated biphenyls (PCBs), DDTs and technical mixtures of polybrominated diphenyl ethers (PBDEs), all included in the Stockholm Convention list of persistent organic pollutants (POPs). Other OHCs, currently under evaluation to be included among the POPs i.e. short chain chlorinated paraffins (SCCPs) and hexabromocyclododecane (HBCDD) are also found in these environments as well as a whole range of other OHCs. The main objective of this thesis is to increase the knowledge about the presence of OHCs in a high trophic Arctic shark species, the Greenland shark (Somniosus microcephalus). The Greenland shark is an opportunistic feeder, occasionally feeding at the top of the Arctic marine food chain. Furthermore may this species have a life span in excess of 100 years and is probably among the oldest of any fish species. These traits make the shark prone to accumulate elevated concentrations of OHCs. This has shown to be true for the Greenland sharks studied and most of the targeted OHCs were determined in the species. The highest concentrations were observed for the DDTs, ranging up to 26 μg/g fat. Other OHCs reported that are of special interest are SCCPs and brominated flame retardants used as replacement products to PBDEs; pentabromoethylbenzene (PBEB) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE). Also a range of OHCs whose origin is assumed to be natural, were shown to be present in Greenland sharks. This thesis is stressing the fact that even though the use of certain OHCs has been banned for decades they are still present at high concentrations in the deep waters of the Arctic. Therefore it is of major importance to continue to monitor the fate of traditional and emerging OHCs in the environment, and for this purpose the Greenland shark is an excellent species.