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Growing evidence suggests that complex spatial structure occurs within the Scotian Shelf and southern Grand Banks (SSGB) Atlantic halibut stock, yet large knowledge gaps remain about diversity of migratory and spawning behaviors. Here, 71 pop-up satellite archival tags were deployed on large Atlantic halibut (FL: 87–166 cm) between 2012 and 2020. Migration tracks were successfully reconstructed for 43 fish using a hidden Markov geolocation model, and temperature and depth time series were available for an additional nine fish (total n = 52). Five migratory behavior categories were identified: shelf residency, slope residency, shelf-channel migration, shelf-slope migration, and dispersal. High-resolution data for four of 20 physically recovered tags provided evidence of putative spawning behavior in deep channels on the continental shelf and along the continental slope between January and February. Additionally, four halibut displayed previously undocumented periods of sustained, oscillatory vertical movements along the continental slope between November and February. The high migratory diversity observed in this study provides support for the existence of multiple resident and migratory contingents in the SSGB stock in the apparent absence of significant genetic structure. [ABSTRACT FROM AUTHOR]

Reproductive timing, location, and behavior are important characteristics that determine marine population dynamics, structure, and resilience to threats, including fishing and climate change. It is challenging to evaluate factors driving variability in these reproductive traits in wild fishes because of the difficulty observing individuals in their natural environments. In the present study, we used high‐resolution depth, temperature, and acceleration time series recorded by pop‐up satellite archival tags to (1) identify and characterize patterns in depth and acceleration that may be indicative of spawning events in large Atlantic halibut (Hippoglossus hippoglossus), and (2) estimate the effects of individual traits (body size and sex) and environmental factors (location and temperature) on spawning time and frequency. Unique rapid rises observed in the winter depth profiles were interpreted as spawning events. The initiation of the first presumed spawning rise was negatively correlated to water temperature experienced during the prespawning season, suggesting that currently increasing water temperature in the Gulf of St. Lawrence may induce phenological change in halibut spawning time. The number of rises of batch‐spawning females was unrelated to female body size. The present study demonstrates how electronic tagging can be used for in‐depth characterization of timing, location, and behaviors associated with spawning in a large flatfish species. Such information can inform spatiotemporal management and conservation measures aiming to protect species from directed fishing and by‐catch during spawning. [ABSTRACT FROM AUTHOR]

With the influence of climate change on marine systems expanding, climate adaptation will be fundamental for the future of fisheries management. An exponential increase in Atlantic halibut Hippoglossus hippoglossus landings over the past decade has coincided with warming ocean temperatures. Here, we explore how historical changes in abundance have been linked to changing thermal habitat conditions and project trends with a warming climate under different emissions scenarios. From 1990 to 2018, available thermal habitat increased by 11.6 ± 7.35% and growing degree days have increased by 13.5 ± 7.86 °C·days across the region. With warming, the probability of occurrence is projected to increase up to 20.5% in Canada by 2085 under RCP 8.5 for Atlantic halibut. Our results suggest that shifting patterns of halibut distribution and abundance are linked to thermal conditions and that continued warming will likely continue to enhance habitat conditions, leading to increased abundance in the Canadian range. Collectively, these results illustrate the influence of shifting environmental conditions on population dynamics and emphasize the importance of adaptive management practices in a dynamic future climate.

The ability to identify sex is necessary in population biology for a proper understanding of the dynamics of a population. In Atlantic halibut, phenotypic sex identification is not possible due to the lack of significant external morphological differences. We developed an Illumina SNP panel for Atlantic halibut with 4000 SNPs spread evenly throughout the genome with a minor allele frequency MAF ≥ 0.4, except for N = 249 SNPs located in a sex-determining region on chromosome 12, N = 176 of these SNPs were selected to genetically identify male and female individuals using a DAPC analysis. The genomic identification of sex allows for non-lethal sex determination and validation of sex identification in the field. The SNP panel is a new genomic resource for Atlantic halibut that will make it possible to generate the genotypic data for the large number of individuals needed to estimate population abundance using genomics and the Close Kin Mark Recapture (CKMR) approach, an emerging component of fisheries management and stock monitoring. [ABSTRACT FROM AUTHOR]

Abstract Background Tandem mass tag spectrometry (TMT labeling-LC-MS/MS) was utilized to examine the global proteomes of Atlantic halibut eggs at the 1-cell-stage post fertilization. Comparisons were made between eggs judged to be of good quality (GQ) versus poor quality (BQ) as evidenced by their subsequent rates of survival for 12 days. Altered abundance of selected proteins in BQ eggs was confirmed by parallel reaction monitoring spectrometry (PRM-LC-MS/MS). Correspondence of protein levels to expression of related gene transcripts was examined via qPCR. Potential mitochondrial differences between GQ and BQ eggs were assessed by transmission electron microscopy (TEM) and measurements of mitochondrial DNA (mtDNA) levels. Results A total of 115 proteins were found to be differentially abundant between GQ and BQ eggs. Frequency distributions of these proteins indicated higher protein folding activity in GQ eggs compared to higher transcription and protein degradation activities in BQ eggs. BQ eggs were also significantly enriched with proteins related to mitochondrial structure and biogenesis. Quantitative differences in abundance of several proteins with parallel differences in their transcript levels were confirmed in egg samples obtained over three consecutive reproductive seasons. The observed disparities in global proteome profiles suggest impairment of protein and energy homeostasis related to unfolded protein response and mitochondrial stress in BQ eggs. TEM revealed BQ eggs to contain significantly higher numbers of mitochondria, but differences in corresponding genomic mtDNA (mt-nd5 and mt-atp6) levels were not significant. Mitochondria from BQ eggs were significantly smaller with a more irregular shape and a higher number of cristae than those from GQ eggs. Conclusion The results of this study indicate that BQ Atlantic halibut eggs are impaired at both transcription and translation levels leading to endoplasmic reticulum and mitochondrial disorders. Observation of these irregularities over three consecutive reproductive seasons in BQ eggs from females of diverse background, age and reproductive experience indicates that they are a hallmark of poor egg quality. Additional research is needed to discover when in oogenesis and under what circumstances these defects may arise. The prevalence of this suite of markers in BQ eggs of diverse vertebrate species also begs investigation.

Knowledge of the larval ecology of winter‐spawning fish from the Estuary and Gulf of St. Lawrence, Canada, remains scarce due to the seasonal ice cover that prevents ichthyoplankton sampling using conventional methods. Two winter‐spawning species, Atlantic halibut (AH, Hippoglossus hippoglossus) and Greenland halibut (GH, Reinhardtius hippoglossoides), support the most important groundfish fisheries of this area. In March 2020, the authors captured 10 halibut larvae ranging in size from 5 to 14 mm during an opportunistic survey in the GSL onboard an icebreaking vessel. Of these, eight were AH and two GH. Judging by their very small size, the larvae were only a few days old, suggesting that the spawning grounds are close to the capture sites. This effort constitutes a first step in validating the putative spawning areas for these two important GSL stocks. This knowledge is important for the conservation and sustainable management of these fisheries. [ABSTRACT FROM AUTHOR]

Background: Tandem mass tag spectrometry (TMT labeling-LC-MS/MS) was utilized to examine the global proteomes of Atlantic halibut eggs at the 1-cell-stage post fertilization. Comparisons were made between eggs judged to be of good quality (GQ) versus poor quality (BQ) as evidenced by their subsequent rates of survival for 12 days. Altered abundance of selected proteins in BQ eggs was confirmed by parallel reaction monitoring spectrometry (PRM-LC-MS/MS). Correspondence of protein levels to expression of related gene transcripts was examined via qPCR. Potential mitochondrial differences between GQ and BQ eggs were assessed by transmission electron microscopy (TEM) and measurements of mitochondrial DNA (mtDNA) levels. Results: A total of 115 proteins were found to be differentially abundant between GQ and BQ eggs. Frequency distributions of these proteins indicated higher protein folding activity in GQ eggs compared to higher transcription and protein degradation activities in BQ eggs. BQ eggs were also significantly enriched with proteins related to mitochondrial structure and biogenesis. Quantitative differences in abundance of several proteins with parallel differences in their transcript levels were confirmed in egg samples obtained over three consecutive reproductive seasons. The observed disparities in global proteome profiles suggest impairment of protein and energy homeostasis related to unfolded protein response and mitochondrial stress in BQ eggs. TEM revealed BQ eggs to contain significantly higher numbers of mitochondria, but differences in corresponding genomic mtDNA (mt-nd5 and mt-atp6) levels were not significant. Mitochondria from BQ eggs were significantly smaller with a more irregular shape and a higher number of cristae than those from GQ eggs. Conclusion: The results of this study indicate that BQ Atlantic halibut eggs are impaired at both transcription and translation levels leading to endoplasmic reticulum and mitochondrial disorders. Observation of these irregularities over three consecutive reproductive seasons in BQ eggs from females of diverse background, age and reproductive experience indicates that they are a hallmark of poor egg quality. Additional research is needed to discover when in oogenesis and under what circumstances these defects may arise. The prevalence of this suite of markers in BQ eggs of diverse vertebrate species also begs investigation. [ABSTRACT FROM AUTHOR]

Interactions between spatial dynamics and stock structure in marine fishes have largely focused on stocks in decline; stock structure is rarely re-visited for expanding species. Here, the spatial ecology of Atlantic halibut (Hippoglossus hippoglossus L.), managed as four stocks in the Northwest Atlantic, is reviewed. Halibut collapsed under high exploitation in the mid-19th century, but the Canadian fisheries value has increased seven-fold since the early 2000s. Atlantic halibut's thermal habitat has increased due to warming, possibly contributing to its expansion. Genomic evidence differentiates two populations in the four management units, whereas there is non-genetic spatial structure within each of the stock boundaries. There are different core juvenile areas and a diversity of spawning migration patterns influenced by timing, fish size, maturity state, and distance between summer-feeding and over-wintering habitats. From tagging studies, multiple estimates of median distance at recapture (⁓3-90 km) are much less than the spatial domain of each stock. Growth rates are faster in the warmer south, as predicted by growing degree day. The current perspective of Atlantic halibut spatial structure is that there are two distinct populations, and within each, there are subpopulations composed of multiple migratory contingents. The level of mixing on common spawning grounds both among and within subpopulations is only partly understood. [ABSTRACT FROM AUTHOR]

Uncertainties in fish tracking studies limit their integration into conservation and fisheries management plans. This is especially true for archival tagging studies that rely on geolocation models to infer fish tracks from recorded environmental variables. Hidden Markov Models (HMMs) are increasingly popular to geolocate marine fish equipped with archival tags; however, true errors and sensitivity of geolocation HMMs are seldom evaluated. In this study, we first review validation methods and implementations of geolocation HMMs to adapt to regional oceanography, fish species and tag data. We then use a case‐study to evaluate strengths and limitations of each validation approach and to illustrate the sensitivity of geolocation HMMs to implementation assumptions. Simulated and fixed tag locations are the most widely implemented methods, but less common methods relying on true fish tracking, that is double‐tagging or distance from recapture experiments, provide more informative estimates of model accuracy and precision. Results showed that model performance can be improved using simple assumptions when pre‐processing tag data rather than using a complex movement behaviour model. In addition, accelerometer show potential to further parameterise geolocation models. Overall, results from our case‐study and previous studies showed that current geolocation HMMs have average errors of ca. 30–50 and 120 km for demersal and large pelagic fish, respectively. We suggest that these errors are acceptable for investigations at the scale of fisheries management units. [ABSTRACT FROM AUTHOR]

Abstract Background The effects of temporal data resolution on the interpretation of fish behaviours are questions fundamental to research programs using electronic tags with finite data storage and data transmission capacities. However, understanding these effects requires sub-sampling high-resolution data at multiple temporal resolutions. In pop-up satellite archival tags (PSATs), data transmissions via satellite are limited, so temporal resolution is a decreasing function of the deployment duration. Physical recovery of PSATs overcomes this limitation, providing data on temperature, depth, etc., at rates at least 15–30 times greater than transmitted data. Results Using PSATs physically recovered from Atlantic halibut (Hippoglossus hippoglossus), we evaluated the effects of data resolution (2, 30, 60 min) on interpreting vertical movements including rapid ascents during the expected spawning season. Putative ‘spawning rises’ of 6–20 min were only present within highest temporal resolution data. Vertical movement rates during spawning rises identified with high-resolution data exceeded rates in all other periods; such movement rates were virtually absent in all other tagged fish within the spawning period. Mean maximum ascent rates were 13 and 23 times higher when the sampling interval was 2 versus 30 or 60 min, respectively. Conclusions We illustrate the limitations of using satellite-transmitted data to quantify vertical movement rates and detect potential spawning events in marine teleosts. Such low temporal resolution data suggest spurious results by masking important behaviours that archived data reveal as occurring at high frequencies. We highlight new technologies that facilitate PSAT recoveries at sea to overcome these limitations and facilitate analyses of high-frequency archived data.

Atlantic halibut are a "Species of Concern" in US waters and little is known about their movements and stock structure. Recent stock assessments drew attention to the paucity of information for assessing and managing this stock. To investigate movement patterns and stock structure, halibut were tagged off Massachusetts and Maine within US waters of the Gulf of Maine region using pop-up satellite archival tags and data storage tags. A hidden Markov model (HMM) geolocation method previously developed for other groundfish species was adapted to estimate the movement tracks of the tagged halibut (n  =   25) based on the tag-recorded depth and temperature. Total distance travelled based on geolocation ranged from 36 to 1701 km, whereas straight line distance between tagging and end locations ranged from 0.4 to 440.7 km. Estimated movement rates varied between 2.7 and 10 km day−1. Two tagged halibut made long-distance movements to putative spawning habitat in the Northeast Channel off Georges Bank. Thirteen (13) out of 25 geolocated individuals were estimated to have reached Canadian waters. Geolocation results revealed home range, return movement, and seasonal migration movement patterns exhibited by the tagged halibut. The HMM geolocation method could be a useful tool in providing information on halibut movements that can inform stock assessment and management decisions. [ABSTRACT FROM AUTHOR]

Abstract Atlantic halibut is a cold-water pleuronectiform of the North Atlantic with a high market price and a small wild stock, therefore it has a large potential in farming. However, the halibut is difficult to grow and although work aimed at domestication has been going on since the late 1980ies, there are still only a few commercial farms. The purpose of the present study was to establish a time-point for early weaning of Atlantic halibut larvae, using feed intake as a proxy. First, three commercial diets (Otohime, Gemma Micro and AgloNorse) were compared at 28 days post first-feeding (dpff), with respect to feed intake during 5 days after weaning, using four replicate tanks. The number of larvae per tank out of 28 which had filled guts on the different diets, was 26.7 ± 2.3 (Otohime), 12.0 ± 0.6 (Gemma Micro) and 14.7 ± 1.2 (AgloNorse), respectively. Otohime was chosen for an experiment where feed intake for 5 days after weaning was monitored, starting at 15, 22 and 28 dpff. There was a gradual increase in success with larval age. At 15 dpff the larvae did not eat and there was an almost 100% mortality, at 22 dpff, 12 ± 1 out of 17 larvae survived and 7.3 ± 1.5 had filled guts. At 28 dpff, 14 ± 3 out of 17 larvae survived and all of them had filled guts. The development seems to correlate with the development of larval type digestion. Based on feed intake, successful weaning can be achieved at 28 dpff, however, further studies are needed to determine growth, survival and juvenile quality of Atlantic halibut larvae that have been weaned early on formulated diets. Highlights • The purpose of this study is to find a time-point for early weaning of Atlantic halibut larvae. • Feed intake was tested with three diets at 28 days post first-feeding (dpff). • The diet with the best feed intake was chosen for feed intake studies at 15, 22 and 28 dpff. • Mortality and gut filling rates indicated that Atlantic halibut larvae can be fed a formulated diet from 28 dpff. [ABSTRACT FROM AUTHOR]

Abstract In nonmammalian vertebrates, photoreception takes place in the deep brain already early in development, but knowledge is lacking about the functions of these nonvisual photoreceptive systems. Prior to hatching, Atlantic halibut has a transient bilateral cluster of photoreceptive cells in the hindbrain. The cluster is imbedded in a neuronal network projecting to the narrow belt of hatching glands in the yolk sac. In halibut, hatching is inhibited in light and activated by transfer to darkness and c -fos analysis during hatching shows that the hindbrain cluster and hatching glands have neural activation. Unexpectedly, the hindbrain cluster expresses dual photopigments, vertebrate ancient opsin and melanopsin. Evolutionarily, these opsins are believed to belong to different classes of photopigments found in rhabdomeric and ciliary photoreceptors. The concept that an organism develops transient light sensitivity to target critical aspects of life history transitions as hatching provides a fascinating landscape to investigate the timing of other biological events. Highlights • Halibut has a transient bilateral cluster of photoreceptive cells in the hindbrain. • The photoreceptor cells show dual expression of melanopsin and VA opsin. • The cluster is imbedded in a neuronal network projecting to the hatching glands. • Removal of light activates the hindbrain cluster and glands, - inducing hatching. [ABSTRACT FROM AUTHOR]

To establish if the developmental changes in the primary barrier and osmoregulatory capacity of Atlantic halibut skin are modified during metamorphosis, histological, histochemical, gene expression and electrophysiological measurements were made. The morphology of the ocular and abocular skin started to diverge during the metamorphic climax and ocular skin appeared thicker and more stratified. Neutral mucins were the main glycoproteins produced by the goblet cells in skin during metamorphosis. Moreover, the number of goblet cells producing neutral mucins increased during metamorphosis and asymmetry in their abundance was observed between ocular and abocular skin. The increase in goblet cell number and their asymmetric abundance in skin was concomitant with the period that thyroid hormones (THs) increase and suggests that they may be under the control of these hormones. Several mucin transcripts were identified in metamorphosing halibut transcriptomes and Muc18 and Muc5AC were characteristic of the body skin. Na+, K+-ATPase positive (NKA) cells were observed in skin of all metamorphic stages but their number significantly decreased with the onset of metamorphosis. No asymmetry was observed between ocular and abocular skin in NKA cells. The morphological changes observed were linked to modified skin barrier function as revealed by modifications in its electrophysiological properties. However, the maturation of the skin functional characteristics preceded structural maturation and occurred at stage 8 prior to the metamorphic climax. Treatment of Atlantic halibut with the THs disrupter methimazole (MMI) affected the number of goblet cells producing neutral mucins and the NKA cells. The present study reveals that the asymmetric development of the skin in Atlantic halibut is TH sensitive and is associated with metamorphosis and that this barrier’s functional properties mature earlier and are independent of metamorphosis. [ABSTRACT FROM AUTHOR]

Atlantic halibut (Hippoglossus hippoglossus) is an increasingly valued commercial fish and its recent population growth has attracted the attention of fisheries scientists and managers both within and outside Canada. With renewed transnational interests in this species, fishery managers have relied on existing, but limited, ecological information for multilateral discussions on shared allocations of catch. To address this dearth of information, we modeled species distribution using maximum entropy, where by survey catch data were related to environmental data to quantify habitat suitability. We then calculated the amount of suitable habitat for juvenile Atlantic halibut per Northwest Atlantic Fisheries Organization (NAFO) divisions, within and outside Canada's Exclusive Economic Zone. Among NAFO divisions, we found a strong relationship between the availability of suitable habitat for juvenile Atlantic halibut, and both current and historical fisheries landings. Results are consistent with the nursery-size hypothesis which states that the amount of available juvenile habitat is related to the level of adult production. The majority of occupied suitable habitat is found on the southwestern half of Canada's Scotian Shelf, whereas the U.S. and international waters off Newfoundland have ample suitable habitat to support larger populations. Quantifying habitat suitability and linking this suitability to stock abundance and distribution is an important step toward an ecosystem approach for the management of Atlantic halibut. [ABSTRACT FROM AUTHOR]

Summary:   Several studies on heritability in twins aim at understanding the different contribution of environmental and genetic factors to specific traits. Considering the national merit twin study, our purpose is to analyse correctly the influence of socio‐economic status on the relationship between twins’ cognitive abilities. Our methodology is based on conditional copulas, which enable us to model the effect of a covariate driving the strength of dependence between the main variables. We propose a flexible Bayesian non‐parametric approach for the estimation of conditional copulas, which can model any conditional copula density. Our methodology extends the work of Wu, Wang and Walker in 2015 by introducing dependence from a covariate in an infinite mixture model. Our results suggest that environmental factors are more influential in families with lower socio‐economic position. [ABSTRACT FROM AUTHOR]

Atlantic halibut go through a period with reduced or no feed intake during their spawning period. This study with male Atlantic halibut aimed to assess the effect of a two-month starvation period corresponding to the naturally occurring spawning induced starvation. The actual loss of nutrients compared to initial body burden, was estimated to 25% for gross energy, 32% for total lipid, 14% for crude protein, and 40% and 44% respectively, for the essential fatty acids EPA (C20:5 n-3) and DHA (C22:6 n-3). This indicates that lipid is the preferred energy source during starvation related to spawning, and the n-3 fatty acids are used to a larger extent than other fatty acids, although mono-unsaturated fatty acids (MUFAs) comprised the largest energy reserve. The difference in relative amount of energy and nutrients used should be considered when formulating diets for re-feeding broodstock of annual spawners like the Atlantic halibut. • Male Atlantic halibut used lipids as the primary energy source during starvation. • Two months starvation reduced the total body protein and lipid by 14 and 32%. • >90% of the total body lipid was found in the dressed-out carcass. • Essential omega-3 fatty acids (EPA and DHA) were not conserved during starvation. [ABSTRACT FROM AUTHOR]

Juvenile Atlantic halibut (~100 mg, Hippoglossus hippoglossus) were exposed to Vibrio proteolyticus, a Vibrio spp. isolate, Photobacterium damselae ssp. damselae and five different isolates of Aeromonas salmonicida ssp. achromogenes via an hour-long bath immersion to ascertain their variation in pathogenicity to this fish species. Results were analysed using Kaplan-Meier survival analysis. Analysis of the data from challenges using A. salmonicida ssp. achromogenes revealed three survival values of zero and a spread of values from 0 to 28.43. Challenges using a Vibrio spp isolate, V. proteolyticus and P. damselae resulted in Kaplan-Meier survival estimates of 31.21, 50.41 and 57.21, respectively. As all bacterial species tested could induce juvenile halibut mortalities, they must all be considered as potential pathogens. However, the degree of pathogenicity of A. salmonicida is isolate dependent. [ABSTRACT FROM AUTHOR]

In the early 1990s, the Northwest Atlantic Ocean underwent a fisheries-driven ecosystem shift. Today, the iconic cod ( Gadus morhua) remains at low levels, while Atlantic halibut ( Hippoglossus hippoglossus) has been increasing since the mid-2000s, concomitant with increasing interest from the fishing industry. Currently, our knowledge about halibut ecology is limited, and the lack of recovery in other collapsed groundfish populations has highlighted the danger of overfishing local concentrations. Here, we apply a Bayesian hierarchical spatiotemporal approach to model the spatial structure of juvenile Atlantic halibut over 36 years and three fisheries management regimes using three model parameters to characterize the resulting spatiotemporal abundance structure: persistence (similarity of spatial structure over time), connectivity (coherence of temporal pattern over space), and spatial variance (variation across the seascape). Two areas of high juvenile abundance persisted through three decades whereas two in the northeast are now diminished, despite the increased abundance and landings throughout the management units. The persistent areas overlap with full and seasonal area closures, which may act as refuges from fishing. Connectivity was estimated to be 250 km, an order of magnitude less than the distance assumed by the definition of the Canadian management units (~2,000 km). The underlying question of whether there are distinct populations within the southern stock unit cannot be answered with this model, but the smaller ~250 km scale of coherent temporal patterns suggests more complex population structure than previously thought, which should be taken into consideration by fishery management. [ABSTRACT FROM AUTHOR]

Background: The effects of temporal data resolution on the interpretation of fish behaviours are questions fundamental to research programs using electronic tags with finite data storage and data transmission capacities. However, understanding these effects requires sub-sampling high-resolution data at multiple temporal resolutions. In pop-up satellite archival tags (PSATs), data transmissions via satellite are limited, so temporal resolution is a decreasing function of the deployment duration. Physical recovery of PSATs overcomes this limitation, providing data on temperature, depth, etc., at rates at least 15-30 times greater than transmitted data. Results: Using PSATs physically recovered from Atlantic halibut (Hippoglossus hippoglossus), we evaluated the effects of data resolution (2, 30, 60 min) on interpreting vertical movements including rapid ascents during the expected spawning season. Putative 'spawning rises' of 6-20 min were only present within highest temporal resolution data. Vertical movement rates during spawning rises identified with high-resolution data exceeded rates in all other periods; such movement rates were virtually absent in all other tagged fish within the spawning period. Mean maximum ascent rates were 13 and 23 times higher when the sampling interval was 2 versus 30 or 60 min, respectively. Conclusions: We illustrate the limitations of using satellite-transmitted data to quantify vertical movement rates and detect potential spawning events in marine teleosts. Such low temporal resolution data suggest spurious results by masking important behaviours that archived data reveal as occurring at high frequencies. We highlight new technologies that facilitate PSAT recoveries at sea to overcome these limitations and facilitate analyses of high-frequency archived data. [ABSTRACT FROM AUTHOR]

Deiodinase 3 (Dio3) plays an essential role during early development in vertebrates by controlling tissue thyroid hormone (TH) availability. The Atlantic halibut ( Hippoglossus hippoglossus ) possesses duplicate dio3 genes ( dio3a and dio3b ). Expression analysis indicates that dio3b levels change in abocular skin during metamorphosis and this suggests that this enzyme is associated with the divergent development of larval skin to the juvenile phenotype. In larvae exposed to MMI, a chemical that inhibits TH production, expression of dio3b in ocular skin is significantly up-regulated suggesting that THs normally modulate this genes expression during this developmental event. The molecular basis for divergent dio3a and dio3b expression and responsiveness to MMI treatment is explained by the multiple conserved TREs in the proximal promoter region of teleost dio3b and their absence from the promoter of dio3a. We propose that the divergent expression of dio3 in ocular and abocular skin during halibut metamorphosis contributes to the asymmetric pigment development in response to THs. [ABSTRACT FROM AUTHOR]

Catch-and-release (C&R) of Atlantic halibut ( Hippoglossus hippoglossus ) has been heavily debated as a management strategy to reduce fishing mortality of this species while maintaining angling opportunities in Norwegian recreational fisheries. However, little information exists on what proportion of the fish survive post release. To test if C&R affects short- and long-term survival of Atlantic halibut, halibut (>120 cm; N = 11) were caught on angling gear using commonly used fishing lures, and tagged with both pop-up satellite archival tags (PSATs) and acoustic transmitters. Survival was determined by the vertical migration patterns of individuals measured by the tags during individual monitoring periods ranging from 3 to 248 days (median 80 days) after the C&R event. No short-term mortality was observed post release. In terms of long-term survival, eight halibut were confirmed to have survived the monitoring periods while one halibut had insufficient data. For the other two individuals, the acoustic transmitters showed a cessation of vertical movement after 38 and 44 days, which could neither be verified nor disproven by the PSAT recordings (due to earlier detachment and tag malfunction of the PSATs). Since premature tag shedding was frequent in this study, it cannot be concluded if the cessation of vertical movement was because of tag shedding or delayed mortality. The results of this study indicate that Atlantic halibut is resilient to C&R angling, and that C&R of Atlantic halibut may be an effective management strategy to reduce fishing-induced mortality. However, the effects of severe hooking injuries, impacts on smaller individuals, and potential sublethal consequences of C&R were not covered in this study, and are still poorly understood. To minimize negative impacts of C&R and to promote fish welfare, fisheries managers are encouraged to implement best practice C&R angling guidelines for Atlantic halibut. [ABSTRACT FROM AUTHOR]

Ocean acidification and rising seawater temperature are environmental stressors resulting from the continuous increase of the atmospheric CO 2 concentration due to anthropogenic activities. As a consequence, marine fish are expected to undergo conditions outside of their tolerance range, leading to physiological challenges with possible detrimental implications. Our research group has previously shown that exposure to elevated CO 2 modulated the immune system of the Atlantic halibut. To further investigate this finding, we analysed non-specific immune components in blood plasma of Atlantic halibut ( Hippoglossus hippoglossus ) juveniles acclimated to six different temperatures (5, 10, 12, 14, 16 and 18 °C), and to water pH of 8.0 (control) or 7.6 (predicted for year 2100) for three months. Plasma ions (K + , Na + , Ca ++ , Cl − ) and lactate concentrations were also measured. The analysis of plasma ions did not show any trends related to temperature or CO 2 exposure, and the majority of the experimental fish were able to maintain ionic balance. The results show that both innate immune components (lysozyme and alternative complement system) had increased activities in response to elevated CO 2 , representing a CO 2 -related impact on the halibut's immune system. The increased activity of lysozyme and complement system is possibly part of the acclimatization process, and might be protective. [ABSTRACT FROM AUTHOR]

The ontogenic development of neurosensory structures in larval Atlantic halibut, Hippoglossus hippoglossus (L.) was examined using microscopy imaging techniques and analysis. Larval samples were preserved at developmental stages of 444, 486, 528, 570, 612, and 666 degree-days, respectively. Larvae were measured and photographed macroscopically. The fish were then embedded in paraffin for histological processing. 5 μm sequential sections of the anterior of the larvae were cut and stained using hematoxylin and eosin dyes. The resulting sections were examined using an Olympus BX60 compound microscope. The development of neurosensory structures such as neuromasts and sensory papillae were observed throughout all developmental stages of larvae and early development of the lateral line was observed at 666 degree-days. Neuromast frequency increased as larvae matured, suggesting that larvae were approaching their first feeding event towards the end of the sampling period. Possible implications of development on larval first feeding are discussed. [ABSTRACT FROM AUTHOR]

With growing world trends in the consumption of raw and undercooked aquatic products, anisakiasis, resulting from infection by anisakid nematodes, currently affects over 2000 people per annum worldwide. In response to new EC regulatory requirements regarding the processing of farmed fish to reduce the risk of nematode infections, the aim of this study was to provide evidence of the prevalence and intensity of anisakids in relevant Scottish mariculture species and to identify potential probability of nematode infection by analysing the current farming practices for these species. A sample of 225 marine rainbow trout, Oncorhynchus mykiss , and 150 Atlantic halibut, Hippoglossus hippoglossus , was obtained from three and two farms, respectively, on the West Coast of Scotland. A further 12 Atlantic halibut were obtained from wild fisheries. Fish flesh examined for nematode larvae using standard techniques provided no evidence for the presence of anisakid nematodes in any of the farmed fish sampled. In addition, no food items other than pelleted feed were found in the stomach and intestines of any farmed fish. Sampled wild halibut showed a prevalence of 75% and intensity of 12.75 ± 25.81 of Anisakis simplex although no Pseudoterranova decipiens were found. An analysis of current farm practices for the culture of halibut, rainbow trout and sea trout, Salmo trutta , in Scotland suggests that the probability of infection with anisakids is extremely low. To acquire an infection, a fish must consume infected prey, and as commercial aquaculture in Scotland relies on processed, pelleted feed, the probability of wild infected prey being consumed is very low, particularly since fish are generally fed to satiation. Given the results of this study and evidence from previous studies, it must be concluded that under current farming practices, the risk of contracting anisakiasis from Scottish farmed halibut and rainbow trout is extremely low to negligible. Consequently, they do not pose a significant risk to consumers in terms of the ingestion of these parasites. [ABSTRACT FROM AUTHOR]

We investigated conflicting perspectives over a transboundary species (Atlantic Halibut-Hippoglossus hippoglossus L.) assumed to be one population spanning the border separating the USA and Canada. In Canada, the fishery is certified as sustainable by the international Marine Stewardship Council (2013). In the USA, that same population is listed as a "Species of Concern" under the US Endangered Species Act (1973). There are fishery-independent trawl surveys conducted by both USA and Canada on juvenile halibut abundance across the border. The data are sorted and both nations use their own jurisdictional boundaries to define the geographical area of their separate stock assessments. Here, we undertake a spatially unified, in-depth comparison of juvenile halibut distribution and abundance, and quantify the amount of suitable habitat for halibut across both sides of the border from 1965 to 2014. Juvenile halibut abundance was, on average, five times greater in Canada than in USA waters. The median per cent of occupied sets in Canada was about four times greater than in the US (2.5%). These differences could not be explained by the availability of "suitable" habitat. The lack of halibut in US waters, in contrast to Canada, suggests a finer-scale stock structure exists and that halibut have not re-established in the USA due to historical serial overfishing. A gradient from high occupancy of halibut in Canada to lower occupancy in the USA is evident, suggestive of connectivity between the two areas and supported by a lag correlation analysis of temporal abundance trends. The USA may now be a sink to Canada's source of halibut. While both countries have been correct in their individual assessments, a bilateral assessment of halibut would benefit both nations, and could include analyses of how fishing patterns in Canada will influence the magnitude and speed of halibut re-colonization in the USA. [ABSTRACT FROM AUTHOR]

Halibut ( Hippoglossus hippoglossus ) and shrimps ( Pandalus borealis ) are regular foodstuffs for communities in northern Norway and important species for the coastal fishing industry. This is the first study to present a comprehensive overview of the contaminant status of these species, with emphasis on unregulated perfluoroalkylated substances (PFAS). The contaminant concentrations were low and within tolerable levels for human dietary exposure. Median Σpolychlorinated biphenyls (PCB) were 4.9 and 2.5 ng/g ww for halibut and unpeeled shrimps, respectively. Concentrations of perfluorooctane sulfonate (PFOS) – the most abundant PFASs – were 0.9 and 2.7 ng/g ww in halibut and shrimp, respectively. The halibut fillets were dominated by PCBs, which contributed to 50% of the total POPs load, followed by ΣDDTs; 26% and PFASs (18%), whereas shrimps were dominated by PFASs (74%). ΣPBDEs (polybrominated diphenyl ethers) contributed to 1–4% of the total POP load. Local sources are not contributing significantly to the contaminant burden in these species. [ABSTRACT FROM AUTHOR]

Understanding the distribution and reproductive behavior of marine species can inform ocean spatial management to address conservation needs and reduce risks of conflicts among various marine and coastal industries. Combining spatial data on species behavior with fish harvesters' knowledge can be particularly effective for identifying spatiotemporal overlaps between human activities and critical events at various life stages of marine species. In the present study, the migratory behavior of Atlantic halibut (Hippoglossus hippoglossus), a flatfish of great economic importance in the Gulf of St. Lawrence, was characterized using electronic tags, and potential ocean industry impacts to the halibut population were identified using fish harvesters' knowledge reported at public meetings and during semi-structured interviews. Results from electronic tagging analyses, including potential seasonal migration paths and presumed spawning locations, were presented to halibut harvesters who responded by identifying industries that could impact the halibut population. Harvesters identified the potential for halibut bycatch in the developing redfish trawl fishery as the main risk to the current high halibut abundance levels, which they attributed to the reduction of Gulf trawling and halibut bycatch since the 1990s. Other potential impacts to halibut identified by harvesters included offshore oil and gas drilling, and effluent discharge from a paper mill transformation project. The present study demonstrates that utilizing complementary data from both fish tracking devices and fish harvesters' knowledge can help identify and anticipate potential conflicts between fisheries and other ocean industries, and ultimately inform the ecosystem-based marine spatial management of large marine ecosystems. • Fish tracking devices combined with fish harvesters' knowledge revealed spatial overlaps of fisheries and other ocean uses. • Atlantic halibut presumed spawning habitats overlap with potential trawling areas of a re-emerging redfish fishery. • Halibut may also be impacted by oil drilling and paper pulp effluent in locations that overlap with halibut migrations. • Using complementary data sources can identify ocean use conflicts and inform ecosystem-based marine spatial management. [ABSTRACT FROM AUTHOR]

Atlantic halibut (Hippoglossus hippoglossus) have a long history of exploitation in the Northwest Atlantic and have gone through several periods of high biomass followed by a population crash. An assessment model using data collected on the Scotian Shelf and southern Grand Banks shows that the population peaked in 1984, then decreased sharply to a low in 1993. Several management measures were taken during the decline, including reductions in total allowable catch and a minimum size limit. Concurrently, removals by the otter trawl fishery were drastically reduced following the collapse of the cod (Gadus morhua) fishery. In 2003, recruitment increased and continued to be high for 6 years. Fishing mortality rates were moderate in the late 1990s and 2000s and the population increased. By 2009, the Atlantic halibut population was highly productive with both high biomass and high levels of recruitment. The coincidence in the timing of population recovery and management actions indicates that effective management contributed to the recovery of Atlantic halibut. [ABSTRACT FROM AUTHOR]

In the Northwest Atlantic, emerging evidence suggests that different stocks of Atlantic halibut (Hippoglossus hippoglossus) exist in Canadian and U.S. waters. To examine the movement of Atlantic halibut that occupy the Gulf of Maine in U.S. waters during the summer, two types of electronic tags were attached to large adult fish (n = 70) in 2007-2009. None of the recovered tags (n = 12) provided evidence that the fish occupied the relatively deep waters of the continental slope during the winter, where Canadian Atlantic halibut have been shown to spawn. This observation provides additional evidence for the hypothesis that different stocks of Atlantic halibut exist in Canadian and U.S. waters. Furthermore, this observation requires reexamination of the long-standing assumptions made by fisheries scientists that all Atlantic halibut spawn in deep water on the continental slope and that the majority of mature Atlantic halibut spawn annually. This information may be important for understanding the population dynamics of Atlantic halibut in U.S. waters. [ABSTRACT FROM AUTHOR]

Historically, to compensate for declining catches, fishers have usually shifted from species characterized by high catch rate onto less easily caught species or have moved into new fishing grounds. Such shifts are poorly documented for areas with a long history of exploitation (i.e. North Sea) as they occurred long time before the start of the regular assessments of the marine resources. The Swedish longline fisheries in the Kattegat-Skagerrak and North Sea have a long history that spans over several centuries. These fisheries have historically targeted large demersal predator fish as ling ( Molva molva), cod ( Gadus morhua), Atlantic halibut ( Hippoglossus hippoglossus) and skates (mainly Dipturus spp.). In this study, data from the Swedish longline fisheries from 1859 to 1960 have been collated. The data show that the geographical expansion of the fishery was extensive. At the turn of the 20th century, offshore longlining became concentrated north and west of the Shetlands and Hebrides, and after the WWII, the fishery expanded to Iceland and Rockall. In the offshore fishery, CPUE for the main target species, ling, remained stable, whereas for the other species, with the exception of tusk ( Brosme brosme), CPUE showed a dramatic decline over time. In contrast, in the coastal longlining fishery, severe declines were revealed for all major target species except cod. We argue that the constant search for new fishing grounds in the Northeast Atlantic reflects a dwindling resource, where the fishermen kept the catch rates of ling high by travelling to more and more distant fishing grounds. [ABSTRACT FROM AUTHOR]

A previously undescribed species of Entobdella is reported from the skin of the Greenland halibut, Reinhardtius hippoglossoides (Pleuronectiformes, Pleuronectidae). Entobdella whittingtoni sp. nov. differs from other species of Entobdella, including skin parasites of the related pleuronectids Hippoglossus hippoglossus (Atlantic halibut) and H. stenolepis (Pacific halibut), in lacking papillae on the ventral surface of the haptor. Other characteristics of E. whittingtoni are as follows: the absence of vitelline follicles lateral to the pharynx thereby exposing gut caeca in this region of whole mounts; the presence of a circular feature of unknown function, resembling a rosette in sections, attached to the wall of the internal male accessory reservoir; the lack of eyes. Papillae are also absent from the ventral surface of the haptor of the gill-parasitic entobdelline Branchobdella pugetensis, a gill parasite of the pleuronectid Atheresthes stomias. This raises the question as to whether this gill parasite has evolved from a skin-parasitic ancestor similar to E. whittingtoni. An answer to this question requires a more detailed study of the male reproductive apparatus of B. pugetensis and the use of molecular techniques to explore the relationship between B. pugetensis and E. whittingtoni [ABSTRACT FROM AUTHOR]

Hormones and neuropeptides play a crucial role in the appetite control system of vertebrates, yet few studies have focused on their importance during early teleost development. In this study, we analysed the expression patterns of the appetite-controlling factors ghrelin, neuropeptide Y (NPY), peptide YY (PYY), pro-opiomelanocortin (POMC-C), and cocaine-amphetamine-related transcript (CART) by quantitative PCR. Transcript expression was investigated in response to feeding in developing Atlantic halibut larvae: before (premetamorphic stage 5) and during metamorphosis (stages 8 and 9B), and also in response to a fast–refeed challenge. We show that ghrelin transcript expression increased in synchrony with stomach development, while CART was significantly reduced during larval development. PYY was up-regulated 1 and 3 h after feeding in stage 5. Transcript abundance of other appetite-controlling factors did not change in response to feeding. Fasting–refeeding trials (majority of larvae in metamorphosing stage 7) revealed a down-regulation of POMC-C 30 min after refeeding, while ghrelin, PYY and NPY transcript expression increased 2, 4 and 5 h after refeeding, respectively. In summary, transcripts for key appetite-controlling factors were detected early during development in Atlantic halibut and their emergence was not correlated with metamorphosis, with the exception of ghrelin. Our results suggest that PYY may mediate satiety early in larval development. The differing response times of POMC-C, ghrelin, PYY and NPY to a meal are intriguing and require further exploration to understand the role of each player in appetite control. [ABSTRACT FROM AUTHOR]

Variation in oocyte quality affects sustainability of finfish aquaculture products including Atlantic halibut ( Hippoglossus hippoglossus L.). To have an insight into role of major egg yolk constituents in the oocyte quality, egg fatty acid ( FA), amino acid ( AA) and folate contents were related to normal blastomere symmetry, and fertilization and hatching success. Significant correlations were found between dihomo-γ-linolenic acid ( DGLA, 20:3n6), palmitic acid ( PA, 16:00) and docosapentaenoic acid ( DPA, 22:5n3), and normal blastomere symmetry and survival success. Egg concentrations of myristic acid ( MA, 14:0), oleic acid ( OA, 18:1n9), stearidonic acid ( SA, 18:4n3) and eicosadienoic acid ( EDA, 20:2n6) explained 56 % variation in fertilization success. OA and EDA explained 70 % of variation in blastomere symmetry. Palmitoleic acid ( POA, 16:1n7) and linolenic acid ( LNA, 18:3n3) concentrations explained 57% of variation in hatching success. Egg valine concentrations correlated with fertilization rates, and aspartic acid and leucine correlated with normal blastomere symmetry. Alanine and valine concentrations explained together 45% of variation in fertilization. Glutamic acid and tyrosine concentrations explained 68% of variation in normal blastomere symmetry while serine, arginine and valine explained 36% of variation in hatching. These FAs and AAa may be potential indicators of oocyte quality in Atlantic halibut. [ABSTRACT FROM AUTHOR]

A new aquareovirus was isolated from cultured Atlantic halibut ( Hippoglossus hippoglossus) fry at a facility where massive mortalities had occurred during the start-feeding phase. The same virus was also detected in juveniles (about 10 grams) of the 2013 generation at two other production sites, but not in larger fish from generations 2007-2012. The virus replicated in BF-2 and CHSE-214 cell cultures and produced syncytia and plaque-like cytopathic effects. This Atlantic halibut reovirus (AHRV) was associated with necrosis of the liver and pancreas, syncytium formation in these tissues, and distinct viroplasm areas within the syncytium in halibut fry. Transmission electron microscopy revealed that the viroplasm contained virions, non-enveloped, icosahedral particles approximately 70 nm in diameter with a double capsid layer, amorphous material, and tubular structures. The RNA-dependent RNA polymerase (RdRp) gene from the AHRV isolates showed the highest amino acid sequence identity (80 %) to an isolate belonging to the species Aquareovirus A, Atlantic salmon reovirus TS (ASRV-TS). A partial sequence from the putative fusion-associated small transmembrane (FAST) protein of AHRV was obtained, and this sequence showed the highest amino acid sequence identity (46.8 %) to Green River Chinook virus which is an unassigned member of the genus Aquareovirus, while a comparison with isolates belonging to the species Aquareovirus A showed <33 % identity. A proper assessment of the relationship of AHRV to all members of the genus Aquareovirus, however, is hampered by the absence of genetic data from members of several Aquareovirus species. AHRV is the first aquareovirus isolated from a marine coldwater fish species and the second reovirus detected in farmed fish in Norway. A similar disease of halibut fry, as described in this paper, has also been described in halibut production facilities in Canada and Scotland. [ABSTRACT FROM AUTHOR]