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The offshore Greenland halibut (Reinhardtius hippoglossoides) fishery, west Greenland, employs demersal trawl gear at depths of 800–1400 m. In contrast to many deep-sea fisheries, the target stock appears stable and the fishery is of significant economic importance. Recent Marine Stewardship Council certification of this fishery highlighted the paucity of knowledge of benthic habitats and trawling impacts, which this study aimed to address using a towed benthic video sled. The spatially discrete northern and southern areas of the fishery were found to be distinct in terms of the communities present, which non-metric multidimensional scaling suggests is primarily driven by temperature. Extensive physical evidence of trawling was observed. Trawling effort was significantly linked with community composition, with a negative association between trawling effort and abundance of some taxa, including some vulnerable marine ecosystem (VME) indicator species. Three potential VMEs are identified: (i) Flabellum alabastrum cup coral meadows; (ii) a Halipteris finmarchica sea pen field; and (iii) areas exhibiting mixed assemblages of VME indicators. Of immediate conservation concern is a H. finmarchica field, which seems to be at least regionally rare, is situated within the fringes of existing trawling effort and is currently afforded no protection by management measures.

The Indian halibut (Psettodes erumei) is an important flatfish species in tropical and subtropical waters of the northern Indian Ocean. However, inappropriate aging methods used in previous studies of Indian halibut limited the use of age and growth data from those studies. This study highlights the importance of correct aging methods and identification of sexually dimorphic growth, particularly if growth characteristics are used to estimate mortality rates. Counts of opaque zones in whole otoliths of Indian halibut were almost always fewer than those in their corresponding sections, particularly for older individuals. Multiple validation methods demonstrate opaque zones form annually in otoliths of Indian halibut. Although the frequency of females increased with size, due to sexually dimorphic growth, males attained a greater maximum age (16 versus 11 years). Because of the greater ages and rapid early growth of Indian halibut described in this study, natural mortality estimates calculated by using Pauly’s equation, particularly for males, were higher than estimates derived from the same equation in previous studies, which employed growth parameter estimates based on ages derived from whole otoliths, vertebrae, or monthly length–frequency trends and, typically, did not account for sexually dimorphic growth. In northwestern Australia, spawning in Indian halibut commences when water temperature and day length begin to increase and occurs between early spring and late summer.

Characterizing the nature of genetic differentiation among individuals and populations and its distribution across the genome is increasingly important to inform both conservation and management of exploited species. Atlantic Halibut (Hippoglossus hippoglossus) is an ecologically and commercially important fish species, yet knowledge of population structure and genomic diversity in this species remains lacking. Here, we use restriction-site associated DNA sequencing and a chromosome-level genome assembly to identify over 86 000 single nucleotide polymorphisms mapped to 24 chromosome-sized scaffolds, genotyped in 734 individuals across the Northwest Atlantic. We describe subtle but significant genome-wide regional structuring between the Gulf of St. Lawrence and adjacent Atlantic continental shelf. However, the majority of genetic divergence is associated with a large putative chromosomal rearrangement (5.74 megabases) displaying high differentiation and linkage disequilibrium, but no evidence of geographic variation. Demographic reconstructions suggest periods of expansion coinciding with glacial retreat, and more recent declines in Ne. This work highlights the utility of genomic data to identify multiple sources of genetic structure and genomic diversity in commercially exploited marine species.

Pacific halibut (Hippoglossus stenolepis) supports one of the most valuable groundfish fisheries in the North Pacific Ocean and the north American component has been managed by the International Pacific Halibut Commission since 1923. From its establishment, IPHC’s work has been focused on data collection and research programs to better understand stock dynamics, extent, and behavior across its range. In this review we summarize the 100 years of migration research available for Pacific halibut, with a focus on tagging experiments. A visual representation of all tags deployed and recovered is included, and all of the information available from different research (e.g. genetic analyses, oceanographic models, catch trends, IBM) has been unified into a conceptual model of Pacific halibut movement from southern California through the Bering Sea. From spawning grounds in the Gulf of Alaska, eggs and larvae are transported westward, some crossing Aleutian Island passes into the Bering Sea. Once settled, there is compensatory migration as some juveniles move back into the Gulf of Alaska. In the Gulf of Alaska, juveniles and adults exhibit net migration eastward and southward along the continental shelf of the US and Canadian coasts. Adults undertake seasonal migrations from feeding grounds to spawning grounds. While little information is available for the western side of the Pacific halibut range, research suggests a constant exchange across the Bering Sea between the eastern and western grounds. The hypothesis of multiple migratory behaviors is suggested. This review will serve as a guide for current modeling efforts and future research planning.

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 e...

A detailed account of a variety of species foraging on Greenland halibut (Reinhardtius hippoglossoides (Walbaum, 1792)) fisheries discards associated with a commercial fishing vessel in central Baffin Bay, Nunavut, Canada is presented. Species observed included three marine mammals: northern bottlenose whales (Hyperoodon ampullatus (Forster, 1770)), sperm whales (Physeter macrocephalus Linnaeus, 1758), and a hooded seal (Cystophora cristata (Erxleben, 1777)), and two marine bird species: northern fulmars (Fulmarus glacialis (Linnaeus, 1761)) and glaucous gulls (Larus hyperboreus Gunnerus, 1767). Interspecies and intraspecies interactions were observed while species were in close proximity to the stern and starboard of a commercial fishing vessel confirming anecdotal reports from boat captains. Improved understanding of marine mammal and bird interactions with fisheries in the Arctic is required to accurately assess financial and ecological (i.e., bycatch) losses, potential for entanglement and to predict the likely impact on energy flow and transport of these resource subsidies throughout the Arctic marine ecosystem.

Deep-sea marine fishes support important fisheries but estimates of their distributions are often incomplete as the data behind them may reflect fishing practices, access rights, or political boundaries, rather than actual geographic distributions. We use a simple suitable habitat model based on bottom depth, temperature, and salinity to estimate the potential distribution of Greenland halibut (Reinhardtius hippoglossoides). A large presence-only dataset is examined using multivariate kernel densities to define environmental envelopes, which we link to spatial distribution using a pan-Arctic oceanographic model. Occurrences generally fit the model well, although there were gaps in the predicted circum-Arctic distribution likely due to limited survey activity in many of the ice-covered seas around the Arctic Ocean. Bottom temperature and depth were major factors defining model fit to observations, but other factors, such as ecosystem interactions and larval drift could also influence distribution. Model predictions can be tested by increasing sampling effort in poorly explored regions and by studying the connectivity of putative populations. While abundances of Greenland halibut in the High Arctic are currently low, some areas are predicted to be suitable habitat for this species, suggesting that on-going sea-ice melt may lead to fisheries expansion into new areas.

Stocks of demersal and pelagic fish species are assessed for the bottom layer over the outer shelf and upper continental slope between Cape Olyutorsky and Cape Navarin (northwestern Bering Sea) on the data of bottom trawl survey conducted aboard RV Professor Levanidov over the isobaths 20-400 m in the summer of 2019. The total biomass of demersal fish in the surveyed polygon was estimated as 682,262 t; the portion of pacific cod was 51.50 %, arrowtooth flounder — 9.80 %, great sculpin — 9.64 %, rock sole — 4.60 %, alaska skate — 4.57 %, flathead flounders — 2.56 %, yellow irish lord — 2.30 %, and < 2 % for other species. The total biomass of pelagic fish species in the bottom layer was estimated as 759,639 t (species-specific coefficients of catchability were used); the portion of adult walleye pollock was 85.12 %, its juveniles — 9.94 %, pacific herring — 4.67 %, and other pelagic species — 0.27 % in sum. Mean ratios of the species stock between the surveyed polygon and other areas of the northwestern Bering Sea, as the Gulf of Anadyr and the deeper continental slope (below 400 m), were evaluated using the data of bottom trawl surveys conducted in 2005-2017. Some species as yellow irish lord, saffron cod, pacific halibut, arrowtooth flounder, great sculpin, kamchatka flounder, rock sole, and aleutian skate distributed mostly within the polygon and their mean biomass in the outside areas varied from 0.5 % to 69.2 % relative to the biomass in the polygon surveyed in 2019. On the contrary, the portions of pacific cod, greenland halibut, alaska skate, and walleye pollock were larger outside the polygon — from 102.9 to 190.4 %, and almost entire stocks were in the outside areas for alaska plaice, flathead flounders, and pacific herring — from 533.4 % to 1380.5 % relative to the biomass accounted within the polygon. The stocks assessed in 2019 reflected both the state of populations and their spatial and bathymetric redistribution, mostly because of the St. Lawrence Cold Water Pool shrinkage at the bottom of the Gulf of Anadyr. The stocks fluctuations are reasoned mainly by natural factors, rather than fishery impact.

Stepwise multidimensional regressive analysis was carried out based on the long-term data (1971–2018), including biological statistics and series of observations on 10 climate indices, allowing to identify the most meaningful climatic factors affecting the numbers of some fish species at different stages of the ontogenesis in the Eastern part of the Sea of Okhotsk. All the results obtained indicate of existing true correlations with the number of the two-years-old individuals and the number of the fish reached the age of the mass (>50%) maturation. Threedimension regression models, describing the dynamics of the initial number of some fish satisfactorily. Were made, based on the obtained equations of multiple regression of the relationship between the number of the fish and the most effective climatic indices selected. The major indices affecting the abundance of different fish species are: SST, NPGO, SanSpot – Pacific herring; NPA – saffron cod; PDO – Pacific cod; NPA, SanSpot – great sculpin; SanSpot, PNA, AO – yellowfin sole; PDO, SSTa – Pacific halibut; Ice SanSpot, NPGO – Greenland turbot. Pelagic, demersal and bottom species are under the complex influence of the oceanographic, meteorological and planetary-space indices.

In September 2019, the R/V “Professor Levanidov” carried out comprehensive studies in the Laptev Sea from 140 ° to 110 ° E at depth range of 60–950 m. High positive anomalies of air and surface water temperatures were noted up to + 2 + 3 °C and +1.5 °C respectively with an abnormally low sea ice cover. Cold Arctic and desalinated waters of the river flow dominated in the upper 200 m layer. Atlantic waters were traced in the layer from 180–300 m to the bottom, and their core — at a maximum temperature of + 1.6 + 1.92 °C at 240–280 m. By the time of the survey, the active vegetation of phytoplankton had finished. Oxygen saturation in the almost the entire surface layer was below 100 %. Primary production was limited by mineral nitrogen concentration. Low concentrations of phosphates, nitrates and silicates in the intermediate waters indicated the penetration of Atlantic waters. The average biomass of plankton on the shelf was 239,8 mg/m3, on the slope — 374,2 mg/m3. Copepods and chaetognaths with considerable contribution of hyperiids and euphausiids dominated in plankton by weight. The bulk of zooplankton was large organisms, while small and medium fractions were 22 and 10 %. Brittle star, starfish, and shrimp dominated in trawl benthos. 25 demersal fish species of 14 families were found in bottom trawl catches. Zoarcidae, Liparidae and Gadidae were the most diverse. Polar cod was recorded along the entire route with highest concentrations in Atlantic waters at depths of 217–460 m. Copepods dominated in the diet of Polar cod juveniles, while that of adults was supplemented by large pelagic crustaceans and fish with high level of cannibalism. Greenland halibut was found along the entire continental slope at 270–750 m while the largest catches were in its central and western parts. The increase of halibut number and occurrence was due to the wide distribution of Atlantic waters on the slope. The main component of its diet was Polar cod.

Knowledge of movement ecology, habitat use, and spatiotemporal distribution is critical to inform sustainable fisheries management and conservation. Atlantic halibut in the Gulf of St. Lawrence (GSL) is of great economic value, although little is known about its spatiotemporal distribution, seasonal migrations, and spawning areas. To investigate these aspects, 114 pop-up satellite archival tags (PSATs) were deployed on halibut from 2013 up to 2018 throughout the GSL. A total of 62 physically recovered PSATs provided complete archived datasets with high temporal resolution. PSAT detachment locations revealed specific summer site fidelity. In contrast, the reconstruction of movement tracks with a geolocation model revealed that all fish converged to the Gulf’s deep channels to overwinter and spawn. This suggests strong mixing during the spawning period and thus one reproductive population within the GSL. These findings illustrate the utility of large-scale PSAT tagging combined with dedicated PSAT-recovery surveys to reveal critical stock-scale information on movements and spawning locations. This information addresses important gaps in the movement ecology of this halibut stock, revealing that reported summer site fidelity, based on years of conventional tagging, also conceals important winter mixing that is only apparent through analyses of movement on the time scale of annual cycles.

Accurate characterization of oocyte development is essential to understanding foundational aspects of reproductive biology and successful management of Pacific halibut (Hippoglossus stenolepis). Here this study provides complete histological descriptions for eight oocyte developmental stages in addition to postovulatory follicles and demonstrates the potential for oocyte size frequency distribution to act as a proxy for ovarian developmental stage and future maturity assessments. Importantly, it provides the first histological evidence that Pacific halibut have a group‐synchronous ovarian developmental pattern with determinate fecundity and support for their batch‐spawning strategy.

Compensatory growth has been reported in stunted fish by several researchers, and the same has been applied at field level for enhancing the fish production. Many of the commercially important marine finfishes such as European seabass (Adakli & Tasbozan, 2015), Gilthead sea bream (Bavcevic, Klanjscek, Karamarko, Anicic, & Legovic, 2010), Atlantic halibut (Foss et al., 2009), Atlantic cod (Jobling, Meloey, Santos, & Christiansen, 1994) and Alaska yellowfin sole (Paul, Paul, & Smith, 1995) have exhibited compensatory growth after stunting. Hyperphagia in stunted fish has been successfully applied for growth enhancement (Charan, Suresh Babu, Venugopal, Chadha, & Sreeramamurthy, 2014; Limbue & Jumanne, 2014), better feed utilization (Morshedi, Kochanian, Ahmadi-Niko, Azodi, & Pasha-Zanoosi, 2013; Ruan et al., 2015) and also to tide over unfavourable environmental conditions (Cho & Cho, 2009). Snubnose pompano, Trachinotus blochii, is a potential candidate species for mariculture as its seed production technology has been standardized, possess good market demand and it readily accepts pellet feed (Abdul Nazar et al., 2012; Jayakumar et al.., 2014; Kalidas et al., 2012). Even though the fish fetches better price in the market, the culture duration to attain marketable size needs to be reduced to improve economic benefits in the farming facilities such as ponds, cages and recirculating aquaculture systems. One proven approach to reduce the culture duration is to use stunted fingerlings as the stocking material, which is widely being practised in many farming systems (Bavcevic et al., 2010; Charan et al., 2014; Radheshyam & Saha, 2009; Santiago, Gonzal, Aralar, & Arcilla, 2004; Tian & Qin, 2003). Compensatory growth pattern varies from species to species and depends on the mode of growth deprivation. Ali, Nicieza, and Wootton, (2003) have summarized different pattern of compensatory growth in various fish. However, studies on compensatory growth pattern in stunted Snubnose pompano in marine conditions have not been reported so far. The present study was carried out to assess and delineate the compensatory growth pattern in T. blochii at varying stunting durations. Snubnose pompano fingerlings (

Monitoring distributional shifts in Arctic and subarctic fish species as environmental conditions change can be difficult due to sparse or infrequent surveys. Pacific halibut (Hippoglossus stenolepis) are found as far north as the Bering Strait, and future changes in sea temperatures and prey distribution may lead to an expanded range. For this and other species, it is therefore important to use as much survey data as is available when estimating density indices and other quantities of interest. Setline and trawl surveys in the eastern Bering Sea provide partial coverage each year, but the two gear types capture different size distributions of fish. We apply a calibration method to data from the setline and trawl surveys to produce consistent, spatially indexed estimates of indices of local density. The resulting estimates are then combined through spatiotemporal models that can incorporate environmental covariates to provide reliable density indices and to map the dynamic distribution of Pacific halibut. Such approaches may become increasingly important as climate change affects species distribution relative to historical survey footprints, and scientists must adapt to the use of new and variable data sources.

The British Columbia longline fishery for Pacific halibut (Hippoglossus stenolepis) has experienced important recent management changes, including the introduction of comprehensive electronic catch monitoring on all vessels; an integrated transferable quota system; a reduction in Pacific halibut quotas; and, beginning in 2016, sharp decreases in quota for yelloweye rockfish (Sebastes ruberrimus, an incidentally caught species). We describe this fishery before integration, after integration, and after the yelloweye rockfish quota reduction using spatial clustering methods to define discrete fishing opportunities. We calculate the relative utilization of these fishing opportunities and their overlap with areas with high encounter rates of yelloweye rockfish during each of the three periods. The spatial footprint (area fished) increased before integration, then decreased after integration. Each period showed shifts in utilization among four large fishing areas. Immediately after the reductions in yelloweye rockfish quota, fishing opportunities with high encounter rates of yelloweye rockfish had significantly lower utilization than areas with low encounter rates, implying rapid avoidance behaviour.

This study provides evidence of two subpopulations of Atlantic halibut (Hippoglossus hippoglossus) in the southern Gulf of St. Lawrence. The migrations of 20 Atlantic halibut captured in the coastal waters of Prince Edward Island, Canada, were evaluated using pop-up satellite archival tags (PSAT). Geolocation data showed that Atlantic halibut migrated north to the Laurentian Channel via distinct eastern or western routes. Floy tagging and recapture (recapture of 18.4%) showed that less than 7.0% of Atlantic halibut exhibited dispersive behaviour outside of their annual migratory route. Overwintering occurred on the slope and in the deepest waters of the Laurentian Channel. Atlantic halibut in the deepest waters of the Laurentian Channel exhibited rapid, ∼100 m rises, presumed to be associated with spawning from January to March. The eastern and western migratory cohorts exhibited this behaviour ∼350 km apart, suggesting reproductive isolation as the basis of subpopulations. The results of this study indicate a need to reconsider the management of Gulf of St. Lawrence Atlantic halibut as one continuous population.

Catch rates were compared between gillnets with and without bait in the Greenland halibut Reinhardtius hippoglossoides (Walbaum) fishery off Baffin Island, Canada. Two different types of baiting techniques were compared: bait bags where squid were placed into 2‐mm mesh bags, and tied bait where squid were tied into meshes. Both types of baited gillnets significantly increased the capture of the target species, Greenland halibut, with increases of 253.8% and 149.7% for the bait bag and tied bait, respectively. Common bycatch species showed mixed effects, with roughhead grenadier Macrourus berglax Lacepede showing no increase in catch per unit effort (CPUE) for either bait type (p > 0.05), and porcupine crab Neolithodes grimaldii (Milne‐Edwards and Bouvier) only had a higher CPUE with baited gillnets when bait bags were placed on the footrope. Less common bycatch species—but with threatened populations—showed an increase in CPUE, including Greenland shark Somniosus microcephalus (Bloch and Schneider) and Northern wolffish Anarhichas denticulatus Kroyer. Baiting gillnets affected the CPUE of gillnets in the Greenland halibut fishery, and management should consider how the increased CPUE of both target and bycatch species are affected by this new fishery trend.

The width of trophic niches of the Kamchatka flounder Atheresthes evermanni, the Pacific halibut Hippoglossus stenolepis, and the Greenland halibut Reinhardtius matsuurae have been assessed quantitatively on the Western Kamchatka shelf of the Sea of ​​Okhotsk using the data of isotopic signatures of carbon (δ13C) and nitrogen (δ15N) of their prey. According to the corrected standard ellipse area, the trophic niche widths of the Kamchatka flounder, Pacific halibut, and Greenland halibut are 11.35, 9.41, and 12.36, respectively. The range of δ15N isotopic signatures (8.80–17.61) corresponds to the trophic level 2.63–5.22. According to the limits of variation of δ13C (–14.99… –22.9), the basic carbon sources for halibuts are the prey groups belonging to plankton, nekton, and nectobenthos. The maximum value of the niche overlap belongs to the Kamchatka flounder (93.25%) in the niche of the Greenland halibut; the minimum, on the contrary, belongs to the Greenland halibut (73.19%) in the niche of the Kamchatka flounder. The high degree in similarity of system-wide niche indicators calculated from the isotopic signatures of halibut/flounder prey is balanced by the differences of other parameters in specific habitats: depth, temperature, and food spectra variability in ontogenesis.

Identification of stocks and quantification of their relative contribution to recruitment are major objectives toward improving the management and conservation of marine exploited species. Next‐generation sequencing allows for thousands of genomic markers to be analyzed, which provides the resolution needed to address these questions in marine species with weakly differentiated populations. Greenland Halibut (Reinhardtius hippoglossoides) is one of the most important exploited demersal species throughout the North Atlantic, in particular in the Gulf of St. Lawrence, Canada. There, two nurseries are known, the St. Lawrence Estuary and the northern Anticosti Island, but their contribution to the renewal of stocks remains unknown. The goals of this study were (a) to document the genetic structure and (b) to estimate the contribution of the different identified breeding stocks to nurseries. We sampled 100 juveniles per nursery and 50 adults from seven sites ranging from Saguenay Fjord to offshore Newfoundland, with some sites sampled over two consecutive years in order to evaluate the temporal stability of the contribution. Our results show that after removing sex‐linked markers, the Estuary/Gulf of St. Lawrence represents a single stock which is genetically distinct from the Atlantic around Newfoundland (F ST = 0.00146, p‐value = .001). Population assignment showed that recruitment in both nurseries is predominantly associated with the St. Lawrence stock. However, we found that the relative contribution of both stocks to the nurseries is temporally variable with 1% contribution of the Newfoundland stock one year but up to 33% for the second year, which may be caused by year‐to‐year variation in larval transport into the Gulf of St. Lawrence. This study serves as a model for the identification of stocks for fisheries resources in a context where few barriers to dispersal occur, in addition to demonstrating the importance of considering sex‐linked markers and temporal replicates in studies of population genomics.

Based on the materials collected in 2019, the authors consider some peculiarities of bottom fish fishing (halibut, stingrays, giant grenadie, cod, lycodes, and broadbanded thornyhead) in the North Okhotsk subzone of the Sea of Okhotsk. The accompanying problems are shown; the measures to optimize fishing are proposed.

Dynamics of the greenland halibut biomass in the fishery districts of the Okhotsk Sea (or subzones) is considered. The biomass variation in the East-Sakhalin subzone has a significant (p < 0.05) negative correlation with the number of 3+ fish in other subzones, with the time lag of 3 years (r = –0.53) and 4 years (r = –0.49), that is interpreted as alternative distribution of the halibut recruitment from the common spawning area either to this district or other ones. From other hand, the recruits abundance in other districts is significantly and positively associated (r = 0.52, p < 0.05) with the index of zonal atmosphere transfer in January and with the index of meridional atmosphere transfer in March of the years of hatching. The recruitment dependence on the spawning stock could be explained by Beaverton-Holt equation with the residuals significantly and positively (r = 0.64, p = 0.03) related with the Arctic Oscillation index. Transport of the eggs, larvae and juveniles of greenland halibut from the spawning grounds at western Kamchatka to the western Okhotsk Sea is considered as the mechanism of its recruitment distribution between the districts in relation with atmospheric indices. The transport was simulated for 1993–2017 using the circulation model JCOPE2 as the movement of 250,000 artificial passive particles, imitating eggs and larvae, with water flows at the depth 40–50 m where their main aggregations are supposed. The particles were released in the area at western Kamchatka where the maximal concentration of spawning females occurred. Number of the particles reached the sections off eastern Sakhalin and their arrival times were computed, their pathways were tracked. The portion of particles released in December and reached northern Sakhalin within 150 days changed in significant positive correlation (r = 0.44, p < 0.05) with dynamics of the halibut stock in the East-Sakhalin subzone, with the time lag 6 years. Even closer correlation (r = 0.94, p < 0.05) could be found for the optimum income of the particles released in October or November in the general additive model of the stock. Using the model results for the recent years, the greenland halibut stock decreasing in the East-Sakhalin subzone is forecasted for the next 6 years.

Olive flounder (Paralichthys olivaceus) also referred to as bastard halibut is a marine carnivorous species with great commercial value. The production of olive flounder has been dominated by aquac...

The North Atlantic Fisheries Organization (NAFO) has continuously lowered their advice regarding the Total Allowed Catch (TAC) for the coastal Greenland halibut fisheries in Western Greenland. This is due to concerns of overexploitation of the fishery. This paper investigates how the fishing intensity in the fishery for Greenland halibut (Reinhardtius hippoglossoides) in the Disko Bay, Greenland, affects the current and future income opportunities of coastal fishers. Through bio-economic modelling, I find presence of economic overexploitation of the Greenland halibut fish stock in the Disko Bay. Specifically, the actual Greenland halibut stock in 2019 is found to constitute only 56 pct. of the economic optimal stock size in the baseline scenario. The actual profit is almost 40 million DKK lower than the optimal profit due to higher costs of harvesting, which arise because the actual stock size is lower than the optimal and because of a suboptimal split of the TAC between vessels (above 6 m in length) and boats (6 m or below in length) in the fishery. The results presented in this article show that there is significant scope for economic optimization of the coastal Greenland halibut fishery through a temporary reduction in harvest of Greenland halibut to regenerate the stock to its optimal size and a transfer of TAC from the boat segment to the vessel segment. Notably, this article does not find that the stock of Greenland halibut in the Disko Bay is further decreasing at current (2019) harvest levels, however, this finding is contingent on the length of the data series used for the estimation of the growth model.

Despite the commercial importance of Greenland Halibut (Reinhardtius hippoglossoides), important gaps still persist in our knowledge of this species, including its reproductive biology and sex determination mechanism. Here, we combined single-molecule sequencing of long reads (Pacific Sciences) with chromatin conformation capture sequencing (Hi-C) data to assemble the first chromosome-level reference genome for this species. The high-quality assembly encompassed more than 598 Megabases (Mb) assigned to 1594 scaffolds (scaffold N50 = 25 Mb) with 96% of its total length distributed among 24 chromosomes. Investigation of the syntenic relationship with other economically important flatfish species revealed a high conservation of synteny blocks among members of this phylogenetic clade. Sex determination analysis revealed that similar to other teleost fishes, flatfishes also exhibit a high level of plasticity and turnover in sex determination mechanisms. A low-coverage whole-genome sequence analysis of 198 individuals revealed that Greenland Halibut possesses a male heterogametic XY system and several putative candidate genes implied in the sex determination of this species. Our study also suggests for the first time in flatfishes that a putative Y-autosomal fusion could be associated with a reduction of recombination typical of the early steps of sex chromosome evolution.

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