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ABSTRACT Effective management of shark bycatch is urgently needed to reverse widespread population declines, especially in longline fisheries that are estimated to be responsible for half of global shark catch. Management of shark catch typically focuses on the safe release of landed sharks, with limited attention to reducing the initial catch. Where controls on fishing effort or catch do exist, management frameworks tend to treat fishing fleets as homogeneous units. The underlying assumption is that fishers have similar abilities to catch target species and avoid bycatch. We test this assumption by analysing variability in shark bycatch rates among individual vessels in an industrial tuna longline fleet operating in the Western Pacific. Controlling for factors such as geographic location, time of day and gear depth, we find that individual vessels drive highly variable bycatch rates of blue (Prionace glauca) and silky sharks (Carcharhinus falciformis) – two shark species with the highest global catch volumes. Additionally, we found that the operating company can influence fisher performance. As countries and regional organisations increasingly adopt shark conservation plans and make international conservation commitments, it is crucial to identify viable new strategies that do not unduly burden the industry or penalise good actors. Tailoring management actions to individual fishers and companies – holding high‐bycatch fishers accountable and incentivising low‐bycatch fishers to continuously improve – presents a crucial opportunity to address the overfishing of sharks and other global bycatch challenges. [ABSTRACT FROM AUTHOR]

To support ecosystem-based fisheries management, monitoring data from at-sea observer (ASO) programs should be leveraged to understand the impact of fisheries on discarded species (bycatch). Available techniques to estimate fishery-scale quantities from observations range from simple mean estimators to more complex spatiotemporal models, each making assumptions with differing degrees of support. However, the resulting implementation and analytical trade-offs are rarely discussed when applying these techniques in practice. Using blue shark (Prionace glauca) bycatch in the Canadian pelagic longline fishery as a case study, we evaluated the performance of seven contrasting approaches to estimating total annual discard amounts and assessed their trade-offs in application. Results demonstrated that simple approaches such as mean estimator and nearest neighbors are feasible to implement and can be as efficient for prediction as complex models such as random forest and mixed-effects models. The traditionally used catch-ratio estimator consistently underperformed among all tested models, likely due to misspecified correlative relationships between target and bycatch species. Overall, efforts in model-based approaches were rewarded with very small gains in predictive ability, suggesting that such models relying on environmental, biological, spatial, and/or temporal patterns to improve prediction of bycatch may lack sufficient foundation in data-limited contexts. [ABSTRACT FROM AUTHOR]

Populations of marine top predators have been sharply declining during the past decades, and one‐third of chondrichthyans are currently threatened with extinction. Sustainable management measures and conservation plans of large pelagic sharks require knowledge on population genetic differentiation and demographic connectivity. Here, we present the case of the Mediterranean blue shark (Prionace glauca, L. 1758), commonly found as bycatch in longline fisheries and classified by the IUCN as critically endangered. The management of this species suffers from a scarcity of data about population structure and connectivity within the Mediterranean Sea and between this basin and the adjacent Northeast Atlantic. Here, we assessed the genetic diversity and spatial structure of blue shark from different areas of the Mediterranean Sea and the Northeast Atlantic through genome scan analyses. Pairwise genetic differentiation estimates (FST) on 203 specimens genotyped at 14,713 ddRAD‐derived SNPs revealed subtle, yet significant, genetic differences within the Mediterranean sampling locations, and between the Mediterranean Sea and the Northeast Atlantic Ocean. Genetic differentiation suggests some degree of demographic independence between the Western and Eastern Mediterranean blue shark populations. Furthermore, results show limited genetic connectivity between the Mediterranean and the Atlantic basins, supporting the hypothesis of two distinct populations of blue shark separated by the Strait of Gibraltar. Although reproductive interactions may be limited, the faint genetic signal of differentiation suggests a recent common history between these units. Therefore, Mediterranean blue sharks may function akin to a metapopulation relying upon local demographic processes and connectivity dynamics, whereby the limited contemporary gene flow replenishment from the Atlantic may interplay with currently poorly regulated commercial catches and large‐scale ecosystem changes. Altogether, these results emphasise the need for revising management delineations applied to these critically endangered sharks. [ABSTRACT FROM AUTHOR]

This article explores the presence of site fidelity, or philopatry, in blue sharks. While blue sharks are typically known for their wide-ranging movements, this study documents the repeated sightings of two blue sharks at a specific location in the Azores archipelago. The sharks were attracted to the area by local dive operators who regularly provide food. These findings challenge the belief that blue sharks are strictly oceanic wanderers and suggest that they may exhibit some form of site fidelity to predictable feeding areas. The study emphasizes the importance of citizen science and collaboration between scientists and the diving industry in gathering valuable information for the management and conservation of marine migratory species. However, further research using longer-term satellite telemetry is necessary to gain a better understanding of the behavioral ecology of these sharks and its implications for their management and conservation. [Extracted from the article]

Simple Summary: Blue shark populations are currently declining, caused mainly by the impact of overfishing from industrial fishing vessels in the open oceans. However, there is a paucity of comprehensive biological and habitat data concerning the reproductive characteristics of blue shark species in the Indian Ocean. In response to the call made by the Indian Ocean Tuna Commission (IOTC) to provide valuable parameters for the conservation of blue shark resources, this study collected observer data from the Indian Ocean longline fishery targeting tuna between 2010 and 2020. Through rigorous statistical analysis, it was determined that the estimated length at sexual maturity for male blue sharks is 161.4 cm and 179.3 cm for females. Moreover, the average litter size was found to be 33.7 pups. The study suggests the existence of a possible seasonal migratory pattern for pregnant blue sharks, with the first and fourth quarters of the year being potential mating grounds in proximity to the equatorial region of the Indian Ocean. Additionally, the temperate marine areas of the Indian Ocean were identified as crucial habitats for parturition and juvenile development of blue shark species. Consequently, it is strongly recommended to implement more scientifically informed and ecologically sustainable operational strategies in these designated areas. Due to the limited biological research on the blue shark in the Indian Ocean, such as the lack of a clear understanding of its reproductive biology and distribution, our study analyzed and evaluated the fork length distribution, sexual maturity length, reproductive capacity, and spatiotemporal distribution of blue sharks based on biological data and capture location information collected in the western Indian Ocean from 2010 to 2020. The objective of this study is to provide reliable biological information important in performing future stock assessments vital for species conservation in this region. A total of 791 male (33–249.5 cm FL) and 803 female (12–349.6 cm FL) blue sharks were collected in the West Indian Ocean. We used the morphology of the sexual organs to ascertain their sexual maturity. Results show that the observed size at 50% sexual maturity of male blue sharks in the West Indian Ocean was 161.4cm FL (192.4 cm TL) for males and 179.3 cm FL (213.9 cm TL) for females based on logistic curve analysis. The average litter size of pregnant blue sharks was 33.7 pups. There were significant differences in the distribution of blue shark individuals with different sexual maturity levels in different quarters (p < 0.05). This study suggests that the area near the equator in the Indian Ocean from October to March of the following year may be the mating ground for blue sharks, while the temperate waters in the Indian Ocean are the nursery ground and parturition ground for pregnant and juvenile throughout the whole year. Therefore, it is recommended to adopt a more scientific and reasonable operational method in these areas. [ABSTRACT FROM AUTHOR]

Natural mortality rates (M) are poorly quantified and commonly identified as a key source of uncertainty in fish stock assessments. Increasingly, stock assessments account for size- and age-dependence in M instead of using a constant M for all sizes and ages, as has traditionally been the default assumption. Empirical studies show that M is approximately inversely proportional to body length in fish populations, and this generalization has been used together with a von Bertalanffy growth curve to derive an age-dependent M. Here we extend this approach to the three commonly used growth functions of the Richards family (i.e., Logistic, von Bertalanffy, and Gompertz growth models). These models allow flexible production of various growth curves with a sigmoid shape and an upper asymptote, making them useful for displaying diverse growth curves for various long-lived fishes. The influences of growth parameters on predicted M were investigated, and the outcomes were compared among the three growth models. Age-dependent M for blue sharks (Prionace glauca) were estimated as an example. [ABSTRACT FROM AUTHOR]

Understanding population dynamics, movements, and fishing mortality is critical to establish effective shark conservation measures across international boundaries in the ocean. There are few survival and dispersal estimates of juveniles of oceanic shark species in the North Atlantic despite it being one of the most fished regions in the world. Here we provide estimates of dispersal, survival, and proportion of fishing mortality in the North Atlantic for two threatened oceanic sharks: the blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus). Our results are based on multi‐event models applied to tag‐recovery data of 700 blue sharks and 132 shortfin makos tagged over a decade. A total of 60 blue sharks (8.57% of tagged) and 30 makos (22.73%) were recovered by the longline fishery between 2009 and 2017. Tag‐reporting rate (percentage of returned information when a tagged shark was caught) was estimated to be high (0.794 ± 0.232 SE). Mean annual survival, as predicted from the models, was higher for blue shark (0.835 ± 0.040 SE) than for shortfin mako (0.618 ± 0.189 SE). Models predicted that fishing caused more than a half of total mortality in the study area for both species (0.576 ± 0.209), and more than a third of tagged individuals dispersed from the study area permanently (0.359 ± 0.073). Our findings, focused mainly on juveniles from oceanic areas, contribute to a better understanding of shark population dynamics in the North Atlantic and highlight the need for further conservation measures for both blue shark and shortfin mako, such as implementing efficient bycatch mitigation measures and static/dynamic time–area closures in the open ocean. [ABSTRACT FROM AUTHOR]

The blue shark Prionace glauca is a top predator with one of the widest geographical distributions of any shark species. It is classified as Critically Endangered in the Mediterranean Sea, and Near Threatened globally. Previous genetic studies did not reject the null hypothesis of a single global population. The blue shark was proposed as a possible archetype of the "grey zone of population differentiation," coined to designate cases where population structure may be too recent or too faint to be detected using a limited set of markers. Here, blue shark samples collected throughout its global range were sequenced using a specific RAD method (DArTseq), which recovered 37,655 genome‐wide single nucleotide polymorphisms (SNPs). Two main groups emerged, with Mediterranean Sea and northern Atlantic samples (Northern population) differentiated significantly from the Indo‐west Pacific samples (Southern population). Significant pairwise FST values indicated further genetic differentiation within the Atlantic Ocean, and between the Atlantic Ocean and the Mediterranean Sea. Reconstruction of recent demographic history suggested divergence between Northern and Southern populations occurred about 500 generations ago and revealed a drastic reduction in effective population size from a large ancestral population. Our results illustrate the power of genome scans to detect population structure and reconstruct demographic history in highly migratory marine species. Given that the management plans of the blue shark (targeted or bycatch) fisheries currently assume panmictic regional stocks, we strongly recommend that the results presented here be considered in future stock assessments and conservation strategies. [ABSTRACT FROM AUTHOR]

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IntroductionLongline fishing gear has a higher by-catch rate than any other type of commercial fishing gear. Nowadays, there is an urgent need to find efficient management strategies to mitigate by-catch and the use of new hook types could be one of them. This study investigates the effects of a longline fishery (which targets swordfish, Xiphias gladius, in the South Adriatic Sea) replacing the traditional J-type hook with a circle hook (C-type hook) on target and by-catch species.MethodsFor this purpose, a fishing trip of nine days – with seven fishing sets – was monitored. For both targeted swordfish and by-catch specimens caught (i.e., blue shark, Prionace glauca; pelagic stingray, Pteroplatytrygon violacea; and loggerhead turtle, Caretta caretta), data about the hook type used (J-type vs. C-type), the specimen size, and their capture condition were collected.Results and discussionWith all species, we observed no significant difference in catch-per-unit-effort (CPUE) or specimen lengths between the two hook types. In addition, the hook type did not significantly affect the capture condition of swordfish, pelagic stingray, or loggerhead turtle specimens; however, it significantly affected the capture condition of blue sharks. The percentage of blue shark specimens found in healthy condition was higher when using a C-type hook (71.5%) than when using a J-type hook (22.6%). Overall, these preliminary results suggest that the use of a C-type hook improves the condition of by-caught blue sharks without affecting the CPUE or size of the target species. In conclusion, the use of a C-type hook could reduce the detrimental effects of by-catch on some species in the Adriatic Sea; however, this finding needs to be confirmed by a study with a larger sample size.

Copyright of Spanish Journal of Palaeontology is the property of Socieadad Espanola de Paleontologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pop-up satellite archival tags (PSATs) have been widely used to study the behavior, habitat selection, and survival rates of sharks. Longitudinal data on shark behavior is needed to understand seasonal migration, spatiotemporal shifts of distribution with the ontogenetic/reproductive stage and the long-term impact of anthropogenic activities. Therefore, long-lasting techniques to secure PSATs to the body of the subject with little harm to its survival are essential. We developed four methods for externally attaching PSATs on the deck to blue sharks (Prionace glauca) in the northwestern Pacific and evaluated the performance of several different methods in terms of tag retention and post-release mortality. Analysis of time-to-event data suggested differences in tag retention rates (here, 'survival rates') among the attachment methods. Our Method C, whereby an umbrella-type dart was inserted into the dorsal musculature, penetrating the vertical septum, and the tag body was positioned along anteroposterior body axis and secured to the first dorsal fin base using a cable tie, provided the best performance among the four methods in terms of greater restricted mean survival time (RMST), higher rate of days at liberty, moderate post-release mortality, and less time required for attachment. A meta-analysis based on data published to date indicated that the 'one-point attachment' method has been the main approach with blue sharks, and that the tag survival rate differs largely depending on the type of dart head and tether configuration even in the same approach. The RMST from Method C was slightly greater than that with one-point attachment method with an 'umbrella dart–monofilament or fluorocarbon tether' combination, which was the most frequently used across previous studies, but the one-point attachment method with a 'Wilton dart (large or small) or titanium dart–stainless steel tether' combination outperformed methods compared. Combining available information on the biology of this species with the results of the current study, we propose the following procedure as the most effective to decrease drag and prevent swinging of the tag: pretreat the tag with an anti-biofouling agent; position the tag along the anteroposterior axis of the shark's body; allow the dart to penetrate the vertical septum of the subject; and, additional fixation of the tag to the dorsal fin. Although further data are needed to evaluate some aspects (e. g., dart-head type and tagging location), application of appropriate steps depending on the situation will increase the probability of obtaining long-term data for this highly migratory species. • Attachment methods of PSAT with long-term retention were developed for blue shark. • Effectiveness of several attachment methods was evaluated by survival analysis. • Pretreatment and placement of tag and focus on the vertical septum are important. • Depending on the situation, adoption of available approaches is recommended. [ABSTRACT FROM AUTHOR]

On 25 December 2012, a specimen of Prionace glauca (Linnaeus, 1758) was caught by a swordfish longliner along with 9 swordfish together off Fethiye at a depth of 1200 m. The specimen caught was measured as TL and weighed (kg), and photographed. The specimen was 85 cm TL and 7 kg. According to the previous studies, blue sharks especially observed abundantly in northern Aegean Sea, and can be accepted very rare incidental catch from the Turkish coasts owing to weak presuppose of swordfish fishery. However, there is an important place of blue sharks in the global fin trade area. Therefore, population trend of this shark species is swift decreasing.

Climate-driven expansions of ocean hypoxic zones are predicted to concentrate pelagic fish in oxygenated surface layers, but how expanding hypoxia and fisheries will interact to affect threatened pelagic sharks remains unknown. Here, analysis of satellite-tracked blue sharks and environmental modelling in the eastern tropical Atlantic oxygen minimum zone (OMZ) shows shark maximum dive depths decreased due to combined effects of decreasing dissolved oxygen (DO) at depth, high sea surface temperatures, and increased surface-layer net primary production. Multiple factors associated with climate-driven deoxygenation contributed to blue shark vertical habitat compression, potentially increasing their vulnerability to surface fisheries. Greater intensity of longline fishing effort occurred above the OMZ compared to adjacent waters. Higher shark catches were associated with strong DO gradients, suggesting potential aggregation along suitable DO gradients contributed to habitat compression and higher fishing-induced mortality. Fisheries controls to counteract deoxygenation effects on shark catches will be needed as oceans continue warming.

The objectives of this research were to obtain blue shark liver oil using supercritical CO2 and to characterize the physicochemical parameters of the oil, and the contents of squalene and vitamin A. Supercritical extractions were performed at 50 and 60 °C and pressures from 100 to 300 bar. The oil yield obtained was up to 60% and presented a profile equivalent to that of refined oils for density (0.920 – 0.922 g/mL); viscosity (52.55 – 56.47 Pas.s); refractive index (1.4760 – 1.4785); acid value (1.13 – 2.22% oleic acid); peroxides (10.47 – 24.04 meq of active O2 /kg of oil); saponification value (171.37 – 556.03 mg KOH/g oil), and iodine value (120.05 – 149.21g I2 /100g oil). The fatty acid profile indicated a majority of unsaturated fatty acids. High levels of squalene and vitamin A corroborate the high nutritional quality of this oil from an underexploited by-product with great processing potential.

The blue shark Prionace glauca (Linnaeus, 1758) is a pelagic fish, belonging to the Carcharhinidae family. It is one of the top predators placed at the top of the food chain and for this reason it must be followed to preserve it against any illegal fishing. Its presence in the landings of the Moroccan fleet by both longliners and boaters shows that this species has become highly exploited and needs to be followed. The main objective of this work is to know its place in the ecological niche determining the ecological role of this predator in the ecosystem. The study of Prionace glauca diet is intended to highlight, in the short term, feeding periods and prey preferences according to the state of maturity of the animal and will allow in the medium term to understand the behavior of this species in the marine ecosystem. Since February 2015, biological sampling has been collected at the wholesale fish market of Casablanca where the catches of Prionace glauca transit from several Moroccan ports. Investigations included size measurements, sex determination and stomach recovery for macroscopic analysis. The frequency of occurrence showed that European pilchard Sardina pilchardus is the main prey in Prionace glauca. The immature individuals eating preference is the European pilchard Sardina pilchardus although for mature are rays and sharks. The cephalopods and rays are more consumed by females whereas Birdbeak dogfish Deania calceus and the swordfish Xiphias gladius by males. The emptiness rate show that 56% of the dissected stomachs were empty indicating that there are periods of low Prionace glauca feeding during the "autumn-winter" seasons.

This study documented the parasite faunas of the spiral valves of blue sharks Prionace glauca (L. 1758) and common thresher sharks Alopias vulpinus (Bonnaterre, 1788) caught in the California Current Large Marine Ecosystem (CCLME) north of the Mexican border. The spiral valves of 18 blue and 19 thresher sharks caught in the CCLME from 2009 to 2013 were examined for parasites. Seven parasite taxa were found in blue sharks and nine in threshers. The tetraphyllidean cestode Anthobothrium sp. (78% prevalence) was the most common parasite in blue sharks, and the phyllobothriid cestode Paraorygmatobothrium sp. (90% prevalence) was the most common in threshers. An adult nematode of the genus Piscicapillaria was found in threshers for the first time and may be a new species. Adult individuals of Hysterothylacium sp. were found in both shark species. The adult acanthocephalan Rhadinorhynchus cololabis and remains of the parasitic copepod Pennella sp. – both parasites of Pacific saury, Cololabis saira – were found in the intestines of threshers, indicating recent feeding on saury. This study paves the way for a more comprehensive examination, including more samples and a wider variety of shark species, to provide a greater understanding of shark feeding behaviour and possibly provide information on shark population biology. [ABSTRACT FROM AUTHOR]

Species-specific monitoring through large shark fin market surveys has been a valuable data source to estimate global catches and international shark fin trade dynamics. Hong Kong and Guangzhou, mainland China, are the largest shark fin markets and consumption centers in the world. We used molecular identification protocols on randomly collected processed fin trimmings (n = 2000) and non-parametric species estimators to investigate the species composition of the Guangzhou retail market and compare the species diversity between the Guangzhou and Hong Kong shark fin retail markets. Species diversity was similar between both trade hubs with a small subset of species dominating the composition. The blue shark (Prionace glauca) was the most common species overall followed by the CITES-listed silky shark (Carcharhinus falciformis), scalloped hammerhead shark (Sphyrna lewini), smooth hammerhead shark (S. zygaena) and shortfin mako shark (Isurus oxyrinchus). Our results support previous indications of high connectivity between the shark fin markets of Hong Kong and mainland China and suggest that systematic studies of other fin trade hubs within Mainland China and stronger law-enforcement protocols and capacity building are needed. [ABSTRACT FROM AUTHOR]

Indoleamine 2 3-dioxygenase (IDO) is a protein usually described in mammals, which, among other functions, participates in the maternal-fetal tolerance process. The blue-shark, Prionace glauca (Linnaeus, 1758) is a viviparous placentary species in which the yolk sac develops during the pregnancy, turning into a placenta for matrotrophic nutrition of the embryo. The purpose of this study was to investigate the expression of IDO in the P. glauca maternal-fetal interface along three gestation phases and describe its distribution and the meaning of its presence. The results showed IDO labelling during the yolk sac/placenta development in the ectoderm on the three development phases and in the endoderm at the two first phases. In the uterine epithelium, IDO was observed in the last two phases. These interface tissues are major contact areas between the mother and the semiallogeneic conceptus and this relation could induce an immunological response against the fetus. Therefore, the presence of IDO may indicate that it could have a similar role in the mechanism of maternal-fetal tolerance in the P. glauca placental interface, as described in eutherian mammals. • New findings on Indoleamine 2,3-dioxygenase in relation to sharks pregnancy and developmental biochemistry: • First finding of IDO in Chondrichthyes. • IDO distribution on vertebrates. • Morphological changes in maternal fetal interface in sharks along development. [ABSTRACT FROM AUTHOR]

Among pelagic sharks, the Blue shark, Prionace glauca (Carcharhiniformes, Carcharhinidae) is known to be the most abundant. Although, blue shark is relatively productive, concerns have been raised related to the decline in population of these apex fish predators; and this decline can affect the marine ecology. This paper presents catch per unit effort (CPUE) data of blue sharks obtained from observers’ on-board Chinese pelagic longline fishing vessels from 2009–2014 in the Pacific Ocean. All the blue shark species were incidentally captured (without shark hook). Nominal CPUE ranged from 0 individual per 1000 hooks to 5.21 individuals per 1000 hooks; the highest annual average nominal CPUE recorded in this study was 0.89 individual per 1000 hooks in 2011 while, 0.58 was the lowest recorded in 2010. Our results equally indicates that, blue shark population was so close to MSY level showing that fishing mortality rate might surpass MSY level in the future, since decrease in catches were observed. Therefore, additional management measures should be implemented in the Pacific Ocean in order to achieve a healthy stock status of this species. [ABSTRACT FROM AUTHOR]

The majority of morphological abnormalities reported for elasmobranchs are cases of bicephalia. This contribution describes the third confirmed case worldwide and the first in the South Atlantic of diprosopus tetrophthalmus (craniofacial duplication) in a foetus of blue shark, Prionace glauca (Linnaeus, 1758), from a female caught off the Brazilian coast (26°36′11′′S, 45°56′00′′W) in July 2007. The specimen is described and compared to normal specimens from the same size and to another one with similar deformities from Chile. The embryo is smaller than a normal embryo, with deformities in the skull, head muscles and curvature of the vertebral column.

Abstract Background Blue sharks (Prionace glauca) are among the most abundant and widely distributed of oceanic elasmobranchs. Millions are taken annually in pelagic longline fisheries and comprise the highest component of auctioned fin weight in the international shark fin trade. Though studies of blue sharks outnumber those of other large pelagic sharks, the species’ complicated and sexually segregated life history still confound current understanding of Atlantic movement patterns. Lack of detailed information regarding movement and vertical behavior continues to limit management efforts that require such data for stock assessment and sustainable catch modeling. Therefore, this study aims to describe behavioral and ecological patterns distinct to aggregating and migrating blue sharks, and compare the findings to existing Atlantic movement models. Results Data collected from 23 blue sharks instrumented with pop-up satellite archival tags were used in statistical predictive regression models to investigate habitat use during a localized aggregation in the northwest Atlantic, while undergoing seasonal migrations, and with respect to environmental variables. Deployment durations ranged from 4 to 273 days, with sharks inhabiting both productive coastal waters and the open ocean, and exhibiting long-distance seasonal movements exceeding 3700 km. While aggregating on the continental shelf of the northwest Atlantic, blue sharks displayed consistent depth use independent of sex and life stage, and exhibited varied response to environmental (temperature and chlorophyll a) factors. As sharks dispersed from the aggregation site, depth use was influenced by bathymetry, latitude, demography, and presence in the Gulf Stream. Mature females were not observed at the New England tagging site, however, two mature females with recent mating wounds were captured and tagged opportunistically in The Bahamas, one of which migrated to the Mid-Atlantic Ridge. Conclusions Vertical behaviors displayed by blue sharks varied greatly among locales; depth use off the continental shelf was significantly greater, and individuals exhibited a greater frequency of deep-diving behavior, compared to periods of aggregation on the continental shelf. Sexual segregation was evident, suggesting mature and immature males, and immature females may be subjected to high levels of anthropogenic exploitation in this region during periods of aggregation. Analysis of the spatio-temporal tracks revealed that nine individuals traveled beyond the United States EEZ, including a mature female captured in The Bahamas that migrated to the Mid-Atlantic Ridge. These results reflect and augment existing Atlantic migration models, and highlight the complex, synergistic nature of factors affecting blue shark ecology and the need for a cooperative management approach in the North Atlantic.

The ability of human tissues to self-repair is limited, which motivates the scientific community to explore new and better therapeutic approaches to tissue regeneration. The present manuscript provides a comparative study between a marine-based composite biomaterial, and another composed of well-established counterparts for bone tissue regeneration. Blue shark skin collagen was combined with bioapatite obtained from blue shark's teeth (mColl:BAp), while bovine collagen was combined with synthetic hydroxyapatite (bColl:Ap) to produce 3D composite scaffolds by freeze-drying. Collagens showed similar profiles, while apatite particles differed in their composition, being the marine bioapatite a fluoride-enriched ceramic. The marine-sourced biomaterials presented higher porosities, improved mechanical properties, and slower degradation rates when compared to synthetic apatite-reinforced bovine collagen. The in vivo performance regarding bone tissue regeneration was evaluated in defects created in femoral condyles in New Zealand rabbits twelve weeks post-surgery. Micro-CT results showed that mColl:BAp implanted condyles had a slower degradation and an higher tissue formation (17.9 ± 6.9 %) when compared with bColl:Ap implanted ones (12.9 ± 7.6 %). The histomorphometry analysis provided supporting evidence, confirming the observed trend by quantifying 13.1 ± 7.9 % of new tissue formation for mColl:BAp composites and 10.4 ± 3.2 % for bColl:Ap composites, suggesting the potential use of marine biomaterials for bone regeneration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Elasmobranch species composition and spatiotemporal variability can often be characterized from landing surveys of local fisheries, with important management implications. In the present study, we describe the elasmobranch landing composition of 4 major artisanal fishing ports in northwestern Baja California, Mexico. Sampling was conducted opportunistically between 1995 and 2010 and included an effort of 684 fishing days. Species composition was gear-dependent and varied with the fishing area, with thresher sharks (Alopias vulpinus) and spiny dogfish (Squalus suckleyi) dominating the catches landed by coastal gill net fisheries, and blue sharks (Prionace glauca) and shortfin mako sharks (Isurus oxyrhinchus) dominating the catches landed by the offshore longline fishery. Size-structure analysis indicated that catches were composed primarily of juveniles for most species, although the catch of mature soupfin sharks (Galeorhinus galeus) increased in longline fisheries during the winter. The results indicate that minor regional differences in elasmobranch species composition occur along the Pacific coast of Baja California and are most likely related to regional oceanographic or habitat differences. The results of this study may form the basis for future efforts to monitor species composition changes over time, to more completely assess elasmobranch populations. [ABSTRACT FROM AUTHOR]

This study reports for the first time a case of multiple morphological abnormalities in a blue shark Prionace glauca embryo collected on the Peruvian coast, southeast Pacific. External exploration and radiograph picture showed duplicated parts in the cephalic region (mouths and eye sockets) and trunk anomalies (thoracic lordosis and rolled caudal fin). The duplicate face parts in a single head seen in the embryo, suggest a diprosopia anomaly. [ABSTRACT FROM AUTHOR]

The blue shark Prionace glauca is the most abundant species in the artisanal driftnet fishery off the coastal waters of Ivory Coast. The reproductive parameters were investigated with the aim of providing basic information on the reproductive biology for fisheries management. A total of 424 specimens (256 males and 168 females) ranging from 170–330 cm in total length (TL) were sampled between August 2014 and November 2016. Sample for embryonic sex ratio was obtained from 18 litters of 503 individuals (255 males and 248 females). The embryonic sex ratio was not significantly different from 1:1 (χ2 = 0.10, P > 0.05, N = 503). The size at 50% maturity (L50) was 218.1 cm TL for males and 223.3 cm TL for females. The litter size based on the number of embryos varied from 6 to 62, with an average of 30 embryos. Mating started in July whereas ovulation, fertilization and uterine eggs occurred in late October–November. Smallest embryos of 3–5 cm in stretch total length (STL) appeared in uterus from November to January. The embryo size varied widely among months, and well-pigmented embryos were already present in April–May samples, although most of them occurred in August–September, suggesting a gestation period of around 11 months. The absence of neonates in catches, as well as parturition females, does not support a hypothesis that parturition takes place in the Gulf of Guinea. [ABSTRACT FROM AUTHOR]

Blue shark and shortfin mako are key pelagic shark species distributed throughout the temperate and tropical waters of the world's oceans. These species are caught in the North Pacific by Japanese longline fisheries as bycatch and occasionally targeting blue shark. Japanese research and training vessels (JRTVs) have been collecting fishery-independent data on these sharks in the western and central North Pacific since 1992. However, the catch per unit of effort (CPUE) estimated from the fishery-independent data had not been used for stock assessments due to an issue concerning reporting after the 2000s. In this study, a statistical filtering method was used to remove unreliable set-by-set data collected by JRTVs. The nominal CPUE of the JRTVs was then standardized using the spatio-temporal generalized linear mixed model to provide the spatial and temporal changes in the CPUEs of these sharks in the North Pacific. The hotspots of blue shark appeared in temperate waters of the western and central North Pacific, whereas those of shortfin mako were distributed in coastal and offshore waters along the Kuroshio-Oyashio transition zone and the Mixed Water Region. The yearly changes in the CPUE of blue shark illustrated a downward trend until 2008 and an upward trend thereafter, whereas those of shortfin mako exhibited a flat trend with large fluctuations from 1994 to 2008, and a down-and-up trend thereafter. The information predicted from the fishery-independent data is very useful for improving the stock assessment and management of these sharks as it provides an understanding of spatio-temporal changes in the hotspots and temporal changes in the catch rates. [ABSTRACT FROM AUTHOR]

The blue shark belongs to the group of the most widespread pelagic sharks in the world. It inhabits the pelagic zone of almost all warm and temperate seas and oceans. As it is one of the most abundant shark species, it is frequently caught in different types of fishing gear operated in the pelagic zone. This study provides the first data on the reproduction of this species in Montenegrin waters (in the Southeastern Adriatic Sea). Six newborn blue sharks were found during our field excursions. For three of them, detailed morphometric measurements are presented. Alongside the newborns, a gravid female was also recorded. The data was collected in the period from April to October 2017. According to the published literature and the data presented in this paper, species reproduction is likely to be seasonal. A review of the areas where the specimens were recorded was carried out in order to infer if the adult females choose them specifically as their parturition grounds. [ABSTRACT FROM AUTHOR]

Blue shark Prionace glauca is a species that represents a great economic and ecological importance. However, the information related to its biology and others aspects of its population is limited. Nevertheless these kinds of studies are very important for a suitable management of fishery activities. The aim of this research was to develop a historical review for all biological, ecological and toxicological studies made in the coastal and marine ecosystems of the Ecuadorian Pacific. A review of the specializedliteraturewas carried out for many documents such as thesis, technical reports, scientific papers,and others. According to results obtained, in Ecuador there have been four scientific research studies from 2012: These were two of Biology (one of reproductive aspects in Santa Rosa de Salinas and another about age and growth in Manta) and the others two of Ecology and Toxicology (one on mercury bioaccumulation and bio-magnification of mercury, and another on the concentration of mercury and cadmium; both conducted in Santa Rosa de Salinas).The works were developed by state and private universities through thesis, while a draft was in preparation for scientific publication as part of a research project in a private institution of higher education

Highlights • Age and growth was estimated for the Indian Ocean blue shark. • A 2-parameter von Bertalanffy growth model with fixed size-at-birth was considered the most adequate. • There were differences between sexes, with females growing slower than males. • The maximum age estimated was 25 years. • The maximum age estimated is the oldest attributed age to this species so far. Abstract Since there is still a lack of biological information regarding Prionace glauca in the Indian Ocean, specifically in terms of age estimation and growth modelling, the age and growth of this species was studied by analysing vertebral samples. All samples were collected from specimens captured by pelagic longliners between March 2013 and September 2016, with sizes ranging from 82 to 301 cm fork length (L F). Two growth models were fitted to the age data, a three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L 0 (size at birth) and a two-parameter VBGF with a fixed L 0. The latter was considered the most adequate to describe the growth of the species, with the estimated parameters being L ∞ = 283.8 cm L F , k = 0.13 year−1 for males and L ∞ = 290.6 cm L F , k = 0.12 year−1 for females. These results suggest that females have a slower growth than males. The maximum age estimated was 25 years, representing the oldest attributed age to this species so far. Further work is needed regarding P. glauca in the Indian Ocean, but this study adds important life-history information that can contribute for the management and conservation of the species. [ABSTRACT FROM AUTHOR]

Four new malformations observed in blue shark embryos in the western coast of Baja California Sur, Mexico are reported in this study. The embryos of blue shark samples were obtained on board the industrial fishing boat 'Damasta'; the organisms were frozen and transferred to CIBNOR Fish Ecology Laboratory where the corresponding measurements were taken and malformations observed. The first malformation was the presence of one nostril in two female embryos that showed short and crushed snouts. The second one was observed in a female with two jaws and the middle portion of the column trunk in screw-shape. The third one was an embryo with dicephaly, two separate vertebral columns, two first dorsal fin pairs, absence of the second dorsal fin, five pelvic fins and two joint caudal fins. The fourth malformation observed was an embryo with incomplete development and undifferentiated sex. Malformations are still a mystery and also an object of study because they affect different organisms, not only sharks but also fish. It is highly relevant to know the causes and perform further studies to understand if the origin is either genetic or anthropogenic. [ABSTRACT FROM AUTHOR]

Abstract Few studies have focused so far on plastic ingestion by sharks in the Mediterranean Sea. The aim of this paper was to determine, for the first time, the plastic litter ingested by blue sharks (Prionace glauca), categorized as "Critically Endangered" in the Mediterranean Sea by IUCN, caught in the Pelagos Sanctuary SPAMI (North-Western Mediterranean Sea). The analysis of the stomach contents was performed following the MSFD Descriptor 10 standard protocol implemented with FT-IR spectroscopy technique. The results showed that 25.26% of sharks ingested plastic debris of wide scale of sizes from microplastics (<5 mm) to macroplastics (>25 mm). The polyethylene sheetlike user plastics, widely used as packaging material, are the most ingested debris. This research raises a warning alarm on the impact of plastic debris on a threatened species, with a key role in the food web, and adds important information for futures mitigation actions. Highlights • The high occurrence of debris in blue sharks raises a warning alarm. • Juvenile blue sharks seem more likely to ingest marine litter than adults. • Blue sharks ingested mainly transparent sheet-like items composed by polyethylene. • Sizes scale of ingested plastic debris from microplastics to macroplastics. [ABSTRACT FROM AUTHOR]

There is worldwide concern about the status of elasmobranchs, primarily as a result of overfishing and bycatch with subsequent ecosystem effects following the removal of top predators. Whilst abundant and wide-ranging, blue sharks (Prionace glauca) are the most heavily exploited shark species having suffered marked declines over the past decades, and there is a call for robust abundance estimates. In this study, we utilized depth data collected from two blue sharks using pop-up satellite archival tags, and modelled the proportion of time the sharks were swimming in the top 1-meter layer and could therefore be detected by observers conducting aerial surveys. The availability models indicated that the tagged sharks preferred surface waters whilst swimming over the continental shelf and during daytime, with a model-predicted average proportion of time spent at the surface of 0.633 (SD = 0.094) for on-shelf, and 0.136 (SD = 0.075) for off-shelf. These predicted values were then used to account for availability bias in abundance estimates for the species over a large area in the Northeast Atlantic, derived through distance sampling using aerial survey data collected in 2015 and 2016 and modelled with density surface models. Further, we compared abundance estimates corrected with model-predicted availability to uncorrected estimates and to estimates that incorporated the average time the sharks were available for detection. The mean abundance (number of individuals) corrected with modelled availability was 15,320 (CV = 0.28) in 2015 and 11,001 (CV = 0.27) in 2016. Depending on the year, these estimates were ~7 times higher compared to estimates without the bias correction, and ~3 times higher compared to the abundances corrected with average availability. When the survey area contains habitat heterogeneity that may affect surfacing patterns of animals, modelling animals’ availability provides a robust alternative to correcting for availability bias and highlights the need for caution when applying “average” correction factors. [ABSTRACT FROM AUTHOR]

Accounting for components of fishing mortality, including post-release mortality (Fr), is necessary for robust assessments of the effects of fishing. Forty-eight blue (Prionace glauca) and 35 silky sharks (Carcharhinus falciformes) were tagged with pop-up satellite archival tags to monitor Fr rates from pelagic longline vessels in the western tropical Pacific Ocean. There is a paucity of Fr studies at low latitudes and identifying factors that significantly explain Fr is critical for understanding fishing mortality. Mean Fr rates were 0.17 [95% CI 0.09-0.30] for blue shark and 0.20 [95% CI 0.10-0.36] for silky shark. When it occurred, Fr was acute with 87% of mortalities within 2 days of release. Several prognostic operational, environmental, biological and handling variables were evaluated to assess their influence on survival outcomes. Using Kaplan-Meier survival curves, logistic regression, accelerated failure time and Cox proportional hazards models to screen variables, the only significant prognostic or risk variable was health condition at haulback. There was close correspondence (~ 83% accuracy) between condition at capture and survival outcomes. Reliable methods to classify at-vessel condition represent an inexpensive and simple metric for estimating both Fr and at-vessel (Fc) mortality rates. Examining Fc rates in detail in longline fisheries using capture information on depth, temperature and dissolved oxygen that may act in synergy with condition code and hooking duration is a research priority. Results suggest that a large proportion of shark survive following release and that Fr rates can be increased by improving the haulback condition of captured sharks. [ABSTRACT FROM AUTHOR]

Le requin peau-bleue (Prionace glauca) est un requin pélagique, hautement migrateur, qui est classé depuis 2016 en "danger critique" par l'UI CN en mer Méditerranée, mais les autorités n'ont à ce jour adopté aucune mesure pour contrôler son exploitation. Il est communément considéré comme capture accessoire des pêcheries palangrières artisanales. Notre étude analyse les tendances au sein de cette pêcherie durant ces dernières années dans les eaux Méditerranéennes espagnoles. Les résultats montrent que le requin peau-bleue subit une forte pression des flottes palangrières, particulièrement de la flotte industrielle andalouse. Les résultats suggèrent que le requin peau-bleue ne peut plus être considéré comme une espèce accessoire mais qu'il est délibérément ciblé par les pêcheurs. Cela impliquerait la prise de mesures urgentes pour réguler la pêche, de même que de nouvelles études pour savoir si, oui ou non, la pêche au requin peau-bleue peut se poursuivre dans cette zone du globe. [ABSTRACT FROM AUTHOR]

Summary: Accurate determination of age is essential for the comprehensive assessment and management of exploited shark populations. Enhancement of growth bands is necessary to accurately and efficiently determine age. However, most traditional techniques do not describe an efficiency of a series of procedures and the detailed protocol for different‐sized sharks. We describe a simple and highly successful technique for ageing vertebrae of blue shark (Prionace glauca) that we refer to as “burn method”, derived from the “break and burn method” and “shadowing method”—a simple procedure requiring an alkaline treatment to clean the vertebral centra and a burning treatment to enhance growth band visualization. We described optimal times for sharks of precaudal length of 50, 100, 150, and 200 cm as 44.9, 88.7, 134.0, 183.5 s of alkaline treatment, and 6.8, 8.9, 10.2, and 11.5 min of burning treatment; both longer and shorter exposure times resulted in higher failed sample frequencies. Using our burn method, it is possible to do ageing a sample from a wide angle, with the reader able to obtain information on growth bands from different perspectives. To critique different technique efficiencies, the index of average percent error (IAPE) and mean coefficient of variation (CV) are compared for independent readers using the burn method and other techniques (silver nitrate impregnation and the unstained shadowing methods). The precision of the burn method (IAPE, 4.1%; CV, 5.7%) was similar to that of silver nitrate impregnation (IAPE, 5.8%; CV, 8.2%) and unstained shadowing method (IAPE, 8.3%; CV, 11.8%). For younger specimens, the IAPE and CV of the burn method were lower than those of the other techniques, but, compared with other ageing methods, precision decreased for older sharks. We demonstrate that the burn method to be accurate for age determination of blue sharks, especially for specimens with less than 10 bands, but recommend simultaneous use of other methods, such as thin sectioning (the most common for structure‐based ageing) and bomb carbon dating, to accurately determine the age of older individuals. [ABSTRACT FROM AUTHOR]

The blue shark Prionace glauca, among the most common and widely studied pelagic sharks, is a top predator, exhibiting the widest distribution range. However, little is known about its population structure and spatial dynamics. With an estimated removal of 10-20 million individuals per year by fisheries, the species is classified as "Near Threatened" by International Union for Conservation of Nature. We lack the knowledge to forecast the long-term consequences of such a huge removal on this top predator itself and on its trophic network. The genetic analysis of more than 200 samples collected at broad scale (from Mediterranean Sea, North Atlantic and Pacific Oceans) using mtDNA and nine microsatellite markers allowed to detect signatures of genetic bottlenecks but a nearly complete genetic homogeneity across the entire studied range. This apparent panmixia could be explained by a genetic lag-time effect illustrated by simulations of demographic changes that were not detectable through standard genetic analysis before a long transitional phase here introduced as the "population grey zone." The results presented here can thus encompass distinct explanatory scenarios spanning from a single demographic population to several independent populations. This limitation prevents the genetic-based delineation of stocks and thus the ability to anticipate the consequences of severe depletions at all scales. More information is required for the conservation of population(s) and management of stocks, which may be provided by large-scale sampling not only of individuals worldwide, but also of loci genomewide. [ABSTRACT FROM AUTHOR]

The first record of the Ganges shark Glyphis gangeticus from anywhere in its range in over a decade is reported from the Arabian Sea. One female specimen was recorded at Sassoon Docks in Mumbai, India in February 2016, measuring 266 cm total length. In light of the Critically Endangered status of this species and its rarity, urgent management actions are needed to determine population size and trends in abundance in combination with fisher education and awareness campaigns. [ABSTRACT FROM AUTHOR]

Abstract: Management and conservation of marine predator species relies on a fundamental knowledge of their movements and behaviour. Pop‐up satellite archival tags were used to investigate the vertical movement patterns of five blue sharks (Prionace glauca) and one thresher shark (Alopias vulpinus) within the southeastern Indian Ocean. Sections of similar depth distribution, identified using a split moving window analysis, were investigated in relation to the thermal structure of the water column and activity rates. Minimum horizontal displacement of between 66 and 5,187 km for blue sharks and 16 km for the thresher shark were recorded over 863 tracking days. Maximum depths ranged from 540 to 807 m for blue sharks and 144 m for the thresher shark. All sharks displayed plasticity in their depth distribution, with diel vertical movements and surface‐oriented movements the two most common patterns. Diel movement of prey is the most likely explanation for diel vertical movements of thresher and blue sharks. This study has improved our understanding of the vertical movement patterns of these pelagic predators and the relationship between their depth distribution, temperature, and activity. [ABSTRACT FROM AUTHOR]