In vivo assessment of marine vs bovine origin collagen-based composite scaffolds promoting bone regeneration in a New Zealand rabbit model.

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.

Reproductive Biology and Distribution of the Blue Shark (Prionace glauca) in the Western Indian Ocean.

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.

Juvenile survival and movements of two threatened oceanic sharks in the North Atlantic Ocean inferred from tag-recovery data.

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.

Isolation and Biochemical Properties of Type II Collagen from Blue Shark (Prionace glauca) Cartilage.

Numerous studies have shown that type II collagen (CII) has a potential role in the treatment of rheumatoid arthritis. However, most of the current studies have used terrestrial animal cartilage as a source of CII extraction, with fewer studies involving marine organisms. Based on this background, collagen (BSCII) was isolated from blue shark (Prionace glauca) cartilage by pepsin hydrolysis and its biochemical properties including protein pattern, total sugar content, microstructure, amino acid composition, spectral characteristics and thermal stability were further investigated in the present study. The SDS-PAGE results confirmed the typical characteristic of CII, comprising three identical α1 chains and its dimeric ß chain. BSCII had the fibrous microstructure typical of collagen and an amino acid composition represented by high glycine content. BSCII had the typical UV and FTIR spectral characteristics of collagen. Further analysis revealed that BSCII had a high purity, while its secondary structure comprised 26.98% of ß-sheet, 35.60% of ß-turn, 37.41% of the random coil and no α-helix. CD spectra showed the triple helical structure of BSCII. The total sugar content, denaturation temperature and melting temperature of BSCII were (4.20 ± 0.03)%, 42 °C and 49 °C, respectively. SEM and AFM images confirmed a fibrillar and porous structure of collagen and denser fibrous bundles formed at higher concentrations. Overall, CII was successfully extracted from blue shark cartilage in the present study, and its molecular structure was intact. Therefore, blue shark cartilage could serve as a potential source for CII extraction with applications in biomedicine.

Understanding the role of ecological factors affecting mercury concentrations in the blue shark (Prionace glauca).

Human activities have increased environmental concentrations of pollutants in marine ecosystems, which can cause harmful effects on marine organisms. Top predators are particularly susceptible to bioaccumulation and biomagnification of pollutants through the food webs and are described as good sentinels for monitoring metal accumulation such mercury (Hg) in marine ecosystems. However, to be used as sentinels, it is important to understand the main ecological factors affecting the concentrations of pollutants in these organisms. In the present study, our main objective was to investigate the effect of body size, sex, trophic niche and geographic area on Hg concentrations in a top marine top predator, the blue shark (Prionace glauca). We analysed Hg in muscle samples from male and female blue sharks of different body sizes collected from the waters surrounding the Canary Islands and the South of Portugal, in the Atlantic Ocean, to waters of the north-western Mediterranean Sea. The results revealed that the sampling area was an important factor explaining Hg concentrations, showing higher values in the Mediterranean blue sharks. We also found a positive relationship between Hg concentrations and body size of blue sharks, indicating a bioaccumulation process of this pollutant in relation with body size. Moreover, we observed a relationship between Hg concentrations and δ13C values, a proxy of the use of inshore-offshore marine habitats. Individuals with depleted δ13C values that potentially foraged in offshore waters showed higher Hg values. Importantly, most of the analysed blue sharks presented Hg concentrations that exceeded the limits established by the European Union for human consumption.

Stepping up to genome scan allows stock differentiation in the worldwide distributed blue shark Prionace glauca.

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.

The relative importance of biological and environmental factors on the trophodynamics of a pelagic marine predator, the blue shark (Prionace glauca).

Marine ecosystems have been significantly altered by the cumulative impacts of human activities. Pelagic sharks have become vulnerable to increases in mortality rates caused by fishing. The decrease in number of these top predators could have substantial cascading effects on wider marine communities. Concerns about these potential impacts, and the critical need for effective management, have led to an increased interest in assessing the trophic ecology of sharks. While stable isotope analyses have been used to provide relevant insights about the trophic ecology of sharks, the causal factors leading to trophic variation between individuals has been largely overlooked. Here, we investigated the relative effect of biological factors, geographic location, and environmental factors on the spatial trophodynamics of the blue shark (Prionace glauca). Specifically, stable isotope values of δ15N and δ13C, and the estimated trophic position (TP) were analysed for 180 blue sharks collected from south of the Canary Islands in the Atlantic Ocean, to the north-western Mediterranean Sea. The results showed that models which included combined variables explained the variation in δ15N, TP and δ13C values better than models which considered only stand-alone predictors. The independent contributions of environmental variables and biological factors seemed to be more important than geographic location for δ15N and TP. δ15N and TP increased in a curvilinear fashion with body size, and TP was higher for females. In the case of δ13C values, only an effect from sex was observed. Among environmental variables, chlorophyll-a, pelagic productivity, and sea-surface temperature proved to be reliable predictors, particularly for δ15N and TP, most likely due to their relationship with productivity and prey availability. This study provides new information on ranking the factors that influence the trophodynamics of the blue shark, namely the environment, the geographic location, and the biological factors of the species.

Growth Factor-Free Vascularization of Marine-Origin Collagen Sponges Using Cryopreserved Stromal Vascular Fractions from Human Adipose Tissue.

The successful integration of transplanted three-dimensional tissue engineering (TE) constructs depends greatly on their rapid vascularization. Therefore, it is essential to address this vascularization issue in the initial design of constructs for perfused tissues. Two of the most important variables in this regard are scaffold composition and cell sourcing. Collagens with marine origins overcome some issues associated with mammal-derived collagen while maintaining their advantages in terms of biocompatibility. Concurrently, the freshly isolated stromal vascular fraction (SVF) of adipose tissue has been proposed as an advantageous cell fraction for vascularization purposes due to its highly angiogenic properties, allowing extrinsic angiogenic growth factor-free vascularization strategies for TE applications. In this study, we aimed at understanding whether marine collagen 3D matrices could support cryopreserved human SVF in maintaining intrinsic angiogenic properties observed for fresh SVF. For this, cryopreserved human SVF was seeded on blue shark collagen sponges and cultured up to 7 days in a basal medium. The secretome profile of several angiogenesis-related factors was studied throughout culture times and correlated with the expression pattern of CD31 and CD146, which showed the formation of a prevascular network. Upon in ovo implantation, increased vessel recruitment was observed in prevascularized sponges when compared with sponges without SVF cells. Immunohistochemistry for CD31 demonstrated the improved integration of prevascularized sponges within chick chorioalantoic membrane (CAM) tissues, while in situ hybridization showed human cells lining blood vessels. These results demonstrate the potential of using cryopreserved SVF combined with marine collagen as a streamlined approach to improve the vascularization of TE constructs.

Microplastic contamination and risk assessment in blue shark (Prionace glauca) from the eastern tropical Pacific Ocean.

We quantified the abundance and characteristics of microplastics in the blue shark, Prionace glauca, found in the eastern tropical Pacific Ocean and investigated the potential microplastic pollution risks. Microplastics (MPs) were detected in 39.1 % of specimens, up to 0.15 ± 0.38 items/g wet weight of the posterior part of the pylorus, and were sized 45.87 to 3220.12 µm. The majority were fibrous in shape (83.3 %) and blue in color (72.2 %). Both sexes of sharks had similar MP abundance and characteristics, except for polymers, with polyethylene terephthalate and polypropylene representing the dominant type in males and females, respectively. Most individuals experienced low pollution, but one male P. glauca exhibited a high ecological risk level owing to the high MP abundance and detection of polyvinyl chloride. This study provides an important baseline for the ingestion of microplastics by pelagic shark species and is a preliminary quantitative measure that could be used in future studies of the risk of MPs.

Metal concentrations and metallothionein metal detoxification in blue sharks, Prionace glauca L. from the Western North Atlantic Ocean.

BACKGROUND: Elasmobranchs are particularly vulnerable to environmental metal contamination, accumulating these contaminants at high rates and excreting them slowly. The blue shark Prionace glauca L. is one of the most heavily fished elasmobranchs, although information regarding metal contamination and detoxification in this species is notably lacking. METHODS: Blue sharks were sampled in the western North Atlantic Ocean, in offshore waters adjacent to Cape Cod, Massachusetts. Total and metallothionein-bound liver and muscle metal concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS), metallothionein detoxification and oxidative stress endpoints were determined by UV-vis spectrophotometry. RESULTS: Metallothionein detoxification occurred for As, Cd, Cs, Cu, Hg, Pb, Se, Ti and Zn in liver, and for As, Cd, Cs, Pb, Se, and Zn in muscle, while reduced glutathione defenses seem to be related to Co and Zn exposure. CONCLUSION: This is the first report for several metals (Ag, Co, non-radioactive Cs, Sb, Ti and V) for this species, which will aid in establishing baseline elemental data for biomonitoring efforts, health metrics, and conservation measures.

Climate-driven deoxygenation elevates fishing vulnerability for the ocean's widest ranging shark.

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.

Does Subunit Composition Influence the Intermolecular Crosslinking of Fish Collagen? A Study with Hake and Blue Shark Skin Collagens.

Acid-soluble collagens from European hake and Blue shark skin were isolated, characterized, and compared. As the structure of collagen determines its function, the final objective of this study was to investigate biochemical differences between both collagens to identify future potential applications. Chromatographic behavior revealed differences in collagen from both species. Increases of temperature and stirring time produced no effect on European hake collagen solubility in the mobile phase, resulting in the same chromatographic profiles. Conversely, the application of temperature and stirring-time increments showed a positive effect on Blue shark collagen solubility, resulting in different chromatographic profiles and observing higher molecular weight components when sample is incubated at 50 °C (15 min) after 48 h stirring. To test if the different chromatographic behavior exhibited by both collagens could be influenced by differences in subunit composition (alpha-chains), cation exchange chromatography was employed to separate collagen subunits. The electrophoretic patterns and gel permeation chromatography with light-scattering detection (GPC-LS) results of the obtained cation exchange peak fractions revealed differences regarding subunit composition between both species, influencing the crosslinking pattern. This is the first comparative study using GPC-LS to provide information of European hake and Blue shark collagen subunit composition.

Spiral valve parasites of blue and common thresher sharks as indicators of shark feeding behaviour and ecology.

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.

Presence of the protein indoleamine 2,3-dioxygenase (IDO) in the maternal-fetal interface of the yolk sac placenta of blue shark, Prionace glauca.

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.

Evaluation of Differentiated Bone Cells Proliferation by Blue Shark Skin Collagen via Biochemical for Bone Tissue Engineering.

Collagen from a marine resource is believed to have more potential activity in bone tissue engineering and their bioactivity depends on biochemical and structural properties. Considering the above concept, pepsin soluble collagen (PSC) and acid soluble collagen (ASC) from blue shark (Prionace glauca) skin were extracted and its biochemical and osteogenic properties were investigated. The hydroxyproline content was higher in PSC than ASC and the purified collagens contained three distinct bands α1, α2, and ß dimer. The purity of collagen was confirmed by the RP-HPLC profile and the thermogravimetric data showed a two-step thermal degradation pattern. ASC had a sharp decline in viscosity at 20⁻30 °C. Scanning electron microscope (SEM) images revealed the fibrillar network structure of collagens. Proliferation rates of the differentiated mouse bone marrow-mesenchymal stem (dMBMS) and differentiated osteoblastic (dMC3T3E1) cells were increased in collagen treated groups rather than the controls and the effect was dose-dependent, which was further supported by higher osteogenic protein and mRNA expression in collagen treated bone cells. Among two collagens, PSC had significantly increased dMBMS cell proliferation and this was materialized through increasing RUNX2 and collagen-I expression in bone cells. Accordingly, the collagens from blue shark skin with excellent biochemical and osteogenic properties could be a suitable biomaterial for therapeutic application.

Large-scale genetic panmixia in the blue shark (Prionace glauca): A single worldwide population, or a genetic lag-time effect of the "grey zone" of differentiation?

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.

Mercury in blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) from north-eastern Atlantic: Implication for fishery management.

Pelagic sharks (blue shark Prionace glauca and shortfin mako Isurus oxyrinchus) caught by long-line Spanish and Portuguese fleets in the NE Atlantic, were sampled at Vigo fish market (Spain) for total mercury (Hg) analysis. Hg concentration in white muscle increased with size and weight in both species, but at a higher rate in shortfin mako than in the blue shark. No difference was found with sex, year and season. Spatial variation was observed in the blue shark with higher Hg values in the North of the Azorean archipelago, but not in the shortfin mako. These high-level predators are particularly susceptible to bioaccumulate contaminants (Hg) in their tissues (muscle). However, a significant positive relationship between Hg concentration and trophic level (δ15N) of individuals was observed only in the shortfin mako. Most sharks landed were juveniles which presented Hg concentration lower than the maximum limit allowed by the European Union (1mgkg-1 wet weight) for marketing. However, concentrations above this threshold were most recorded in blue sharks larger than 250cm total length (TL) and in shortfin makos larger than 190cm TL, raising the question of the commercialization of large-sized individuals.

Genetic differentiation and phylogeography of Mediterranean-North Eastern Atlantic blue shark (Prionace glauca, L. 1758) using mitochondrial DNA: panmixia or complex stock structure?

BACKGROUND: The blue shark (Prionace glauca, Linnaeus 1758) is one of the most abundant epipelagic shark inhabiting all the oceans except the poles, including the Mediterranean Sea, but its genetic structure has not been confirmed at basin and interoceanic distances. Past tagging programs in the Atlantic Ocean failed to find evidence of migration of blue sharks between the Mediterranean and the adjacent Atlantic, despite the extreme vagility of the species. Although the high rate of by-catch in the Mediterranean basin, to date no genetic study on Mediterranean blue shark was carried out, which constitutes a significant knowledge gap, considering that this population is classified as "Critically Endangered", unlike its open-ocean counterpart. METHODS: Blue shark phylogeography and demography in the Mediterranean Sea and North-Eastern Atlantic Ocean were inferred using two mitochondrial genes (Cytb and control region) amplified from 207 and 170 individuals respectively, collected from six localities across the Mediterranean and two from the North-Eastern Atlantic. RESULTS: Although no obvious pattern of geographical differentiation was apparent from the haplotype network, Φst analyses indicated significant genetic structure among four geographical groups. Demographic analyses suggest that these populations have experienced a constant population expansion in the last 0.4-0.1 million of years. DISCUSSION: The weak, but significant, differences in Mediterranean and adjacent North-eastern Atlantic blue sharks revealed a complex phylogeographic structure, which appears to reject the assumption of panmixia across the study area, but also supports a certain degree of population connectivity across the Strait of Gibraltar, despite the lack of evidence of migratory movements observed by tagging data. Analyses of spatial genetic structure in relation to sex-ratio and size could indicate some level of sex/stage biased migratory behaviour.

Biogeophysical and physiological processes drive movement patterns in a marine predator.

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.