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.

Substantial global population declines in pelagic sharks have led to the introduction of management and conservation measures, including gear restrictions and no-retention policies, to curb declines and encourage stock recovery. As the rate of discarding sharks increases, there is a growing need to understand prognostic factors that influence their post-release survival (PRS) outcomes.PRS was measured with survival pop-up satellite archival tags attached to shortfin mako (Isurus oxyrinchus) and silky sharks (Carcharhinus falciformis) released or discarded from pelagic tuna longline fishing vessels operating in the Western and Central Pacific Fisheries Commission Convention Area. In total, 117 tags were deployed on 60 mako and 57 silky sharks captured as bycatch during commercial pelagic longline fishing trips in New Zealand (n = 35), Fiji (n = 58), New Caledonia (n = 10) and the Republic of the Marshall Islands (n = 14).Mako engaged in long-distance movements between New Zealand, Australia, Fiji and New Caledonia, while silky sharks tagged in the Marshall Islands showed evidence of seasonal movements eastward.PRS was determined for 110 sharks (57 mako, 53 silky sharks). Most tagged sharks of both species were uninjured (89%) at capture and most sharks (88%) survived post-release until tag loss or the programmed pop-up date (60 days). However, when considering a complete fishing interaction (haulback, handling, release), PRS estimates were markedly reduced to 48.6% and 52.3% for mako and silky sharks, respectively. For both species, survivorship was greater in large (>150 cm fork length) uninjured sharks and sharks released with low shark length to trailing branchline ratios.While these findings suggest that retention bans offer sharks an increased chance of survival, continued efforts should be made to improve handling and release practices, reduce trailing gear and minimize pelagic shark bycatch.

The taxon Elasmobranchii (sharks and rays) contains one of the long-established evolutionary lineages of vertebrates with a tantalizing collection of species occupying critical aquatic habitats. To overcome the current limitation in molecular resources, we launched the Squalomix Consortium in 2020 to promote a genome-wide array of molecular approaches, specifically targeting shark and ray species. Among the various bottlenecks in working with elasmobranchs are their elusiveness and low fecundity as well as the large and highly repetitive genomes. Their peculiar body fluid composition has also hindered the establishment of methods to perform routine cell culturing required for their karyotyping. In the Squalomix consortium, these obstacles are expected to be solved through a combination of in-house cytological techniques including karyotyping of cultured cells, chromatin preparation for Hi-C data acquisition, and high fidelity long-read sequencing. The resources and products obtained in this consortium, including genome and transcriptome sequences, a genome browser powered by JBrowse2 to visualize sequence alignments, and comprehensive matrices of gene expression profiles for selected species are accessible through https://github.com/Squalomix/info.

Spatial segregation is a key component to understand the ecology of highly migratory species; however, this aspect is poorly known for many pelagic shark species. We investigated spatial segregation by sex and life-history stage in blue sharks Prionace glauca in the northwestern Pacific, using satellite tracking data gathered from 74 electronic tags as well as fisheries-dependent size-measurement datasets, which allowed us to update a schematic diagram of the migration patterns of this population. Blue sharks were tracked for 30 to 271 d (mean 125 d) during which they moved extensively between temperate and subtropical waters. Juveniles were distributed mainly in the North Pacific Transition Zone (30°-45°N), but expanded their range southward as they grew, while adults in the entire northwestern Pacific showed clear spatial segregation by sex. Adult females migrated seasonally between temperate and subtropical areas for reproduction, while adult males occupied a broad distribution area yet mainly in temperate waters (30°-40°N), and their habitats partially overlapped with those of juveniles of both sexes. These findings provide new insights for updating the schematic migration diagram of this population, especially because adult males were previously thought to distribute mainly in tropical and subtropical waters. Furthermore, a majority of adult females found north of 30°N exhibited fresh mating scars; this observation suggests that the mating ground of blue sharks in the northwestern Pacific is broader (20°-40°N) than previously thought (20°-30°N), and partially overlaps with the parturition and nursery grounds of this species (30°-50°N).

Information on the movements of highly migratory species is important to understand their ecology, including habitat use, population connectivity, and stock structure, to implement appropriate management and conservation measures. The blue shark Prionace glauca (Carcharhinidae) is highly migratory, has a global distribution, and is ecologically and economically important as one of the most abundant apex marine predators; however, the migration patterns of pregnant females are unknown. Here, we used pop-up satellite archival tags to elucidate seasonal migration of pregnant blue sharks in the northwestern Pacific. Of 24 tagged adult females, archival data were subsequently obtained for 21 individuals (141.1-243.3 cm precaudal length). Based on ultrasonography or analysis of sex steroid hormones, 17 of these females were confirmed to be pregnant at the time of release. Females with small embryos moved in a northeasterly direction, from subtropical (10-30°N) into temperate (30-40°N) waters during autumn and the following spring; 2 of these females returned to subtropical waters in spring and summer. In contrast, females with large embryos moved in a southwesterly direction, from temperate into subtropical waters during spring and autumn. Tagged sharks also showed regional differences in diving behaviors, reflecting thermal habitats in the ocean environment. Our findings indicate that pregnant blue sharks undergo a seasonal northeast-southwest migration within a year to give birth to pups in productive temperate waters. This is the first report on seasonal reproductive migration of pregnant blue sharks in the global ocean.

Plasma concentrations of progesterone (P4 ) and 17β-oestradiol (E2 ) in juvenile, pre-ovulatory, early, mid- or late pregnancy stages of female blue sharks Prionace glauca were analysed. Concentrations of P4 were significantly higher in pregnant than in non-pregnant individuals, whereas E2 concentrations increased with embryonic and follicular development. A highly accurate (86.1%) random forest classification model was developed to predict shark pregnancy. It is proposed that hormone concentrations could be used for the subsequent non-lethal determination of female P. glauca reproductive state.

Accurate estimation of growth parameters is vital for stock assessments and management of exploited species. To determine if changes in sex-specific growth parameters of the blue shark (Prionace glauca) have occurred in the North Pacific Ocean following population declines in the 1980s and 1990s, we analyzed data obtained from the vertebrae of 659 male and 620 female sharks that had precaudal lengths (PCLs) of 33.4-258.3 cm and were captured over a wide geographic area between 2010 and 2016. Maximum counts of growth bands were 18 for males and 17 for females. Significant (P<0.001) between-sex differences were detected in growth parameters. We estimated parameters of the von Bertalanffy growth function: for males, the theoretical asymptotic length (L-infinity) was 284.9 cm PCL, the growth coefficient (k) was 0.117/year, and the theoretical age at zero length (t(0)) was -1.35 years, and, for females, L-infinity was 257.2 cm PCL, k was 0.146/year, and t(0) was -0.97 years. Sexual discrepancies in growth rates are likely a function of differences in energy allocation relating to reproduction between sexes. Given that no remarkable change in growth parameters was observed over 3 decades, life history parameters of this population do not appear to have been affected by shifts in stock abundance or environmental fluctuation.

Sharks, which maintain the role of top predator in aquatic ecosystems, have a reproductive system and life history traits that are quite different from those of most teleosts, including internal fertilization, slow growth, high age at maturity, and the live birth of only a few well-formed offspring. Although shark species show diversity in many traits such as body size, morphology, diet, habitat (vertically, horizontally, and latitudinally), and reproductive system (ovoviviparous and viviparous), sexual difference in various phenotypic traits is one of their major characteristics. Sex-specific phenotypic traits such as life history parameters and sexual segregation are illustrated, focusing on shortfin mako and other species. A survey of the literature on growth suggests that slow growth and large body size in females are a major trend in sharks with significant intersexual difference in growth. Sexual segregation of sharks is reported with varying degrees of resolution, but its pattern is variable depending on the species, and the underlying mechanisms are largely unclear. The implication of intersexual difference in life history and behavioral traits is discussed from both evolutional and practical points of view. Existing studies that have evaluated the effect of sexual difference suggest the importance of including sex-specific traits in stock assessment and management, especially for species with marked sexual difference. Given its significance, both the study of sexual difference in the biological characteristics and the collection of sex-specific information on fishery statistics are important for understanding population dynamics and the sustainable exploitation of shark species.

The reproductive biology of the blue shark (Prionace glauca) in the western North Pacific Ocean was investigated to contribute to future stock assessments because of limitations of recent studies and the lack of information about the reproductive cycle. Reproductive data were obtained from 490 males (precaudal length (PCL), 33.4–252.0cm) and 432 females (PCL, 33.4–243.3cm). Size at 50% maturity was estimated to be 160.9cm for males and 156.6cm PCL for females. Litter size varied from 15 to 112 (mean 35.5) and was positively correlated with maternal PCL. Parturition, ovulation and mating occurred sequentially from spring to summer. The gestation period was estimated to be 11 months. The ovarian follicles of pregnant females developed synchronously throughout the gestation period along with embryonic growth, indicating that females reproduce annually. Our results showed that the productivity of North Pacific blue sharks is higher than previously thought, based on larger fecundity and a shorter reproductive cycle. These new findings will improve future stock assessments and provide management advice.

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T.obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5-65.0cm in fork length (FL)], 43 yellowfin (31.6-93.5cm FL) and 32 bigeye tuna (33.5-85.5cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100m, but occasionally dived to around 150m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow theselective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.

Based on nucleotide substitutions in four mitochondrial DNA regions, we developed multiplex PCR assays for identifying species/lineages in yellowfin Thunnus albacares and bigeye T. obesus tunas. The validity of the assays was tested on 3247 individuals of seven Thunnus tuna species (T. orientalis, T. thynnus, T. maccoyii, T. alalunga, T. albacares, T. obesus, and T. tonggol). Bigeye and yellowfin tunas were almost completely discriminated. Of the two intraspecific mitochondrial lineages—alpha (clade II) and beta (clade I)—of bigeye tuna, the former is known to predominate in the Atlantic but to be almost nonexistent in the Indo-Pacific. The multiplex PCR methods we developed were able to discriminate these two lineages. These multiplex PCR assays were more rapid and robust than conventional methods for identifying these tunas and their intraspecific lineages.

Longline surveys have been conducted in the Northwest Pacific Ocean from 2000 to 2014 using chartered commercial longline vessels. Each year, two cruises were conducted offshore of northeastern Japan from mid-April to mid-June. For each longline set during the surveys, onboard scientists collected detailed biological information about the species caught, such as the size and sex, and recorded the catch numbers for all species. Blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) have eurythermal distributions, but the application of a generalized additive model (GAM) showed that the sea surface temperatures (SSTs) at catch sites positive for shortfin mako were warmer than those for blue shark. On the basis of the GAM, the probabilities of occurrence of both sharks differed by size category: small sharks had a narrower SST range than that of large sharks. Most catches of both sharks were juveniles, and the nominal catch rate of blue shark was more than 10 times that of shortfin mako. The standardized catch per unit effort (CPUE) for both species was calculated using a generalized linear model (GLM) with negative binomial errors, or a delta-lognormal GLM. The standardized CPUE for blue shark in the second quarter of the year peaked in the mid-2000s and then decreased, but it has been increasing since 2012. The CPUE for shortfin mako in the second quarter generally increased, with fluctuations.

The number and weight of shortfin mako caught by the Japanese tuna longline vessels in the Atlantic was estimated based on the logbook data and the standardized CPUE from 1994 to 2010. Live releases and dead discards were estimated based on the information on the life status which was collected in the observer program. The catch number was estimated at 1,9164,395 t for the North (from the equator to South of 50 degrees North) and 665-6,720 t for the South, and the catch weight was estimated at 72-227 t for the North and 32-308 t for South.

Knowledge of a species’ distribution is an important element in its effective management and conservation. The porbeagle (Lamna nasus) is a common by-catch shark in the tuna longline fishery in the southern hemisphere, but its distribution and abundance are largely unknown. The investigation of observer data from the tuna longline fishery and other fishery survey data has revealed that (1) porbeagles are distributed in the pelagic waters across the oceans of the southern hemisphere, (2) juveniles and adults are distributed in cooler environments than are neonates, (3) pregnant females occur in the pelagic waters of the Indian Ocean and the Tasman Sea, most being frequently recorded around the Cape of Good Hope between June and July and (4) the standardised catch per unit effort (CPUE) based on tuna longline fishery (1994–2011) and driftnet survey (1982–1990) data indicate no continuous decreasing trend in the abundance of the southern porbeagle, contrary to the declining trend reported in a limited region in the South Atlantic. Considering its circumglobal distribution, stock status of this population should be assessed using information from the areas of its major distribution, including pelagic waters, and international coordination across oceans is necessary for the effective management of this population.

The knowledge on distribution is important element for the effective management and conservation of species. For bycatch species, fundamental information on its range and distributional pattern is often insufficient. Porbeagle (Lamna nasus) in the Southern Hemisphere is the common bycatch sharks in the tuna longline fishery but its distribution and abundance are largely unknown. Investigation of the fishery and survey data revealed the common occurrence of porbeagle in the pelagic waters in the South Pacific, southeastern Indian Ocean and off Cape in all seasons. Analysis of temperature at catch and ontogenetic stage suggested that porbeagles penetrate into higher latitude according to growth. Pregnant females were recorded in the Indian Ocean and Tasman Sea, but most frequently recorded around Cape between June and July. The trend of abundance estimated from the longline fishery and driftnet survey data indicated no continuous decreasing trend for porbeagle in Considering the circumglobal distribution, stock status of this population should be assessed using information from coastal and pelagic waters and the international coordination across the oceans is necessary for the effective management of this population.