Female Sharks Research Articles

A longitudinal behavioral analysis of aquarium whale sharks (Rhincodon typus): insights into anticipatory cues, individual variation, and social interaction

Rhincodon typus, or the whale shark, is the largest extant fish in the world and is classified as endangered on the IUCN’s Red List. Due to their enormous size and conservation status, whale sharks are rarely housed in aquaria. Here we present a behavioral analysis culminating from a large effort by 89 observers from 2008–2012 to study four R. typus (ID codes: AL, TA, TR, YU) longitudinally in an aquarium setting. We found that relatively simple behavioral metrics such as swim speed, depth occupation, swimming direction, and lead-follow interactions demonstrated R. typus individual variation and responses to habitat changes. All sharks displayed increased swim speeds 30-minutes before regimented feed times, when there was scent of food being fed to other animals in the habitat. Consistently in the habitat, one male shark (YU) was recorded swimming more at depth, faster, almost exclusively clockwise, and engaged in fewer close proximity interactions with others than expected by chance. In contrast, a larger female shark (AL) was observed swimming the slowest, at the surface more than others, led other sharks more than she followed, and had strong lead-follow interactions with another shark of the opposite sex (TA). TA and TR did not differ from each other in depth profiles or speed, but did differ in their proclivity to lead or follow. Depth preferences and lead-follow interactions suggest some partitioning of the habitat and the possibility of social hierarchy in this species. These results represent the first longitudinal behavioral analysis of aquarium R. typus, offering meaningful similarities and contrasts to field observations.

Businesswomen’s Persuasive Language in Vietnamese and American English Negotiation Conversations: A Case Study

The current study is investigating the different persuasive language in negotiations between Vietnamese and American business women in business and media contexts. With descriptive and mixed method, the data recorded from 10 negotiating conversations in Shark Tank Vietnam and Shark Tank US – a real TV program were transcribed and analyzed under Aristotle’s modes of persuasion, in the assistance of SPSS analysis tool to reveal the different strategic tactics by female sharks (known as investors) in 2 programs and the various combination of sub-type appeals (logos, pathos, and ethos) in each speech in Shark Tank Vietnam and US. The findings significantly contributed to the differences of female communication style at work in two nations.

Observations of biennial reproduction in Caribbean reef sharks ‘Carcharhinus perezi’

Effective management and conservation of threatened species biodiversity requires knowledge of reproductive biology, such as cyclicity, mode, and age at maturity. We combined reproductive endocrinology and in-situ ultrasonography to examine reproductive characteristics of female Caribbean reef sharks Carcharhinus perezi, a widely distributed, threatened marine predator which remains largely understudied throughout its range. Unique to this study was the opportunity to conduct longitudinal assessments of two individuals, recaptured across multiple seasons during sampling in The Bahamas. Within-individual, paired hormone analyses and in-situ ultrasounds of female sharks that were confirmed as either pregnant, non-pregnant, or reproductively active, suggest a biennial reproductive cycle for Carcharhinus perezi. This unique opportunity to assess the reproductive biology of the same individuals over time underscore the importance of repeated sampling for elucidating population reproductive cyclicity of highly mobile sharks in the wild.

Individual residency behaviours and seasonal long-distance movements in acoustically tagged Caribbean reef sharks in the Cayman Islands.

Understanding how reef-associated sharks use coastal waters through their ontogeny is important for their effective conservation and management. This study used the horizontal movements of acoustically tagged Caribbean reef sharks (Carcharhinus perezi) to examine their use of coastal space around the Cayman Islands between 2009 and 2019. A total of 39 (59.1%) tagged sharks (male = 22, female = 17, immature = 18, mature = 21) were detected on the islands wide network of acoustic receivers. The detection data were used to calculate values of Residency Index (RI), Site-Fidelity Index (SFI) and minimum linear displacement (MLD), as well as for network analysis of individual shark movements to test for differences between demographics, seasons, and diel periods. Sharks were detected for up to 1,598 days post-tagging and some individuals showed resident behaviour but the majority of tagged individuals appear to have been one-off or only occasional transient visitors to the area. Generally, individuals showed strong site-fidelity to different areas displaying linear home ranges of < 20 km. The evidence indicates that there was no pattern of diel behaviour. Tagged sharks generally showed increased movements within and between islands during the summer (April-September), which may be related to breeding activity. Some individuals even made occasional excursions across 110 km of open water > 2,000 m deep between Grand Cayman and Little Cayman. One mature female shark showed a displacement of 148.21 km, the greatest distance reported for this species. The data shows that the distances over which some sharks moved, greatly exceeded the extent of any one of the islands' marine protected areas indicating that this species may be more mobile and dispersive than previously thought. This study provides support for the blanket protection to all sharks throughout Cayman waters, which was incorporated within the National Conservation Act in 2015.

Genetic evidence for plastic reproductive philopatry and matrotrophy in blacktip reef sharks (Carcharhinus melanopterus) of the Moorea Island (French Polynesia)

The exploitation of sharks and the degradation of their habitats elevate the urgency to understand the factors that influence offspring survival and ultimately shark reproductive success. We monitored and sampled blacktip reef sharks (Carcharhinus melanopterus) in nursery habitats of Moorea Island (French Polynesia), to improve knowledge on shark reproductive behavior and biology. We sampled fin clips and morphometrics from 230 young-of-the-year sharks and used microsatellite DNA markers to process parentage analysis to study the reproductive philopatric behavior in female sharks and the matrotrophy within litters. These traits are driving the success of the local replenishment influencing selection through birth site and maternal reserves transmitted to pups. Parentage analysis revealed that some female sharks changed their parturition areas (inter-seasonally) while other female sharks came back to the same site for parturition, providing evidence for a plastic philopatric behavior. Morphometrics showed that there was no significant relationship between body condition indices and nursery locations. However, similarities and differences in body condition were observed between individuals sharing the same mother, indicating that resource allocation within some shark litters might be unbalanced. Our findings further our understanding of the reproductive biology and behavior that shape shark populations with the aim to introduce these parameters into future conservation strategies.

Relationships in Shark Skin: Mechanical and Morphological Properties Vary between Sexes and among Species.

Shark skin is a composite of mineralized dermal denticles embedded in an internal collagen fiber network and is sexually dimorphic. Female shark skin is thicker, has greater denticle density and denticle overlap compared to male shark skin, and denticle morphology differs between sexes. The skin behaves with mechanical anisotropy, extending farther when tested along the longitudinal (anteroposterior) axis but increasing in stiffness along the hoop (dorsoventral or circumferential) axis. As a result, shark skin has been hypothesized to function as an exotendon. This study aims to quantify sex differences in the mechanical properties and morphology of shark skin. We tested skin from two immature male and two immature female sharks from three species (bonnethead shark, Sphyrna tiburo; bull shark, Carcharhinus leucas; silky shark, Carcharhinus falciformis) along two orientations (longitudinal and hoop) in uniaxial tension with an Instron E1000 at a 2 mm s-1 strain rate. We found that male shark skin was significantly tougher than female skin, although females had significantly greater skin thickness compared to males. We found skin in the hoop direction was significantly stiffer than the longitudinal direction across sexes and species, while skin in the longitudinal direction was significantly more extensible than in the hoop direction. We found that shark skin mechanical behavior was impacted by sex, species, and direction, and related to morphological features of the skin.

The successful use of a submersible ultrasound to confirm pregnancy on free swimming bull sharks, Carcharhinus leucas, in a provisioned shark site

A prototype, fully submersible, high definition ultrasound was used to determine the reproductive state of wild, free-swimming bull sharks, Carcharhinus leucas, at a provisioned shark diving site in Playa del Carmen, Mexico. During two opportunistic dives, the presence of embryos was confirmed in three female sharks (greater than 2.0 m total length) and emphasizes the importance of developing and linking emerging technologies with shark diving sites for the conservation of elasmobranch species.

Observations on heterodonty within the dentition of the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), from the north-central Gulf of Mexico, USA, with implications on the fossil record.

The Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), is the most common small coastal requiem shark in the north-central Gulf of Mexico, USA. Despite this fact, little is known about the dental variation within this taxon. To help rectify this shortcoming, we examined 126 male and female R. terraenovae jaws sets across all maturity stages to document the various types of heterodonty occurring in the dentition of this taxon. Quantitative data gathered from a subset of our sample allowed for us to place teeth within the dentition of R. terraenovae into standardized upper and lower parasymphyseal/symphyseal, anterior lateral, and posterior tooth groups. As with all carcharhinid sharks, the dentition of R. terraenovae exhibits monognathic and dignathic heterodonty. We also observed significant ontogenetic heterodonty in the species, as the teeth and dentition progress through five generalized developmental stages as the shark matures. The ontogenetic development of serrations on the teeth appears to be closely related to documented dietary changes as the shark matures. Initial diets are comprised of high percentages of invertebrate prey like shrimp, crabs, and squid, but this transitions through ontogeny to a diet that is more reliant on fishes. We also provide the first documentation of gynandric heterodonty in mature male R. terraenovae, with development of these seasonal teeth likely enabling a male to grasp female sharks during copulation. Our analysis revealed a tremendous amount of variation in the dentition of R. terraenovae, which has direct implications on the taxonomy of fossil Rhizoprionodon. A comparison of the jaws in our sample to those of the extant species of Rhizoprionodon and the morphologically similar Loxodon, Scoliodon, and Sphyrna allowed us to formulate a list of generic-level characteristics to assist with the identification of isolated teeth. When applied to the fossil record, it is shown that some species previously assigned to Rhizoprionodon likely belong to one of the other aforementioned genera. The earliest occurrence of unequivocal Rhizoprionodon teeth in the fossil record are those of the Eocene †R. ganntourensis (Arambourg, 1952), the oldest records of which occur in early Ypresian deposits in Alabama and Mississippi, USA. The early Eocene occurrence of unequivocal fossil Rhizoprionodon teeth in Alabama predates the first occurrence of Negaprion, Galeocerdo, and Carcharhinus teeth in the state, supporting published molecular and morphological phylogenies positing a basal position for Rhizoprionodon within the Carcharhinidae.

Contrast-enhanced computed tomography and cross-sectional anatomy of the trunk in the brownbanded bamboo shark (Chiloscyllium punctatum).

Computed tomography (CT) is used in veterinary medicine for the diagnosis of bones and soft tissue diseases in various species. In addition, CT has recently been used to diagnose aquatic animals, including Selachimorpha, which are difficult to diagnose out of water. However, because Selachimorpha do not have adipose tissue in the coelomic cavity, the coelomic organs cannot be fully identified using non-contrast CT (NCCT). The aim of this study is to present the anatomical features of the cadaver, NCCT, and contrast-enhanced CT (CECT) as well as the change in CT values of the coelomic organs and musculature of the brownbanded bamboo shark. NCCT scans were performed under anaesthesia in one male and one female shark. CECT was performed 30 min after iopamidol was administered intravenously. The sharks were euthanized, frozen at -20°C, and sliced in the same position in which they were scanned. Using electric band saw, 10-mm transversal sections were obtained. The anatomical structures of both males and females were identified by transversal sections, and CT images homologous to transversal sections were then selected. Sagittal and coronal CECT images were also obtained to facilitate understanding of the location and size of coelomic organs. Although bone structure and air in organs could be sufficiently discriminated on NCCT image, the coelomic organs were almost indistinguishable. On the other hand, CECT images obtained sufficient contrast to identify most coelomic organs in addition to bone and air. The results provide an atlas of a cross-sectional anatomy and CECT images, which is useful information for the medical diagnosis of coelomic organs in live Selachimorpha.

Underwater ultrasonography and blood sampling provide the first observations of reproductive biology in free-swimming whale sharks

We report on a non-invasive technique for observing the reproductive states of wild, free-swimming whale sharks Rhincodon typus for the first time. Female whale sharks (n = 22) were assessed using underwater ultrasonography and a novel blood-sampling technique at Darwin Island in the Galapagos Marine Reserve, Ecuador. Despite the widely held assumption among researchers that the post-pelvic distention of large females is indicative of pregnancy, ultrasound provided no evidence of embryos or egg cases. However, the presence of follicles (diameter: 28.5-83.6 mm) was confirmed in 2 female sharks of 11-12 m total length (TL). Additionally, 3 steroid hormones (estradiol, testosterone, and progesterone) were analyzed in blood plasma from 6 female sharks (11-12 m TL). Hormone levels were similar to, or lower than, those obtained from an immature female in the Okinawa Churaumi Aquarium. Based on these results, we infer that female whale sharks (TL &gt;11 m) in this study were mature but not pregnant. The techniques used here for whale sharks can be successfully used to obtain non-lethal field data on the biology and reproductive anatomy of this globally endangered fish, and are adaptable for use in other large marine species.

Demographic Analysis of Shortfin Mako Shark (Isurus oxyrinchus) in the South Pacific Ocean.

The shortfin mako shark (Isurus oxyrinchus) demonstrates low productivity and is thus relatively sensitive to fishing. Natural mortality (M) and fishing mortality (F) data are critical to determine their population dynamics. However, catch and fishing effort data are unavailable for this species in the South Pacific Ocean, making stock assessments difficult. Demographic quantitative methods aid in analyzing species with limited data availability. We used a two-sex stage-structured matrix population model to examine the demographic stock status of mako sharks. However, data-limited models to determine fishery management strategies have limitations. We performed Monte Carlo simulations to evaluate the effects of uncertainty on the estimated mako shark population growth rate. Under unfished conditions, the simulations demonstrated that the mako sharks showed a higher finite population growth rate in the 2-year reproductive cycle compared to the 3-year reproductive cycle. Protecting immature mako sharks led to a higher population growth rate than protecting mature mako sharks. According to the sex-specific data, protecting immature male and female sharks led to a higher population growth rate than protecting mature male and female sharks. In conclusion, sex-specific management measures can facilitate the sustainable mako shark conservation and management.

Reproductive Cycle and Periodicity of In Situ and Aquarium Female Sand Tiger Sharks Carcharias taurus from the Western North Atlantic

Fundamental characteristics of the reproductive biology of female sand tiger sharks Carcharias taurus are needed to understand the periodicity, seasonality and environmental factors essential for reproduction in this iconic species. Animals in managed care, such as aquariums, provide the unique opportunity for longitudinal study in contrast to in situ sharks that are examined opportunistically, and at a single point in time. Additionally, comparison of reproductive observations from successfully reproducing in situ sharks and aquarium sharks may help elucidate reasons for lack of reproduction among aquarium sharks and aid the development of assisted reproductive techniques for managed populations. Reproductive status of in situ and aquarium female sharks was assessed using ultrasonography and plasma hormone (17β-estradiol, testosterone, and progesterone) monitoring. The reproductive cycle was divided into eight stages based on ovarian activity and uterine contents. In situ sharks were sampled from Delaware Bay (n = 29), North Carolina (n = 39) and South Carolina (n = 11) during April-November from 2015–2020. Nineteen aquarium females from five aquaria were examined longitudinally for two or more consecutive years. Reproductive regionalization was observed among in situ females with the majority (83%) of North Carolina females in an active state of reproduction and all Delaware females in a resting reproductive state. All aquarium females had a pattern of reproductive cycling that was consistent with alternating years of activity and rest with confirmed biennial (n = 7) or triennial (n = 3) reproductive cycles with spring seasonality. In contrast to in situ females, aquarium females often retained uterine eggs for 9-20 months after ovulation in the absence of a developing embryo(s). Pre-ovulatory aquarium females had significantly higher concentrations of 17β-estradiol, testosterone and progesterone than other reproductive stages. For females in the ovulatory stage, in situ females had higher testosterone than aquarium females. Endocrine differences between successfully reproducing in situ females and aquarium females likely contribute to the limited reproductive success observed for this species in managed care and may be a reflection of diminished seasonal cues and environmental differences.

First descriptions of the seasonal habitat use and residency of scalloped hammerhead (Sphyrna lewini) and Galapagos sharks (Carcharhinus galapagensis) at a coastal seamount off Japan

BackgroundThe Northwestern Pacific is a data-poor region for studies into the movements and habitat use of open ocean and pelagic sharks. However, this region experiences considerable pressure from commercial fishing. Therefore, shark movement data from this region carry significant implications for conservation and management, particularly for threatened species. Here, we provide the first data on seasonal residency and movements of scalloped hammerhead (Sphyrna lewini) and Galapagos sharks (Carcharhinus galapagensis), using acoustic and satellite telemetry, and dive logbooks, off Japan.ResultsEight female sharks, four of each species, were tagged around a coastal seamount off southeastern Japan (Mikomoto Island) in August 2015, and monitored for a period of up to 363 days using an array of six receivers around the island. Analyses of the more abundant scalloped hammerhead acoustic data suggest high seasonal residency predominantly from August to November associated with lower chlorophyll-a concentrations, before sharks then leave the island and return the following summer. Residency for scalloped hammerhead sharks were highest among those receivers closest to the Kuroshio Current, which produces strong coastal upwelling, however SST was not found to be predictive of occurrence at Mikomoto. Shark presence was corroborated by analysis of dive-log data from a local ecotourism operator. We also produced two unique satellite tracks, whereby a scalloped hammerhead exhibited a 200-km dispersal into a coastal embayment west of the tagging location and a Galapagos shark migrated over 800 km offshore into the high seas.ConclusionThis study provided some of the first behavioral and movement data for scalloped hammerhead and Galapagos sharks in Japan. Our findings suggest varying spatial and temporal visitation of two shark species to a coastal seamount, underscored by some degree of seasonal residency and site fidelity and linked, for scalloped hammerhead sharks at least, to varying productivity. Furthermore, we provided preliminary evidence for long-distance dispersal of these species, and some site fidelity to seamounts in the region. This study highlights the importance of describing shark movements to aid in filling critical data gaps for poorly understood, endemic populations of threatened species.

Using stable isotopes analysis to understand ontogenetic trophic variations of the scalloped hammerhead shark at the Galapagos Marine Reserve.

Changes in life-history requirements drive trophic variations, particularly in large marine predators. The life history of many shark species is still poorly known and understanding their dietary ontogeny is a challenging task, especially for highly migratory species. Stable isotope analysis has proven as a useful method for examining the foraging strategies of sharks and other marine predators. We assessed the foraging strategies and ontogenetic changes of scalloped hammerhead sharks, Sphyrna lewini, at Galapagos Marine Reserve (GMR), by analysing δ13C and δ15N signatures in different maturity stages. Our isotopic results suggest ontogenetic shifts in resource use between sub-adult and adult stages, but not between adult and juvenile stages. Carbon isotopic signatures found in the juvenile stage were enriched in contrast to sub-adults (~0.73‰) suggesting a combination of the maternal input and the use of coastal resources around the Galapagos Islands. Adult female sharks also showed enrichment in δ13C (~0.53‰) in comparison to sub-adult stages that suggest feeding in high primary productivity areas, such as the GMR. This study improves the understanding of the trophic ecology and ontogenetic changes of a highly migratory shark that moves across the protected and unprotected waters of the Eastern Tropical Pacific.

Data‐limited approach to the management and conservation of the pelagic thresher shark in the Northwest Pacific

AbstractThe pelagic thresher shark is among the most heavily exploited shark species in the commercial fisheries of the tropical Indo‐Pacific oceans. Despite this severe exploitation, little is known about pelagic thresher population dynamics, particularly the species' life history traits, and overall stock status. The pelagic thresher exhibits slow growth and extremely low fecundity, indicating the need for reassessment of the population status of this globally threatened shark. Because information on catch and effort of this bycatch species is scarce, several data‐limited methods—quantitative demographic methods, per‐recruit analysis, and risk assessment—were employed in this study to provide an accurate measurement of the status of pelagic thresher shark stocks. For each sex, the composite risk assessments indicated that the probability of the current fishing mortality increasing beyond any level of yield‐per‐recruit (YPR) was approximately zero given the biological reference points (BRPs). Moreover, the current spawning potential ratio (SPR) was found to be significantly below the target reference point of SPR60%, but slightly above the limit reference point of SPR40%. However, because SPR‐based BRPs are much less sensitive to input parameter uncertainties than YPR‐based BRPs, results derived from the SPR model are more suitable for species management. Management strategy simulations based on demographic two‐sex models indicated that without mortality from fishing, female pelagic threshers have a higher population growth rate than males. However, the stock status of female pelagic thresher shark is poorer than that of males under current conditions. The findings suggest that sex‐specific management decisions must be made to achieve the sustainable utilization of this species. Overall, both the sex‐specific per‐recruit and demographic models determined that recruitment overfishing has occurred in the female pelagic thresher population of the Northwest Pacific Ocean, indicating that close monitoring of female sharks is urgent and necessary to ensure that stocks remain sustainable.

Mode of uterine milk secretion in the white shark.

Examination of the uterus of a dead female white shark (Carcharodon carcharias), which contained the earliest known white shark embryos, revealed that the uterine wall produces lipid-rich secretion (histotroph or "uterine milk") for embryonic nutrition. Uterine tissue was processed for light and electron microscopy, and immunohistochemical techniques to identify its secretory mechanism. Our results indicate that the white shark uterus secretes lipids via holocrine secretion. This type of secretion is characterized by the release of large lipid droplets accumulated in the epithelial cells into the uterine lumen through cell disintegration. The secretory epithelium of the uterus is stratified, and new surface epithelial cells are continuously supplied from deeper epithelial layers to replace the dead secretory cells at the surface. This vertical replacement possibly facilitates the active renewal of the surface epithelium, which is necessary for maintaining holocrine secretory mechanisms. These secretory mechanisms are different from those of myliobatiform stingrays, another elasmobranch taxon that exhibits lipid histotrophy. This may reflect the different origins of lipid histotrophy between these taxa.

Environmental Drivers of Fine-Scale Predator and Prey Spatial Dynamics in Sydney Harbour, Australia, and Adjacent Coastal Waters

Greater Sydney is the largest coastal city in Australia and is where bull sharks (Carcharhinus leucas) are present every summer and autumn. A decade of acoustic telemetry data was used to identify drivers of space use for bull sharks and their potential prey, according to standardised 6-h intervals using dynamic Brownian bridge movement models. Influences of environmental, physical, and biological variables on the areas of space use, location, and predator–prey co-occurrence were investigated with generalised additive mixed models. Rainfall in the catchment affected space use for all animals (i.e. teleost species and both sexes of sharks), with varying temporal responses. Male sharks responded most promptly to high rainfall moving upstream in < 1 day, followed by teleosts (2 to 7 days), and female bull sharks after 4 days. Environmental luminosity affected male shark dispersal and space use, possibly indicating use of visual cues for foraging. Physical characteristics of habitat were important factors driving spatial overlaps between predator and prey in estuarine areas. In sandy embayments < 10-m deep, males and female bull sharks overlapped with different species, whereas males and silver trevally (Pseudocaranx georgianus) co-occurred in deep holes (> 30 m). Shark size influenced overlap between sexes, with smaller females less likely to co-occur with larger males (~ 50 cm). Variability in space use suggests spatial segregation by sex and size in bull sharks, with individuals targeting similar prey, yet either in different areas or at different times, ultimately enabling them to exploit different resources when in the same habitats.

Differential horizontal migration patterns of two male salmon sharks (Lamna ditropis) tagged in the Bering Sea

BackgroundThe salmon shark (Lamna ditropis) is a widely distributed apex predator in the North Pacific Ocean. Many salmon sharks from the eastern North Pacific, specifically Prince William Sound, Alaska, have been satellite tagged and tracked, but due to the sexual segregation present in salmon sharks, most of these tagged sharks were female. Consequently, little information exists regarding the migration patterns of male salmon sharks. To better understand the migration and distribution of this species, information on the male component of the population as well as from sharks outside of Prince William Sound, Alaska, is needed. In this study, we deployed satellite transmitters on two mature male salmon sharks caught in the Bering Sea.ResultsThe two mature male salmon sharks tagged in the Bering Sea exhibited distinct migration patterns. The first male, tagged in August 2017, traveled to southern California where it remained from January to April after which it traveled north along the United States’ coast and returned to the Bering Sea in August 2018. The second male, tagged in September 2019, remained in the North Pacific between 38° N and 50° N before returning to the Bering Sea in July of year one and as of its last known location in year two. The straight-line distance traveled by the 2017 and 2019 sharks during their 12 and 22 months at liberty was 18,775 km and 27,100 km, respectively.ConclusionsBefore this study, our understanding of salmon shark migration was limited to female salmon sharks satellite tagged in the eastern North Pacific. The 2017 male salmon shark undertook a similar, but longer, north–south migration as tagged female sharks whereas the 2019 shark showed little overlap with previously tagged females. The different migration patterns between the two male sharks suggest distinct areas exist for foraging across the North Pacific. The return of both sharks to the Bering Sea suggests some fidelity to the region. Continued tagging efforts are necessary to understand the population structure of salmon sharks in the North Pacific. This tagging study highlights the importance of opportunistic efforts for obtaining information on species and sex with limited distribution data.

Biology aspect and parameter population the scalloped hammerhead (Sphyrna lewini Griffith & Smith, 1834) caught from coastal fisheries in the eastern Indian Ocean

The scalloped hammerhead, Sphyrna lewini, have a circumglobally distribution in tropical and warm-temperate waters. Generally, in Indian ocean this species is a bycatch of the tuna longline, however, in Tanjung Luar, this species is a target species. The life history from this species is still limited. The study aimed to assess the biology aspect and growth of the scalloped hammerhead in the period February 2013 to December 2016. The result showed that 2449 individuals were caught with size between 43-395 cm TL (average 198,03 cm) for females and males ranged between 47-340 cm TL (average 161.61 cmTL). The sex ratio that was dominated by female sharks was 2.69: 1. The clasper length and total length relationship were positive with a linear regression equation of CL = 0.0902*TL-4.4402 (R2=0.6837). It showed that the length of the claspers increases proportionally with the length of the body. Application of age at length data for produced von Bertalanffy growth model parameter estimates of female L∞ = 397 cm TL, K = 0.27 year−1, for male S. lewini was L∞ = 381 cm TL, K = 0.17/ year. The total mortality rate (Z) the scalloped hammerhead was 1.15/ years, natural mortality (M) is 037/ years and the fishing mortality (F) was 0.78/ years with exploitation rate (E) = 0.68

Triennial migration and philopatry in the critically endangered soupfin shark Galeorhinus galeus

Abstract Globally, one quarter of shark and ray species are threatened with extinction due to overfishing. Effective conservation and management can facilitate population recoveries. However, these efforts depend on robust data on movement patterns and stock structure, which are lacking for many threatened species, including the Critically Endangered soupfin shark Galeorhinus galeus, a circumglobal coastal‐pelagic species. Using passive acoustic telemetry, we continuously tracked 34 mature female soupfin sharks, surgically implanted with coded acoustic transmitters, for 7 years via 337 underwater acoustic receivers stationed along the west coast of North America. These sharks and an additional six were also externally fitted with spaghetti identification tags. Our tagging site was a shallow rocky reef off La Jolla (San Diego County), California, USA, where adult females were observed to aggregate every summer. Tagged soupfin sharks were highly migratory along the west coast of North America, between Washington, USA and Baja California Sur, Mexico. However, every 3 years, they returned to waters off La Jolla, California, where they underwent gestation. This is the first conclusive evidence of triennial migration and philopatry (‘home‐loving’) in any animal, which is apparently driven by this species’ unusual triennial reproductive cycle. Females of other shark and ray species with triennial reproductive cycles are also likely to exhibit triennial cycles of migration and philopatry. At least six (15%) of our tagged soupfin sharks were killed in commercial gillnets in Mexico. Policy implications. Identifying multiennial migratory cycles in mature female sharks can reveal hidden stock structure in the form of discrete breeding cohorts, which are spatially and temporally segregated as they cycle through different reproductive phases. Accounting for this complexity may improve the performance of spatially structured stock assessment models, particularly when fishery removals are spatially heterogeneous, as well as inform the spatiotemporal design of fishery‐independent surveys. In the United States, the soupfin shark is neither actively managed nor recognized as a Highly Migratory Species; however, given the highly migratory behaviour we report, this designation should be revisited by the US Pacific Fishery Management Council. Finally, given the extensive fishery removals in Mexico, any future management must be internationally cooperative.