Sand Tiger Shark Carcharias Taurus Research Articles

Interactive three-dimensional atlas of the mineralized skeleton of the sand tiger shark Carcharias taurus.

Non-invasive computed tomography (CT) of an adult sand tiger shark Carcharias taurus Rafinesque, 1810 is used to provide an interactive three-dimensional 'general' shark (Selachimorpha) anatomy atlas. Given its post-cranial body morphology, the sand tiger shark appeared to be a well-chosen candidate and through comparison of the sand tiger shark with several other representatives of all eight established orders of sharks, we confirm that the relatively large degree of mineralization of the endoskeleton, along with the overall size, makes the sand tiger shark an ideal candidate for skeletal segmentation and construction of a skeletal atlas using conventional CT. This atlas both increases accessibility to the internal morphological features of the sand tiger shark and provides a more generalized overview of the skeletal anatomy of sharks and can aid as a supplement to destructive fresh dissection of specimens in the future and the construction of future skeletal atlases of other less mineralized sharks.

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.

Association behavior between sand tiger sharks and round scad is driven by mesopredators.

In marine systems, behaviorally-mediated indirect interactions between prey, mesopredators, and higher trophic-level, large predators are less commonly investigated than other ecologic interactions, likely because of inherent difficulties associated with making observations. Underwater videos (n = 216) from SharkCam, a camera installation sited beneath Frying Pan Tower, a decommissioned light house and platform, on a natural, hard bottom site approximately 50 km off Cape Fear, North Carolina, were used to investigate association behavior of round scad Decapterus punctatus around sand tiger sharks Carcharias taurus. Videos containing sand tiger sharks were analyzed for the simultaneous presence of round scad, and six species of scad mesopredators, with scad-shark interactions assigned to one of three categories of association: no visible interaction, loosely associated, or tightly associated. The likelihood of scad being loosely or tightly associated with sharks was significantly higher in the presence of scad mesopredators, suggesting that sharks provide a predation refuge for scad. This behaviorally-mediated indirect interaction has important implications for trophic energy transfer and mesopredator control on hard bottoms, as scad are one of the most abundant planktivorous fish on hard bottoms in the western Atlantic Ocean. Although we were not able to provide statistical evidence that sand tiger sharks also benefit from this association behavior, we have clear video evidence that round scad association conceals and attracts mesopredators, enhancing predation opportunities for sand tiger sharks. These interactions potentially yield additional trophic consequences to this unique association and highlight the value of exploring behaviorally-mediated interactions in marine communities.

Telemetry‐validated nitrogen stable isotope clocks identify ocean‐to‐estuarine habitat shifts in mobile organisms

Abstract Throughout their life history, many animals transition among heterogeneous environments to facilitate behaviours such as reproduction, foraging and predator avoidance. The dynamic environmental and biological conditions experienced by mobile species are integrated in the chemical composition of their tissues, providing retrospective insight into movement. Here, we present a unique application of nitrogen stable isotope clocks (‘isotopic clocks’), which integrate tissue turnover rates, consumer stable isotope ratios and habitat‐specific isotope baselines to predict time‐since‐immigration and the timing of habitat shifts in a migratory species. Nitrogen stable isotope values of blood plasma collected from juvenile sand tiger sharks Carcharias taurus, a species known to undertake seasonal movements between ocean and estuarine environments, were used to derive estimates of time‐since‐immigration and the timing of seasonal habitat shifts undertaken by this species. Nitrogen isotopic clocks estimated for 65 juvenile sand tiger sharks sampled across 6 years indicated that individual sharks predominantly arrived to estuarine habitats between June and July, with some individuals arriving as early as mid‐May. These estimates were validated by comparing isotope‐derived estuarine arrival times with those from acoustically tracked individuals. The median estuarine arrival day estimates from our isotopic approach aligned with estimates from acoustic telemetry for each sampling population. Sensitivity analyses indicated that isotopically inferred time‐since‐immigration and estuarine arrival estimates were robust to variation in isotopic turnover rate and diet tissue discrimination factors under multiple modelling scenarios. This suggests that parameterization of the nitrogen isotopic clock provides reliable estimates of time‐since‐immigration and day of arrival into new habitats if isotopic variation exists between origin and new locations. Our study presents a unique application of telemetry‐validated isotope clocks to derive retrospective estimates of time‐since‐immigration and timing of habitat shifts for animals that seasonally traverse heterogeneous environments. This approach can be readily applied across many temporal and spatial scales, and to other species and ecosystems, to facilitate rapid assessment of changes in animal habitat use and broader ecosystem structure.

Sexual conflicts in sand tiger sharks Carcharias taurus (Rafinesque, 1810) in an artificial environment

Sexual conflicts in sand tiger sharks Carcharias taurus (Rafinesque, 1810) in an artificial environment

Testosterone and semen seasonality for the sand tiger shark Carcharias taurus†.

Understanding the fundamental reproductive biology of a species is the first step toward identifying parameters that are critical for reproduction and for the development of assisted reproductive techniques. Ejaculates were collected from aquarium (n=24) and in situ (n=34) sand tiger sharks Carcharias taurus. Volume, pH, osmolarity, sperm concentration, motility, status, morphology, and plasma membrane integrity were assessed for each ejaculate. Semen with the highest proportion of motile sperm was collected between April and June for both in situ and aquarium sand tiger sharks indicating a seasonal reproductive cycle. Overall, 17 of 30 semen samples collected from aquarium sharks from April through June contained motile sperm compared to 29 of 29 of in situ sharks, demonstrating semen quality differences between aquarium and in situ sharks. Sperm motility, status, morphology, and plasma membrane integrity were significantly higher (P<0.05) for in situ compared to aquarium sand tiger sharks. Testosterone was measured by an enzyme immunoassay validated for the species. Testosterone concentration was seasonal for both aquarium and in situ sharks with highest concentrations measured in spring and lowest in summer. In situ sharks had higher (P<0.05) testosterone concentration in spring than aquarium sharks. This study demonstrated annual reproduction with spring seasonality for male sand tiger sharks through marked seasonal differences in testosterone and semen production. Lower testosterone and poorer semen quality was observed in aquarium sharks likely contributing to the species' limited reproductive success in aquariums.

Bite performance and feeding behaviour of the sand tiger shark Carcharias taurus.

This study examines the feeding behaviour and kinematics of three sub-adult sand tiger sharks Carcharias taurus on display at Mystic Aquarium (Mystic, Connecticut, USA). Using high-speed video data from 52 bites, we identify kinematic variables associated with the expansive and compressive phases of the bite. The mean bite duration from the onset of the expansive phase to the conclusion of the compressive phase is mean (± SE) 0.14 ± 0.01 s and across the 10 fastest bites of each individual, the maximum performance average is 0.13 ± 0.01 s. Values of maximum performance do not vary significantly among individuals. When compared with kinematic bite data from species studied previously, these results indicate that body size is not the only determinant factor of bite duration. This study also provides detailed descriptions of feeding behaviours in C. taurus and presents documentation of tooth loss both prior to and during feeding, suggesting that there are multiple mechanisms of tooth loss and use in C. taurus. Finally, we discuss the behavioural and ecological components of prey capture in C. taurus and suggest points of consideration to facilitate interspecific comparisons of prey capture performance in ram-feeding, macrophagous elasmobranchs.

A new report on the clasper movements of a captive Sand Tiger Shark Carcharias taurus (Lamniformes: Odontaspididae) and a possible reason for the behaviour

Elasmobranchs present four clasper movements, which can be seen in different contexts from mating to no obvious reason. Three movements have been reported in Carcharias taurus and here the first occurrence of clasper flaring in this species is described. Clasper flaring was observed while other species were in a reproductive state and their aggressive behaviour towards the subject of this study was also observed.

Social Network Analysis Reveals Potential Fission-Fusion Behavior in a Shark

Complex social networks and behaviors are difficult to observe for free-living marine species, especially those that move great distances. Using implanted acoustic transceivers to study the inter- and intraspecific interactions of sand tiger sharks Carcharias taurus, we observed group behavior that has historically been associated with higher order mammals. We found evidence strongly suggestive of fission-fusion behavior, or changes in group size and composition of sand tigers, related to five behavioral modes (summering, south migration, community bottleneck, dispersal, north migration). Our study shows sexually dimorphic behavior during migration, in addition to presenting evidence of a potential solitary phase for these typically gregarious sharks. Sand tigers spent up to 95 consecutive and 335 cumulative hours together, with the strongest relationships occurring between males. Species that exhibit fission-fusion group dynamics pose a particularly challenging issue for conservation and management because changes in group size and composition affect population estimates and amplify anthropogenic impacts.

Implantation and Recovery of Long-Term Archival Transceivers in a Migratory Shark with High Site Fidelity.

We developed a long-term tagging method that can be used to understand species assemblages and social groupings associated with large marine fishes such as the Sand Tiger shark Carcharias taurus. We deployed internally implanted archival VEMCO Mobile Transceivers (VMTs; VEMCO Ltd. Nova Scotia, Canada) in 20 adult Sand Tigers, of which two tags were successfully recovered (10%). The recovered VMTs recorded 29,646 and 44,210 detections of telemetered animals respectively. To our knowledge, this is the first study to demonstrate a method for long-term (~ 1 year) archival acoustic transceiver tag implantation, retention, and recovery in a highly migratory marine fish. Results show low presumed mortality (n = 1, 5%), high VMT retention, and that non-lethal recovery after almost a year at liberty can be achieved for archival acoustic transceivers. This method can be applied to study the social interactions and behavioral ecology of large marine fishes.

Habitat selection of a coastal shark species estimated from an autonomous underwater vehicle

Quantifying habitat selection in marine organisms is challenging because it is diffi- cult to obtain species location information with multiple corresponding habitat measurements. In the ocean, habitat conditions vary on many spatiotemporal scales, which have important conse- quences for habitat selection. While macroscale biotic and abiotic features influence seasonal movements (spatial scales of 100�1000 km), selectivity of conditions on mesoscales (1�100 km) reflects an animal's response to the local environment. In this study, we examined habitat selec- tivity by pairing acoustic telemetry with environmental habitat parameters measured by an autonomous underwater vehicle (AUV), and demonstrate that migrating sand tiger sharks Carcharias taurus along the East Coast of the USA did not randomly use the coastal environment. Of the variables examined, we found evidence to suggest that sand tigers were selecting their habitat based on distance to shore, salinity, and colored dissolved organic matter (CDOM). Notably, temperature was not predictive of habitat use in our study. We posit that during their coastal migration, sand tigers select for specific mesoscale coastal habitats that may inform navi- gation or feeding behaviors. To our knowledge, this is the first empirical measure of mesoscale habitat selection by a coastal marine organism using an AUV. The applications of this method extend beyond the habitat selectivity of sand tigers, and will prove useful for future studies com- bining in situ observations of marine habitats and animal observations.

Structure and mechanical properties of normal and anomalous teeth in the sand tiger shark Carcharias taurus.

This study reports and characterises an anomalous condition in teeth of captive sand tiger sharks Carcharias taurus . Abnormal shed teeth from captive sand tiger sharks which were soft to the touch were structurally and chemically characterised and compared to the structure and composition of normal teeth of the species. Normal specimens exhibited the expected tooth morphology with a well-developed tooth crown consisting of a central cusp and two lateral cusplets with smooth and sharp margins, while in the anomalous specimens the crown height was much reduced and the overall shape did not follow this pattern. Lateral cusplets were also considerably reduced in size and with blunt margins. Scanning electron images showed a distinct absence of crystalline structures in the anomalous specimens. Raman microscopy analysis confirmed the low volume of fluoroapatite in the outer layers of the anomalous teeth, while the composition of the inner layers corresponding to dentine was comparable to the normal tooth specimens. Nanoindentation-derived mechanical properties showed significant differences between the anomalous and normal teeth. The mean values for enameloid elastic modulus and hardness of all three normal teeth were 75.92±3.4 GPa and 3.27±0.41 GPa, respectively. On the other hand, mean values of elastic modulus and hardness for anomalous teeth were 7.81±3.27 GPa and 0.39±0.25 GPa, respectively. However, mechanical property values of the dentine of normal and anomalous teeth were similar. The mean values of dentine elastic modulus and hardness of the normal teeth were 25.66±2.14 GPa and 0.89±0.01 GPa, respectively, while mean values for the anomalous teeth were 25.34±1.54 GPa and 0.83±0.03 GPa. Although the morphological, mechanical and chemical differences between the normal and anomalous teeth are quite evident, establishing the causes of this condition are not possible at this stage.

Mechanical properties of sand tiger sharkCarcharias taurusvertebrae in relation to spinal deformity

Approximately 35% of sand tiger sharks (Carcharias taurus) in public aquaria exhibit spinal deformities ranging from compressed vertebrae and loss of intervertebral space to dislocated spines with vertebral degeneration and massive spondylosis caused by excessive mineralization both within vertebrae and outside the notochordal sheath. To identify the mechanical basis of these deformities, vertebral centra from affected (N=12) and non-affected (N=9) C. taurus were subjected to axial compression tests on an MTS 858 Bionix material testing system, after which mineral content was determined. Vertebral centra from affected sharks had significantly lower mineral content and material behavior in nearly all variables characterizing elasticity, plasticity and failure. These mechanical deficiencies are correlated with size at capture, capture method, vitamin C and zinc deficiency, aquarium size and swimming behavior in public aquaria. Non-affected C. taurus had greater stiffness and toughness even though these properties are generally incompatible in mineralized structures, suggesting that the biphasic (mineralized, unmineralized phases) nature of chondrichthyan vertebrae yields material behavior not otherwise observed in vertebrate skeletons. However, vertebral centra from non-affected sharks had lower mineral content (33%), stiffness (167 MPa), yield strain (14%) and ultimate strength (16 MPa) than other species of sharks and bony vertebrates, indicating that biomechanical precautions must be taken in the husbandry of this species.

Seasonal residency, habitat use, and site fidelity of juvenile sand tiger sharks Carcharias taurus in a Massachusetts estuary

Seasonal residency, habitat use, and site fidelity of juvenile sand tiger sharks Carcharias taurus in a Massachusetts estuary

Young's modulus and hardness of shark tooth biomaterials

To date, the majority of studies on feeding mechanics in sharks have focused on the movement of cranial components and muscle function, with little attention to tooth properties or function. Attributes related to mechanical properties, such as structural strength, may also be subjected to natural selection. Additionally it is necessary to characterize these properties in order to construct biomechanical models of tooth function. The goal of this study was to determine hardness and elastic modulus for the shark tooth materials enameloid, osteodentine, and orthodentine. Five teeth each from one carcharhiniform species, the bonnethead Sphyrna tiburo, and one lamniform, the sand tiger shark Carcharias taurus, were utilized for nanoindentation testing. Each tooth was sectioned transversely, air-dried, and polished. Both enameloid and dentine were tested on each tooth via a Berkovich diamond tip, with nine 2 μm deep indentations per material. t-Tests were used to determine if there were differences in hardness and Young's modulus between the tooth materials of the two species. There was no significant difference between the two species for the material properties of enameloid, however both hardness and Young's modulus were higher for osteodentine than for orthodentine. This may be due to differences in microanatomy and chemical composition, however this needs to be studied in greater detail.

How can the feeding habits of the sand tiger shark influence the success of conservation programs?

AbstractThe feeding habits of the sand tiger shark Carcharias taurus, one of the most threatened sharks of the world, are poorly known. Sand tiger sharks are critically endangered in the South‐west Atlantic. Since 2007, the law requires that all individuals caught in recreational fisheries off Argentina must be released. Using data from a north Patagonian recreational fishery (n=164 stomachs with contents), we analyzed the diet of sand tiger sharks in relation with size, sex, maturity stage and season; assessed prey consumption patterns and hooking location; and estimated diet overlap with fishery landings. Sand tiger sharks consumed mainly teleosts (55.4% of the total prey number, N) and elasmobranchs (41.84%N), and ate more benthic elasmobranchs (batoids and angel sharks) as they become larger. Sharks swallowed prey mostly in one piece (93.7%) and were hooked mainly in internal organs (87.4%, n=175), causing occlusion and perforation of the esophagus and stomach, and lacerations to the pericardium, heart and liver. Sand tiger sharks fed on the most heavily landed species, overlapping almost completely (&gt;90%) with fishery landings. Conservation plans should take into account that releasing hooked sharks could be insufficient to minimize fishing mortality and that competition for food with fisheries is likely to occur.

Tooth row counts, vicariance, and the distribution of the sand tiger shark Carcharias taurus

Geographic variation in tooth row counts among sand tiger sharks Carcharias taurus (Chondrichthyes), from the SW Atlantic, NW Atlantic and the East China Sea is analyzed in this paper. We found significant differences between sand tigers from the SW Atlantic (Southern Hemisphere population) and each of the other two (Northern Hemisphere) regions in the number of upper lateral tooth rows, and between individuals from the SW Atlantic and the East China Sea in the total number of upper tooth rows. Sand tiger sharks from the two Northern Hemisphere populations did not differ in any of the studied variables. Our results agree with comparisons of vertebral counts between sand tiger sharks from Southern and Northern Hemispheres. Both lines of evidence suggest that Southern and Northern Hemisphere populations of C. taurus were isolated to a larger extent than populations of the Northern Hemisphere. The fossil record of the genus Carcharias begins in the Early Cretaceous and C. taurus is certainly known since the Late Miocene. During the Miocene, the Tethys Sea separating northern and southern land masses was still present and it provided a continuous temperate shallow sea that could allow dispersal of sand tiger sharks along Northern Hemisphere seas. Independent observations on the distribution and evolutionary history of the genera Myripristis, Neoniphon, Sargocentron and Aphanius, and genetic studies on the temperate shark genus Mustelus that indicate a close relationship between the Indo‐Pacific M. manazo and the Mediterranean M. asterias suggest that this hypothesis is plausible and deserves to be tested.

Seasonal variation in abundance and sex ratio of Grey Nurse (Sand Tiger) Sharks Carcharias taurus in northern New South Wales, Australia: a survey based on observations of recreational scuba divers

The Grey Nurse or Sand Tiger Shark Carcharias taurus is a protected species in Australian waters. In order to gain an insight into this shark's migratory habits and relative abundance at popular recreational diving sites, a survey was conducted using the observations of recreational divers' in northern New South Wales coastal waters over 15 months from August 1996 to October 1997. The bulk of shark sightings were reported during seasons of low diver activity and when sea surface temperatures were around 20?21?C. The number of reported sightings in each month was adjusted for variations in diver activity (i.e., sampling effort) to give an index of shark abundance. More southerly sites experienced peak shark abundance from August to November 1996, whereas sharks were most common at more northerly sites from April to June 1997, suggesting either that the sharks were migrating northwards, or that seasonal movement into shallower waters was occurring later at the northern sites. The sex ratio of the population shifted from a majority of females in spring to a majority of males in autumn/winter at the northern sites, indicating that the movements of the sexes may differ. Management strategies for this species, such as providing adequate protection of habitat at critical localities and times, require more detailed knowledge of this shark's migratory pattern, and the timing of reproductive events.