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We present the first photographic records of the tiger shark (Galeocerdo cuvier) at the remote Rapa Nui (Easter Island) in the south‐east Pacific. Previous anecdotal sightings exist for tiger sharks in this region; however these records have not been reported within the scientific domain. The present sighting occurred in a period of unusually warm sea surface temperature, which has been shown to influence tiger shark range extensions elsewhere. Novel and historic species occurrence records are valuable for determining and predicting species' environmental tolerances, migratory routes, and distributional limits. [ABSTRACT FROM AUTHOR]

Sharks are an important attraction for aquaria; however, larger species can rarely be kept indefinitely. To date, there has been little work tracking shark movements post‐release to the wild. The authors used high‐resolution biologgers to monitor a sub‐adult tiger shark's pre‐ and post‐release fine‐scale movements following 2 years of captivity in an aquarium. They also compared its movement with that of a wild shark tagged nearby. Despite the differences in movement between the two sharks, with vertical oscillations notably absent and greater levels of turning seen from the released shark, the captive shark survived the release. These biologgers improve insight into post‐release movements of captive sharks. [ABSTRACT FROM AUTHOR]

While a growing body of literature has shown that tourism provisioning can influence the behaviour of wildlife, how physiological state might be related to the nature and magnitude of these effects remains poorly understood. Physiological state, including reproductive and nutritional status, can have profound effects on an individual's behaviour and decision making. In the present study, we used multiple physiological markers related to reproductive (testosterone, 17β-oestradiol and progesterone), metabolic (corticosteroids) and nutritional ecology (stable isotopes and fatty acids), integrated with ultrasonography and passive acoustic telemetry to explore the possible relationship between physiological condition and space use of tiger sharks, Galeocerdo cuvier , exposed to dive tourism provisioning. Large, nongravid female tiger sharks, with higher plasma steroid levels (i.e. testosterone, 17β-oestradiol, relative corticosteroid), enriched δ15N and elevated nutritional status (in terms of fatty acids) spent proportionally more time at food provisioning sites compared to conspecifics. Testosterone levels also were positively correlated with the proportion of time spent at provisioning sites. Based on these results, we speculate that physiological condition plays a role in shaping the spatial behaviour of female tiger sharks within the context of food provisioning, whereby larger individuals, exhibiting higher testosterone levels and elevated nutritional status, show selective preferences for provisioning dive sites, where they outcompete conspecifics of relatively smaller size, lower testosterone levels and depressed nutritional state. While more studies are needed to explore whether sharks are making these decisions because of their physiological state or whether spending more time at provisioning sites results in altered physiological state, our findings highlight the importance of considering animal life stage, endocrine regulation, and nutritional condition when evaluating the biological impacts of provisioning tourism. • Larger female tiger sharks spent proportionally more time at food provisioning sites. • Testosterone levels were correlated with the time spent at provisioning sites. • Sharks exhibiting high use for provisioning sites had higher plasma steroid levels. • Sharks exhibiting high use for provisioning sites had elevated nutritional status. • Physiological condition seems to an important decision-making determinant. [ABSTRACT FROM AUTHOR]

A juvenile, male tiger shark (Galeocerdo cuvier) developed illness after capture in Florida waters and was euthanized. Gross lesions included mild skin abrasions, hepatic atrophy, and coelomic fluid. Histologically, gills contained multifocal lamellar epithelial cell necrosis and thromboses. Scattered gill and esophageal epithelial cells had large, basophilic, intracytoplasmic, and intranuclear inclusions. Ultrastructurally, lamellar epithelial cells contained arrays of intracytoplasmic viral particles and scattered intranuclear nucleocapsids. Capsulated virions were 148 ± 11 nm with an 84 ± 8 nm icosahedral nucleocapsid and an electron-dense core. Next-generation sequencing, quantitative polymerase chain reaction, and in situ hybridization performed on formalin-fixed tissue confirmed a herpes-like viral infection. The viral polymerase shared 24% to 31% protein homology with other alloherpesviruses of fish, indicating a divergent virus. This report documents the pathologic findings associated with a molecularly confirmed novel herpes-like virus in an elasmobranch. [ABSTRACT FROM AUTHOR]

Globally, marine animal distributions are shifting in response to a changing climate. These shifts are usually considered at the species level, but individuals are likely to differ in how they respond to the changing conditions. Here, we investigate how movement behaviour and, therefore, redistribution, would differ by sex and maturation class in a wide-ranging marine predator. We tracked 115 tiger sharks (Galeocerdo cuvier) from 2002 to 2020 and forecast class-specific distributions through to 2030, including environmental factors and predicted occurrence of potential prey. Generalised Linear and Additive Models revealed that water temperature change, particularly at higher latitudes, was the factor most associated with shark movements. Females dispersed southwards during periods of warming temperatures, and while juvenile females preferred a narrow thermal range between 22 and 23 °C, adult female and juvenile male presence was correlated with either lower (< 22 °C) or higher (> 23 °C) temperatures. During La Niña, sharks moved towards higher latitudes and used shallower isobaths. Inclusion of predicted distribution of their putative prey significantly improved projections of suitable habitats for all shark classes, compared to simpler models using temperature alone. Tiger shark range off the east coast of Australia is predicted to extend ~ 3.5° south towards the east coast of Tasmania, particularly for juvenile males. Our framework highlights the importance of combining long-term movement data with multi-factor habitat projections to identify heterogeneity within species when predicting consequences of climate change. Recognising intraspecific variability will improve conservation and management strategies and help anticipate broader ecosystem consequences of species redistribution due to ocean warming. [ABSTRACT FROM AUTHOR]

A Short-finned Pilot Whale, Globicephala macrorhynchus, was found dead and with shark bites along its body on a beach in northeast Brazil. The present study aimed to identify the shark species responsible for the bites as well as to estimate its/their total length. Species identification was performed using the bite marks, which were of the same diameter, suggesting they were inflected by one or more Tiger sharks of similar size. The characteristics of the bites and the shape and distribution of the marks left by the teeth pointed to the Tiger Shark, Galeocerdo cuvier. The total length of the Tiger Shark or sharks was estimated at between 257 and 288 cm, based on the perimeter contour of each bite and the interdental distance inferred from the marks on the whale. This suggests that the bites were inflicted by one or more sub-adult specimens. [ABSTRACT FROM AUTHOR]

Climate change is altering distributions and abundances of marine species through both gradual and acute changes in temperature and productivity. Due to their high mobility and metabolic rates, elasmobranchs (sharks and rays) are likely to redistribute across latitudes and depths as they thermoregulate, but little is known about their responses to these climatic changes, which could vary widely across this diverse group of species.Here, we assessed how species with differing mobility and ecology responded to gradual changes in daily sea surface temperature (SST) and acute temperature anomalies, caused by the El Niño–Southern Oscillation (ENSO), at Cocos Island, Costa Rica, the site of multiple marine heatwaves.We used generalized linear mixed models to analyse 34,342 records of relative abundance or frequency of occurrence for seven shark and ray species collected in 27 years (1993–2019) by a dive company. We compared effect sizes for SST and the Oceanic Niño Index across the different species, which vary widely in body size and mobility.Large, mobile species responded strongly but inconsistently to temperature. For scalloped hammerhead sharks Sphyrna lewini, a 1℃ rise in SST reduced counts by over 14%, and dropped the occurrence of their large schools by almost one‐fifth (19.4%). Mobula ray occurrence also declined substantially with a few degrees rise in SST, whereas tiger shark Galeocerdo cuvier occurrence sharply increased. These species also had divergent responses to the ENSO: S. lewini and G. cuvier were sighted with greater frequency during La Niña events, and their abundance dropped considerably during El Niño events—over a twofold decline between a strong La Niña and strong El Niño for S. lewini. In contrast, Mobula rays showed little response to ENSO. The smaller and sedentary Triaenodon obesus exhibited the weakest response of all species to both SST and the ENSO, reflecting its lower metabolic rates and mobility.Climate change will continue to impact elasmobranchs, even for smaller and more localized species, with the potential to impact the effectiveness of marine protected areas (MPAs). Our results compel further work on the diversity of elasmobranch responses to environmental change. [ABSTRACT FROM AUTHOR]

Animals follow specific movement patterns and search strategies to maximize encounters with essential resources (e.g. prey, favourable habitat) while minimizing exposures to suboptimal conditions (e.g. competitors, predators). While describing spatiotemporal patterns in animal movement from tracking data is common, understanding the associated search strategies employed continues to be a key challenge in ecology. Moreover, studies in marine ecology commonly focus on singular aspects of species' movements, however using multiple analytical approaches can further enable researchers to identify ecological phenomena and resolve fundamental ecological questions relating to movement. Here, we used a set of statistical physics‐based methods to analyze satellite tracking data from three co‐occurring apex predators (tiger, great hammerhead and bull sharks) that predominantly inhabit productive coastal regions of the northwest Atlantic Ocean and Gulf of Mexico. We analyzed data from 96 sharks and calculated a range of metrics, including each species' displacements, turning angles, dispersion, space‐use and community‐wide movement patterns to characterize each species' movements and identify potential search strategies. Our comprehensive approach revealed high interspecific variability in shark movement patterns and search strategies. Tiger sharks displayed near‐random movements consistent with a Brownian strategy commonly associated with movements through resource‐rich habitats. Great hammerheads showed a mixed‐movement strategy including Brownian and resident‐type movements, suggesting adaptation to widespread and localized high resource availability. Bull sharks followed a resident movement strategy with restricted movements indicating localized high resource availability. We hypothesize that the species‐specific search strategies identified here may help foster the co‐existence of these sympatric apex predators. Following this comprehensive approach provided novel insights into spatial ecology and assisted with identifying unique movement and search strategies. Similar future studies of animal movement will help characterize movement patterns and also enable the identification of search strategies to help elucidate the ecological drivers of movement and to understand species' responses to environmental change. [ABSTRACT FROM AUTHOR]

Galeocerdo cuvier Peron and Lesueur, 1822 is a tiger shark, a common predatory shark distributed in temperate and tropical countries globally. G. cuvier is also synonymised as G. arcticus (Faber, 1829) and G. rayneri (Mc Donald & Barron, 1868). We report the first observation of one male and one female tiger shark captured by otter trawler at Mudasalodai landing centre, Cuddalore coastal waters, southeast coast of India. Sex was identified by the presence of pair of claspers observed in the ventral side. Male specimen weighed about 1.9 kg and female weighed about 1.65 kg. The morphometric characters of the shark were measured and tabulated. The present study confirmed the occurrence of G. cuvier along the southeast coast of India particularly in the Tamil Nadu coastal waters. [ABSTRACT FROM AUTHOR]

Sharks are commonly listed as predators of the large ocean sunfishes (genera Mola and Masturus), yet documented shark predation events on adult sunfish are exceedingly infrequent in the literature. Here we recount two Australian observations of tiger shark (Galeocerdo cuvier) predation on sunfish of ca. 1.3 and 2 m total length, respectively. The attacks demonstrate that tiger sharks are both able and willing to predate on large sunfish; however, based on a paucity of sunfish remains in tiger shark stomach analyses, and a lack of reports of the common sunfish parasite Molicola horridus in tiger sharks, these observations likely represent opportunistic predation events. The seemingly limited interactions may reflect differing habitat use by sunfish and tiger sharks within their overlapping distribution ranges, alternatively, large sunfish may comprise low quality or undesired prey for tiger sharks. Further, despite indications of prey debilitation during both accounts, the attacks likely represent indiscriminate tiger shark feeding events with no particular prey handling strategy. [ABSTRACT FROM AUTHOR]

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The tiger shark (Galeocerdo cuvier) is a common widespread coastal–pelagic shark species whose population genetic structure has only recently been the object of genetic studies.In this study, the tiger's shark mitochondrial DNA control region was sequenced for a sample of 172 individuals from the western Atlantic and from Australia's east coast in the Pacific Ocean.The results show a moderate variation in genetic diversity (h = 0.615 ± 0.038, π = 0.00184 ± 0.00021) with a strong population structure between Atlantic areas (ΦST = 0.28141, P = 0.00001).The maternal lineage has high site fidelity, which paradoxically is coupled with connectivity across open ocean stretches to Fernando de Noronha Archipelago, which is identified as an important hotspot for this species. These results help with the understanding of what drives the displacement of this shark, at intra‐ and/or inter‐ocean basins levels, and can help inform the implementation of future conservation and management measures.We recommend that the conservation of genetic diversity should be maintained at a global level and its maintenance should be pursued diligently in all populations of tiger shark. As the Fernando de Noronha region in the western Atlantic appears to contain the largest global genetic diversity of the species, this area should be treated as a marine reserve or ecological refuge for the tiger shark. [ABSTRACT FROM AUTHOR]

Plastic waste is currently a major threat to marine ecosystems, and the ever-growing production of plastic materials suggests that this scenario will not change soon. Understanding cryptic effects of plastic debris on keystone marine species is warranted to address ecosystem-level impacts caused by plastic pollution. This study reports on plastic entanglement in top predator tiger sharks, Galeocerdo cuvier , from the western South Atlantic Ocean. Circular plastic straps produced severe trauma in 3 % of all tiger sharks sampled and led to abnormal anatomical development, indicating worrisome incidence and consequences of plastic entanglement in this species. Removing the plastic strap from one shark which had been entangled for at least 9 months was probably the cause for the shark having experienced post-release mortality. This suggests that, in some circumstances, strap removal is not effective to promote the survival of entangled sharks. Eliminating the circular integrity of plastic materials at first use should contribute to mitigate some of the impacts of plastic pollution on marine megafauna since this shape might be determinant in the process of shark entanglement. • We recorded the incidence and effects of shark entanglement in plastic debris off northeast Brazil. • A relevant proportion of the tiger sharks sampled was affected by entanglement in circular plastic debris. • Plastic entanglement produced severe trauma and anatomical deformities in tiger sharks. • Removing an embedded plastic strap from a tiger shark likely resulted in post-release mortality. • Circular plastic straps in the ocean may be inducing significant tiger shark cryptic mortality. [ABSTRACT FROM AUTHOR]

The ability to predict animal movement based on environmental change is essential for understanding the dynamic nature of their spatial ecology, and in turn the effectiveness of conservation strategies. We used a large marine predator that displays partial migration (the tiger shark Galeocerdo cuvier) as a model to test the role of oceanic conditions in predicting the space-use of different size classes. By using generalized additive mixed models (GAMMs), we revealed that environmental variables (sea surface temperature, primary productivity, thermal fronts, and bathymetry) had much greater predictive power for the movements of large, migratory tiger sharks than for small, resident individuals. We also found that coverage of tiger shark movements within “shark sanctuaries” (protected areas specifically for sharks) in the northwest Atlantic could be increased from 12 to 52% through inclusion of Bermuda’s waters. However, as large tiger sharks are migratory, over 80% of potential longline fisheries interactions would still occur outside the boundaries of even the expanded protected areas. This emphasises that management of highly migratory species needs to be dynamic and account for changing interactions with fisheries over time, which in a changing climate may rely on predicting movements based on oceanic conditions to be effective. [ABSTRACT FROM AUTHOR]

Population genetic structure using nine polymorphic nuclear microsatellite loci was assessed for the tiger shark (Galeocerdo cuvier) at seven locations across the Indo-Pacific, and one location in the southern Atlantic. Genetic analyses revealed considerable genetic structuring (FST > 0.14, p

The tiger shark (Galeocerdo cuvier) has a global distribution in tropical and warm temperate seas, and it is caught in numerous fisheries worldwide, mainly as bycatch. It is currently assessed as near threatened by the International Union for Conservation of Nature (IUCN) Red List. In this study, we identified nine microsatellite loci through next generation sequencing (454 pyrosequencing) using 29 samples from the western Atlantic. The genetic diversity of these loci were assessed and revealed a total of 48 alleles ranging from 3 to 7 alleles per locus (average of 5.3 alleles). Cross-species amplification was successful at most loci for other species such as Carcharhinus longimanus, C. acronotus and Alopias superciliosus. Given the potential applicability of genetic markers for biological conservation, these data may contribute to the population assessment of this and other species of sharks worldwide.

The shape of shark teeth varies among species, but traditional testing protocols have revealed no predictive relationship between shark tooth morphology and performance. We developed a dynamic testing device to quantify cutting performance of teeth. We mimicked head-shaking behaviour in feeding large sharks by attaching teeth to the blade of a reciprocating power saw fixed in a custom-built frame. We tested three tooth types at biologically relevant speeds and found differences in tooth cutting ability and wear. Teeth from the bluntnose sixgill (Hexanchus griseus) showed poor cutting ability compared with tiger (Galeocerdo cuvier), sandbar (Carcharhinus plumbeus) and silky (C. falciformis) sharks, but they also showed no wear with repeated use. Some shark teeth are very sharp at the expense of quickly dulling, while others are less sharp but dull more slowly. This demonstrates that dynamic testing is vital to understanding the performance of shark teeth.

One male and one female specimen of tiger shark, Galeocerdo cuvier (Péron & Lesueur, 1822), were accidentally caught by a drifting longline for swordfish in the south Mediterranean (Libyan waters). This finding confirms beyond any doubt that the tiger shark may be encountered in the waters of the Mediterranean Sea. Although records of this species has previously been reported, the information is partial or dubious, due to the lack of a description of the individuals found or the uncertain provenance of preserved material. Our finding confirms the record of this species in the southern part of the Mediterranean basin. Images, as well as morphometrics and information on stomach contents are given. Based on the size of the individuals, it is considered that the two specimens were born recently, presumably inside the Mediterranean Sea and likely close to the area where the individuals were found. [ABSTRACT FROM AUTHOR]

The "landscape of fear" model has been proposed as a unifying concept in ecology, describing, in part, how animals behave and move about in their environment. The basic model predicts that as an animal's landscape changes from low to high risk of predation, prey species will alter their behavior to risk avoidance. However, studies investigating and evaluating the landscape of fear model across large spatial scales (tens to hundreds of thousands of square kilometers) in dynamic, open, aquatic systems involving apex predators and highly mobile prey are lacking. To address this knowledge gap, we investigated predator- prey relationships between tiger sharks (Galeocerdo cuvier) and loggerhead turtles (Caretta caretta) in the North Atlantic Ocean. This included the use of satellite tracking to examine shark and turtle distributions as well as their surfacing behaviors under varying levels of home range overlap. Our findings revealed patterns that deviated from our a priori predictions based on the landscape of fear model. Specifically, turtles did not alter their surfacing behaviors to risk avoidance when overlap in shark-turtle core home range was high. However, in areas of high overlap with turtles, sharks exhibited modified surfacing behaviors that may enhance predation opportunity. We suggest that turtles may be an important factor in determining shark distribution, whereas for turtles, other life history trade-offs may play a larger role in defining their habitat use. We propose that these findings are a result of both biotic and physically driven factors that independently or synergistically affect predator-prey interactions in this system. These results have implications for evolutionary biology, community ecology, and wildlife conservation. Further, given the difficulty in studying highly migratory marine species, our approach and conclusions may be applied to the study of other predator- prey systems. [ABSTRACT FROM AUTHOR]

With the development of genetics methods, it becomes possible to study the population structure and some aspects of the reproductive behaviour of endangered sharks. Here we describe the isolation of 20 polymorphic microsatellite markers in the bull shark Carcharhinus leucas (Carcharhinidae) and their characteristics. Two to 10 alleles per locus were detected. Observed and expected heterozygosities ranged from 0.00 to 0.78 and from 0.05 to 0.80, respectively. Four markers showed deviations from Hardy-Weinberg equilibrium; among them, three showed presence of null alleles. No linkage disequilibrium was detected among any of the loci. Moreover, four, 11 and 19 of these 20 markers successfully cross-amplified in the tiger shark Galeocerdo cuvier, the sandbar shark Carcharhinus plumbeus and the dusky shark Carcharhinus obscurus, respectively. [ABSTRACT FROM AUTHOR]

Animals are often faced with complex movement decisions, particularly those that involve long-distance dispersal. Partial migrations, ubiquitous among all groups of vertebrates, are a form of long-distance movement that occurs when only some of the animals in a population migrate. The decision to migrate or to be a resident can be dependent on many factors, but these factors are rarely quantified in fishes, particularly top predators, even though partial migrations may have important implications for ecosystem dynamics and conservation. We utilized passive acoustic telemetry, with a Brownian bridge movement model and generalized additive mixed models, to explore the factors regulating partial migration in a large marine predator, the tiger shark, throughout the Hawaiian Islands. Although sharks tended to utilize a particular "core" island, they also demonstrated inter-island movements, particularly mature females that would swim from the northwestern Hawaiian Islands to the main Hawaiian Islands (MHI). Immigration to another island was a function of season, sea surface temperature (SST), and chlorophyll a concentration. Our results predict that 25% of mature females moved from remote French Frigate Shoals atoll to the MHI during late summer/early fall, potentially to give birth. Females with core home ranges within the MHI showed limited movements to the NWHI, and immigration to an island was better explained by SST and chlorophyll a concentration, suggesting a foraging function. Dispersal patterns in tiger sharks are complex but can be considered a mix of skipped-breeding partial migration by mature females and individual-based inter-island movements potentially linked to foraging. Therefore, sharks appear to use a conditional strategy based on fixed intrinsic and flexible extrinsic states. The application of Brownian bridge movement models to electronic presence/absence data provides a new technique for assessing the influence of habitat and environmental conditions on patterns of movement for fish populations. [ABSTRACT FROM AUTHOR]

Tiger Sharks,Galeocerdo cuvier, are large top-level predators usually solitary as adults. Observation of their scavenging activity on the carcass of a dead whale offered a rare opportunity for better understanding the pattern of intra-specific behaviour within the aggregations of these large predators. In January 2002, the stranding, subsequent death and consumption of a 17.4 m total length (TL) blue whale,Balaenoptera musculus, was observed and filmed in Prony Bay, southern New Caledonia. After three weeks of confinement in the bay, the cetacean was killed by adult bullsharksCarcharhinus leucas. The first adult Tiger Shark was subsequently observed around the carcass after 36 h. The fat slicks from the carcass attracted further Tiger Sharks which arrived after an additional 24 h. The use of photo-identification on video footage collected during four observation sessions over an eight-day period identified 46 individual Tiger Sharks (primarily adult females between 3.3 and 4 m TL) participating in the feeding aggregation. Only four animals were identified in two seperate observation sessions (over two consecutive days), suggesting a short-term residency pattern of several hours (<36 h) around the carcass. As the arrival time of Tiger Sharks to the carcass differed, most arrivals of a new participant were followed by a frenzied period of intense intra-specific interaction. Different biting and agonistic behaviours were demonstrated by the Tiger Sharks on the carcass, including three new behaviours previously undescribed for this species. Size and level of aggressiveness appeared to be the determining factors of dominance amongst Tiger Sharks. These observations and analysis demonstrate that systematic study of feeding aggregations supported by photo-identification could contribute to knowledge of large shark ecology when coupled with capture-recapture, genetic fingerprinting and tagging techniques. [ABSTRACT FROM AUTHOR]

Although not widely appreciated, prey can manage predation risk by modifying the sequence of their behavioural states. We explored this phenomenon in dugongs (Dugong dugon) subject to spatially and temporally variable risk of tiger shark (Galeocerdo cuvier) predation in Shark Bay, Australia. Dugong behaviour was assayed using focal follows and organised into sequences of foraging, resting, and travelling bouts. We used log-linear analysis to test for sequence differences in relation to habitat (deep, shallow) and predation danger (sharks present, largely absent). Dugongs modified their behavioural sequences between periods of high and low shark abundance: those at risk alternated more frequently between foraging, which constrains anti-predator vigilance, and travelling, which facilitates predator detection. Dugongs also avoided continuous series of resting bouts, during which awareness is reduced, when sharks were present. These changes were only observed in relatively dangerous shallow habitat, which is hunted disproportionately by tiger sharks; behavioural responses to sharks in deep habitat were modest. We conclude that dugongs in risky habitat resort to safer behavioural sequences in response to sharks. Given that human disturbance and predators are perceived similarly by many species, some forms of vessel interaction could compromise the fitness of sirenians by eliciting similar behavioural adjustment. Animals can reorder their behaviours to better detect predators. We found that dugongs at risk from tiger sharks alternated more often between foraging, during which they could not watch for sharks, and travelling, during which they could be more vigilant. By implication, dugongs fear sharks and reshuffle their behavioural states to maintain a more consistent level of wariness when threatened. [ABSTRACT FROM AUTHOR]

Large sharks have the potential to help structure ecosystem dynamics through top-down impacts on their prey, including sea turtles. Studies of interactions between large sharks and sea turtles, however, are practically nonexistent along the Brazilian coast. Between September 2002 and May 2011 we examined 655 sea turtles - including green turtles Chelonia mydas (n = 607), olive ridleys Lepidochelys olivacea (n = 10), hawksbills Eretmochelys imbricata (n = 33), and loggerheads Caretta carelta (n = 5) - that stranded on Paraiba coast, northeastern Brazil. A total of 63 green turtles (10.4%), two olive ridleys (20.0%) and one hawksbill (3.0%) had shark-inflicted bites. Most bites could not be definitively attributed to scavenging or attacks on living turtles, but the presence of healed shark bites and freshly bleeding bites suggests that some attacks occurred pre-mortem. Bite characteristics suggest that tiger sharks Galeocerdo cuvier were responsible for most bites that could be identified to a particular species. Within green turtles, the only species with sufficient sample size, the probability of carcasses having been bitten increased with carapace length but did not vary across seasons and years. However, there was spatial variation in the probability of a carcass having been bitten by sharks. Our estimates of the minimum proportion of turtles attacked while alive (~4%) and bitten overall are similar to other areas where shark-turtle interactions have been studied. Turtles likely are an important food for tiger sharks in northeastern Brazil, but further studies are needed to determine the relative frequencies of scavenging and predation. [ABSTRACT FROM AUTHOR]

Abstract: Suitable long term species-specific catch rate and biological data are seldom available for large shark species, particularly where historical commercial logbook reporting has been poor. However, shark control programs can provide suitable data from gear that consistently fishes nearshore waters all year round. We present an analysis of the distribution of 4757 Galeocerdo cuvier caught in surface nets and on drumlines across 9 of the 10 locations of the Queensland Shark Control Program (QSCP) between 1993 and 2010. Standardised catch rates showed a significant decline (p <0.0001) in southern Queensland locations for both gear types, which contrasts with studies at other locations where increases in tiger shark catch per unit effort (CPUE) have been reported. Significant temporal declines in the average size of tiger sharks occurred at four of the nine locations analysed (p <0.05), which may be indicative of fishing reducing abundance in these areas. Given the long term nature of shark control programs along the Australian east coast, effects on local abundance should have been evident many years ago, which suggests that factors other than the effects of shark control programs have also contributed to the decline. While reductions in catch rate are consistent with a decline in tiger shark abundance, this interpretation should be made with caution, as the inter-annual CPUE varies considerably at most locations. Nevertheless, the overall downward trend, particularly in southern Queensland, indicates that current fishing pressures on the species may be unsustainable. [Copyright &y& Elsevier]

To estimate tag retention time, 39 acoustic transmitters were hand-fed to bull sharks Carcharhinus leucas, lemon sharks Negaprion acutidens and tiger sharks Galeocerdo cuvier, in the Shark Reef Marine Reserve, Fiji. Minimum tag retention times ranged from less than 24 h to 34 days, and bull sharks could be tracked for a minimum mean duration of 6.8 days. Feeding acoustic transmitters wrapped in bait to free-ranging sharks is an alternative and viable method to obtain presence-absence data from free-ranging sharks. [ABSTRACT FROM AUTHOR]

Host and microhabitat or site selection is universal among parasites, although to varying degrees between species and groups. The selection of a specific site by a copepod parasite is determined by a set of mostly unknown factors. The spatial distribution of Kroyeria dispar, Kroyeria papillipes and Eudactylina pusilla on the gill filaments of Galeocerdo cuvier was investigated to determine whether niche restriction occurs in the different planes on the gills. In order to do this, the complete sets of left gills of 14 tiger shark hosts were examined and the species, location (hemibranch, horizontal distribution, longitudinal distribution), orientation and gender of each copepod noted. Kroyeria dispar was dominant on most hosts and exhibited a prevalence of 100% and a mean intensity of 73 individuals per shark. Kroyeria papillipes was dominant on the remaining hosts and displayed a prevalence of 78.6% and a mean intensity of 33 individuals per shark while E. pusilla had a prevalence of 85.7% and a mean intensity of 20 individuals per shark on the examined hosts. No evidence of intra- or interspecific competition or microniche restriction was found even though all three species occupy the same fundamental niche. However, distributional preference was observed, and the compound populations of all three species on tiger sharks were aggregated, most likely as a result of their need to reproduce. [ABSTRACT FROM AUTHOR]

Foraging and vigilance are mutually exclusive for some foraging tactics but not others. Thus, in response to changes in predation danger, prey species with multiple foraging tactics may switch facultatively between them, allowing for differential levels of vigilance. Using data from focal observations collected over 4 years (2002–2004, 2006) in Shark Bay, Western Australia, we explored the use of two tactics, cropping and excavation, by dugongs, Dugong dugon, foraging under risk of predation by tiger sharks, Galeocerdo cuvier. Overall, dugongs predominantly used the cropping tactic, which allows for regular visual scans, to harvest temperate sea grass species. Dugongs only used the excavation tactic, which precludes regular visual scans but allows individuals to access the nutritious rhizomes of preferred tropical sea grass species, in months when tropical species were most available (February–May). However, during these months the time dugongs allocated to excavation was inversely related to shark abundance rather than the availability of these sea grass species. We conclude that use of foraging tactics by dugongs is sensitive to predation danger, and that individuals manage their risk of mortality via reduced use of a profitable but potentially hazardous tactic when the likelihood of encountering predators is high. Excavating dugongs are more likely to disrupt sea grass meadow structure and promote succession than are those engaged in cropping. Thus, by altering the time dugongs devote to these alternative tactics, tiger sharks may exert an indirect effect on sea grass patch composition and structure and, ultimately, benthic communities. [Copyright &y& Elsevier]

Apex marine predators can structure marine communities, so factors underlying their abundance are of broad interest. However, such data are almost completely lacking for large sharks. We assessed the relationship between tiger shark abundance, water temperature, and the availability of a variety of known prey over 5 years in Western Australia. Abundance of sharks in four size categories and the density of prey (cormorants, dugongs, sea snakes, sea turtles) were indexed using daily catch rates and transects, respectively. Across all sizes, thermal conditions were a determinant of abundance, with numerical peaks coinciding with periods of high water temperature. However, for sharks exceeding 300 cm total length, the inclusion of dugong density significantly improved temperature-based models, suggesting that use of particular areas by large tiger sharks is influenced by availability of this sirenian. We conclude that large marine predator population models may benefit from the inclusion of measures of prey availability, but only if such measures consider prey types separately and account for ontogenetic shifts in the diet of the predator in question. [ABSTRACT FROM AUTHOR]

When threatened with predation, foraging prey can cease feeding and seek refuge or shift to feeding sites (microhabitats) offering increased safety. Predator-induced microhabitat shifts by large herbivores are of interest to ecologists because spatial patterns of foraging by these animals shape plant communities. The influence of predation risk on microhabitat use by large herbivores in marine systems remains poorly understood. We explored the relationship between microhabitat use by dugongs, Dugong dugon, and tiger shark, Galeocerdo cuvier, predation risk in an Australian embayment over 3 years. Use by foraging dugongs of two seagrass microhabitats, edge (lower-quality seagrass, swift escape from sharks) and interior (higher-quality seagrass, fewer escape options), was monitored in seven survey zones. We indexed predation danger using catch rates of tiger sharks that were greater than 3.0m in total length. The degree of dissimilarity between forager densities in edge and interior microhabitats was a function of tiger shark abundance: foragers underused edge (safe) microhabitat when sharks were scarce, overused it when sharks were common, and responded to daily changes in shark abundance in a threat-sensitive fashion, showing the greatest preference for edges when shark abundance was highest. We conclude that dugongs manage their probability of death by allocating more time to safe but lower-quality feeding microhabitats when the likelihood of encountering sharks is elevated. Dugong grazing can influence seagrass biomass and patch composition, so tiger sharks probably affect the microhabitat structure of seagrass meadows, and ultimately their benthic communities, indirectly by altering the way that dugongs use feeding patches. [Copyright &y& Elsevier]

High levels of fishing have resulted in declines among many of the oceans top predators, including the globally distributed tiger shark ( Galeocerdo cuvier). Overexploitation of this species has led to declines in parts of its distribution, which may have important ecological consequences given the tiger shark's trophic position as a large bodied, generalist predator. To assess the population genetics of this species, an enrichment protocol was used to isolate a suite of nine di- and tetra-nucleotide microsatellite loci within the tiger shark, which were subsequently characterized using genomic DNA derived from 40 individuals sampled from Hawaiian waters. The number of alleles per locus ranged from 3 to 23, and the average expected heterozygosities across loci ranged from 0.30 to 0.93. Analyses suggested a low frequency of null alleles across markers, and all loci conformed to both Hardy-Weinberg and linkage equilibrium at P > 0.01. [ABSTRACT FROM AUTHOR]

La prédation intra-guilde (PIG), la déprédation de requins pris sur des hameçons et le cannibalisme ont déjà été décrits pour le requin tigre Galeocerdo cuvier et le requin bouledogue Carcharhinus leucas, essentiellement à propos d'animaux de grande taille se nourrissant sur de plus petits requins. Dans cette note, nous rapportons deux cas d'étude dans l'océan Indien et l'océan Pacifique qui montrent une déprédation cumulative inter et intra-spécifique de ces deux espèces, impliquant de la déprédation entre gros adultes sur les derniers stades. Ces informations renforcent l'hypothèse que la PIG et le cannibalisme entre gros animaux existent potentiellement à l'état naturel et interfèrent avec les dynamiques proiesprédateurs en milieu marin tropical. [ABSTRACT FROM AUTHOR]