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New approaches to abundance surveying utilizing unoccupied aerial vehicles (UAVs) are proving to be effective tools in marine and terrestrial environments. We explored UAV efficacy for surveys in the Galapagos Marine Reserve (GMR), where relative abundance patterns of juvenile sharks and subsequent classifications of putative nursery areas based on environmental drivers are lacking. The UAV method allowed greater temporal and spatial coverage. We expanded classification of shark nursery habitat through monthly drone surveys and environmental data collection at 14 sites around San Cristobal Island (GMR) from November 2018 to July 2019. In the period of surveying, 56 flights identified 453 juvenile Carcharhinus limbatus (blacktip shark). Classification of nurseries followed three criteria, necessitating higher density, short‐term residency, and annual site fidelity in target locations. We developed preliminary generalized linear models to elucidate potential environmental parameters influencing the perceived abundance and habitat preference of juveniles. Four sites were identified as either potential nurseries or nursery areas for the target species based on previous excursions. An averaged model was subsequently created from the models found to best explain deviance patterns (R2 = 0.10–0.44) in perceived shark abundance and habitat preference. Relative variable importance (RVI) values further clarified the parameters most associated with higher juvenile presence. This approach provides a systematic method of abundance surveying while simultaneously beginning the process of defining when and where we expect to find higher abundance through environmental modelling of most influential parameters to perceived abundance in this environment. [ABSTRACT FROM AUTHOR]

Despite indications that sharks have an exceptional capacity to heal from traumatic injuries, no detailed microscopic observations of integumental wounds have been reported for sharks. This study details the histopathological features of such wounds in a free‐ranging shark. An adult male Blacktip Shark Carcharhinus limbatus was collected in 2017 during fisheries‐independent sampling efforts in the coastal southeastern U.S. Atlantic. The shark had numerous lesions on his head, torso, and left pectoral fin that were compatible with shark bites. Representative samples from two wounds on the head were examined by light microscopy. The epidermal changes included hyperplasia and hypertrophy; intracellular edema; and the absence of goblet cells, denticles, and chromatophores. In the dermis, fibrinocellular exudation, granulation tissue, and marked skeletal muscle necrosis and regeneration were observed. The above features were comparable to wound healing in bony fish, albeit minor differences were found. Although this case documents exceptionally good regeneration of skeletal muscle in the shark, we found no evidence of unique morphological healing patterns. Further studies on wound healing are needed because recent molecular and genetic findings do suggest evolutionary adaptations enhancing healing in sharks. [ABSTRACT FROM AUTHOR]

The integration of eDNA analysis into the population assessment and monitoring of sharks could greatly improve temporal and spatial data used for management purposes. This study aimed to compare eDNA detection against well-established seasonal changes in blacktip shark (Carcharhinus limbatus) abundance in Terra Ceia Bay (FL, USA). We used a species-specific real-time PCR approach to detect C. limbatus eDNA in the bay on a near monthly basis from spring through mid-fall in 2018 and 2019. Previous studies have shown that C. limbatus give birth in the bay in early summer and immature sharks occur there until late fall, when decreasing water temperatures cause them to move offshore and southwards. Water samples (2 L) were collected (4–6 per month) and filtered in the field, with each then being subjected to real-time PCR. Carcharhinus limbatus 'positive' filters were significantly more commonly collected during the April-July sampling period than during the August-October sampling period. While following the predicted pattern, eDNA concentration was generally too low for accurate quantification. Our results show that C. limbatus eDNA detection follows known seasonal residency patterns consistently over 2 years of monitoring. Species-specific eDNA analysis using real-time PCR could therefore represent a cost-effective, scalable sampling tool to facilitate improved shark population monitoring in semi-enclosed marine habitats. [ABSTRACT FROM AUTHOR]

Globally, the frequency of shark bites is rising, resulting in an increasing demand for shark deterrents and measures to lessen the impact of shark bites on humans. Most existing shark protection measures are designed to reduce the probability of a bite, but fabrics that minimise injuries when a shark bite occurs can also be used as mitigation devices. Here, we assessed the ability of the Ocean Guardian Scuba7 and Kevlar material to reduce the likelihood of blacktip reef sharks, Carcharhinus melanopterus, from feeding, and to minimise injuries from shark bites. Sharks were enticed to consume a small piece of local reef fish (bait) placed between the two Scuba7 electrodes with the deterrents randomly being turned on or kept off. In the second experiment, the bait was attached to a small pouch made of either standard neoprene or neoprene with a protective layer of Kevlar around it. The Scuba7 reduced the proportion of baits being taken by 67%, (from 100% during control trials to 33%). Sharks also took more time to take the bait when the device was active (165 ± 20.40 s vs. 38.9 ± 3.35 s), approached at a greater distance (80.98 ± 1.72 cm vs. 38.88 ± 3.20 cm) and made a greater number of approaches per trial (19.38 ± 2.29 vs. 3.62 ± 0.53) than when the Scuba7 was inactive. The sizes of punctures from shark bites were significantly smaller on neoprene with Kevlar compared to standard neoprene (3.64 ± 0.26 mm vs. 5.88 ± 0.29 mm). The number of punctures was also fewer when Kevlar was used (14.92 ± 3.16 vs. 74.1 ± 12.44). Overall, the Ocean Guardian Scuba7 and Kevlar reduced the impact of blacktip reef shark bites. These findings may help consumers make informed decisions when purchasing shark deterring and protective products. [ABSTRACT FROM AUTHOR]

A wide diversity of elasmobranch species has been reported for waters off Venezuela; however, information regarding this group is lacking for most coastal regions. This study aimed to determine the species composition in catches made by the artisanal fishery of Sucre State, Venezuela, and to analyze size structure by sex for the most common species. During the study period (January 2016-September 2017), visits were made to the main fish markets in the city of Cumaná, Sucre State, and a total of 2,167 elasmobranchs belonging to 24 species (15 sharks and 9 rays) were quantified. The most frequently captured elasmobranch species were Mustelus higmani (36.2%), Mustelus canis (18.0%), Hypanus guttatus (15.1%), and Hypanus americanus (7.1%). The size ranges for these species were 29.3-73.7 cm total length (TL), 34.0-86.0 cm TL, 17.0-138.0 cm disc diameter (DD), and 48.0-108.0 cm DD, respectively. Considering national conservation assessments (following International Union for Conservation of Nature criteria), 7 of the species reported for the study area (M. higmani, Carcharhinus limbatus, Carcharhinus falciformis, Isurus oxyrinchus, Alopias superciliosus, Prionace glauca, and Aetobatus narinari) are listed as vulnerable, and the remaining species (n = 17) have not been assessed. Current conservation efforts in Venezuela are deficient given the collapse of government institutions responsible for the management of fisheries. This has led to noncompliance with fishing regulations designed for elasmobranchs. In the future, great effort must be made to continue generating information; however, future advances in scientific research and conservation will depend largely on the recovery of the economic and political stability in Venezuela. [ABSTRACT FROM AUTHOR]

We tagged 12 Carcharhinus limbatus with acoustic transmitters and monitored their presence at five piers along the north‐east coast of South Carolina, USA in 2016 and four piers in 2017 using acoustic receivers. Data were analysed with pier association indices (PAI), mixed models and fast Fourier transformation analyses to identify potential factors related to residence time and presence at piers and any cyclical patterns in visits to piers. While the majority of monitored C. limbatus were infrequently detected at piers, three (25.0%) were highly associated with piers (PAI ≥ 0.50). Of the C. limbatus that were detected after initial capture, three (25.0%) recorded detection events only at the pier where they were tagged and two individuals (16.7%) recorded at least one detection event at all monitored piers. The best‐fit model explaining C. limbatus residence time at piers included terms for pier location and diel cycle (wi = 0.88), whereas the best fit model explaining presence–absence of C. limbatus at piers included terms for tidal height, diel cycle, barometric pressure and angler count (wi = 0.98). Carcharhinus limbatus did not appear to display cyclical patterns in their visits to piers. Along the north‐east coast of South Carolina, association of C. limbatus with piers is a phenomenon for a proportion of mature individuals, but continued research is necessary to understand if this behaviour is driven by attraction to and feeding on angler discards or increased foraging opportunities resulting from the attraction of potential prey to the physical structure provided by piers. [ABSTRACT FROM AUTHOR]

Fish physiology is significantly affected by temperature variability. During fisheries interactions, fish are often exposed to air and subjected to rapid temperature changes. Fish thermal dynamics during such exposure, and the possible outcomes to their physiology, depend on how heat is distributed across their bodies, the speed at which their body temperatures change, and the size of the individual. Nevertheless, such thermal patterns remain unknown for sharks. This study employed a novel application of thermal imaging to evaluate external body temperature profiles of blacktip sharks (Carcharhinus limbatus) above-water exposure after capture. We found that above-water exposure duration, shark total length, and air temperature on the day of capture significantly influenced body surface temperatures of the analyzed sharks (N=28). Body surface temperature significantly increased with increasing exposure; however, thermal profiles of immature sharks (<140 cm) were significantly warmer than those of mature sharks. Moreover, blacktip surface body temperatures were significantly higher during days when air temperatures were at least 2.5°C warmer than water temperatures. We discuss these results as they relate to the ecology of blacktip sharks and their potential vulnerability to fisheries capture due to such changes in peripheral body temperature. [ABSTRACT FROM AUTHOR]

This study reports on the metabolic rate of the blacktip shark Carcharhinus limbatus and the energetic costs of external tag attachment. Metabolic rates, swimming speed and tail‐beat (BT) frequency were measured in a static respirometer with untagged animals and animals equipped with a small data logger. Tagged sharks showed significantly higher routine oxygen consumption and lower swimming speeds than untagged animals, indicating that tagging significantly affected the swimming efficiency and energetic requirements in these small sharks, and that these effects must be accounted for when interpreting telemetry data from free‐ranging individuals. [ABSTRACT FROM AUTHOR]

We analysed the stomach contents of 69 silky sharks Carcharhinus falciformis, 44 blacktip sharks Carcharhinus limbatus and 24 whitenose sharks Nasolamia velox caught in the Ecuadorian Pacific from August 2003 to December 2004. Prey included bony fishes, elasmobranchs, molluscs, crustaceans and turtles, with bony fishes being the most important to the diets of all three sharks, suggesting they are piscivorous predators. Based on the index of relative importance, the C. falciformis diet includes Thunnus albacares, Thunnus sp. and Auxis thazard, as well as some squid, fish and turtles. Similarly, the C. limbatus diet was dominated by T. albacares, Exocoetus monocirrhus, A. thazard, Katsuwonus pelamis, members of the Ophichthidae family and other elasmobranchs. Meanwhile, N. velox consumed mainly Dosidicus gigas, Larimus argenteus, Cynoscion sp. and Lophiodes spilurus. There is little competition for food between these tertiary carnivores: C. limbatus prefers prey from coastal-oceanic habitats; C. falciformis consumes mostly oceanic prey and N. velox focuses on prey from coastal habitats. The lack of information on the biology of sharks in Ecuador hinders the development of appropriate management and conservation plans to protect shark resources. This study increases our knowledge and understanding of sharks in Ecuador, thus contributing to their conservation. [ABSTRACT FROM AUTHOR]

The blacktip shark (Carcharhinus limbatus) is a common coastal species in tropical and subtropical waters around the world. To examine the fine-scale movement ecology of this species in a Caribbean nursery, 17 neonate blacktip sharks were acoustically tagged in May, 2012 and tracked for one year in Coral Bay, St John, USVI. By quantifying linear movement and shifts in position from a fixed Inner harbor location, we identified a diel movement pattern where blacktip sharks spend daylight hours within core habitat of Inner Coral Harbor and move each night to the central and outer portions of the Bay, a linear shift of 174-934 m. When compared to standard home range calculations applied to the overall movement data, these nightly positions were outside of the 95% activity space and, therefore, undetected using traditional space utilization methods, despite their predictable daily occurrence. Cluster analysis and nonmetric multidimensional scaling indicated distinct movement periods and locations: daytime (sun up) within Inner Coral Harbor; nighttime (sun down) in the center of the Bay; and brief periods approximately six hours after sunset at the mouth of the Bay. This diel shift in habitat use is likely associated with nocturnal foraging because it coincides with similar shifts in potential prey species. Habitat and resource management that incorporates the blacktip shark movements described herein is critical to the protection of these vulnerable life stages. The findings of this paper advance the understanding of blacktip shark behavior and acoustic telemetry experimental design. [ABSTRACT FROM AUTHOR]

Understanding population dynamics is essential for implementing effective conservation and management of coastal sharks. Fisheries-independent surveys can offer valuable information for such data-limited situations. A 12-year (2004–2015) standardized, shallow water longline survey was conducted monthly in the coastal waters of Bimini, Bahamas. Each monthly survey comprised five longline sets, totaling 75 hooks, with a soak time of 24 h. A total of 770 sharks from nine species were caught over the course of the study, with tiger ( Galeocerdo cuvier ), nurse ( Ginglymostoma cirratum ), blacktip ( Carcharhinus limbatus ) and lemon ( Negaprion brevirostris ) sharks comprising 95% of the catch. The majority of tiger (87%), nurse (62%), blacktip (67%), and lemon (82%) sharks were of immature lengths. A greater number of captured tiger (77%) and blacktip (66%) sharks were female, while nurse (55%) and lemon sharks (73%) were predominantly male. Poisson generalized additive models were used to analyze local abundance trends and examine how catch rates were influenced by year, month, location, tide, hour of capture, and lunar cycle. Seasonal trends indicate greater catches of the nurse, blacktip and lemon sharks during the summer months. Annual trends indicated relatively stable catch rates for the tiger, blacktip and lemon shark. Nurse shark catch rates were highly variable during the survey. Results from this study improve our understanding of the coastal shark assemblage in Bimini, Bahamas, and provide important local abundance trend information that could be beneficial for conservation and regional assessments. [ABSTRACT FROM AUTHOR]

Key methodological assumptions regarding the degree of natural variability and influence of sample handling and storage of elasmobranch vertebral chemistry were assessed using laser-ablation inductively coupled plasma mass spectrometry. Vertebral chemistry of juvenile blacktip sharks Carcharhinus limbatus was examined to identify whether differences existed among different regions of the vertebral column, between thoracic vertebrae of individual fish or within individual vertebrae. Additionally, the effects of bleach exposure and storage in ethanol on vertebral chemistry were compared. No significant variation in vertebral chemistry was found among different regions of the vertebral column or between thoracic vertebrae, but significant differences among transect locations within individual vertebrae were observed. The variation at all three levels appears comparable with published data on sagittal otoliths of bilaterally symmetrical teleost fishes. The experimental assessment of potential treatment effects indicated vertebral chemistry was not significantly affected by bleach or exposure to ethanol. Taken together, these results support the idea that vertebrae taken from the same region of the vertebral column can be treated as equivalent and at least certain elements remain robust to exposure to bleach and ethanol. [ABSTRACT FROM AUTHOR]

Elasmobranchs are commonly landed without fins and heads; however, the knowledge of total length is necessary for fishery management. We provide useful equations to extrapolate partial from elasmobranch carcasses lengths, to total lengths. Length-Length Relationships ( LLR) are described for 16 commercial elasmobranch species all included in the IUCN Red List: Hexanchus nakamurai, Heptranchias perlo, Squalus cubensis, Squatina dumeril, Scyliorhinus boa, Mustelus minicanis, M. higmani, M. norrisi, Carcharhinus acronotus, C. falciformis, C. limbatus, Galeocerdo cuvier, Rhizoprionodon lalandii, R. porosus, Sphyrna lewini and Pseudobatos percellens. This study provide new LLR equations and rsepresent an improvement in the knowledge of these species. [ABSTRACT FROM AUTHOR]

Information on how shark populations respond to fishing mortality ( F ) is critical to developing successful management and conservation strategies. However, data on catch, fishing effort and species abundance are often lacking for shark populations – preventing stock assessments from being conducted. Static demographic models circumvent this issue as they only require life history parameters. Age-structured Leslie Matrix models were developed and applied for silvertip shark Carcharhinus albimarginatus and common blacktip shark Carcharhinus limbatus sampled from heavily fished populations in the Indo-Pacific. Stochasticity was introduced to these models by varying vital rates though Monte Carlo simulations. Varying levels of F were introduced to the analyses to determine how both species respond to fishing pressure. Management scenarios were further developed to determine strategies that could facilitate sustainable harvesting. The demographic estimates demonstrated that without fishing both species would have increasing populations ( λ = 1.06 yr −1 for C. albimarginatus and 1.05 yr −1 for C. limbatus ) until density dependent effects occur. However, both populations would decline when low levels of F (>0.1 yr −1 ) were applied to all age-classes. The matrix elasticities revealed that changes to fertility elements had little effect on λ, while changes in juvenile survival led to the largest changes. However, age-at-first-capture analysis suggests protecting the juvenile life stage of both species would be an ineffective management strategy as both species mature at old ages. An age-at-last-capture analysis suggests these species could be harvested while maintaining increasing populations through a gauntlet fishery. This required F to be restrained to individuals <100 cm TL while protecting the older age-classes to preserve the breeding stock. This strategy would allow up to 16% and 13% of this size class to be harvested for C. limbatus and C. albimarginatus, respectively, until density dependent effects begin to manifest. However, this strategy depends on the ability to successfully protect all other age-classes from fishing – a strategy that may not be pragmatic in developing nations where little regulation occurs. [ABSTRACT FROM AUTHOR]

As top predators, sharks play important ecological roles in coastal marine ecosystems. Yet, environmental changes in many coastal regions are likely altering the composition of ecological communities, the interspecific interactions sharks have within coastal waters, and subsequently the ecological roles sharks play within these ecosystems. As such, understanding interactions among sharks, and how extrinsic factors shape these interactions, is important for predicting the consequences of future human impacts and environmental changes. Elucidating the contexts under which species co-occur and the implications of co-occurrence is an important step in developing such a predictive framework. Blacktip shark ( Carcharhinus limbatus) and bull shark ( Carcharhinus leucas) concentrations were quantified using long-term coastal gill net survey data across five bay systems in Texas. Relationships between co-occurrence, and environmental factors and shark sizes were examined within and across species. Co-occurrence of blacktip sharks and bull sharks varied spatially and temporally, with a significant increase in interspecific co-occurrence from the 1970s to 2010s, and a significant decrease in bull shark concentrations through time. Changes in environmental conditions, specifically increasing salinities, may have been responsible for increased blacktip and bull shark co-occurrence, and potential interspecific competition, which in turn may have led to decreased bull shark concentrations to reduce intraspecific competition. However, more refined questions are needed before predictive frameworks can be developed concerning the contexts under which co-occurrence is prevalent. Quantifying resource use among coastal sharks will help elucidate the drivers and implications of co-occurrence, and the potential for competitive interactions within and across species. [ABSTRACT FROM AUTHOR]

The ability to produce estimates of the metabolic rate of free-ranging animals is fundamental to the study of their ecology. However, measuring the energy expenditure of animals in the field has proved difficult, especially for aquatic taxa. Accelerometry presents a means of translating metabolic rates measured in the laboratory to individuals studied in the field, pending appropriate laboratory calibrations. Such calibrations have only been performed on a few fish species to date, and only one where the effects of temperature were accounted for. Here, we present calibrations between activity, measured as overall dynamic body acceleration (ODBA), and metabolic rate, measured through respirometry, for nurse sharks (Ginglymostoma cirratum), lemon sharks (Negaprion brevirostris) and blacktip sharks (Carcharhinus limbatus). Calibrations were made at a range of volitional swimming speeds and experimental temperatures. Linear mixed models were used to determine a predictive equation for metabolic rate based on measured ODBA values, with the optimal model using ODBA in combination with activity state and temperature to predict metabolic rate in lemon and nurse sharks, and ODBA and temperature to predict metabolic rate in blacktip sharks. This study lays the groundwork for calculating the metabolic rate of these species in the wild using acceleration data. [ABSTRACT FROM AUTHOR]

The response to capture is important in fisheries because it can reveal potential threats to species beyond fishing mortalities resulting from direct harvest. To date, the vast majority of studies assessing shark stress responses have used physiology or biotelemetry to look at sensitivity after capture, leaving a gap in our understanding of the behaviours of sharks during capture. We examined the behavioural responses of sharks to capture by attaching accelerometers to fishing gear and measuring the immediate and prolonged forces they exerted while on the line. We recorded acceleration vectors and derived the rate of intense fighting behaviours of 23 individual sharks comprising three species. Results suggest that blacktip sharks ( Carcharhinus limbatus) exhibited intense bouts of fighting behaviour at the onset of hooking, while nurse ( Ginglymostoma cirratum) and tiger sharks ( Galeocerdo cuvier) displayed more subdued acceleration values during capture. We also obtained plasma lactate from a subset of individuals and detected a strong correlation with maximum acceleration. These results align with previously published values and suggest that shark movement during fisheries capture is an important factor during bycatch and catch-and-release interactions. [ABSTRACT FROM AUTHOR]

Se registra la presencia de dos juveniles de Carcharhinus limbatus (Valenciennes, 1839) capturados por pescadores artesanales en el sector de la desembocadura del río Don Diego (11°18'N-73°43'W) al norte de la zona de influencia del Parque Nacional Natural Tayrona en el Caribe colombiano. Este constituye el primer registro de la especie para el área local y se describen los ejemplares examinados.The presence of two young Carcharhinus limbatus (Valenciennes, 1839) is documented. The individuals were collected by artisanal fishers in the area around the Don Diego River mouth (11°18'N-73°43'W) at the north of the Tayrona National Natural Park influence zone in the Colombian Caribbean. This is the first record of this species in the area. The specimens examined are described herein.

Comparisons between shark nursery populations are limited, however recent work has shown different populations exhibit distinct space use patterns. This study examined the residency and space use of young of the year (YOY) and juvenile Australian blacktip sharks, Carcharhinus tilstoni in a northern Australian nursery using acoustic telemetry. Presence and space use patterns exhibited by C. tilstoni were highly variable among individuals. In contrast to other shark nursery populations, the majority of YOY individuals left the nursery area within three months of release, while most juveniles exhibited long-term residency (6 months - 1 year). In addition, YOY individuals used smaller amounts of space than juveniles. Variable activity space size and location indicated individuals used different areas and often moved into new areas. High individual variation in juvenile populations is atypical for carcharhinid sharks, and contrasts with other nursery species, including the common blacktip shark C. limbatus, which are known to exhibit residency and consistent space use patterns in nursery areas. The unique patterns observed among C. tilstoni may be due to a number of factors, including differences in nursery habitat and population structure, or strategies to improve survival. This study highlights the importance of investigating nursery behaviour across different habitats and populations. [ABSTRACT FROM AUTHOR]

Southeast Florida witnesses an enormous seasonal influx of upper trophic level marine predators each year as massive aggregations of migrating blacktip sharks (Carcharhinus limbatus) overwinter in nearshore waters. The narrow shelf and close proximity of the Gulf Stream current to the Palm Beach County shoreline drive tens of thousands of sharks to the shallow, coastal environment. This natural bottleneck provides a unique opportunity to estimate relative abundance. Over a four year period from 2011–2014, an aerial survey was flown approximately biweekly along the length of Palm Beach County. A high definition video camera and digital still camera mounted out of the airplane window provided a continuous record of the belt transect which extended 200 m seaward from the shoreline between Boca Raton Inlet and Jupiter Inlet. The number of sharks within the survey transect was directly counted from the video. Shark abundance peaked in the winter (January-March) with a maximum in 2011 of 12,128 individuals counted within the 75.6 km-2 belt transect. This resulted in a maximum density of 803.2 sharks km-2. By the late spring (April-May), shark abundance had sharply declined to 1.1% of its peak, where it remained until spiking again in January of the following year. Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25°C. Shark abundance was also correlated with day of the year but not with barometric pressure. Although shark abundance was not correlated with photoperiod, the departure of the sharks from southeast Florida occurred around the vernal equinox. The shark migration along the United States eastern seaboard corresponds spatially and temporally with the spawning aggregations of various baitfish species. These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase. [ABSTRACT FROM AUTHOR]

At least fourteen species of sharks live in the Marine Protected Area of Isla del Coco National Park (ICNP), some are resident species such as the whitetip reef shark (Triaenodon obesus); others are migratory and visit the National Park throughout the year, e.g. the scalloped hammerhead shark (Sphyrna lewini) and the whale shark (Rhincodon typus). Between March 2010 and August 2012 six expeditions out to the ICNP were carried, during this period 25 night trips (from 18:00 to 22:00 hr) for shark tagging were conducted in the Wafer and Chatham bays. During those trips, 185 sharks were analyzed: 81.1 % were whitetip reef sharks (T. obesus), 16.7 % were blacktip sharks (Carcharhinus limbatus), 1.1 % were blacktip reef sharks (Carcharhinus melanopterus) and 1.1% were silvertip sharks (Carcharhinus albimarginatus). The most common species in Bahía Chatham was T. obesus, while the most common one in Bahía Wafer was C. limbatus, which represented 80.9 % and 80.5 % of the total sharks caught, respectively. Regarding T. obesus, a sex ratio of 1.2 males per female was estimated (X2=0.09; p=0.17); in turn a sex ratio of 1.01 males per female was observed (X2=0.04; p=0.79) for C. limbatus. The average total length for T. obesus and C. limbatus was 103.66±13.91 cm and 76.58±14.56 cm respectively; suggesting that black tip sharks use those bays during immature stages. The results show an interspecific spatial segregation of the most common resident sharks at ICNP, apparently the clear waters and the coral cover of Chatham Bay are preferred by T. obesus; while the turbid waters of the Genio River mouth are preferred by C. limbatus. [ABSTRACT FROM AUTHOR]

A longline survey was conducted from 2004 to 2014 to investigate the demographic population structure and seasonal abundance of the blacktip shark Carcharhinus limbatus in the Bimini Islands, the Bahamas. All individuals sampled ( n = 242) were sub-adult or adults [70·1-145·1 cm pre-caudal length ( LPC) range] with no neonates or YOY recorded in Bimini. Carcharhinus limbatus abundance peaked in September, coincident with the largest ratio of female to male sharks and a peak in fresh mating wounds on females. Mitochondrial control region ( mtCR) DNA sequences were obtained from C. limbatus at Bimini to test whether Bimini C. limbatus are most closely related to geographically proximate populations sampled on the south-eastern coast of the U.S.A., the closest known nursery areas for this species. Nine mtCR haplotypes were observed in 32 individuals sampled at Bimini [haplotype diversity ( h) = 0·821, nucleotide diversity ( π) = 0·0015]. Four haplotypes observed from Bimini matched those previously found in the northern Yucatan (Mexico)-Belize and two matched a haplotype previously found in the U.S.A. Four haplotypes were novel but were closely related to the northern Yucatan-Belizean haplotypes. Pair-wise Φ ST analysis showed that Bimini was significantly differentiated from all of the populations previously sampled (U.S.A. Atlantic, U.S.A. Gulf of Mexico, northern Yucatan, Belize and Brazil). This indicates that C. limbatus sampled from Bimini are unlikely from the described, proximate U.S.A. nurseries. [ABSTRACT FROM AUTHOR]

Animal navigation in the marine environment is believed to be guided by different sensory cues over different spatial scales. Geomagnetic cues are thought to guide long-range navigation, while visual or olfactory cues allow animals to pinpoint precise locations, but the complete behavioral sequence is not yet understood. Terra Ceia Bay is a primary nursery area for blacktip sharks, Carcharhinus limbatus, on southwestern Florida's Gulf of Mexico coast. Young-of-the-year animals show strong fidelity to a specific home range in the northeastern end of the bay and rapidly return when displaced. Older juveniles demonstrate annual philopatry for the first few years, migrating as far south as the Florida Keys each fall, then returning to Terra Ceia Bay each spring. To examine the sensory cues used in homing, we captured neonate (53 weeks old) blacktip sharks from within their home range, fitted them with acoustic tags, and translocated them to sites 8 km away in adjacent Tampa Bay and released them. Intact animals returned to their home range, within 34 h on average, and remained there. With olfaction blocked, fewer animals returned to their home range and they took longer to do so, 130 h on average. However, they did not remain there but instead moved throughout Terra Ceia Bay and in and out of Tampa Bay. Since sharks from both treatments returned at night in tannic and turbid water, vision is likely not playing a major role in navigation by these animals. The animals in this study also returned on incoming or slack tides, suggesting that sharks, like many other fish, may use selective tidal stream transport to conserve energy and aid navigation during migration. Collectively, these results suggest that while other cues, possibly geomagnetic and/or tidal information, might guide sharks over long distances, olfactory cues are required for recognizing their specific home range. [ABSTRACT FROM AUTHOR]

The northwestern Indian Ocean harbors a number of larger marine vertebrate taxa that warrant the investigation of genetic population structure given remarkable spatial heterogeneity in biological characteristics such as distribution, behavior, and morphology. Here, we investigate the genetic population structure of four commercially exploited shark species with different biological characteristics ( Carcharhinus limbatus, Carcharhinus sorrah, Rhizoprionodon acutus, and Sphyrna lewini) between the Red Sea and all other water bodies surrounding the Arabian Peninsula. To assess intraspecific patterns of connectivity, we constructed statistical parsimony networks among haplotypes and estimated (1) population structure; and (2) time of most recent population expansion, based on mitochondrial control region DNA and a total of 20 microsatellites. Our analysis indicates that, even in smaller, less vagile shark species, there are no contemporary barriers to gene flow across the study region, while historical events, for example, Pleistocene glacial cycles, may have affected connectivity in C. sorrah and R. acutus. A parsimony network analysis provided evidence that Arabian S. lewini may represent a population segment that is distinct from other known stocks in the Indian Ocean, raising a new layer of conservation concern. Our results call for urgent regional cooperation to ensure the sustainable exploitation of sharks in the Arabian region. [ABSTRACT FROM AUTHOR]

As coastal species experience increasing anthropogenic pressures there is a growing need to characterise the ecological drivers of their abundance and habitat use, and understand how they may respond to changes in their environment. Accordingly, fishery-independent surveys were undertaken to investigate shark abundance along approximately 400 km of the tropical east coast of Australia. Generalised linear models were used to identify ecological drivers of the abundance of immature blacktip Carcharhinus tilstoni/Carcharhinus limbatus, pigeye Carcharhinus amboinensis, and scalloped hammerhead Sphyrna lewini sharks. Results indicated general and species-specific patterns in abundance that were characterised by a range of abiotic and biotic variables. Relationships with turbidity and salinity were similar across multiple species, highlighting the importance of these variables in the functioning of communal shark nurseries. In particular, turbid environments were especially important for all species at typical oceanic salinities. Mangrove proximity, depth, and water temperature were also important; however, their influence varied between species. Ecological drivers may promote spatial diversity in habitat use along environmentally heterogeneous coastlines and may therefore have important implications for population resilience. [ABSTRACT FROM AUTHOR]

Elasmobranchs can bioaccumulate considerable amounts of persistent organic pollutants (POPs) and utilize several reproductive strategies thereby influencing maternal transfer of contaminants. This study provides preliminary data on the POP transfer from pregnant females to offspring of three species (Atlantic stingrays, bonnethead, blacktip sharks) with different reproduction modes (aplacental, placental viviparity). Polychlorinated biphenyl (PCB) levels were generally higher than any other POPs. Stingrays and blacktip shark embryos contained the lowest POP concentrations while bonnetheads and the blacktip adult female had the highest concentrations. Results suggest that POPs are more readily transferred from the mother to the embryo compared to what is transferred to ova in stingrays. Statistically significant differences in levels of selected POPs were found between embryos from the left and right uterus within the same litter as well as between female and male embryos within the same litter for bonnetheads, but not for the blacktip sharks. [ABSTRACT FROM AUTHOR]

Shark nursery areas are widely regarded as essential habitats for the growth and survival of young individuals. The effective management and protection of shark nursery habitat are contingent upon a clear understanding of how individual species utilize such habitat both spatially and temporally. Although shark nurseries have been identified in the Caribbean, this information is generally lacking. From 2006 to 2012, we used passive acoustic telemetry to monitor the presence, movements, and habitat use of 65 juvenile blacktip sharks ( Carcharhinus limbatus) and 42 juvenile lemon sharks (Negaprion brevirostris) within Fish Bay and Coral Bay, two shark nurseries in St. John, United States Virgin Islands. Both species were present in each bay during all months of the year, but abundance peaked during the summer (June-September). Although telemetry data indicated that blacktip and lemon sharks moved throughout each embayment, each species exhibited strong site fidelity to core areas across all years of the study. Habitat partitioning was observed in both nurseries as blacktip sharks generally occurred in areas characterized by water depths of 1.5-6 m with seagrass and sand/mud substrate, while lemon sharks remained in close proximity to or within shallow (<1 m), mangrove-fringed seagrass habitat. Blacktip sharks were also observed to exhibit greater activity space during the nighttime hours (1900-0659 h) within Coral Bay. The results of this study indicate that Fish Bay and Coral Bay are nursery areas that warrant designation as essential fish habitat and exemplify the need for additional focused management measures. [ABSTRACT FROM AUTHOR]

For free-swimming marine species like sharks, only population genetics and demographic history analyses can be used to assess population health/status as baseline population numbers are usually unknown. We investigated the population genetics of blacktip reef sharks, Carcharhinus melanopterus; one of the most abundant reef-associated sharks and the apex predator of many shallow water reefs of the Indian and Pacific Oceans. Our sampling includes 4 widely separated locations in the Indo- Pacific and 11 islands in French Polynesia with different levels of coastal development. Four-teen microsatellite loci were analysed for samples from all locations and two mitochondrial DNA fragments, the control region and cytochrome b, were examined for 10 locations. For microsatellites, genetic diversity is higher for the locations in the large open systems of the Red Sea and Australia than for the fragmented habitat of the smaller islands of French Polynesia. Strong significant structure was found for distant locations with FST values as high as ~0.3, and a smaller but still significant structure is found within French Polynesia. Both mitochondrial genes show only a few mutations across the sequences with a dominant shared haplotype in French Polynesia and New Caledonia suggesting a common lineage different to that of East Australia. Demographic history analyses indicate population expansions in the Red Sea and Australia that may coincide with sea level changes after climatic events. Expansions and flat signals are indicated for French Polynesia as well as a significant recent bottleneck for Moorea, the most human-impacted lagoon of the locations in French Polynesia. [ABSTRACT FROM AUTHOR]

As large long-lived predators, sharks are particularly vulnerable to exposure to methylmercury biomagnified through the marine food web. Accordingly, nonlethal means were used to collect tissues for determining mercury (Hg) concentrations and stable isotopes of carbon (δC) and nitrogen (δN) from a total of 69 sharks, comprising 7 species, caught off Southwest Florida from May 2010 through June 2013. Species included blacknose ( Carcharhinus acronotus), blacktip ( C. limbatus), bull ( C. leucas), great hammerhead ( Sphyrna mokarran), lemon ( Negaprion brevirostris), sharpnose ( Rhizoprionodon terraenovae), and tiger sharks ( Galeocerdo cuvier). The sharks contained Hg concentrations in their muscle tissues ranging from 0.19 mg/kg (wet-weight basis) in a tiger shark to 4.52 mg/kg in a blacktip shark. Individual differences in total length and δC explained much of the intraspecific variation in Hg concentrations in blacknose, blacktip, and sharpnose sharks, but similar patterns were not evident for Hg and δN. Interspecific differences in Hg concentration were evident with greater concentrations in slower-growing, mature blacktip sharks and lower concentrations in faster-growing, young tiger sharks than other species. These results are consistent with previous studies reporting age-dependent growth rate can be an important determinant of intraspecific and interspecific patterns in Hg accumulation. The Hg concentrations observed in these sharks, in particular the blacktip shark, also suggested that Hg may pose a threat to shark health and fitness. [ABSTRACT FROM AUTHOR]