Carcharhinus Leucas Research Articles

Divergent field metabolic rates highlight the challenges of increasing temperatures and energy limitation in aquatic ectotherms.

Environments where extreme temperatures and low productivity occur introduce energetically challenging circumstances that may be exacerbated by climate change. Despite the strong link between metabolism and temperature in ectotherms, there is a paucity of data regarding how the metabolic ecology of species affects growth and fitness under such circumstances. Here, we integrated data describing field metabolic rates and body condition of two sympatric species of ectotherms with divergent lifestyles, the benthic freshwater (or largetooth) sawfish (Pristis pristis) and the epipelagic bull shark (Carcharhinus leucas) occurring in the Fitzroy River, Western Australia, to test the implications of their differing metabolic ecologies for vulnerability to rising temperatures. Over a temperature range of 18-34°C, sawfish had lower field metabolic rates (63-187mg O2kg-0.86 h-1) and lower temperature sensitivity of metabolic rates [activation energy (EA) = 0.35eV] than bull sharks (187-506mg O2kg-0.86 h-1; EA = 0.48eV). Both species lost body mass throughout the dry season, although bull sharks significantly more (0.17% mass loss day-1) than sawfish (0.07% mass loss day-1). Subsequent bioenergetics modelling showed that under future climate change scenarios, both species would reach potentially lethal levels of mass loss during dry season periods before the end of the century. These results suggest that ectotherms with low metabolic rates may be better suited to extreme environmental conditions, and that even small increases in temperature due to climate change could have substantial impacts on the ability of ectotherms to grow and survive inharsh conditions, including high temperatures and energy-limiting circumstances.

Natural tags identify nursery origin of a coastal elasmobranch Carcharhinus leucas

Abstract Traditional methods for evaluating the importance of elasmobranch nursery habitats have focused on estimating densities or abundances of juveniles within individual nurseries; however, rates of juvenile mortality may vary among nurseries. Thus, abundance may not reflect contribution to adult populations, and contribution estimates require methods to identify the nursery origin of adults. We evaluated the use of natural tags, vertebral chemistry (stable isotope analysis, elemental analysis) and genetic markers, to identify bull shark Carcharhinus leucas nursery origin along the Texas coast (northwestern Gulf of Mexico) at multiple spatial scales. Sharks were most accurately assigned (89% accuracy) to their regional origin (Northern vs. Southern Texas) using a combination of vertebral chemistry and genetic markers. Accuracy decreased when incorporating only one type of natural tag (vertebral chemistry: 58%–84%; genetics: 30%–58%), or when assigning sharks among nurseries grouped into three or four regions (30%–71%; ~100 km spatial scale). Synthesis and applications. We describe a novel method integrating multiple natural tags to identify the nursery origin of a highly migratory coastal elasmobranch, over smaller spatial scales than previously investigated. This framework provides a powerful tool to estimate the relative source (nursery) contributions to adult populations of highly mobile species, which represent production estimates sought in the designation of essential fish habitat and ultimately incorporated into marine spatial planning practices.

Long-term monitoring provides insight into estuarine top predator (Carcharhinus leucas) resilience following an extreme weather event

Chronic environmental change threatens biodiversity, but acute disturbance events present more rapid and immediate threats. In 2010, a cold snap across south Florida had wide-ranging impacts, including negative effects on recreational fisheries, agriculture, and ecological communities. Here, we use acoustic telemetry and historical longline monitoring to assess the long-term implications of this event on juvenile bull sharksCarcharhinus leucasin the Florida Everglades. Despite the loss of virtually all individuals (ca. 90%) within the Shark River Estuary during the cold snap, the catch per unit effort (CPUE) of age 0 sharks on longlines recovered through recruitment within 6-8 mo of the event. Acoustic telemetry revealed that habitat use patterns of age 0-2 sharks reached an equilibrium in 4-6 yr. In contrast, the CPUE and habitat use of age 3 sharks required 5-7 yr to resemble pre-cold snap patterns. Environmental conditions and predation risk returned to previous levels within 1 yr of the cold snap, but abundances of some prey species remained depressed for several years. Reduced prey availability may have altered the profitability of some microhabitats after the cold snap, leading to more rapid ontogenetic shifts to marine waters among sharks for several years. Accelerated ontogenetic shifts coupled with inter-individual behavioral variability of bull sharks likely led to a slower recovery rate than predicted based on overall shark CPUE. While intrinsic variation driven by stochasticity in dynamic ecosystems may increase the resistance of species to chronic and acute disturbance, it may also increase recovery time in filling the diversity of niches occupied prior to disturbance if resistive capacity is exceeded.

Late Pleistocene-Holocene fossils from Mirim Lake, Southern Brazil, and their paleoenvironmental significance: I - Vertebrates

Mirim Lake is located in the southern Brazilian/northeastern Urugayan coastal plain. Fossils of mollusks have been discovered on its shores since the XIX century, and in recent years, several new remains of invertebrates and vertebrates have been found in the Brazilian area of the lake that provide insights on the geological evolution and environmental changes that affected this lake during the late Quaternary. In this first of two papers describing these new findings we focus on vertebrates, consisting of aquatic and terrestrial taxa. The former include the first associated fossil remains of one adult and one juvenile balaenid whale known in Brazil, probably a female and calf of the southern right whale (baleia-franca) Eubalaena australis, besides bull sharks (Carcharhinus leucas) also recorded for the first time in southern Brazil, rays (Dasyatidae and Myliobatidae) and teleost fishes. The fossils of terrestrial vertebrates include several extinct mammals, found on the margins and retrieved from the lake bottom by fishermen at depths of up to 4 m. One molar tooth of Toxodon discovered in situ in one irrigation channel yielded an electron spin resonance (ESR) age of 68 ± 13 ka, in agreement with an age of 32.8 ± 5.1 ka obtained in quartz grains extracted from a caliche nodule collected above that fossil and dated by optically-stimulated luminescence (OSL). Other quartz grains in the same nodule that yielded ages of 16.9 ± 2.5 ka indicate partial dissolution of the caliche by increased rainfall at the beginning of the last glacial-interglacial transition (Termination I) . The lake was invaded by marine waters and organisms during the Holocene sea-level highstand of +3 m around 5–6 ka b2k through paleo-connections with the Atlantic Ocean, becoming a paleo-lagoon. At that time coastal waters were warmer than today, as indicated by the presence of the tropical shark C. leucas. The ESR and OSL ages indicate chronocorrelation with the Pleistocene fossil-bearing Santa Vitória Formation that outcrops to the east. The fossil and sedimentary records indicate that the geological evolution and environmental conditions of the lake were controlled by climate and sea-level oscillations related to glacial-interglacial cycles.

Respirometer in a box: development and use of a portable field respirometer for estimating oxygen consumption of large-bodied fishes.

This study developed a portable, low-cost field respirometer for measuring oxygen consumption rates of large-bodied fishes. The respirometer performed well in laboratory tests and was used to measure the oxygen consumption rates ( O2 ) of bull sharks Carcharhinus leucas (mean: 249.21 ± 58.10 mg O2 kg-1 h-1 at 27.05°C). Interspecific comparisons and assessments of oxygen degradation curves indicated that the respirometer provided reliable measurements of O2 . This system presents a field-based alternative to laboratory respirometers, opening opportunities for studies on species in remote localities, increasing the ability to validate physiological field studies.

Use of historical data to assess changes in the vulnerability of sharks

Shark populations have declined worldwide. However, the lack of data for most species makes it difficult to use conventional population assessments to estimate their status. The productivity and susceptibility analysis (PSA) has been recommended for elasmobranchs as it is a data-poor assessment that uses the best available information of the species and their fisheries to determine their vulnerability. A historical characterisation was performed to define the most important periods for the shark fishery in Campeche, southern Gulf of Mexico, and a PSA was conducted to determine the vulnerability of the eleven most important commercial shark species in each three periods. The periods were defined as: local commercialisation (1940–1979), when all species had their lowest vulnerability values, and Carcharhinus leucas, Negraprion brevirostris, and Sphyrna mokarran were classified as highly vulnerable; developed industry (1980–1998) when there was an increase of the fishing pressure, and most small species changed from low to moderate vulnerability and the large coastal sharks scored their highest vulnerability values; and declining industry (1999–2018), when all species had lower vulnerability values than in the developed industry period. However, Carcharhinus brevipinna, Ginglymostoma cirratum, N. brevisrostris, C. leucas, and S. mokarran were still classified as highly vulnerable and could be suffering the accumulative effects of decades of fishing pressure. This multidisciplinary approach serves to identify the most vulnerable species throughout the history of the fishery and to understand the vulnerability values within a historical context, avoiding the shifting baseline syndrome.

Performance of Two Survey Gears Targeting Elasmobranchs in a Shallow, Subtropical Estuary

AbstractFishery‐independent surveys have become increasingly prevalent in recent decades for monitoring the population trends of highly mobile species like elasmobranchs (sharks and rays). Despite the utility of gear evaluations for streamlining costs and increasing the efficiency of fishery‐independent surveys, these assessments are sparse for elasmobranch‐specific surveys. Catch data were examined from a fishery‐independent longline and gill‐net survey that targeted elasmobranchs in Florida's southern Indian River Lagoon from July 2016 to September 2018. The goal of the study was to assess the effects of the type of longline bait that is used (Striped Mullet Mugil cephalus versus Atlantic Mackerel Scomber scombrus) and the size of gill‐net mesh (15.2‐ versus 20.3‐cm stretch mesh) on the species composition, catch per unit effort (CPUE), and size distribution of captured elasmobranchs. Elasmobranchs were caught more often in the gill net than on the longline. Striped Mullet yielded a significantly higher CPUE of elasmobranchs than Atlantic Mackerel did. Although Striped Mullet caught more sharks than Atlantic Mackerel did, the mean length of the sharks did not differ between groups that were captured with the two bait types. Species composition differed with respect to bait type; significantly more Bull Sharks Carcharhinus leucas and Atlantic Sharpnose Sharks Rhizoprionodon terraenovae were caught with Striped Mullet. Elasmobranch abundances were similar between the two sizes of gill‐net mesh. However, species composition differed, with a greater abundance of both Atlantic Stingrays Hypanus sabinus and Bull Sharks caught in the 15.2‐cm mesh. Elasmobranchs that were caught in the 20.3‐cm mesh were significantly larger than those caught in the 15.2‐cm mesh. The length distributions for the common species (Bull Sharks, Atlantic Stingrays, and Bluntnose Stingrays H. say) differed significantly with respect to the two mesh sizes. This study is the first assessment of a standardized elasmobranch‐specific survey in this nationally significant estuary and increases our understanding of the performance of complementary gear types for targeting sharks and rays in a shallow lagoonal system.

Shark attacks on offshore streamer cables

In the search for new subsea oil fields, geologists use vessels to tow streamer cables, which collects seismic data. This activity attracts bull sharks to the magnetic streamer fields causing shark attacks and hence losses and delays. This paper discusses how shark attacks on streamer cables can be modelled and simulated in cable design and optimization processes. In order to generate a representative simulation model, a large and authentic bull shark jaw was 3D-scanned. The shark jaw was converted to a CAD-model utilizing reverse engineering applications. Numerical models of the streamer cables, capturing the response with respect to friction properties and failure criteria’s, were benchmarked using quasi-static compression tests. Additionally, dynamic bite and impact simulations replicating the shark attack on streamer cables have been conducted. The physical compression tests and simulations show that the streamer cable FE-models are valid. The results indicate that a shark bite can be sufficient to critically damage the cable, but the bite resilience of the streamer cable is strongly correlated to the shark speed upon impact.

SMART drumlines at Réunion Island do not attract bull sharks Carcharhinus leucas into nearshore waters: Evidence from acoustic monitoring

Following a series of shark attacks, local authorities in Reunion Island developed an experimental shark control programme using innovative fishing gear, namely Shark Management Alert in Real Time (SMART) drumlines (SDL). From January to November 2014, four SDL were deployed 24 h per day, four days per week to target bull (Carcharhinus leucas) and tiger (Galeocerdo cuvier) sharks and to test the fishing efficacy of the SDL. Presence and residence time of 19 acoustically tagged bull and 19 tiger sharks, which had been tagged up to two years before the SDL deployment, were modelled against different SDL configurations, which included bait type and presence of bait or catches on the hooks, as well as environmental parameters before, during and after SLD deployment. There was insufficient acoustic data from the tiger sharks for any analyses. Bull sharks spent less time in nearshore waters when drumlines were deployed, and their presence was influenced by sea surface temperatures (SST), rainfall and time of day. There was no difference in the number of bull sharks detected in the SDL deployment area compared with surrounding sites. As SDL catch rates were only poorly correlated with presence of tagged sharks, their efficacy in catching sharks present in the area could not be accurately determined. Overall, the results show that SDL, deployed without chum and baited with small, whole, low-fat fish cannot be considered as “shark magnets”, which could attract dangerous bull sharks inshore where they would pose a threat to the safety of surfers and other sea users. The detection of tagged bull sharks moving into and out of the SDL fishing area indicates that these fishing devices do not provide an impenetrable barrier to the passage of this potentially dangerous species.

Does proximity to freshwater refuge affect the size structure of an estuarine predator (Carcharhinus leucas) in the north-western Gulf of Mexico?

The life histories of estuarine species are often adapted to the environmental variability they experience. However, estuaries are increasingly vulnerable to natural and anthropogenic changes, necessitating an understanding of how shifting conditions affect the survival, behaviour and population structure of estuarine-dependent animals. In this study we used data from fisheries-independent surveys collected across six estuaries with variable salinity regimes in Texas, USA, from 1975 to 2016 to investigate the role sources of freshwater inflow play in shaping juvenile bull shark Carcharhinus leucas size structure. High frequencies of co-occurrence with similarly sized conspecifics (59% of capture events) suggest bull sharks segregated within Texan estuaries based on body size. Bull shark sizes increased with distance to the nearest source of freshwater inflow, although effect sizes were small and access to freshwater habitats may be more important in shaping size-dependent distribution patterns. River mouths were disproportionately used by smaller juveniles (<90-cm total length, TL) and avoided by larger juveniles (>135cm TL). However, the use of river mouths decreased in estuaries characterised by limited freshwater inflow and greater variability in salinities at river mouths, highlighting geographic differences in the functions these habitats provide as potential environmental and predator refugia. Young-of-the-year (i.e. age-0) sharks also increased their use of river mouths throughout the 40-year study period, revealing the growing importance of river mouths as potential nursery habitats.

Effects and effectiveness of lethal shark hazard management: The Shark Meshing (Bather Protection) Program, NSW, Australia

Abstract ‘Shark attack’ presents a considerable social‐environmental challenge. Each year a small number of people are injured or killed by shark bite. Concurrently, sharks and other marine life are subject to unprecedented anthropogenic pressures. Shark hazard management varies globally, but lethal strategies are common, with negative consequences for species and environments. Of particular concern are the effects for threatened species. Lethal strategies have recently come under criticism, based on the negative effects for marine life, effectiveness for human safety and inconsistency with contemporary values. Moves to improve both safety and conservation can be hindered by polarized debate. We present a case study of the world's longest‐running lethal shark hazard management program, the Shark Meshing (Bather Protection) Program, New South Wales, Australia. We take an interdisciplinary approach to bring into conversation factors that contribute to safety and conservation outcomes. To date, most research focuses on one or other of these areas. We seek to synthesize the factors that are not previously considered in relation to each other. Our aims were to: (a) identify and critique the diverse factors that determine the outcomes of the program; (b) assess the negative effects of the program for sharks and other marine life; and (c) assess the effectiveness of the program for reducing threat of shark interactions. We find that: (a) multiple social and environmental factors contribute to program outcomes; (b) total shark numbers and populations of key target species – white shark (Carcharodon carcharias), tiger shark (Galeocerdo cuvier) and bull shark (Carcharhinus leucas) – have declined over the program's 80 years, as have a number of non‐target species; (c) incidence of shark bite has declined since the program's introduction, but two external points warrant attention. First, key factors influencing the shark bite incidence are frequently overlooked, namely changing cultures of beach‐ and ocean‐use, advances in beach patrol, and emergency and medical response. Second, the proportion of bites leading to fatality has decreased significantly in recent decades. Beach patrol and emergency response contribute to human safety and well‐being without the negative consequences of lethal strategies. As such, they offer a focus for future shark hazard management and research. A free Plain Language Summary can be found within the Supporting Information of this article.

First inland record of bull shark Carcharhinus leucas (Carcharhiniformes: Carcharhinidae) in Indonesian Borneo

An individual of bull shark Carcharhinus leucas (Müller & Henle, 1839) with c. 600-700 mm of total length was caught and photographed on 2019 in Barito River, South Kalimantan province, Indonesia. This finding is considered as a first inland record of C. leucas in Indonesian Borneo (Kalimantan). Collecting data using citizen science is needed to asses the occurence of C. leucas and evaluate the importance of riparian system in Kalimantan waters as nursery area or ranging habitat for this species.

Long-term patterns of abundance, residency and movements of bull sharks (Carcharhinus leucas) in Sydney Harbour, Australia

Bull sharks (Carcharhinus leucas) are known to frequent nearshore environments, particularly estuaries, resulting in interactions with humans. Knowledge of the behaviour of large individuals in temperate, estuarine environments is limited. This acoustic telemetry study reports on residency and movement patterns of 40 sub-adult and adult bull sharks in Sydney Harbour, a large temperate estuary, over seven years. Bull sharks exhibited clear seasonal patterns in their occurrence during the austral summer and autumn, with abundance peaking in January and February. This pattern was consistent between sexes and across all sizes. Bull sharks displayed weak diel differences in their spatial distribution, with individuals using areas further from the Harbour entrance more frequently during the day and at low tides. A diel pattern in depth use was apparent, with sharks utilising deeper water during daytime and moving shallower at night. Bull sharks had high individual inter-annual variability in their spatial distribution, however, when data were aggregated among all individuals and years, two locations of increased use were identified. Water temperature was the key predictor for seasonal movements and return behaviour to this estuary, suggesting that increasing water temperatures as a result of climate change may lead to higher shark abundance and possibly longer periods of residency in Sydney Harbour. Understanding the drivers for bull shark abundance and distribution will hopefully facilitate better education and shark smart behaviour by estuarine water-users, especially during summer and autumn months.

Environmental predictive models for shark attacks in Australian waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 631:165-179 (2019) - DOI: https://doi.org/10.3354/meps13138 Environmental predictive models for shark attacks in Australian waters Laura A. Ryan1,*, Samantha K. Lynch1,*, Robert Harcourt1, David J. Slip1,2, Vic Peddemors3, Jason D. Everett4, Lisa-Marie Harrison1, Nathan S. Hart1,** 1Department of Biological Sciences, Macquarie University, Sydney, NSW 2109, Australia 2Taronga Conservation Society Australia, Mosman, NSW 2088, Australia 3New South Wales Department of Primary Industries, Fisheries, Sydney Institute of Marine Science, Mosman, NSW 2088, Australia 4School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia *These authors contributed equally to this work**Corresponding author: nathan.hart@mq.edu.au ABSTRACT: Shark attacks are rare but traumatic events that generate social and economic costs and often lead to calls for enhanced attack mitigation strategies that are detrimental to sharks and other wildlife. Improved understanding of the influence of environmental conditions on shark attack risk may help to inform shark management strategies. Here, we developed predictive models for the risk of attack by white Carcharodon carcharias, tiger Galeocerdo cuvier, and bull/whaler Carcharhinus spp. sharks in Australian waters based on location, sea surface temperature (SST), rainfall, and distance to river mouth. A generalised additive model analysis was performed using shark attack data and randomly generated pseudo-absence non-attack data. White shark attack risk was significantly higher in warmer SSTs, increased closer to a river mouth (<10 km), and peaked at a mean monthly rainfall of 100 mm. Whaler shark attack risk increased significantly within 1 km of a river mouth and peaked in the summer months. Tiger shark attack risk increased significantly with rainfall. We performed additional temporal and spatio-temporal analyses to test the hypothesis that SST anomaly (SSTanom) influences white shark attack risk, and found that attacks tend to occur at locations where there is a lower SSTanom (i.e. the water is relatively cooler) compared to surrounding areas. On the far north coast of eastern Australia—an attack hotspot—a strengthening of the East Australian Current may cause white sharks to move into cooler upwelling waters close to this stretch of the coast and increase the risk of an attack. KEY WORDS: Shark attack · Attack risk · Pseudo-absence data · White shark · Tiger shark · Bull shark Full text in pdf format PreviousNextCite this article as: Ryan LA, Lynch SK, Harcourt R, Slip DJ and others (2019) Environmental predictive models for shark attacks in Australian waters. Mar Ecol Prog Ser 631:165-179. https://doi.org/10.3354/meps13138 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 631. Online publication date: November 21, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Is the Shark Just Drifting, or Does It Take a Quick Nap?

It is unknown if resting sharks can sleep, which is also true for gliding ones. Here, a videotaped bull shark is presented that drifted in an uncontrolled manner for 120 seconds while sinking with 0.1 m/second. Several aspects are discussed to determine if the shown behavior reflects the commonly accepted definition of sleep. Additionally, the idea is also discussed if this state might reflect a “quiet waking state” instead of where the shark still maintained some vigilance despite its general appearance.

Assessing trophic flexibility of a predator assemblage across a large estuarine seascape using blood plasma stable isotope analysis

The northcentral Gulf of Mexico (nGoM) encompasses a range of environments that support a speciose predatory assemblage. Large predatory species are often viewed as trophically-analogous, sharing similar isotopic niches. To investigate the regional and seasonal isotopic variability of a predator assemblage across the coastal waters of the nGoM (Louisiana, Mississippi, and Alabama), we analyzed the stable isotopes of carbon, nitrogen, and sulfur using a fast turnover tissue, blood plasma, for seven dominant predator species. Carbon, nitrogen, and sulfur isotope values varied regionally, with a significant interaction between region and season for nitrogen and sulfur. Species' isotopic niches varied regionally, as well as seasonally, leading to varying levels of isotopic niche overlap among species. Blacktip sharks Carcharhinus limbatus and Atlantic sharpnose sharks Rhizoprionodon terraenovae in particular demonstrated flexibility in their isotopic relationships, whereas blacknose sharks C. acronotus maintained a more consistent isotopic niche regardless of region or season. No biologically significant overlap was observed for blacknose sharks, bull sharks C. leucas, or spinner sharks C. brevipinna, suggesting that these species occupy distinct isotopic space. Overlap calculations using two isotopes (carbon and nitrogen) produced markedly higher overlap versus three isotopes (carbon, nitrogen, and sulfur), which demonstrates that predatory roles may be oversimplified when using only carbon and nitrogen. These findings highlight the value of examining seasonal variation in trophic roles using fast turnover tissues and provide the first triple-isotope characterization of a common predatory assemblage in the northcentral Gulf of Mexico.

Development of highly sensitive environmental DNA methods for the detection of Bull Sharks, Carcharhinus leucas (Müller and Henle, 1839), using Droplet Digital™ PCR

AbstractBackgroundAs apex and mesopredators, elasmobranchs play a crucial role in maintaining ecosystem function and balance in marine systems. Elasmobranch populations worldwide are in decline as a result of exploitation via direct and indirect fisheries mortalities and habitat degradation; however, a lack of information on distribution, abundance, and population biology for most species hinders their effective management. Environmental DNA analysis has emerged as a cost‐effective and non‐invasive technique to fill some of these data gaps, but often requires the development of species‐specific methodologies.AimsHere, we established eDNA methodology appropriate for targeted species detections of Bull Sharks, Carcharhinus leucas, in estuarine waters in the northern Gulf of Mexico.Materials and MethodsWe compared different QIAGEN®DNeasy® extraction kit protocols and developed a species‐specific Droplet Digital™ PCR (ddPCR) assay by designing primers and an internal probe to amplify a 237 base pair portion of the ND2 gene in the mitochondrial genome of C. leucas. To validate the developed methods, water samples were collected from known C. leucas habitat and from an ex situ closed environment containing a single C. leucas individual. The effectiveness of the assay in an open environment was then assessed by placing one C. leucas into a flow‐through mesocosm system and water samples were collected every 30 min for 3 hr.ResultsThe developed C. leucas ‐specific assay has the ability to detect target DNA concentrations in a reaction as low as 0.6 copies/μl. DdPCR reactions performed on water samples from known habitat and 30 min after a shark was added to the closed environment contained 1.62 copies/μl and 166.6 copies/μl of target C. leucas eDNA, respectively. Carcharhinus leucas eDNA was detected in the flow‐through system within 30 min, but concentrations remained low and variable throughout the duration of the experiment.

Residency and spatial distribution of bull sharks Carcharhinus leucas in and around Reunion Island marine protected area

A sudden increase in the rates of shark attacks on humans at Reunion Island has been blamed by some on the implementation of a marine protected area (MPA) along the island’s west coast, where attacks, primarily by bull sharks Carcharhinus leucas, were concentrated. We used passive acoustic telemetry to investigate the spatial distribution of bull sharks (N = 36) by quantifying their residency and their frequentation of the MPA and compared it to outside of the MPA. Over the study duration of 17 mo, 18 sharks were detected in the acoustic receiver array, most of which were detected more frequently outside the MPA (N = 148; mean ± SD = 41.5 ± 56.4 visits mo-1 and 17.6 ± 30.5 h mo-1) than inside the MPA (N = 218; 21.4 ± 28.1 visits mo-1 and 7.2 ± 15.2 h mo-1). However, we found individual variation in the sharks’ use of the MPA. Thirteen sharks spent more time outside the MPA than inside, while 5 sharks (all females) spent significantly more time inside the MPA. These results suggest that the spatial distribution of bull sharks is not primarily centered in the MPA along the west coast of Reunion Island, although we identified specific locations where bull shark encounter probabilities are relatively high during particular times of the year. Such higher-risk areas could be targeted as part of the risk management strategy for changes in human uses in order to reduce the risks of negative shark-human interactions observed during the past decade.

Population structure, connectivity, and demographic history of an apex marine predator, the bull shark Carcharhinus leucas.

Knowledge of population structure, connectivity, and effective population size remains limited for many marine apex predators, including the bull shark Carcharhinus leucas. This large‐bodied coastal shark is distributed worldwide in warm temperate and tropical waters, and uses estuaries and rivers as nurseries. As an apex predator, the bull shark likely plays a vital ecological role within marine food webs, but is at risk due to inshore habitat degradation and various fishing pressures. We investigated the bull shark's global population structure and demographic history by analyzing the genetic diversity of 370 individuals from 11 different locations using 25 microsatellite loci and three mitochondrial genes (CR, nd4, and cytb). Both types of markers revealed clustering between sharks from the Western Atlantic and those from the Western Pacific and the Western Indian Ocean, with no contemporary gene flow. Microsatellite data suggested low differentiation between the Western Indian Ocean and the Western Pacific, but substantial differentiation was found using mitochondrial DNA. Integrating information from both types of markers and using Bayesian computation with a random forest procedure (ABC‐RF), this discordance was found to be due to a complete lack of contemporary gene flow. High genetic connectivity was found both within the Western Indian Ocean and within the Western Pacific. In conclusion, these results suggest important structuring of bull shark populations globally with important gene flow occurring along coastlines, highlighting the need for management and conservation plans on regional scales rather than oceanic basin scale.

First photographic inland records of bull shark Carcharhinus leucas (Carcharhiniformes: Carcharhinidae) in Sumatran waters, Indonesia

Two specimens (c.700 mm) of bull sharks Carcharhinus leucas (Müller &amp; Henle, 1839) were caught and photographed by fishermen using trammel net on 29 September and 1 October 2017 in Musi River, South Sumatra province, Indonesia. These photos are considered as second record after 20 years (1997-2017), and first confirm inland record for Sumatra. Photographic records indicate specimens of C. leucas found in Musi River basin recorded about 75 km inland, and apparently very young juveniles. Further study and monitoring is needed to asses the possibility of the importance of Musi River basin as nursery area of C. leucas.