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Abstract Requiem sharks (genus Carcharhinus) have previously been reported to form large aggregations around marine infrastructures in the eastern Mediterranean Sea. While this behaviour may offer fitness advantages at the individual level, the implications of extended residency at human-altered habitats for population persistence have yet to be assessed. In this work, we investigated the phylogeographic and demographic composition of sharks near a coal-fired power and desalination station in Israel. Our aim was to infer habitat use and the mechanisms underlying the aggregation behaviour, and to highlight potential conservation impacts. We sampled, measured, and released 70 individuals between 2016 and 2022 to assess genetic variability within the cytochrome C oxidase I (COI) region and to analyse the aggregation’s structure based on the sharks’ size and sex distribution. In addition, we performed meristic counts on a reference specimen collected dead at another power station in Israel to supplement species identification using the abovementioned techniques. Our findings indicate size-based sex segregation of adult female dusky and male sandbar sharks (Carcharhinus obscurus and Carcharhinus plumbeus, respectively), with each species comprising two COI haplotypes. In the dusky shark, one haplotype corresponded to an Indo-Pacific lineage, and the other matched an Atlantic lineage. In the sandbar shark, we observed a haplotype previously sampled in the Mediterranean Sea, the Red Sea, the Northwest Indian Ocean, and South Africa, and another haplotype that was unique to our study site and genetically closer to the former than to sequences sampled in other ocean basins. This study provides the first indication of sympatric aggregation amongst phylogeographically distinct dusky and sandbar shark lineages, suggesting that human-altered habitats in the eastern Mediterranean Sea may influence the distribution of these species. Based on the observed segregation pattern, we conclude that the site does not function as a nursery, parturition, or mating area, and discuss other plausible explanations that warrant further research. Finally, we highlight important directions for future research and the implications of our findings for management and conservation.

The global decline of shark populations, largely driven by overfishing to supply the shark fin trade, poses a significant threat to marine ecosystems. Southeast Asia, and particularly Singapore, is a key hub for the transit and trade of shark fins that contribute to the exploitation of these apex predators. Through the use of DNA barcoding techniques, this study aimed to determine what species of shark are involved in the Singapore shark fin trade. Fins were collected from markets, dried goods shops and traditional Chinese medicine halls throughout Singapore. In total, DNA was extracted from 684 fins collected in January 2024 and PCR amplification targeted a fragment of the mitochondrial COI gene for species identification. Results revealed fins from 24 species across 16 genera, with 19 species listed on CITES Appendices II, and 16 listed as threatened on the IUCN Red List (critically endangered = 2, endangered = 4, vulnerable = 10). The top five most frequently identified species were Carcharhinus falciformis, Galeorhinus galeus, Rhizoprionodon oligolinx, Sphyrna lewini and Rhizoprionodon acutus. Of these, four are listed on CITES Appendix II and four are listed as threatened on the IUCN Red List.

This study describes a new species belonging to the genus Cathetocephalus from the spinner shark Carcharhinus brevipinna off the coast of Yucatan, Mexico. Cathetocephalus badilloi n. sp. has a soft scolex transversely positioned to the long axis of the strobila. The scolex is composed of an apical pad, papillate band and rugose base. The papillate band has two papillary segments; the upper segment has numerous papillae, positioned one next to the other in an irregular and heterogeneous way with a spongy texture that remains along the band. The lower papillary segment has numerous papillae positioned one next to the other, without space between them. This papillary band presents flattened rectangular papillae with a division located at the top of each the papilla, giving it the appearance of a molar tooth. Using the 28S rDNA gene and the method of Maximum Likelihood (ML) for phylogenetic analysis, we identified the present material as a new species. We did not collect specimens with mature or gravid proglottids, but since the specific identification of the members of this genus is based on the characteristics of the scolex, our proposal of the new species is determined by the morphology of this organ as well as the molecular results obtained.

This study describes a new species belonging to the genus Cathetocephalus from the spinner shark Carcharhinus brevipinna off the coast of Yucatan, Mexico. Cathetocephalus badilloi n. sp. has a soft scolex transversely positioned to the long axis of the strobila. The scolex is composed of an apical pad, papillate band and rugose base. The papillate band has two papillary segments; the upper segment has numerous papillae, positioned one next to the other in an irregular and heterogeneous way with a spongy texture that remains along the band. The lower papillary segment has numerous papillae positioned one next to the other, without space between them. This papillary band presents flattened rectangular papillae with a division located at the top of each the papilla, giving it the appearance of a molar tooth. Using the 28S rDNA gene and the method of Maximum Likelihood (ML) for phylogenetic analysis, we identified the present material as a new species. We did not collect specimens with mature or gravid proglottids, but since the specific identification of the members of this genus is based on the characteristics of the scolex, our proposal of the new species is determined by the morphology of this organ as well as the molecular results obtained. [Display omitted] • Cathetocephalus badilloi infects Carcharhinus brevipinna 's spiral valve at Yucatan. • Cathetocephalus is highly specific to Carcharhinus sharks. • Cathetocephalus badilloi can be identified by the molar tooth-shaped papillae band. • The phylogenetic analysis supported Cathetocephalus badilloi as a new species. [ABSTRACT FROM AUTHOR]

In elasmobranch fishes, variations in gross structural organization of cerebellum has been extensively explored. The basic histological features of cerebellum although conserved in the group but the comparative account on subtle cellular variations is largely underestimated. The present study aims to explore the histological and cellular variations in different layers of cerebellar cortex of the representative elasmobranchs' species belonging to different habitat. Our findings showed that the histological architecture of cerebellar granular layer between the examined species varies noticeably. By and large increase cellular density were observed in all the layers of cerebellum in the representative species of shark compared to ray. The findings were then compared and discussed with reference to their habitat and behavior. [ABSTRACT FROM AUTHOR]

Simple Summary: Coastal sharks are especially susceptible to anthropogenic pressures due to their use of nearshore habitats. It is therefore necessary to distinguish species-specific variation in occurrence among ocean beaches and identify key environmental drivers that may influence shark distribution patterns. For swell-influenced coastal beaches, however, information on shark abundance and occurrence is still limited. The relative abundance and occurrence of sharks off 42 ocean beaches of New South Wales (NSW), Australia, was investigated using a long-term drone-based monitoring program from 2017–2021. Overall, there were 36,384 drone flights conducted, sighting a total of 281 sharks. Shark observations occurred in <1% of drone flights, indicating that potentially dangerous sharks, and sharks in general, are rare off NSW beaches. Key environmental predictors, such as the distance to the nearest estuary, headland, and island, as well as ocean temperature and wave height, were identified for species-specific shark distribution. This study demonstrated that existing drone-based monitoring programs used to reduce shark bite incidents can also provide valuable information about the distribution of potentially dangerous, vulnerable, and endangered coastal sharks. This information will be beneficial for implementing evidence-based conservation strategies and may also assist in minimising negative human-shark interactions. There is still limited information about the diversity, distribution, and abundance of sharks in and around the surf zones of ocean beaches. We used long-term and large-scale drone surveying techniques to test hypotheses about the relative abundance and occurrence of sharks off ocean beaches of New South Wales, Australia. We quantified sharks in 36,384 drone flights across 42 ocean beaches from 2017 to 2021. Overall, there were 347 chondrichthyans recorded, comprising 281 (81.0%) sharks, with observations occurring in <1% of flights. Whaler sharks (Carcharhinus spp.) had the highest number of observations (n = 158) recorded. There were 34 individuals observed for both white sharks (Carcharodon carcharias) and critically endangered greynurse sharks (Carcharias taurus). Bull sharks (Carcharhinus leucas), leopard sharks (Stegostoma tigrinum) and hammerhead species (Sphyrna spp.) recorded 29, eight and three individuals, respectively. Generalised additive models were used to identify environmental drivers for detection probability of white, bull, greynurse, and whaler sharks. Distances to the nearest estuary, headland, and island, as well as water temperature and wave height, were significant predictors of shark occurrence; however, this varied among species. Overall, we provide valuable information for evidence-based species-specific conservation and management strategies for coastal sharks. [ABSTRACT FROM AUTHOR]

The global decline of shark populations, largely driven by overfishing to supply the shark fin trade, poses a significant threat to marine ecosystems. Southeast Asia, and particularly Singapore, is a key hub for the transit and trade of shark fins that contribute to the exploitation of these apex predators. Through the use of DNA barcoding techniques, this study aimed to determine what species of shark are involved in the Singapore shark fin trade. Fins were collected from markets, dried goods shops and traditional Chinese medicine halls throughout Singapore. In total, DNA was extracted from 684 fins collected in January 2024 and PCR amplification targeted a fragment of the mitochondrial COI gene for species identification. Results revealed fins from 24 species across 16 genera, with 19 species listed on CITES Appendices II, and 16 listed as threatened on the IUCN Red List (critically endangered = 2, endangered = 4, vulnerable = 10). The top five most frequently identified species were Carcharhinus falciformis , Galeorhinus galeus , Rhizoprionodon oligolinx, Sphyrna lewini and Rhizoprionodon acutus . Of these, four are listed on CITES Appendix II and four are listed as threatened on the IUCN Red List., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

In recent decades, a combination of increasing demand and economic globalisation has created a global market for elasmobranch products, especially the highly prized shark fins for Asian markets. Morphological species identification, as well as traditional cytochrome c oxidase subunit I (COI) barcoding of shark fins and other products, become challenging when in a processed state (such as dried or bleached shark fins). Here a mini-barcoding multiplex assay was applied to determine the species of origin in case studies from southern Africa involving confiscated shark fins in different states of processing. This highlights that the illegal shark fin trade in southern Africa to a large extent comprises threatened species. Matching of sequences of the confiscated fins against public databases revealed several threatened species, including the CITES-listed species Carcharodon carcharias, Carcharhinus longimanus, Isurus oxyrinchus, Rhynchobatus djiddensis and Sphyrna lewini. The findings highlight the need for improved trade monitoring, such as to eliminate illegal trade in shark fins, which can in part be achieved through more widespread genetic sampling of internationally traded products. However, a major limitation to DNA barcoding in general lies in the lack of curated voucher specimens available on public databases. To facilitate the application of molecular methods in a more comprehensive evaluation of elasmobranch trade regionally, a concerted effort to create reliable curated sequence data is recommended. [ABSTRACT FROM AUTHOR]

Food and feeding habits of eight species of female elasmobranchs in gestation stages were studied. The low feeding intensity and smaller mean volume of food per fish (in ml) attributed with their gestating activities and cease feeding in the nursery region as protecting measures for young ones. The prey items occurred in guts content of these species were analyzed by index of relative importance (IRI). Carcharhinus macloti and Rhizoprionodon acutus (100 %) were piscivorous which feed exclusively on teleosts found above the bottom. Rhizoprionodon oligolinx (96.5 %) and Scoliodon laticaudus (50.3 %), were generalized predators, feeding throughout the water column and occasionally at bottom chiefly on teleost and small quantities of crustaceans and molluscs. Amphotistius imbricate (86.06 %), Rhinobatos annandalei (68.9 %) and Rhynchobatus djiddensis (61.58 %) were carnivores, feeding mainly on free-living crustaceans and supplemented by teleost at the sea bottom. Pastinachus sephen (76.59 %) showed a predacious carnivorous character exhibiting a tendency to feed mainly on bivalves along with small portion of crustaceans, teleost and mud by browsing at bottom. The prey organisms observed in stomach content of these species conferred with environment biota harvested by single and multi-days trawlers operating off Mumbai waters. [ABSTRACT FROM AUTHOR]

There is still limited information about the diversity, distribution, and abundance of sharks in and around the surf zones of ocean beaches. We used long-term and large-scale drone surveying techniques to test hypotheses about the relative abundance and occurrence of sharks off ocean beaches of New South Wales, Australia. We quantified sharks in 36,384 drone flights across 42 ocean beaches from 2017 to 2021. Overall, there were 347 chondrichthyans recorded, comprising 281 (81.0%) sharks, with observations occurring in Carcharhinus spp.) had the highest number of observations (n = 158) recorded. There were 34 individuals observed for both white sharks (Carcharodon carcharias) and critically endangered greynurse sharks (Carcharias taurus). Bull sharks (Carcharhinus leucas), leopard sharks (Stegostoma tigrinum) and hammerhead species (Sphyrna spp.) recorded 29, eight and three individuals, respectively. Generalised additive models were used to identify environmental drivers for detection probability of white, bull, greynurse, and whaler sharks. Distances to the nearest estuary, headland, and island, as well as water temperature and wave height, were significant predictors of shark occurrence; however, this varied among species. Overall, we provide valuable information for evidence-based species-specific conservation and management strategies for coastal sharks.

Dramatic declines in reef shark populations have been documented worldwide in response to human activities. Marine Protected Areas (MPAs) offer a useful mechanism to protect these species and their roles in coral reef ecosystems. The effectiveness of MPAs notably relies on compliance together with sufficient size to encompass animal home range. Here, we measured home range of 147 grey reef sharks, Carcharhinus amblyrhynchos, using acoustic telemetry in New Caledonia. The distribution of home range was then compared to local MPA sizes. We report a home range of 12 km2 of reef for the species with strong differences between adult males (21 km2), adult females (4.4 km2) and juveniles (6.2 km2 for males, 2.7 km2 for females). Whereas local historic MPA size seemed adequate to protect reef shark home range in general, these were clearly too small when considering adult males only, which is consistent with the reported failure of MPAs to protect sharks in New Caledonia. Fortunately, the recent implementation of several orders of magnitude larger MPAs in New Caledonia and abroad show that recent Indo-Pacific MPAs are now sufficiently large to protect the home ranges of this species, including males, across its geographical range. However, protection efforts are concentrated in a few regions and cannot provide adequate protection at a global scale. [ABSTRACT FROM AUTHOR]

Anecdotal reports from fishers in Southeast Queensland, Australia suggest that shark depredation is a significant issue, however little is known about which species are responsible for depredating catches. This research aimed to identify depredating species in Southeast Queensland line based fisheries, by undertaking a genetic analysis of depredated samples collected by commercial, charter and recreational fishers. The genetic analysis successfully identified ten depredating sharks, all from the genus Carcharhinus (19.2% success). The species identified using mitochondrial DNA included five C. leucas (bull sharks), two C. plumbeus (sandbar sharks), one C. amboinensis (pigeye shark), one C. brevipinna (spinner shark) and one unconfirmed C. plumbeus/C. altimus (bignose shark). While many species of Carcharhinus have been found to depredate catches in Australia, C. leucas has not been highlighted until this research as a potential problematic species. The optimised protocol allowed for the confident identification of shark species responsible for depredation in fisheries using frozen fish samples donated by fishers. [ABSTRACT FROM AUTHOR]

This paper describes the fossil sharks associated with the skeleton of Eschrichtius akishimaensis （GMNH-PV 3210, so called" Akishima-Kujira"）. The fossils consist of twelve isolated teeth（ GMNH-PV 3601 - PV 3607, PV 3609 - PV 3613） and one tooth tip（ GMNH-PV 3608） within an anterior rib fragment of" Akishima-Kujira". Eight fossil teeth（ GMNH-PV 3601-3608） are identified as great white shark, Carcharodon carcharias, based on their morphological characteristics. One fossil tooth （GMNH-PV-3609） is similarly identified as oceanic whitetip shark, Carcharhinus longimanus. And the remaining four teeth are identified as requiem sharks, Carcharhinus spp. These fossils mark the first record of shark fossils from the Komiya Formation and Akikawa-Tamagawa area of the Kazusa Group. Also these records are important as a clue to know the sedimentary environment and oceanographic condition of the paleo bay（ now called the Kanto Plain） in the late Pliocene to early Pleistocene. And GMNH-PV 3608 is recognized as direct evidence of shark-whale interaction and the marine food chain in the early Pleistocene of Japan. [ABSTRACT FROM AUTHOR]

The requiem sharks of the genus Carcharhinus are captured as bycatch in the Indo-Pacific region. The lack of morphometric data due to the common practice of head and fin removal of sharks, hinders the implementation of shark management measures. Carcharhinus specimens found in the waters of Brunei Darussalam were identified using morphological analysis, and their identification was further validated by mitochondrial cytochrome c oxidase subunit I (COI) gene sequence analysis. This study successfully identified twenty-seven specimens as either the blackspot shark, Carcharhinus sealei, or the Indonesian whaler shark, Carcharhinus tjutjot, by molecular genetic analysis, although the difficulty of accurately identifying these sharks solely on morphology was encountered. Mitochondrial COI gene sequence analysis also suggested that C. tjutjot has two genetically distinct populations/groups, while C. sealei had a single panmictic population in the Indio-Pacific region. The findings suggest that C. sealei could be a more highly migratory species than C. tjutjot in the region. [ABSTRACT FROM AUTHOR]

Male mate choice has been documented in different taxa including insects, lizards, fish, birds and mammals. However, in sharks, male mate choice is not clearly reported but field observations suggest that it is probable. In this study, I tested for evidence of male mating preference of the spot-tail shark Carcharhinus sorrah towards three female traits that are typically associated with female fecundity, these are: (1) body size, (2) parasite burden, and (3) mean heterozygosity. I collected data on heterozygosity, age, length and parasite burden of 73 litters of C. sorrah females. I found no association between male mating preference and any of the selected female traits. A possible interpretation is that, given the polygamous mating system of sharks and consequent likelihood of sperm competition, C. sorrah males focus primarily on obtaining fertilization, rather than adjusting their behavior according to potential fitness differences between females. Future research is needed to gain better understanding on the reproductive behavior and social dynamics of C. sorrah to benefit conservation efforts that are needed to effectively manage C. sorrah. [ABSTRACT FROM AUTHOR]

Shark incidents in Recife, Pernambuco state (Brazil), are registered since 1992. The occurrence of those events is in a relatively small area of urban beaches of about 30 km long, making up one of the world's highest indices of shark incidents per unit of area, totaling 64 casualties, of these 24 were fatal. To mitigate shark incidents, the knowledge on shark species involved is crucial given that each species has specific usage of the habitat and dissimilar feeding strategy. Jaws of five species caught along the Pernambuco coast (Brazil), corresponded to 2 specimens of Carcharhinus acronotus, 4 specimens of C. leucas, 1 of C. limbatus, 4 of Galeocerdo curvier and 3 of Sphyrna lewini. Relative Warps Analysis was applied to enhance possible differences among jaw shapes of the studied species. The consensus configuration from the 14 images was obtained. The first two relative warps components explained 70.17% of the total observed variation. Four distinct groups were clearly observed. Three groups were formed by single species, corresponding to G. curvier, C. leucas and S. lewini, respectively, and one group formed by the combination of C. acronotus and C. limbatus. As expected, due to its peculiar skull shape, S. lewini jaws are very different from other analyzed species, thus all observed individuals of this group were found isolated from the others, considering the horizontal axis. Relative warps and curvature analyses show to be useful tools in the forensic study of shark incidents. In general, jaws shape significantly differed among species. [ABSTRACT FROM AUTHOR]

Highlights • Internal lee waves are formed around the summit of a tropical seamount. • The waves are forced predominantly by tides but also surface storms. • The waves are generated at the summit edge where high shark densities occur. • The lee waves transform into hydraulic jumps that flush the summit with cold water. • The waves and hydraulic jumps are likely to be ubiquitous throughout the region. Abstract Oceanographic observations were made with a subsurface oceanographic mooring over the summit and flanks of two neighbouring seamounts in the tropical Indian Ocean to identify processes that may be responsible for the aggregation of silvertip sharks (Carcharhinus albimarginatus) in the deep water drop-off surrounding the summits. The seamounts, which are in the Chagos Archipelago in the British Indian Ocean Territories, are narrow in horizontal extent (<10 km), have steeply sloping (>15°) sides that rise from depths of > 600 m, and flat summits at a depth of 70 m. They are subjected to forcing at subinertial, basin-scales and local scales that include a mixed tidal regime and storm-generated near inertial waves. At the drop-off, at a depth of between 70 and 100 m, isotherms oscillate at both diurnal and semidiurnal frequencies with amplitudes of ∼ 20–30 m. The waves of tidal origin are accompanied by short period (∼5 min) internal waves with amplitudes O (10 m) and frequencies close to the local buoyancy frequency, N , within the thermocline which is the maximum frequency possible for freely propagating internal waves. The tidal oscillations result from internal lee waves with 30 m vertical wavelength generated by the prevailing currents over the supercritical seamount flanks, whereby the bottom slope is greater than the internal tide wave slope. The 'near- N ' waves are due to enhanced shear associated with the hydraulic jumps that form from the lee waves due to the abrupt transition from steeply sloping sides to a relatively flat summit. The jumps manifest themselves as bottom-trapped bores that propagate up the slope towards the summit. Further observations over the summit reveal that the bores subsequently flush the summits with cold water with tidal periodicity. The bores, which have long wave phase speeds more than double that of the bore particle velocities, are characterised by intense vertical velocities (>0.1 m s−1) and inferred local resuspension but relatively little turbulence based on temperature overturns. Our results strongly implicate lee waves as the dynamic mechanism of leading order importance to the previously observed accumulation of biomass adjacent to the supercritical slopes that are commonplace throughout the archipelago. We propose that further investigation should identify the spatiotemporal correlation between internal wave activity and fish schooling around the summit, and whether such schooling attracts predators. [ABSTRACT FROM AUTHOR]

This report describes the first record of the piscicolid leech Pontobdella macrothela from Mozambique waters and the first record of P. macrothela parasitizing a Grey Reef Shark (Carcharhinus amblyrhynchos). The leech, P. macrothela, was found attached externally between the third and fourth gill slits of a shark captured off Vamizi Island, Quirimbas Archipelago, northern Mozambique. [ABSTRACT FROM AUTHOR]

Carcharhinus obsolerus is described based on three specimens from Borneo, Thailand and Vietnam in the Western Central Pacific. It belongs to the porosus subgroup which is characterised by having the second dorsal-fin insertion opposite the anal-fin midbase. It most closely resembles C. borneensis but differs in tooth morphology and counts and a number of morphological characters, including lack of enlarged hyomandibular pores which are diagnostic of C. borneensis. The historic range of C. obsolerus sp. nov. is under intense fishing pressure and this species has not been recorded anywhere in over 80 years. There is an urgent need to assess its extinction risk status for the IUCN Red List of Threatened Species. With so few known records, there is a possibility that Carcharhinus obsolerus sp. nov. has been lost from the marine environment before any understanding could be gained of its full historic distribution, biology, ecosystem role, and importance in local fisheries. [ABSTRACT FROM AUTHOR]

Numerous shark teeth were collected during the recent geological field work (2017-2018) conducted at the well known shark bearing deposits of Makurmatia section of Late Miocene Baripada Beds, Orissa. Scanning Electron Microscope (SEM) analysis of some of the selected shark teeth (Galeorhinus sp., Carcharhinus sp., Carcharodon sp.) were carried out to study the microcrostructural arrangement of the teeth enamel. The scanning electron micrographs of the shark teeth enamel crystals are highly ordered and arranged in different fashions as single crystallite enameloid (SCE), bundle crystallite enameloid (BCE) which can be subdivided into parallel bundle enameloid (PBE) and tangled bundle enameloid (TBE) as compared to the basal neoselachian which present only the single crystallite enameloid (SCE). The TBE of the Carcharodon sp. is more matured and more compacted than the other two Carcharhinus sp. and Galeorhinus sp. The microstructural arrangement of Galeorhinus sp, Carcharhinus sp. and Carcharodon sp. suggest that these sharks belong to the modern Neoselachian group of sharks. [ABSTRACT FROM AUTHOR]

The increase in demand for shark meat and fins has placed shark populations worldwide under high fishing pressure. In the Arabian region, the spot‐tail shark Carcharhinus sorrah and the Blacktip shark Carcharhinus limbatus are among the most exploited species. In this study, we investigated the population genetic structure of C. sorrah (n = 327) along the coasts of the Arabian Peninsula and of C. limbatus (n = 525) along the Arabian coasts, Pakistan, and KwaZulu‐Natal, South Africa, using microsatellite markers (15 and 11 loci, respectively). Our findings support weak population structure in both species. Carcharhinus sorrah exhibited a fine structure, subdividing the area into three groups. The first group comprises all samples from Bahrain, the second from the UAE and Yemen, and the third from Oman. Similarly, C. limbatus exhibited population subdivision into three groups. The first group, comprising samples from Bahrain and Kuwait, was highly differentiated from the second and third groups, comprising samples from Oman, Pakistan, the UAE, and Yemen; and South Africa and the Saudi Arabian Red Sea, respectively. Population divisions were supported by pairwise FST values and discriminant analysis of principal components (DAPC), but not by STRUCTURE. We suggest that the mostly low but significant pairwise FST values in our study are suggestive of fine population structure, which is possibly attributable to behavioral traits such as residency in C. sorrah and site fidelity and philopatry in C. limbatus. However, for all samples obtained from the northern parts of the Gulf (Bahrain and/or Kuwait) in both species, the higher but significant pairwise FST values could possibly be a result of founder effects during the Tethys Sea closure. Based on DAPC and FST results, we suggest each population to be treated as independent management unit, as conservation concerns emerge. Our work showed that two of the overexploited shark species, the spot‐tail shark Carcharhinus sorrah and the blacktip shark C. limbatus, display weak population structure along the coasts of the Arabian Peninsula. We discussed that populations that are weakly differentiated at neutral markers, represented by low but significant Fst values, might have an underlying biological importance that should not be ignored when designing conservation plans. We propose that this could be possible in sharks due to their philopatric behavior. [ABSTRACT FROM AUTHOR]

Abstract: An accurate assessment of the biting shark size is paramount for better understanding the agonistic behavior of a species toward humans. The gray reef shark is involved in many accidental bites. Based on the capture of 35 gray sharks, we calculated the algorithm that allows the assessment of the shark size, through the interdental distance (IDD) inferred from teeth marks on human wounds. Our results show a negative allometric relationship and that IDD calculated from imprints perpetrated by the upper jaw are globally similar with those from the lower jaw, in spite of heterodonty. We applied our findings to two cases of accidental bites by this species. Both of the victims had declared that the shark length was “at least 2 m”. Based on our algorithm, the assessment of the shark TL was approx. 180 and 160 cm, respectively, which correspond to an overestimation of ≥20% by the victims. [ABSTRACT FROM AUTHOR]

In order to assess the performance of major commercial fleets, key factors affecting fishing costs and revenues are provided along with a framework to standardize economic knowledge construction in data-poor fisheries, such as South Brazil's. Additionally, the effects of fuel subsidy policies on profitability were further evaluated among fleets. The unprecedented set of field survey data generated by this study revealed that fuel consumption, fish price, and catch volume were the main factors affecting profitability. Annual gross profit was positive for all fleets. Longliners showed the highest gross profit margin (29%), while single-bottom-trawlers, close to unviability, showed the lowest (0.9%). Overall, subsidies were ineffective in increasing Rio Grande fleet gross profits and may be masking poor economic performance, primarily for single-bottom-trawlers. Specific policy advice aiming to protect both economic performance and natural resources are discussed, including the importance of economic data collection and cost-benefit analysis. [ABSTRACT FROM AUTHOR]

Spatial separation within predator communities can arise via territoriality but also from competitive interactions among and within species. However, linking competitive interactions to predator distribution patterns is difficult and theoretical models predict different habitat selection patterns dependent on habitat quality and how competition manifests itself. While models generally consider competitors to be either equal in ability, or for one phenotype to have a fixed advantage over the other, few studies consider that an animal may only have a competitive advantage in specific habitats. We used  10 years of telemetry data, habitat surveys and behavioral experiments, to show spatial partitioning between and within two species of reef shark (grey reef Carcharhinus amblyrhinchos and blacktip reef sharks C. melanopterus) at an unfished Pacific atoll. Within a species, sharks remained within small ‘sub‐habitats’ with very few movements of individuals between sub‐habitats, which previous models have suggested could be caused by intra‐specific competition. Blacktip reef sharks were more broadly distributed across habitat types but a greater proportion used lagoon and backreef habitats, while grey reef sharks preferred forereef habitats. Grey reef sharks at a nearby atoll where blacktip reef sharks are absent, were distributed more broadly between habitat types than when both species were present. A series of individual‐based models predict that habitat separation would only arise if there are competitive interactions between species that are habitat‐specific, with grey reefs having a competitive advantage on the forereefs and blacktips in the lagoons and backreef. We provide compelling evidence that competition helps drive distribution patterns and spatial separation of a marine predator community, and highlight that competitive advantages may not be constant but rather dependent on habitats. [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]

Sensitivity to overfishing is often estimated using simple models that depend upon life history parameters, especially for species lacking detailed biological information. Yet, there has been little exploration of how uncertainty in life history parameters can influence demographic parameter estimates and therefore fisheries management options. We estimate the maximum intrinsic rate of population increase (rmax) for ten coastal carcharhiniform shark populations using an unstructured life history model that explicitly accounts for uncertainty in life history parameters. We evaluate how the two directly estimated parameters, age at maturity αmat and annual reproductive output b, most influenced rmax estimates. Uncertainty in age at maturity values was low, but resulted in moderate uncertainty in rmax estimates. The model was sensitive to uncertainty in annual reproductive output for the least fecund species with fewer than 5 female offspring per year, which is not unusual for large elasmobranchs, marine mammals, and seabirds. Managers and policy makers should be careful to restrict mortality on species with very low annual reproductive output<2 females per year. We recommend elasmobranch biologists to measure frequency distributions of litter sizes (rather than just a range) as well as improving estimates of natural mortality of data-poor elasmobranchs. [ABSTRACT FROM AUTHOR]

Understanding shark habitat use is vital for informing better ecological management of coastal areas and shark populations. The Queensland Shark Control Program (QSCP) operates over ∼1800 km of Queensland coastline. Between 1996 and 2012, catch, total length and sex were recorded from most of the 1992 bull shark ( Carcharhinus leucas ) caught on drum lines and gill-nets as part of the QSCP (sex and length was not successfully recorded for all individuals). Gear was set at multiple sites within ten locations. Analysis of monthly catch data resulted in a zero-inflated dataset for the 17 years of records. Five models were trialled for suitability of standardising the bull shark catch per unit effort (CPUE) using available habitat and environmental data. Three separate models for presence-absence and presence-only were run and outputs combined using a delta-lognormal framework for generalized linear and generalized additive models. The delta-lognormal generalized linear model approach resulted in best fit to explain patterns in CPUE. Greater CPUE occurred on drum lines, and greater numbers of bull sharks were caught on both gear types in summer months, with tropical sites, and sites with greater adjacent wetland habitats catching consistently more bull sharks compared to sub-tropical sites. The CPUE data did not support a hypothesis of population decline indicative of coastal overfishing. However, the total length of sharks declined slightly through time for those caught in the tropics; subtropical catches were dominated by females and a large proportion of all bull sharks caught were smaller than the size-at-maturity reported for this species. These factors suggest that growth and sex overfishing of Queensland bull shark populations may be occurring but are not yet detectable in the available data. The data highlight available coastal wetlands, river size, length of coastline and distance to the 50 m depth contour are important for consideration in future whole of lifecycle bull shark management. As concerns for shark populations grow, there is an increasing requirement to collate available data from control programs, fisheries, ecological and research datasets to identify sustainable management options and enable informed stock assessments of bull shark and other threatened shark species. [ABSTRACT FROM AUTHOR]