Search Results (38)

Galapagos sharks (Carcharhinus galapagensis) are a large species belonging to the family Carcharhinidae, with poorly understood biology, especially along continental coastlines, which limits effective management of their populations. Here, we report preliminary findings of their movements along the Pacific Coast of Panama and Colombia, derived from satellite telemetry. Sharks were tracked for as long as 1.5 years, during which they moved extensively (~400 km along the Panama/Colombia coastline), with areas with high concentrations of detections that spanned the Panama/Colombia border. Sharks appeared to alter their movements during the diel cycle (more detections at night) and in relation to the wet/dry seasons (more detections during the dry season). Locations of shark detections were most commonly within 20 km of shore and in water less than 100 m deep, although detections were recorded hundreds of kilometers from shore in water thousands of meters deep. Galapagos sharks appear to move more extensively along continental coastlines compared to island locations, where most previous information about their movements and biology has been obtained. Full article

The reef fish communities of the Guanahacabibes National Park have been studied for 20 years using various methodologies that have allowed us to understand aspects of their diversity and structure. However, due to gaps in information about the abundance and distribution of mesopredators (big fish and sharks), a new study was conducted in 2017 to determine their structure, explore the influence of different factors on their spatial variability, and evaluate their behavior. To achieve this, the Baited Remote Underwater Video Surveys (BRUVs) methodology was successfully applied, locating a single set of BRUVs at 90 sites distributed across 9 sectors of the park’s functional zoning. Variability in mesopredator metrics and their potential prey was assessed through a PERMANOVA analysis; a distance-based linear model (DISTLM) was used to explore the relationship between mesopredator abundance and biological, abiotic, and condition variables; and animal behavior was classified as incidental, cautious, or aggressive. A total of 64 fish species were identified, 7 of which were mesopredators, and 3 were sharks. An uneven distribution and abundance were observed among sectors, with the most abundant mesopredators being Carcharhinus perezi, Sphyraena barracuda, and Mycteroperca bonaci. Mesopredator abundance was more closely related to the condition of zone use and its regulations than to biological and abiotic variables. Sharks were more abundant in strictly protected areas, which coincided with relatively murky waters and stronger currents. More than 50% of the observed sharks displayed exploratory and aggressive behavior towards the bait basket. The analyzed metrics validate the effectiveness of the management of the protected area and suggest the presence of healthy and resilient mesopredator fish communities. Full article

Evidence of trophic interactions between sharks and cetaceans is rather widespread in the fossil record, consisting as it does of tooth marks on bones and rarer teeth or tooth fragments embedded in (or associated with) skeletal remains. Here, we reappraise a partial mysticete (baleen whale) forelimb that was collected more than a century ago from Pliocene deposits exposed at the celebrated fossil locality of Orciano Pisano (Tuscany, central Italy). This specimen, which is revealed to originate from an early juvenile individual, features shark tooth marks on both the humerus and radius. Whether these traces are due to active predation or to scavenging cannot be ascertained. During the Pliocene, the Mediterranean Basin was inhabited by a diverse elasmobranch fauna, including a number of mammal-eating forms that no longer inhabit the Mediterranean Sea (e.g., Galeocerdo and some Carcharhinus spp. as well as the extinct Parotodus). Early juvenile mysticetes were also likely more common than today in the Pliocene Mediterranean Sea, which may have contained balaenid and balaenopterid calving grounds, thus providing the Mediterranean mammal-eating sharks with vulnerable, energetically valuable potential prey items. Thus, our results evoke a kind of trophic interaction that was likely common and ecologically relevant in the Pliocene Mediterranean Sea. Full article

Shark bycatch represents a substantial issue in the management of oceanic fisheries. Utilizing data on shark bycatch from the longline fishery, as released by the Western and Central Pacific Fisheries Commission, this study applied the boosted regression tree model to examine the impact of environmental factors on the bycatch per unit effort (BPUE) of key bycatch species, as well as to predict the spatial distribution dynamics of both BPUE and bycatch risk (BR). The findings emphasize that the oxygen concentration, sea surface temperature, and chlorophyll-a concentration are paramount to sharks’ BPUE. Furthermore, the study compared the variations in environmental preferences across diverse shark species, pinpointing key environmental attributes defining the ecological niches of distinct shark populations. The spatial predictions identified the hotspots of BPUE and BR for the bigeye thresher shark (Alopias superciliosus), longfin mako (Isurus paucus), silky shark (Carcharhinus falciformis), and oceanic whitetip shark (Carcharhinus longimanus) in tropical latitudes (10° S to 15° N), and for the blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) in temperate zones (south of 30° S or north of 30° N). The geometric center analysis indicated that all shark species exhibited large annual fluctuations in BPUE and BR, and most populations displayed significant shifting trends. Several grids (5° × 5°) were identified as high-risk areas due to their considerable contribution to bycatch. Furthermore, the geometric centers of BR were observed to shift eastward towards equatorial waters, compared to the geometric centers of BPUE. This underscores the necessity of considering factors beyond BPUE when identifying critical areas for the implementation of area-specific bycatch mitigation measures. The insights derived from this study can enhance and support the development and enforcement of targeted area-based fishery management initiatives. Full article

Unlike other microbothriid monogenean infections in elasmobranchs, limited information is available on the biology and treatment of Dermophthirius melanopteri. As parasitic infection with D. melanopteri was found in 21 juvenile blacktip reef sharks (Carcharhinus melanopterus) at the Lotteworld aquarium in Seoul, South Korea, we aimed to investigate the anatomical features and treatment protocols for D. melanopteri in this study. The parasites were sampled and fixed in 10% neutral-buffered formalin, and examined using light and scanning electron microscopy. The treatments included short-term praziquantel baths, freshwater immersion, and long-term trichlorfon baths. Manual removal of parasites was also attempted. Examination and manual removal revealed that, similar to other microbothriids, D. melanopteri attaches to the placoid scale using opisthaptoral secretion in the posterior region. The effectiveness of the treatments varied, with trichlorfon proving the most effective and safe option for complete parasite eradication. Praziquantel facilitated parasite removal by weakening their attachment, suggesting the potential for higher doses and prolonged exposure times for enhanced antiparasitic effects. To our knowledge, this is the first study providing the microscopic details of D. melanopteri infection and its treatment outcomes in captive blacktip reef sharks, thereby providing valuable insights for future research and management. Full article

In this study, we propose a method for assessing the temporal and spatial distribution of Carcharhinus melanopterus in shallow waters using unmanned aerial vehicles (UAVs). Aerial surveys were conducted in Tien Og Bay (Koh Tao, Thailand) thrice daily (morning, afternoon, evening) along a 360 m transect at a 30 m altitude. Environmental factors, including cloudiness, sea conditions, wind, tide, and anthropogenic disturbance, were recorded for each time slot. We developed a Python/AppleScript application to facilitate individual counting, correlating sightings with GPS data and measuring pixel-based length. Abundance varied significantly across time slots (p < 0.001), with a strong morning preference, and was influenced by tide (p = 0.040), favoring low tide. Additionally, abundance related to anthropogenic disturbance (p = 0.048), being higher when anthropogenic activity was absent. Spatial distribution analysis indicated time-related, sector-based abundance differences (p < 0.001). Pixel-based length was converted to Total Length, identifying juveniles. They exhibited a strong sector preference (p < 0.001) irrespective of the time of day. Juvenile abundance remained relatively stable throughout the day, constituting 94.1% of afternoon observations. Between 2020 and 2022, an underwater video survey was conducted to determine the sex ratio of the individuals. Only females and juveniles were sighted in the bay. Full article

Following preliminary underwater observations of about 1000 h carried out monthly between 2012 and 2023 (except the years 2021 and 2022), 23 specimens of grey reef sharks were spotted and photo-identified off the coast of Nosy Be in Madagascar, on an emerging reef called “Mokarran” at a depth between 15 and 30 m. Over 10 years of observations, eight specimens were re-sighted, identified with a non-invasive photo-identification technique of part of the first dorsal and the caudal fin, and one specimen was re-identified after 1982 days from the first sighting, i.e., after more than 5 years. In addition, six specimens of probably pregnant females were also identified in the same area. The population was entirely made up of females. The aggregation area could represent a new nursery site which, if confirmed after further investigations, will require greater protection. Full article

The Indo-Australian Archipelago (IAA) today exhibits the highest marine biodiversity, which has been evolving since the early Miocene. The existence of this high palaeobiodiversity is attested to by the presence of many fossil invertebrates; however, the region’s fossil fish record is sparse and understudied, which is also the case for cartilaginous fishes. Elasmobranch fossils are dominantly represented by shark and ray teeth in the geological record and can give a quick overview of the composition of the fauna. The first IAA elasmo fossils, shark teeth were described from Java (Indonesia) at the end of the 19th century, and until today, most of the publications are known from this island. In the early and middle of the 20th century, remarkable fossils were also reported from the islands of Madura (NE Java) and Sulawesi, some with detailed taxonomical descriptions. In addition, only sporadic reports on fossil occurrences exist elsewhere from the IAA, but these lack any detailed taxonomic accounts. In 2019 our research group reported a late Miocene elasmobranch fauna from Brunei (Borneo), which is now the most diverse known shallow water fossil assemblage from the entire IAA. This fauna was described from a single fossiliferous outcrop, called Ambug Hill. However, several new localities have been discovered and studied over the years, as a result the number of fossils increased, and their age range extended. Here we provide an overview of these new sites and their elasmobranch fossils, and describe remains from ten taxa among, of which eight are new to the IAA fossil record (Chiloscyllium sp., cf. Hemitriakis sp., Paragaleus sp., Carcharhinus borneensis, C. limbatus, Lamiopsis sp., Scoliodon sp., Rhinobatos sp.). The overall north Bornean elasmo assemblage is then compared with other IAA occurrences. An extended fauna list is given based on literature review and preliminary investigation of the Naturalis Biodiversity Centre collection in Leiden (The Netherlands) where most of the fossil fishes of the early explorations are stored. These assemblages are also briefly summarized, and attention is drawn to some of the unique and thus far unreported taxa (e.g., Dalatias licha). Full article

In recent years, new findings and new methods (stable isotopes of oxygen, zinc, and nitrogen; 2D and 3D modeling; and geometric morphometric analyses of the teeth) have enhanced our knowledge of the Neogene shark fauna and its paleobiology. Several papers deal with the large Otodus (Megaselachus) species, including the construction of a 3D model, as well as insights into its lifestyle and diet. In addition, the skeletal remains of Carcharias gustrowensis, Carcharodon hastalis, and Keasius parvus and a natural tooth set of Carcharodon hubbelli have been described in the last 13 years, and the dentition of the Neogene species Carcharoides catticus, Megachasma applegatei, and Parotodus benedenii has been reconstructed. Stable isotope analyses of the teeth from the Neogene species of Araloselachus, Carcharias, Carcharodon, Galeocerdo, Hemipristris, and Mitsukurina have given insights into the trophic positions of these genera during the Neogene, and shark teeth preserved near the skeletal remains of prey animals (mammals) and shark bite traces on these remains provide direct evidence of trophic interactions. The tooth shape, fossil locality, and paleoenvironment have been used to better understand the taxa Carcharhinus dicelmai, Megalolamna paradoxodon, Pachyscyllium dachiardii, and P. distans. Among extant species, Galeorhinus galeus can be traced back to the Eocene. Alopias superciliosus, Rhincodon typus, and possibly A. vulpinus can be traced back to the Oligocene. Species present by the Miocene include Alopias vulpinus, Carcharhinus amblyrhynchoides, C. amblyrhynchos, C. albimarginatus, C. amboinensis, C. brachyurus, C. brevipinna, C. falciformis, C. glaucus, C. leucas, C. limbatus, C. longimanus, C. macloti, C. obscurus, C. perezi, C. sealei, Centrophorus granulosus, Cetorhinus maximus, Dalatias licha, Deania calcea, Galeocerdo cuvier, Glyphis glyphis, Heptranchias perlo, Isurus paucus, Lamna nasus, Negaprion brevirostris, Odontaspis ferox, Pseudocarcharias kamoharai, Sphyrna media, S. mokarran, and possibly Carcharodon carcharias. First appearing in the Pliocene are Scymnodon ringens, Somniosus rostratus, and Zameus squamulosus. For some extant species (Carcharias taurus, Hexanchus griseus, Isurus oxyrinchus, Notorynchus cepedianus, and Sphyrna zygaena), it is not clear whether the assigned Neogene teeth represent the same species. The application of new methods to more fossil shark taxa, a detailed search for shark fossils, and better knowledge of the dentition of extant species (especially those with minute-sized teeth) will further enhance our knowledge of the evolution and paleobiology of sharks. Full article

Fisheries-independent data on the diversity, relative abundance, and demographic structure of poorly studied, threatened oceanic sharks are absent from much of the western North Atlantic Ocean, where multiple oceanic shark species have experienced significant population declines. Resource-limited management approaches require the identification of critical habitats or aggregation sites worthy of protection and enforcement. Data were collected on oceanic sharks using pelagic longline surveys, targeted baiting, and opportunistic encounters in oligotrophic open-ocean habitats of north-eastern Exuma Sound (NES), The Bahamas. The oceanic epipelagic shark community was also characterized using targeted baiting off Columbus Point, Cat Island (CI), a seamount north of San Salvador (SSSM), and the northwestern tip of Mayaguana. Pelagic longline surveys suggested that the relative abundance of sharks at NES was low (shark catch-per-unit-effort: 0.0007 sharks hook⁻¹ h⁻¹; 2.3 sharks per 1000 hooks). Silky sharks Carcharhinus falciformis, particularly juveniles (134 ± 39 cm stretched total length; mean ± SD STL), were the most common. Targeted baiting suggested oceanic whitetip sharks C. longimanus were abundant at CI, where large adults (245 ± 23 cm STL), most of which were females (83.8%, n = 98 of 117) that were gravid (65.7%; n = 46 of 70 assessed for pregnancy), dominated the aggregation. Many (20.5–26.5%, n = 24–31 of 117 depending on assumptions regarding tag loss) were recaptured or resighted at CI for up to five years. Silky sharks dominated catches at SSSM. Oceanic sharks, particularly adults, were sometimes caught or observed alongside short-finned pilot whales Globicephala macrorhynchus or tunas. Although The Bahamas offers threatened oceanic sharks refuge from fishing across its entire jurisdiction, these data suggest that some fixed features, including sites such as CI and potentially SSSM, are important aggregation sites with high regional conservation value and should be prioritized by fisheries managers and enforcement officials. Full article

Many progressive aquariums worldwide house various elasmobranch species as part of their commitment to conservation awareness and the long-term well-being of these creatures. These aquariums face the challenge of enabling these natural predators to live harmoniously with other fish without triggering natural predation. This research, conducted at Zoomarine Algarve in Southern Portugal, aimed to investigate the behaviour of three elasmobranch species (Carcharhinus melanopterus (1:1:0), Triaenodon obesus (1:0:0), and Pteroplatytrygon violacea (0:3:0)) when exposed to different feeding mechanisms. The goal was to provide them with opportunities for alternative predatory behaviours beyond their typical feeding techniques and to reduce the likelihood of natural predation. The study took place under controlled conditions within a community habitat. Four feeding methods (pole, short buoy, long buoy, and PVC) were tested during morning, afternoon, and evening periods, using five different prey species. The results shed light on which feeding method aligns best with each species’ distinct physiological standards and predatory tendencies and revealed their prey preferences. All three species interacted with all feeding methods, with P. violacea showing a strong preference for the pole method. T. obesus favoured bony fish, while C. melanopterus showed a preference for cephalopods. P. violacea interacted with all prey types but displayed no marked preference. These various feeding methods and prey options also function as environmental enrichment strategies, enhancing the complexity of the habitat and providing the animals with more choices and control, ultimately promoting their welfare in captivity. Full article

The extinct “false mako” shark, Parotodus benedenii (Lamniformes: Otodontidae), is essentially known from large, robust teeth that are widespread but overall rare in Oligocene to Pliocene deposits worldwide. More than 150 years after its description, this species still represents a palaeontological conundrum, as very little is known about its body aspect and palaeoecology. Here, we describe new specimens of P. benedenii from the Pliocene of Tuscany, central Italy. These new finds comprise some of the geologically youngest finds of P. benedenii worldwide, witnessing to the survival of false makos until the Late Pliocene at least, which in turn suggests that P. benedenii may have been the latest surviving member of the family Otodontidae. Building upon a thorough literature review, we provide an updated synthesis of the palaeobiology of P. benedenii. In light of the morphological evidence, and considering previously published suggestions, P. benedenii may be reconstructed as a large-sized, carnivorous shark that dwelt in pelagic settings and fed primarily on large, soft prey and scavenging items. Thus, some ecological partitioning did likely exist between P. benedenii and other elasmobranch apex predators of the Neogene mid-latitude seas (including, in Pliocene times, the extant species Carcharodon carcharias, Carcharhinus leucas and Galeocerdo cuvier). Full article

Unprovoked shark bites have increased over the last three decades, yet they are still relatively rare. Bull sharks are globally distributed throughout rivers, estuaries, nearshore areas and continental shelf waters, and are capable of making long distance movements between tropical and temperate regions. As this species is implicated in shark bites throughout their range, knowledge of the environmental drivers of bull shark movements are important for better predicting the likelihood of their occurrence at ocean beaches and potentially assist in reducing shark bites. Using the largest dataset of acoustically tagged bull sharks in the world, we examined the spatial ecology of 233 juvenile and large (including sub-adult and adult) bull sharks acoustically tagged and monitored over a 5.5-year period (2017–2023) using an array of real-time acoustic listening stations off 21 beaches along the coast of New South Wales, Australia. Bull sharks were detected more in coastal areas of northern NSW (<32° S) but they travelled southwards during the austral summer and autumn. Juveniles were not detected on shark listening stations until they reached 157 cm and stayed north of 31.98° S (Old Bar). Intra-specific diel patterns of occurrence were observed, with juveniles exhibiting higher nearshore presence between 20:00 and 03:00, whilst the presence of large sharks was greatest from midday through to 04:00. The results of generalised additive models revealed that large sharks were more often found when water temperatures were higher than 20 °C, after >45 mm of rain and when swell heights were between 1.8 and 2.8 m. Understanding the influence that environmental variables have on the occurrence of bull sharks in the coastal areas of NSW will facilitate better education and could drive shark smart behaviour amongst coastal water users. Full article

Global warming raises seawater temperatures and creates changes which have been found to affect the movement of large migrating marine species. Understanding the thermal niches of marine species could prove essential to anticipate how the future climate will alter migrations, and how conservation efforts will have to change accordingly. Orot Rabin power station in Hadera, Israel uses seawater to cool its turbine and releases the warm water back into the Mediterranean Sea. As a result, a marine area with artificially elevated temperatures is created around the effluent. Every winter in the past two decades, this area attracts sharks of two species, Carcharhinus obscurus and Carcharhinus plumbeus, presumably to spend the cold months at a higher temperature. This study concentrated on this point of artificial heat dissipation, which maintains a wide gradient of surface temperatures and allowed us to examine the temperature preferences of these species when given a larger range than what is naturally found in the sea. Between 2016 and 2018, 16 sharks were tagged with acoustic tags, 3 of which had temperature sensors, and 2 were additionally tagged with pop-up archival tags also logging temperature data. Results show that the sharks stayed in the elevated temperature, while the ambient sea was cold during the winter, spending several months in the heated area. Both species displayed a similar preferred range, spending 90 percent of their time at a temperature between 21.8 °C and 26.1 °C while the surrounding sea was 15.5–25.5 °C. Considering this chosen thermal niche and the rise in water temperature, it appears that for the past 40 years, the Eastern shores of the Mediterranean have become more suitable for these species, especially during transitional seasons. The question that arises, however, is whether these shark populations will benefit from the expanding range of preferable temperatures, or whether their proximity to shorelines will put them at greater risk in terms of human activities such as fishing and pollution. Full article

Between 2007 and 2022, 112 specimens of newborn and young pelagic sharks were recorded in the waters of Tuscany Region, in the South Ligurian–North Tyrrhenian Seas (north-western Mediterranean basin). The sharks belonged to the Carcharhinus plumbeus (n = 14), Prionace glauca (n = 66), Isurus oxyrinchus (n = 16), Mobula mobular (n = 5) Alopias vulpinus (n = 7) and Hexanchus griseus (n = 4) species. Each animal was correctly identified thanks to the photographs or videos collected. All specimens were incidentally captured with set nets in inshore shallow waters, except bluntnose six-gill sharks, which were bycatch of deep-water bottom-trawl fishery. Body mass, sex, total length and biometric measurements were recorded in 34 baby sharks following the Mediterranean Large Elasmobranches Monitoring (MEDLEM) protocol. The presence of very evident and often non-healed umbilical scar confirmed that some of the sample specimens were newborn. Further confirmation came from the comparison between the total length observed and the size at birth known for the sampled species as reported in the literature. Some baby sharks were preserved in the Museums of Natural History of Pisa and Florence University collections. The importance of the coastal area studied as a possible shark nursery is discussed. Full article