Search Results (144)

Elasmobranch species are considered a global conservation priority due to their susceptibility to fishing pressure. In the Madeira Archipelago, Northeastern Atlantic, most elasmobranch species are caught as bycatch in artisanal drifting longline fishery targeting scabbardfishes. All commercial elasmobranch landings carried out in this archipelago over three decades (1990–2020) were analysed, aiming to provide a reliable overview of Madeira’s elasmobranch fisheries and their evolution. A total of 2316 tonnes of elasmobranchs were landed during the study period, corresponding to approximately EUR 2.1 million in first-sale value. The most representative period occurred from 2003 to 2013, corresponding to 75.21% of the total elasmobranch landings. A general pattern of supply and demand was evident, with mean price values typically showing an inverse trend to landed tonnage. At the species level, Centrophorus squamosus appears as the dominant species, representing about 89% of the total elasmobranch species landed, followed by Prionace glauca, with approximately 3%. The high dominance of C. squamosus in the scabbardfish fishery raises significant ecological and management concerns, as this deep-water shark species is known for its vulnerability to overexploitation. Management measures currently in place need to be updated and ought to be based on studies on the type and size of hooks for each fishery, to ultimately infer about species-specific survival rates, as well as the fishing gears’ soak time. Moreover, studies on the enhancement of food supply through fisheries discards are still missing, even though it is highly likely that this input may alter the dynamics of marine food webs. Full article

Marine environmental pollution has been rapidly increasing in Arctic waters, and the release and bioaccumulation of trace elements in Arctic marine species may pose significant risks to both ecosystem health and human well-being. As a top predator, the Greenland shark is an ideal sentinel species for ecotoxicological studies in this region. In this study, trace element analyses were conducted on various tissues from two Greenland sharks—a male and a female—collected in Kulusuk (southeastern Greenland). Eleven trace elements (Mn55, Co59, Cu63, Zn64, As75, Se82, Rb85, Mo98, Ag107, Cd112, and Pb208) were measured in different skin samples from both specimens and in the muscle and fat of the female using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Principal Component Analyses (PCAs) revealed sex-related differences in skin bioaccumulation patterns, likely due to sampling of different skin regions. Notably, skin tissues from both sharks showed the highest concentration of trace elements, especially for As75 (9.39–41.13 ppm) and Zn64 (24.34–50.99 ppm) and with the exception of Ag107. These findings suggest that environmental exposure may play a more significant role than dietary intake in trace element accumulation in this area. This study represents the first investigation of trace element bioaccumulation in Greenland sharks from Kulusuk. While the results offer important preliminary insights into the species’ ecotoxicology, further research involving more specimens and tissues is needed to confirm these trends. These initial findings contribute to filling key data gaps and have implications for both environmental monitoring and public health within the Greenlandic community. Full article

Shark ecotourism is an ever-expanding reality, with hundreds of thousands of tourists involved annually. Although it represents a fundamental tool for sharing the urgent need to safeguard sharks with the public, the implications for the health and well-being of sharks must be taken into due consideration. In South Africa, cage-diving has been an important form of ecotourism since the 1990s. In Gansbaai, over a 14-year period from 2009 to 2024, excluding the 2020–2021 pandemic years, data was collected from cage diving operators’ boats on the frequency of sightings of white sharks. After approximately 560 h of field observations, averaging about 45 h per year and about 9 h per year between 2023 and 2024, 423 sharks were observed with five re-sightings. We highlighted that the number of sightings did not increase during the presence of cage diving operators and that site fidelity has not been observed by white sharks frequenting this area. Full article

The Eastern Aegean Sea hosts a diverse assemblage of elasmobranchs, many of which are vulnerable or endangered. This study presents a fishery-independent assessment of species composition, catch characteristics, and spatial patterns in bottom trawl fisheries between Lesvos Island and Ayvalik. A total of 48 surveys were conducted between September 2022 and October 2024, identifying nine elasmobranch species, with Scyliorhinus canicula (small-spotted catshark) and Mustelus mustelus (common smooth-hound) dominating the catch. Biological parameters, sex ratios, and condition upon capture and release were recorded, while catch per unit effort (CPUE) and diversity indices were used to evaluate temporal patterns. The survival probability was negatively affected by the trawl duration and elevated temperatures, emphasizing the need for mitigation measures. Spatial models revealed high-density zones that likely function as foraging or nursery grounds. Seasonal shifts in community composition were also evident. Many non-commercial species were discarded irrespective of their size or condition. These findings underscore the ecological importance of this understudied region and support the need for spatially explicit, species-specific management strategies, including gear selectivity improvements, seasonal closures, and Electronic Monitoring. The study offers a critical baseline for enhancing the sustainability of elasmobranch populations in the Eastern Mediterranean. Full article

Research on the trophic transfer of trace elements in food chains, particularly toxic elements like mercury (Hg) and essential elements like selenium (Se), is crucial for understanding their impact on human health. In this work, we assessed the transfer of Hg and Se in the blue shark (Prionace glauca), a top predator with economic importance. Muscle samples from sharks, as well as their main prey (squid, red shrimp, sardine, and mackerel), were analyzed for Hg and Se concentrations. The Hg levels of sharks were below the recommended legal limit for seafood consumption in Mexico (1 µg·g⁻¹ ww), while Se levels were significantly lower than previously reported for the species. Biomagnification was evaluated in this species by calculating biomagnification factors (BMF) for Hg and Se based on predator-prey element concentrations. Hg showed a BMF of 2.8, indicating biomagnification, while Se had a BMF of 0.2, suggesting biodilution. Trophic transfer factor models supported these findings, showing a positive correlation of Hg concentration with trophic level and a negative correlation with Se. However, while a hazard quotient under one does not pose a risk for consumption, a Se:Hg molar ratio under one estimated in the muscle tissue indicates that Hg levels along this food web should be approached with caution. Full article

The Bay of Bengal (BoB) is a global hub for marine elasmobranchs, particularly sharks and rays. These apex predators maintain and structure the balanced marine ecosystem and food webs. Marine elasmobranchs in Bangladesh are under-researched and under-managed, and face threats such as habitat degradation, global warming, pollution, illegal fishing, and overexploitation. This study aimed to evaluate the stock status of marine elasmobranches in the Bay of Bengal (BoB), Bangladesh. This research used catch and effort (CE) data for a period of 21 years (2002–2022). Both the Monte Carlo CMSY and BSM models were applied to assess biomass, exploitation rates, and sustainable yields. The BSM estimated a maximum carrying capacity (k) of 134,000 mt, which is larger than the CMSY estimate of 119,000 mt. The estimated intrinsic annual growth (r) from CMSY was 0.282. The MSY values ranged from 5110 mt (BSM) to 8420 mt (CMSY), with BSM indicating overexploitation, as the 2022 catch (7017 mt) exceeded the BSM-derived MSY. Both models suggested depleted and overfishing stock conditions, with B/B_MSY ratios < 1.0 and F/F_MSY ratios > 1.0. Effective management is crucial to prevent overfishing and ensure sustainable practices. Elasmobranch catches must be kept below the BSM-estimated maximum sustainable yield (MSY) of 5110 metric tons with fishing pressure maintained at or below F/F_MSY = 1.0. It is vital to regulate illegal and unlicensed fishing activities. Because of the aggregation of CE data, the results should be interpreted cautiously and never serve as a substitute for species-level assessments. Full article

Deep-sea trawling in the Mediterranean Sea, while economically significant, has profound ecological implications due to high discard rates and the practice’s impact on deep-sea biodiversity. This study examines the composition of discards and bycatch in Antalya Bay, a key deep-sea fishing area in the Eastern Mediterranean, during a commercial fishing season, focusing on seasonal and depth-related variations. Data were collected from deep-sea bottom trawl operations conducted between September 2016 and April 2017, analyzing species diversity and catch composition in terms of discarded and bycatch species. The results revealed an average discard rate of 70.7% of the total catch, with significant seasonal fluctuations. In total, 75 species were identified, comprising 48 Osteichthyes, 11 Elasmobranchii, 10 Crustacea, 4 Mollusca, 1 Brachiopoda, and 1 Echinodermata. Discarded species primarily consisted of juveniles of commercially valuable species (Merluccius merluccius and Lepidorhombus whiffiagonis), endangered elasmobranchs, and non-target benthic invertebrates. Depth-stratified analysis indicated that higher discard ratios and greater biodiversity loss occur at depths between 200 and 700 m, where slow-growing species and vulnerable deep-sea assemblages dominate. CPUE estimates for target, bycatch, and discarded species were calculated as 72.26, 145.12, and 385.52 kg/h, and CPUA values were calculated as 0.79, 1.59, and 2.92, respectively. These findings underscore the disproportionate impact of bottom trawling on deep-sea ecosystems and highlight the need for sustainable fisheries management strategies. Full article

Human activities significantly contribute to the biodiversity crisis, yet wildlife tourism can promote appreciation for animals and encourage conservation. This study assessed the impact of diving and snorkeling programs at Atlantis Dubai on tourists’ emotional connections with marine life and their conservation attitudes and pro-environmental behavioral intentions. In 2023 and 2024, 346 participants were surveyed before (n = 172) and after (n = 174) their experiences diving and snorkeling with elasmobranchs. Results indicated a notable increase in positive feelings toward sharks and rays, strengthening connections and respect for these creatures. The program positively influenced attitude toward sharks, making participants more inclined to support their protection and foster a deeper connection with the ocean. Although participants’ willingness to recycle improved, overall conservation attitudes and willingness to engage in broader pro-environmental behaviors showed minor change. However, the heightened positive emotions towards sharks resulted in improved perceptions of these animals, stronger conservation attitudes, and a commitment to environmental sustainability. A deeper connection with the ocean reduced fear of sharks. This research suggests that wildlife tourism can facilitate emotional connections with marine life, potentially inspiring conservation action and highlighting the need for targeted strategies to transform these emotional bonds into lasting pro-environmental behaviors. Full article

Elasmobranchs (Chondrichthyes, Elasmobranchii) are exposed to a variety of gastrointestinal parasites acquired through the ingestion of infected prey. An increasing amount of evidence suggests the usefulness of parasitological information to elucidate aspects of the biology and ecology of sharks and rays, to inform the correct management and conservation of their stocks and the appropriate husbandry of captive specimens. This study aims to identify at the morphological and molecular level the helminth parasites found in the stomachs and intestines of various elasmobranchs accidentally caught by Mediterranean fisheries, with the aim of updating and providing new information on the parasitic fauna of these species. Specimens of smooth-hound Mustelus mustelus, blackspotted smooth-hound Mustelus punctulatus, blue shark Prionace glauca, spiny dogfish Squalus acanthias, lesser-spotted dogfish Scyliorhinus canicula, pelagic stingray Pteroplatytrygon violacea and Mediterranean starry ray Raja asterias were examined. The parasitological examination allowed us to identify the nematode Acanthocheilus rotundatus in the two species of smooth-hounds analyzed, the tapeworm species Scyphophyllidium exiguum, S. prionacis, Anthobothrium caseyi and Nybelinia indica in P. glauca, the nematodes Hysterothylacium aduncum and Proleptus obtusus in S. acanthias and S. canicula, respectively, and finally the nematode Pseudanisakis rajae and the tapeworm Nybelinia sp. in Raja asterias. Some observations represent new reports at a geographical level, in particular, those on A. caseyi in P. glauca and H. aduncum in S. acanthias from the Adriatic Sea, or first host records, such as S. exiguum and N. indica in P. glauca or P. rajae. in R. asterias. The results of this survey represent a contribution to broadening the knowledge of the parasitic fauna of these elasmobranchs in the Mediterranean Sea. From more in-depth future studies, it will be possible to reach more solid evidence and general conclusions on aspects relating to the biology, ecology, and health of the investigated species, offering useful information for their conservation and management. 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

Elasmobranch species are susceptible to anthropogenic stressors such as fishing activities, particularly the bycatch in bottom-trawl fisheries. Understanding the diversity, segregation, and population structure of species at risk of capture is critical for enhancing their conservation. This study evaluated the species composition and population structure dynamics of susceptible elasmobranch species caught as bycatch in the Mexican shrimp trawl fishery in the southern Gulf of Mexico. Data were collected by examining bycatch from 55 fishing trips conducted between 2013 and 2017 during closed and commercial fishing seasons. We analyzed the species composition, length, sex ratio, and maturity stages of susceptible species across zones, sampling seasons, and depth. Six dominant species (Rostroraja texana, Gymnura lessae, Narcine bancroftii, Pseudobatos lentiginosus, Squatina dumeril, Hypanus americanus) accounted for >98% of all captures and were found in all fishing zones, seasons, and depths. These species were caught in a range of sizes, from newborns to mature individuals, and showed both inter- and intraspecific segregation patterns across fishing zones, seasons, and depths. The elasmobranch composition and population structure in bycatch are influenced by ontogenetic segregation and bathymetric distribution of the species. Current Mexican shrimp trawl fishery regulations benefit the majority of elasmobranchs by providing comprehensive spatiotemporal protection and selective exclusion mechanisms. However, small-sized ray species and juveniles of larger species continue to face fishing pressure. The preset study highlights the southern Gulf of Mexico as an important reproductive area for demersal elasmobranchs and unravels their complex segregation behavior, leading to the identification of potential risk zones and seasons. The impacts of bycatch on the most susceptible elasmobranchs may be mitigated through improvements in trawl fishing technology and the implementation of additional temporal bans in specific trawling areas, enhancing species-specific conservation efforts. Full article

Marine ecosystems are increasingly threatened by pollutants, including trace elements (TEs) such as heavy metals, which bioaccumulate and pose risks to both marine fauna and human health. Sharks and rays are particularly susceptible to metal uptake and retention, making them sentinel species for assessing environmental contamination. This study investigated the bioaccumulation of 16 TEs across 12 elasmobranch species sampled from the Ionian and Tyrrhenian coasts of Calabria, southern Italy, over an 11-year period. Muscle tissue was analyzed for all species, while additional comparisons among skin, muscle, and brain tissues were conducted for Galeus melastomus. Statistical analyses revealed significant variability in TEs concentrations across trophic levels (TRLs), with higher levels observed in species occupying higher trophic positions. Positive correlations were noted for elements such as Al, Ba, and Se, while negative correlations were found for Co, Cu, Mn, and U, indicating species-specific metabolic adaptations. Tissue-specific analyses identified the skin as a primary site for TEs accumulation, likely due to its barrier functions and external exposure. This study highlights the complex interplay of ecological, dietary, and physiological factors influencing TEs bioaccumulation in elasmobranchs and emphasizes the need for further research to understand the implications for marine food webs and conservation strategies. Full article

Fungal diseases, despite their low incidence in sharks and rays, are considered emerging diseases in this group of animals and can lead to high mortality rates despite treatment. The information available related to the treatment of fungal diseases in elasmobranchs is limited and is frequently based on the empirical knowledge provided by the professionals and clinicians working with these species. The use of azole antifungal drugs, especially voriconazole, has shown promise as a potential treatment option for fungal infections in elasmobranchs, with favorable outcomes in some registered cases. However, scientific knowledge regarding azole pharmacokinetics (PK) in fish remains limited, and despite the recent publication of a PK study with voriconazole in rays, there are still no published PK studies for azoles in sharks. In this study, voriconazole was administered at 4 mg/kg intravenously (IV) and intramuscularly (IM) to nursehound sharks (Scyliorhinus stellaris) (n = 6). Blood samples were collected before administration and at nine predetermined time intervals afterwards (0.25, 0.5, 1, 1.5, 2, 4,8,12, 24, and 36 h). Plasma concentrations were determined using a validated high-performance liquid chromatography (HPLC) method, and pharmacokinetic (PK) parameters were estimated using a non-compartmental model. The mean peak plasma concentrations (C_max) ± SEM after IM administration was 3.00 ± 0.23 µg/mL. The volume of distribution (Vd) after IV and IM administration resulted in 1.39 ± 0.09 L/kg and 1.50 ± 0.18 L/kg, respectively, showing no statistically significant differences between the two routes. Clearance (Cl) values were 0.12 ± 0.01 mL/min after IV administration and 0.29 ± 0.05 mL/min after IM administration. No adverse effects were detected during the study or four weeks after administration. These results support the administration of IV and IM voriconazole in sharks; however, additional studies on toxicity and pharmacodynamics are necessary. Moreover, further research on the susceptibility of fungal pathogens affecting elasmobranchs is needed to establish an optimal dosing regimen for IM voriconazole in the treatment of mycosis in sharks. 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

The previously available coding region for the spiny dogfish (Squalus acanthias) AQP3-2 gene was amplified from cDNAs using PCR. Agarose gel electrophoresis gave a band of the AQP3-2 coding region, as well as multiple smaller splice variant bands. The main AQP3-2 band and the largest and most fluorescently intense pair of these splice variant bands were cloned and sequenced. Amplifications were performed on a range of tissue cDNAs, but AQP3-2 was only expressed in the kidney and brain. Quantitative PCR amplifications using pre-existing kidney cDNA from an environmental salinity acclimation experiment showed that the abundance of mRNA from both the main AQP3-2 transcript and the largest splice variant (Splice Variant 1) was lower in 120% seawater (SW) acclimated fish, although only the values for Splice Variant 1 were statistically significant. A custom-made affinity-purified rabbit polyclonal AQP3-2 antibody was produced, and this gave four bands of around the correct sizes (which were 27 and 32 kDa) for the complete AQP3-2 and Splice Variant 1 proteins. Two of the bands may have been N-glycosylated forms of these proteins. Other bands were also present on the Western blot. No bands were present when the antibody was pre-blocked by the peptide antigen. In tissue sections of the dogfish kidney, immunohistochemical localization experiments showed that AQP3-2 was expressed in the early distal tubule (EDT) and late distal tubule (LDT) nephron segments. The results suggest that AQP3-2 may be involved in cell volume regulation in the EDT and water and urea absorption in the LDT nephron segment. Full article