Sharks of the genus Sphyrna are under intense exploitation globally. In Brazil's northern coast, this genus represents a high proportion of fisheries landings and comprises four species. However, due ...to difficulty of specific identification when specimens are landed, most of the records are limited to the genus level. Here we analyzed the effectiveness of ITS2 (Internal Transcribed Spacer 2 of rDNA) fragment length protocol (Abercrombie et al., 2005) for identifying hammerhead shark species, comparing with the analysis of COI (Cytochrome oxidase subunit I) and ITS2 sequences. We evaluated samples of muscle tissue acquired in the main fishing ports of Maranhão: Carutapera, Raposa e Tutóia. Sampling was conducted between March 2017 to March 2018 and complemented with material deposited in collection (2015). COI results indicated the occurrence of endangered species which are prohibited to be landed. These include Sphyrna mokarran (67%), S. lewini (15%), S. tudes (3%), and S. tiburo (15%). For the ITS2 marker, we investigated the optimization of the protocol developed by Abercrombie (2005) for to improve the use in this geographical area througout design of a new primers.
Background
The hammerhead sharks (family Sphyrnidae) are an immediately recognizable group of sharks due to their unique head shape. Though there has long been an interest in hammerhead development, ...there are currently no explicit staging tables published for any members of the group. The bonnethead Sphyrna tiburo is the smallest member of Sphyrnidae and is abundant in estuarine and nearshore waters in the Gulf of Mexico and Western North Atlantic Ocean. Due to their relative abundance, close proximity to shore, and brief gestation period, it has been possible to collect and document multiple embryonic specimens at progressive stages of development.
Results
We present the first comprehensive embryonic staging series for the Bonnethead, a viviparous hammerhead shark. Our stage series covers a period of development from stages that match the vertebrate phylotypic period, from Stage 23, through stages of morphological divergence to complete development at birth—Stage 35). Notably, we use a variety of techniques to document crucial stages that lead to their extreme craniofacial diversity, resulting in the formation of one of the most distinctive characters of any shark species, the cephalofoil or hammer‐like head.
Conclusion
Documenting the development of hard‐to‐access vertebrates, like this viviparous shark species, offers important information about how new and diverse morphologies arise that otherwise may remain poorly studied. This work will serve as a platform for future comparative developmental research both within sharks and across the phylogeny of vertebrates, underpinning the extreme potential of craniofacial development and morphological diversity in vertebrate animals.
Key Findings
A staging series for one of the smallest hammerhead species.
Observing the developmental timing and growth of fins and cephalofoil in hammerheads.
This work will serve as a platform for future comparative developmental research both with hammerhead sharks and across chondrichthyan fishes.
A refuge can be any space that keeps an organism safe from danger. Prey usually seek protection in the closest refuge available to minimize cost while maximizing survival. Aerial drone footage of ...blacktip sharks, Carcharhinus limbatus, along the coast of southeast Florida, USA, shows adult blacktips fleeing to the shallow water adjacent to the beach when confronted with or chased by a predatory great hammerhead shark, Sphyrna mokarran. To authors’ knowledge, this is the first evidence of adult C. limbatus using shallow waters as a refuge.
•We investigate the trade in shark products from the United Arab Emirates.•We confirm that the United Arab Emirates is a regional hub for the trade.•We observe that at least 37 species are traded ...from this location.•We propose immediate research and a regional approach to conservation.
The rapid growth in the demand for shark products, particularly fins, has led to the worldwide overexploitation of many elasmobranch species. Although there are growing concerns about this largely unregulated and unmonitored trade, little information still exists about its dynamics, the species involved and the impact of this pressure on stocks in various regions. Our study provides the first attempt at characterizing the trade in shark products from the United Arab Emirates (UAE), the fourth largest exporter in the world of raw dried shark fins to Hong Kong. A review of trade records and informal interviews with local traders confirmed that the UAE is being used as hub in the broader North Indian Ocean region for the trade in shark products with the Emirati fishery minimally contributing to this trade. Results based on morphological identification of sharks (n=12,069) and DNA barcoding of tissue samples (n=655) indicated that the trade was made up of at least 37 species. The most abundant families represented at the Dubai study site were the Sphyrnidae (9.3%), Lamnidae (9%) and Alopiidae (5.9%). While information was mostly limited to shark products originating from the UAE and Oman, results indicated that 45.3% of species traded were considered to be at high risk of global extinction based on the IUCN Red List Global Assessments. Since many of the species found during this survey are likely part of stocks shared with other countries, regional cooperation and management will be crucial to ensure their long term survival.
Scalloped Hammerhead shark (Sphyrna lewini) is an endangered species which its populations have been declining globally including in Indonesia, the world's top shark fishing country. However, there ...is a lack of information on the recent population structure of this species to promote proper management and its conservation status. This study aimed to investigate the genetic diversity, population structure, and connectivity of the S. lewini population, in three major shark landing sites: Aceh (n = 41), Balikpapan (n = 30), and Lombok (n = 29). Meanwhile, additional sequences were retrieved from West Papua (n = 14) and the Western Indian Ocean (n = 65) populations. From the analyses of the mitochondrial CO1 gene, a total of 179 sequences of S. lewini, with an average size of 594 bp, and 40 polymorphic loci in four and eight haplotypes for the Indonesian population and the Western Indian Ocean population were identified. The overall values of genetic diversity were high (h = 0.717; qi = 0.013), with the highest values recorded in Aceh (h = 0.668; qi = 0.002) and the lowest in Papua (h = 0.143; qi = 0.000). On the contrary, the overall value was fairly low in the Western Indian Ocean (h = 0.232; qi = 0.001). Furthermore, AMOVA and F.sub.ST showed three significant subdivisions in Indonesia (F.sub.ST = 0.442; P 0.001), with separated populations for Aceh and West Papua, and mixed between Balikpapan and Lombok (F.sub.ST = 0.044; P = 0.091). In contrast, genetic homogeneity was observed within the population of the Western Indian Ocean (F.sub.ST = -0.013; P = 0.612). The establishment of a haplotype network provided evidence of a significantly different population and a limited genetic distribution between the Indonesian and the Western Indian Ocean populations (F.sub.ST = 0.740; P 0.001). This study showed the presence of a complex population of S. lewini with limited connectivity only in Indonesia separated from the Western Indian Ocean and requiring specific management measures based on the population structure at the regional level.
With the aim of assessing health risk to shark consumers, cadmium, mercury, and selenium were measured in muscle of Sphyrna lewini from four coastal states (Baja California Sur, Sinaloa, Nayarit, and ...Colima) in western Mexico. According to length of specimens, three age modes were found: juveniles and neonates (the majority of the individuals), preadults and adults. Average concentrations (μg g−1 dry weight) in all the studied individuals followed the order cadmium (0.06), selenium (0.94), and mercury (1.56). The mean concentrations of cadmium and mercury increased significantly (p < 0.001) with mean length of specimens. Overall, hazard quotient and hazard index values were below one so there is no health risk to consumers. According to molar ratios of Hg and Se in the edible portion (muscle) of sharks, and depending on the areas of collection, individuals from Baja California Sur might not be beneficial to consumers.
Display omitted
•Mean concentrations of Cd and Hg increased according to mean length of sharks.•Overall, HQ and HI values were below one so there is no health risk to consumers.•Health benefit values were positive except in sharks from BCS so they might not be beneficial.
This work aimed to characterize the nursery habitat use patterns of the scalloped hammerhead shark, Sphyrna lewini (SPL), in coastal areas of Jalisco and Colima, through the birth pattern, space–time ...distribution and relationship with environmental conditions. Information was combined from three sources: monitoring bycatch from the artisanal fishery, fishery‐independent samplings, and acoustic tracking and monitoring. From September 2013 to May 2017, 408 juvenile SPL (41.6–100.1 cm total length) were recorded. Births occurred between May and December (rainy‐warmer season), within a radius of 2 km from river mouths in Marabasco, Navidad Bay, Rebalsito‐Tecuan and Cuitzmala mainly in shallow (<20 m), turbid and soft‐bottom areas. Some tagged SPL moved from Marabasco and Rebalsito to Navidad Bay. The peak of catch and births occurred in June–August. Tagged SPL remained near the river mouth in Rebalsito for up to 27 days, showing a mean residency index of 0.29, a home range of 5.55 km2 with a core area of 1.23 km2 located within a 1.5 km radius from the river mouth. In December–January SPL left the river mouth areas and the catch was scarce until the following May–June, except in January 2016, when the catch was high due to El Niño 2015. SPL bycatch was significantly associated with temperature, precipitation and the Oceanic Niño Index.
Neonates of hammerhead sharks (Sphyrnidae), Sphyrna lewini (Griffith and Smith, 1834), the sympatric cryptic species, Sphyrna gilberti Quattro et al., 2013, and their hybrids were captured in the ...western North Atlantic, along the coast of South Carolina, USA, between 2018 and 2019 and examined for gill monogenoids. Parasites were identified and redescribed from the gills of 79 neonates, and DNA sequences from partial fragments of the nuclear 28S ribosomal RNA (rDNA) and cytochrome c oxidase I mitochondrial DNA (COI) genes were generated to confirm species identifications. Three species of monogenoids from Hexabothriidae Price, 1942 and Monocotylidae Taschenberg, 1879 were determined and redescribed. Two species of Hexabothriidae, Erpocotyle microstoma (Brooks, 1934) and Erpocotyle sphyrnae (MacCallum, 1931), infecting both species of Sphyrna and hybrids; and 1 species of Monocotylidae, Loimosina wilsoni Manter, 1944, infecting only S. lewini and hybrids. Loimosina wilsoni 28S rDNA sequences matched those of Loimosina sp. from the southern coast of Brazil. Based on limited morphological analysis, Loimosina parawilsoni is likely a junior synonym of L. wilsoni. This is the first taxonomic study of monogenoids infecting S. gilberti and hybrids of S. gilberti and S. lewini.
Hybridization between closely related species has been documented across a wide range of taxa but has not been well studied in elasmobranchs. Hammerhead sharks have drawn global conservation concern ...because they experience some of the highest mortality rates among sharks when interacting with fisheries. Here we report on the detection of hybrids between the globally distributed scalloped hammerhead ( Sphyrna lewini) and recently described Carolina hammerhead ( S. gilberti) which are only known from the western Atlantic Ocean. Using a genomics approach, 10 first-generation hybrids and 15-17 backcrosses were detected from 554 individuals. The identification of backcrosses demonstrates hybrids are viable, and all backcrosses but one involved a scalloped hammerhead. All hybrids but one possessed Carolina hammerhead mtDNA, indicating sex-biased gene flow between species. Repeated hybridization and backcrossing with scalloped hammerheads could lead to the loss of endemic Carolina hammerheads.
The scalloped hammerhead (Sphyrna lewini) is a globally threatened shark species that has experienced significant declines throughout its range due to overfishing, along with high rates of ...post-release mortality. Because of this, there is a need to obtain data useful for the management of S. lewini populations, including information on nursery areas. This study describes a unique, inshore nursery for northwest Atlantic young-of-year (YOY) S. lewini, in the Tolomato River in northeast Florida, USA. Relative abundance of YOY S. lewini in the Tolomato River was determined over 10 years using bottom longline fishing and compared to that in two nearby estuaries previously shown to serve as communal shark nurseries, the St. Marys River and the Nassau River. Average catch rates were shown to be 10 – 30 times greater in the Tolomato River compared to those in other sites, demonstrating that YOY S. lewini are found more commonly in this river system. YOY S. lewini consistently made up a significant proportion of overall shark catch over the duration of the 10-year survey, demonstrating repeated use across years. YOY S. lewini were caught in the Tolomato River from May to September annually, suggesting that they only use the Tolomato River as a nursery for the first 4 – 5 months of life. This, along with the recapture of 3 individuals ranging from 6 – 59 days post-release, suggests that YOY S. lewini remain in this site for extended periods of time; however, future work using acoustic telemetry is needed to confirm this finding. Overall, this study shows that the Tolomato River meets previously established criteria needed to confirm that it serves as nursery habitat for YOY S. lewini. Future work is needed to examine microhabitat selection by YOY S. lewini in this site, and interactions between this species and other sharks.
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