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Hammerhead sharks are among the most intriguing yet imperiled groups of large sharks globally. Until recently, our understanding of their biology, movements, diet, and life histories was challenged by a lack of studies. In recent years there has been a surge of published studies on this group of sharks, incorporating new information on age and growth, behavior, and the threats they face. Here we summarize and compare what is known on the biology and conservation of the three largest species of hammerhead sharks: the great hammerhead (Sphyrna mokarran), the scalloped hammerhead (Sphyrna lewini), and the smooth hammerhead (Sphyrna zygaena). We chose these species since they are the most well-studied of the hammerheads, and also because they are commonly captured in target and non-target fisheries worldwide. Thus, we also discuss population trends and the vulnerabilities of each species, and make recommendations for future studies on these fascinating and complex elasmobranch fishes.

Sphyrna lewini is a viviparous shark that pups in shallow coastal waters. Given dramatic declines in the S. lewini Eastern Pacific population, it is essential to identify nursery grounds that could potentially increase the resilience of adult populations. Here, we provide evidence of a putative nursery ground for S. lewini at an oceanic island in the Galapagos Marine Reserve. A fortuitous finding of hammerhead shark pups in 2017 led to a series of focused surveys from 2018 onwards, using experimental fishing, baited remote underwater videos stations (BRUVS), and acoustic telemetry, to assess presence and residency patterns of this species at Puerto Grande: a shallow bay at the island of San Cristobal. We caught 66 individuals, of which we measured 54 (mean TL = 52.13 cm). Four individuals were fitted with ultrasonic tags and were detected on an array of 14 receivers in the bay for up to 93 days, showing a high residency index of at least 89%. We actively tracked a single individual for 3 h at night and a further hour a week later. Our results suggest that Puerto Grande is a key habitat for the development of the critically endangered S. lewini.

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.

The population genetic structure and female philopatry to nursery grounds of the scalloped hammerhead shark (Sphyrna lewini) were studied in different mangrove estuaries along the Mexican Pacific coast containing putative nurseries. These nurseries were grouped into northern (Sinaloa-Nayarit), central (Jalisco), and southern (Oaxaca-Chiapas) regions. Neonates and young of the year were collected near estuaries or river inlets, and their genetic variation was compared based on mitochondrial DNA (mtDNA) genome sequences and 11 nuclear microsatellite loci. The mtDNA analysis showed significant differences between the abovementioned regions, accompanied by genetic homogeneity of microsatellites. Based on the genetic divergence of mtDNA and the lack of differences in nuclear markers, our results are congruent with female philopatry to nursery areas, as observed in other shark species. The parentage analysis applied to the microsatellite data showed moderate levels of relatedness among individuals within nurseries, suggesting philopatry as a cause of the observed results. The pattern of nursery grounds of the scalloped hammerhead shark in the Mexican Pacific seems to be regional, as no differences were observed between neighboring estuaries within each studied region. These findings are relevant for delineating conservation plans to preserve key populations and minimize the effects of commercial fisheries.

The aim of this study was to purify and identify peptides with antioxidant properties from protein hydrolysate of scalloped hammerhead (Sphyrna lewini) cartilage. Cartilaginous proteins of the scalloped hammerhead were extracted by guanidine hydrochloride, and three antioxidant peptides, named enzymolysis peptide of scalloped hammerhead cartilage A (SCPE-A), SCPE-B and SCPE-C, were subsequently isolated from the hydrolysate of the cartilaginous proteins using ultrafiltration and chromatography. The amino acid sequences of SCPE-A, SCPE-B and SCPE-C were identified as Gly-Pro-Glu (GPE), Gly-Ala-Arg-Gly-Pro-Gln (GARGPQ), and Gly-Phe-Thr-Gly-Pro-Pro-Gly-Phe-Asn-Gly (GFTGPPGFNG), with molecular weights of 301.30 Da, 584.64 Da and 950.03 Da, respectively. As per in vitro activity testing, SCPE-A, SCPE-B and SCPE-C exhibited strong scavenging activities on 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH•) (half elimination ratio (EC50) 2.43, 2.66 and 1.99 mg/mL), hydroxyl radicals (HO•) (EC50 0.28, 0.21 and 0.15 mg/mL), 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radicals (ABTS+•) (EC50 0.24, 0.18 and 0.29 mg/mL), and superoxide anion radicals ( O 2 − •) (EC50 0.10, 0.14 and 0.11 mg/mL). In addition, SCPE-A showed inhibition activity similar to butylated hydroxytoluene (BHT) in lipid peroxidation in a linoleic acid model system. The amino acid residues of Gly, Pro and Phe could positively influence the antioxidant activities of GPE, GARGPQ and GFTGPPGFNG. These results suggested that GPE, GARGPQ and GFTGPPGFNG might serve as potential antioxidants and be used as food additives and functional foods.

Bycatch poses a significant threat to marine megafauna, such as elasmobranchs. India has one of the highest elasmobranch landings globally, through both targeted catch and bycatch. As elasmobranchs contribute to food and livelihood security, there is a need for holistic approaches to bycatch mitigation. We adopt an interdisciplinary approach to critically assess a range of hypothetical measures for reducing elasmobranch capture in a trawler fishery on India’s west coast, using a risk-based mitigation hierarchy framework. Data were collected through landing surveys, interviews and a literature review, to assess the following potential management options for their technical effectiveness and socio-economic feasibility: (1) Spatio-temporal closures; (2) Net restrictions; (3) Bycatch reduction devices (BRDs) and (4) Live onboard release. Our study provides the first evidence-based and nuanced understanding of elasmobranch bycatch management for this fishery, and suggestions for future conservation and research efforts. Onboard release may be viable for species like guitarfish, with moderate chances of survival, and was the favored option among interview respondents due to minimal impact on earnings. While closures, net restrictions and BRDs may reduce elasmobranch capture, implementation will be challenging under present circumstances due to the potentially high impact on fisher income. Interventions for live release can therefore be used as a step towards ameliorating bycatch, while initiating longer-term engagement with the fishing community. Participatory monitoring can help address critical knowledge gaps in elasmobranch ecology. Spatio-temporal closures and gear restriction measures may then be developed through a bottom-up approach in the long term. Overall, the framework facilitated a holistic assessment of bycatch management to guide decision-making. Scaling-up and integrating such case studies across different species, fisheries and sites would support the formulation of a meaningful management plan for elasmobranch fisheries in India.

A high-performance diffuser is crucial for a high-pressure ratio centrifugal compressor to achieve high efficiency. Pipe diffusers have been proven effective in enhancing the performance of such compressors. However, detailed design methodologies for pipe diffusers are scarcely covered in the existing literature. Thus, this paper provides a comprehensive design methodology specifically for fishtailed pipe diffusers. This methodology begins by defining the throat and outlet areas using gas-dynamic functions and then establishes the centerline by choosing the angle distributions. Finally, various cross-sectional profiles are defined along the centerline, completing the diffuser’s design. To demonstrate the proposed methodology, a fishtailed pipe diffuser is designed to contrast with the original diffuser of the National Aeronautics and Space Administration’s High-Efficiency Centrifugal Compressor (NASA HECC). Numerical analysis shows that the fishtailed pipe diffuser increases the compressor’s total pressure ratio and isentropic efficiency over its whole operating range. At the design operating point, the isentropic efficiency and the total pressure ratio are increased by 2.4 percentage points and 2.7%, respectively. This demonstrates the effectiveness of the proposed design methodology for fishtailed pipe diffusers.

Background The scalloped spiny lobster ( Panulirus homarus ) is a popular seafood commodity worldwide and an important export item from Oman. Annual catches in commercial fisheries are in serious decline, which has resulted in calls for the development of an integrated stock management approach. In Oman, the scalloped spiny lobster is currently treated as a single management unit (MU) or stock and there is an absence of information on the genetic population structure of the species that can inform management decisions, particularly at a fine-scale level. This work is the first to identify genome-wide single nucleotide polymorphisms (SNPs) for P. homarus using Diversity Arrays Technology sequencing (DArT-seq) and to elucidate any stock structure in the species. Results After stringent filtering, 7988 high utility SNPs were discovered and used to assess the genetic diversity, connectivity and structure of P. homarus populations from Al Ashkharah, Masirah Island, Duqm, Ras Madrakah, Haitam, Ashuwaymiyah, Mirbat and Dhalkut landing sites. Pairwise F ST estimates revealed low differentiation among populations (pairwise F ST range = − 0.0008 - 0.0021). Analysis of genetic variation using putatively directional F ST outliers (504 SNPs) revealed higher and significant pairwise differentiation ( p  < 0.01) for all locations, with Ashuwaymiyah being the most diverged population (Ashuwaymiyah pairwise F ST range = 0.0288–0.0736). Analysis of population structure using Discriminant Analysis of Principal Components (DAPC) revealed a broad admixture among P. homarus , however, Ashuwaymiyah stock appeared to be potentially under local adaptive pressures. Fine scale analysis using Netview R provided further support for the general admixture of P. homarus . Conclusions Findings here suggested that stocks of P. homarus along the Omani coastline are admixed. Yet, fishery managers need to treat the lobster stock from Ashuwaymiyah with caution as it might be subject to local adaptive pressures. We emphasize further study with larger number of samples to confirm the genetic status of the Ashuwaymiyah stock. The approach utilised in this study has high transferability in conservation and management of other marine stocks with similar biological and ecological attributes.

Marginal bone loss (MBL) is a key factor in long-term implant success rate. Among the different factors that influence MBL, it is the different implant shoulder designs, such as scalloped or non-scalloped, which have been widely studied on screw retained but not on cemented retained implants. Thus, the aim of the present study was to evaluate the MBL around scalloped and non-scalloped cemented retained dental implants after 4 years of loading, in humans. A total of 15 patients were enrolled in the present study. A radiographic and clinical examination was performed after implant placement (T0) and after 4 years from it (T1). The results demonstrated a differential MBL (T1-T0) of 2.436 ± 1.103 mm and 1.923 ± 1.021 mm, respectively for test (scalloped) and control (non-scalloped) groups with a statistically significant difference between them. On the other hand, no statistically significant differences were found between the groups in terms of prosthetic complication and abutment decementation, whilst ceramic crowns chipping was shown in both groups. In conclusion, the use of a scalloped platform did not provide better results on the maintenance of MBL after 4 years follow-up. In this study, this probably was determined by multiple factors, among which was the subcrestal insertion of scalloped implants.

Riblets are a series of small protrusions formed along the flow direction, which have been extensively studied as a passive turbulent drag reduction technique. Experiments and numerical simulations have shown that well-designed riblets can significantly reduce drag in turbulent flows, making them highly promising and valuable for various applications. In this study, we focus on a scalloped riblet, which is designed by smoothly connecting two third-order polynomials, and thus the sharpness of the tip and the curvature of the valley can be well defined. We conduct direct numerical simulations of turbulent channel with smooth plate, scalloped riblet-mounted and triangular riblet-mounted walls. Width in wall units of W + = 20 and height-width ratio of γ = 0.5 are selected for both riblet cases. Compared with the smooth plate case, the scalloped riblet case achieves an 8.68% drag reduction, while the triangular riblet case achieves a 4.79% drag reduction. The obtained drag reduction rate of the triangular riblet is consistent with previous experiments and simulations, and the results indicate that the scalloped riblet is more effective in reducing drag and deserves further investigation. We compare turbulent statistics of the scalloped riblet case with those of the triangular riblet case. The mean velocity profiles of riblets are similar, but both the Reynolds shear stress and second-order statistics of velocity fluctuations and Liutex are significantly reduced in the scalloped riblets controlled turbulent channel, indicating that the scalloped riblet can more effectively suppress the spanwise and wall-normal turbulent intensity near the wall. We also compare the pre-multiplied spectra of streamwise velocity and streamwise Liutex component for the three cases to investigate the energy distribution and characteristics of Liutex distribution. The Liutex vortex identification method is also utilized to analyze the instantaneous flow field, which provides insights into the flow field and could be beneficial for the further optimization of riblet.