French naiad (Bivalvia: Margaritiferidae,Unionidae) species distribution models: prediction maps as tools for conservation

The aim of this study was to determine whether juvenile scalloped hammerhead sharks (Sphyrna lewini) use the south-eastern Gulf of California as a nursery and feeding area. This information could help lay the groundwork required for the conservation of this endangered species. To address this, we carried out stable isotope (δ¹⁵N and δ¹³C) and stomach content analyses of sharks caught between 2000 and 2004 in Mazatlan, Mexico. Stomach contents and δ¹³C values indicated that S. lewini is a predator that feeds on benthic prey near the coast. Differences in δ¹⁵N average values between sizes classes (<100 vs. >100 cm) suggest that there was an ontogenetic change in this shark’s feeding habits and also in their living environment (from benthic areas to pelagic areas). The trophic position indicated that S. lewini is a tertiary consumer, but with a high degree of trophic plasticity, and thus, different trophic roles, highlighting the importance of this predator as a regulator of prey populations. Finally, the linear isotopic relationship between S. lewini and its prey indicates a long residency within the Mazatlan area. Our results demonstrate that the south-eastern Gulf of California is a nursery area that offers abundant food for juvenile scalloped hammerhead sharks.     

New microsatellite loci for the endangered scalloped hammerhead shark, Sphyrna lewini

We isolated 15 microsatellite markers for the scalloped hammerhead shark, Sphyrna lewini. Loci were tested on 80 specimens of S. lewini from four Eastern Pacific samples. The number of alleles per locus ranged from 6 to 31 (mean = 14). Observed and expected levels of heterozygosity per locus ranged from 0.39 to 0.91 (mean = 0.70) and from 0.54 to 0.90 (mean = 0.76), respectively. No pairs of loci were in gametic disequilibrium after Bonferroni correction of α. One locus showed significantly lower heterozygosity than expected under Hardy–Weinberg proportions in two populations, possibly caused by null alleles.     

Stomach content analysis of juvenile, scalloped hammerhead shark Sphyrna lewini captured off the coast of Mazatlán, Mexico

We quantified the diet of juvenile, scalloped hammerhead shark Sphyrna lewini in the area off Mazatlan, Sinaloa, Mexico, to understand their feeding ecology this shark. The prey species of Sphyrna lewini were identified and quantified from stomach content analysis. In addition, we determined the variations between genders. During two fishing seasons (2000–2001 and 2001–2002), we analyzed 232 stomachs, of which 85% contained food. The trophic spectrum was composed of three species of cephalopods, six of crustaceans and 19 species of fish from mainly pelagic and benthic habitats. According to the Index of Relative Importance (%IRI), the cephalopod Loliolopsis diomedeae with IRI = 18%, fish of the family Carangidae IRI = 25% and family Synodontidae IRI = 19% constituted the main prey in general. The trophic niche width was <0.4, which indicated that S. lewini juveniles in this area feed on a wide range of prey items, though they showed a preference for a few prey items.     

Notes on the long‐term transport of the scalloped hammerhead shark (Sphyrna lewini)

The capture and transport of scalloped hammerhead sharks (Sphyrna lewini Griffith and Smith, 1834) historically has represented a difficult, expensive, and uncertain undertaking for the public aquarium community. In this study, techniques were developed to improve the successful long‐term transport of S. lewini by mitigating some of the deleterious effects associated with hyperactivity and impaired swimming patterns. The relationship between the transport vessel size and shark sizes, numbers, and swimming behavior was considered when formulating the transport regime. By balancing these factors and adopting a comprehensive water treatment method, it was possible to extend the duration of a successful transport by up to 60 hr. Implications for the future transport of S. lewini and other free‐swimming sharks are discussed. Zoo Biol 21:243–251, 2002. © 2002 Wiley‐Liss, Inc.     

Identification of young‐of‐the‐year great hammerhead shark Sphyrna mokarran in northern Florida and South Carolina

Two sharks, visually identified in the field as young‐of‐the‐year (YOY) scalloped hammerhead Sphyrna lewini, were identified as great hammerhead Sphyrna mokarran based on nuclear‐encoded single nucleotide polymorphisms (SNP) and sequences of mtDNA. Individuals were captured and released in Bulls Bay, SC, and Saint Joseph Bay, FL, in 2013 and 2014, respectively. These findings indicate S. mokarran may be pupping in or around these areas and highlight new regions that may be a productive focus for future research on early life history of S. mokarran.     

Periodicity of the growth-band formation in vertebrae of juvenile scalloped hammerhead shark Sphyrna lewini from the Mexican Pacific Ocean

The age of 296 juvenile scalloped hammerhead sharks Sphyrna lewini caught by several fisheries in the Mexican Pacific Ocean from March 2007 to September 2017 were estimated from growth band counts in thin-sectioned vertebrae. Marginal-increment analysis (MIA) and centrum-edge analysis (CEA) were used to verify the periodicity of formation of the growth bands, whereas elemental profiles obtained from LA-ICP-MS transect scans in vertebrae of 15 juveniles were used as an alternative approach to verify the age of the species for the first time. Age estimates ranged from 0 to 10+ years (42–158.7 cm total length; L_T). The index of average percentage error (I_APE 3.6%), CV (5.2%), bias plots and Bowker's tests of symmetry showed precise and low-biased age estimation. Both MIA and CEA indicated that in the vertebrae of juveniles of S. lewini a single translucent growth band was formed during winter (November–March) and an opaque band during summer (July–September), a period of faster growth, apparently correlated with a higher sea surface temperature. Peaks in vertebral P and Mn content spatially corresponded with the annual banding pattern in most of the samples, displaying 1.19 and 0.88 peaks per opaque band, respectively, which closely matched the annual deposition rate observed in this study. Although the periodicity of growth band formation needs to be verified for all sizes and ages representing the population of the species in the region, this demonstration of the annual formation of the growth bands in the vertebrae of juveniles should lead to a re-estimation of the growth parameters and productivity of the population to ensure that it is harvested at sustainable levels.     

New insights into the trophic ecology of the scalloped hammerhead shark,Sphyrna lewini,in the eastern tropical Pacific Ocean

Scalloped hammerhead shark, Sphyrna lewini, is considered a generalist predator, showing individual specializations and different trophic levels. This species inhabits both oceanic islands and coastal nursery areas in the eastern tropical Pacific (ETP) Ocean. Existing trophic ecology studies on S. lewini have been focused on stomach contents. This study provides new insights into its foraging preferences, habitat use, and trophic position, using stable isotope analysis (SIA) of muscle tissue. Stable isotope signatures of δ¹³C and δ¹⁵N were determined in S. lewini muscles (n?=?29) from the Ecuadorian Pacific in 2013. Trophic position (TP), isotopic niches, and overlap of S. lewini were estimated by sex, age, and maturity stages to infer their dietary habits throughout life stages. SIA revealed complex movement patterns related to sex and age classes of S. lewini, highlighting high degrees of dietary plasticity and habitat use, with a stronger relation to coastal regions than previously reported. This study provides crucial information regarding essential areas and the related migration behavior of S. lewini, with important implications for their conservation and management in the ETP.

     

Estimation of daily energetic requirements in young scalloped hammerhead sharks, Sphyrna lewini

Juvenile scalloped hammerhead sharks, Sphyrna lewini, are apex predators within their nursery ground in Kāne‘ohe Bay, Ō‘ahu, Hawai‘i. Understanding daily maintenance requirements of a top-level predator is an important step toward understanding its ecological impact within a nursery ecosystem. Juvenile S. lewini were fed a range of daily ration levels to examine the effect of feeding rate on growth and gross conversion efficiency. The von Bertalanffy growth model yielded the best fit to the data, predicting a maintenance ration of 115 kJ kg⁻¹ day⁻¹ (3.4% body weight (BW) day⁻¹) and a maximum growth rate of 38 kJ kg⁻¹ day⁻¹. This finding is in agreement with the previous prediction of high energetic requirements for S. lewini. In combination with the hypothesized food limitation within Kāne‘ohe Bay, this result may explain the observed high mortality rates of S. lewini. Gross conversion efficiency, K ₁, ranged from −36% to 34%, with maximum efficiency at feeding levels of 5.1% BW day⁻¹. The growth conversion efficiency of S.␣lewini is similar to that of lemon sharks and teleost fishes. Growth rates of juvenile S. lewini are possibly restricted by their high metabolic rate, limited food availability and foraging inexperience. By directly examining the effect of ration size on growth and food conversion, it was possible to resolve discrepancies between earlier studies, which used respiratory metabolism and gut content analyses.     

Global-scale genetic identification of hammerhead sharks: Application to assessment of the international fin trade and law enforcement

The future status of sharks is an issue of widespread conservation concern due to declines in many species in the face of high levels of exploitation to satisfy market demands for products, especially fins. Substantial declines in the large-bodied hammerhead sharks, Sphyrna lewini, S. mokarran and S. zygaena, even in regions where some management occurs, indicate that informed conservation measures are warranted for these circumglobally distributed species. Despite the importance of assessing shark catch and trade on a species-specific basis to detect potential overexploitation of individual species, achieving this goal for hammerheads has proven elusive due to difficulties in identification of their products. Here, we present the development and application of a diagnostic, streamlined, five-primer multiplex polymerase chain reaction assay utilizing species-specific primers based on nuclear ribosomal ITS2 for the three hammerhead species throughout their global distribution. Application of this assay to investigations of the fin market confirmed the presence of hammerhead fins in the international trade. A study of the world’s largest fin market in Hong Kong revealed a high concordance between specific Chinese-name trade categories and fins from these three species (“Bai Chun” with S. lewini, “Gui Chun” with S. zygaena and “Gu Pian” with S.␣mokarran), and clear species preferences. This concordance information allows the use of market records for monitoring species-specific trends in trade and exploitation rates. The assay is also proving useful for identification of shark body parts in U.S. fisheries law-enforcement activities. Screening of morphologically identified “ S. lewini” from globally distributed areas using this assay with subsequent whole ITS2 sequencing suggests a cryptic species closely related to S. lewini occurs off the SE USA coast.     

Report on fetal mummification in the scalloped hammerhead shark Sphyrna lewini

This study describes the fetal mummification process in two embryos of a 310 cm total length scalloped hammerhead shark Sphyrna lewini caught in southeastern Brazil, in December 2017. Fourteen embryos were observed in total, in which two males in the left uterus presented different stages of mummification. Both mummified embryos were covered by an exudate (i.e., a mucous substance), indicating a hematic mummification process. All embryos were at the placentotrophic stage of development, indicating that they were close to parturition. An intrinsic characteristic is suggested as possible etiology for this condition, such as umbilical torsion, because both embryos were at different sizes and, therefore, at different development stages. In addition, the sample size did not allow the authors to presume any pollution effect once only one female was observed. Finally, fetal mummification and other embryonic development disorders might have populational impacts due to reduction in embryo survival and, consequently, recruitment. For this reason and considering that S. lewini is categorized as a “critically endangered species,” this study's results have conservational relevance.     

Potential expansion in the spatial distribution of subtropical and temperate west Australian sharks

Fishery-dependent and -independent data collected since 1975 were examined to explore the spatial distribution of 30 shark and ray species in the west coast of Australia. Bigeye sixgill (Hexanchus nakamurai), tiger (Galeocerdo cuvier) and spinner (Carcarhinus brevipinna) sharks, and scalloped hammerhead (Sphyrna lewini) were observed >1000 and 300 km to the east of the edge of their reported distributions. Broadnose sevengill sharks (Notorhyncus cepedianus) and southern sawsharks (Pristiophorus nudipinnis) were observed >1000 km to the west of the edge of their reported distributions. Our study highlights the value of collecting and examining long time-series of data for understanding the spatial distribution of large marine predators.     

Assessing multiple paternity in three commercially exploited shark species: Mustelus mustelus,Carcharhinus obscurus and Sphyrna lewini

In this study, multiple paternity (MP) was investigated in three commercially important shark species, common smoothhound Mustelus mustelus, dusky shark Carcharhinus obscurus and scalloped hammerhead Sphyrna lewini occurring in southern Africa. Reduced marker panels of between five and six microsatellite loci were constructed for each species and used to genotype and assess the presence of MP in a total of 60 M. mustelus individuals from six litters, 90 C. obscurus individuals from 14 litters and 54 S. lewini individuals from 13 litters. Analysis in GERUD and COLONY revealed the presence of MP in all three species. Multiple paternities were observed in 67, 35 and 46% of the litters of M. mustelus, C. obscurus and S. lewini, with corresponding average sire size of 1·6, 1·4 and 2·0, respectively. The variation in the rate of MP among the three species is in accordance with previous studies whilst the comparatively high frequency of MP observed for M. mustelus, matches what has previously been reported for shark species demonstrating aggregation behaviour.     

The Species and Origin of Shark Fins in Taiwan’s Fishing Ports,Markets, and Customs Detention: A DNA Barcoding Analysis

The increasing consumption of shark products, along with the shark’s fishing vulnerabilities, has led to the decrease in certain shark populations. In this study we used a DNA barcoding method to identify the species of shark landings at fishing ports, shark fin products in retail stores, and shark fins detained by Taiwan customs. In total we identified 23, 24, and 14 species from 231 fishing landings, 316 fin products, and 113 detained shark fins, respectively. All the three sample sources were dominated by Prionace glauca, which accounted for more than 30% of the collected samples. Over 60% of the species identified in the fin products also appeared in the port landings, suggesting the domestic-dominance of shark fin products in Taiwan. However, international trade also contributes a certain proportion of the fin product markets, as four species identified from the shark fin products are not found in Taiwan’s waters, and some domestic-available species were also found in the customs-detained sample. In addition to the species identification, we also found geographical differentiation in the cox1 gene of the common thresher sharks (Alopias vulpinus), the pelagic thresher shark (A. pelagicus), the smooth hammerhead shark (Sphyrna zygaena), and the scalloped hammerhead shark (S. lewini). This result might allow fishing authorities to more effectively trace the origins as well as enforce the management and conservation of these sharks.     

The biology and conservation status of the large hammerhead shark complex: the great,scalloped, and smooth hammerheads

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.     

Age,growth and maturity of the pelagic thresher Alopias pelagicus and the scalloped hammerhead Sphyrna lewini

Indonesia has the greatest reported chondrichthyan catches worldwide, with c.110,000 t caught annually. The pelagic thresher (Alopias pelagicus) and scalloped hammerhead (Sphryna lewini) together comprise about 25% of the total catches of sharks landed in Indonesia. Age and growth parameters were estimated for A. pelagicus and S. lewini from growth‐band counts of thin‐cut vertebral sections. Alopias pelagicus (n = 158) and S. lewini (n = 157) vertebrae were collected from three Indonesian fish markets over a 5 year period. A multi‐model analysis was used to estimate growth parameters for both species. The models of best fit for males and females for A. pelagicus was the three‐parameter logistic (L_∞ = 3169 mm L_T, k = 0·2) and the two‐parameter von Bertalanffy models (L_∞ = 3281 mm L_T, k = 0·12). Age at maturity was calculated to be 10·4 and 13·2 years for males and females, respectively, and these are the oldest estimated for this species. The samples of S. lewini were heavily biased towards females, and the model of best fit for males and females was the three‐parameter Gompertz (L_∞ = 2598 mm L_T, k = 0·15) and the two‐parameter Gompertz (L_∞ = 2896 mm L_T, k= 0·16). Age at maturity was calculated to be 8·9 and 13·2 years for males and females, respectively. Although numerous age and growth studies have previously been undertaken on S. lewini, few studies have been able to obtain adequate samples from all components of the population because adult females, adult males and juveniles often reside in different areas. For the first time, sex bias in this study was towards sexually mature females, which are commonly lacking in previous biological studies on S. lewini. Additionally, some of the oldest aged specimens and highest age at maturity for both species were observed in this study. Both species exhibit slow rates of growth and late age at maturity, highlighting the need for a re‐assessment of the relative resilience of these two globally threatened sharks at current high levels of fishing mortality throughout the eastern Indian Ocean.     

Age,growth and reproductive biology of the silky shark,Carcharhinus falciformis,and the scalloped hammerhead,Sphyrna lewini,from the northwestern Gulf of Mexico

Synopsis The silky shark, Carcharhinus falciformis, and scalloped hammerhead, Sphyrna lewini, represent >80% of the shark by-catch of the winter swordfish/tuna longline fishery of the northwestern Gulf of Mexico. This catch represents a potential supplemental fishery, yet little is known of the life histories of the two species. This report relates reproductive biology data to age and growth estimates for 135 C. falciformis and 78 S. lewini. Unlike other regional populations, C. falciformis in the Gulf of Mexico may have a seasonal 12 month gestation period. Males mature at 210–220 cm TL (6–7 yr); females at >225 cm TL (7–9 yr). Application of age at length data for combined sexes produced von Bertalanffy growth model parameter estimates of L_∞ = 291 cm TL, K = 0.153, t₀ = −2.2 yr. Adult male S. lewini outnumbered adult females in catches because of differences in the distributions of the sexually segregated population. Males mature at 180 cm TL (10 yr); females at 250 cm TL (15 yr). von Bertalanffy parameter estimates for combined sexes of this species were L_∞ = 329 cm TL, K = 0.073, t_o = −2.2 yr.     

Husbandry of scalloped hammerhead sharks Sphyrna lewini () at Reef HQ Aquarium,Townsville, Australia

Reef HQ Aquarium (Townsville, Australia) has successfully hosted two scalloped hammerhead sharks (Sphyrna lewini) in captivity in its 2.5 ML Coral Reef Exhibit since late 2011. Here we document this experience after 2.5 years including collection and period of acclimation to captivity, transport, introduction into display, husbandry issues encountered, behavioural observations, health and growth observations, and management considerations.     

Response of the hammerhead shark olfactory epithelium to amino acid stimuli

Sharks and rays are highly sensitive to chemical stimuli in their natural environment but several hypotheses predict that hammerhead sharks, with their expanded head and enlarged olfactory epithelium, have particularly acute olfactory systems. We used the electro-olfactogram (EOG) technique to compare the relative response of the scalloped hammerhead shark (Sphyrna lewini) olfactory epithelium to 20 proteinogenic amino acids and determine the sensitivity for 6 amino acids. At micromolar concentrations, cysteine evoked the greatest EOG response which was approximately twice as large as that of alanine. The weakest response was obtained for proline followed by aspartic acid and isoleucine. The olfactory epithelium showed adaptation to sequential stimulation, and recovery was related to the inter-stimulus time period. Estimated EOG response thresholds were in the sub-nanomolar range for both alanine (9.2 × 10⁻¹¹ M) and cysteine (8.4 × 10⁻¹⁰ M) and in the micromolar range for proline and serine. These thresholds from 10⁻¹⁰ to 10⁻⁶ M for the scalloped hammerhead shark are comparable or lower than those reported for other teleost and elasmobranch species. Future work should focus on binary and more complex compounds to test for competition and cross-adaptation for different classes of peripheral receptors, and their responses to molecules found in biologically relevant stimuli.     

Discovery of a multispecies shark aggregation and parturition area in the Ba Estuary,Fiji Islands

Population declines in shark species have been reported on local and global scales, with overfishing, habitat destruction and climate change posing severe threats. The lack of species‐specific baseline data on ecology and distribution of many sharks, however, makes conservation measures challenging. Here, we present a fisheries‐independent shark survey from the Fiji Islands, where scientific knowledge on locally occurring elasmobranchs is largely still lacking despite the location's role as a shark hotspot in the Pacific. Juvenile shark abundance in the fishing grounds of the Ba Estuary (north‐western Viti Levu) was assessed with a gillnet‐ and longline‐based survey from December 2015 to April 2016. A total of 103 juvenile sharks identified as blacktip Carcharhinus limbatus (n = 57), scalloped hammerhead Sphyrna lewini (n = 35), and great hammerhead Sphyrna mokarran (n = 11) sharks were captured, tagged, and released. The condition of umbilical scars (68% open or semihealed), mean sizes of individuals (±SD) (C. limbatus: 66.5 ± 3.8 cm, S. lewini: 51.8 ± 4.8 cm, S. mokarran 77.4 ± 2.8 cm), and the presence of these species over recent years (based on fishermen interviews), suggest that the Ba Estuary area is a critical habitat for multiple species that are classified as “Near Threatened” or “Endangered.” Specifically, the area likely acts as a parturition ground over the studied period, and potentially as a subsequent nursery area. We identified subareas of high abundance and found that temperature, salinity and depth acted as small‐scale environmental drivers of shark abundance. The data suggests a tendency for species‐specific spatial use, both horizontally (i.e., between sampling areas) and vertically (i.e., across the water column). These results enhance the understanding of shark ecology in Fiji and provide a scientific basis for the implementation of local conservation strategies that contribute to the protection of these threatened species.     

First observation on the mating behaviour of the endangered scalloped hammerhead shark <Emphasis Type="Italic">Sphyrna lewini</Emphasis> in the Tropical Eastern Pacific

Here we provide a detailed analysis of the first complete sequence of a mating event for the endangered scalloped hammerhead shark, Sphyrna lewini. This analysis is based on a mating event recorded at Isla del Coco National Park, Costa Rica, where large schools of hammerhead sharks are frequently encountered. S lewini mating sequence can be characterized by: (1) an open water encounter, (2) pre-copulatory biting, (3) grabbing of pectoral fin/copulation, (4) free fall, (5) separation and (6) following. Based on this single observation we found that only one male appears to be involved in a copulation cycle and that mating took place in a high current zone potentially to favor respiration when both individuals are unable to swim. This observation highlights the difficulty in observing mating behavior for this species since mating is likely to occur in open waters.