A minimally invasive technique to assess several life‐history characteristics of the endangered great hammerhead shark Sphyrna mokarran

A dorsal‐fin photo‐identification technique paired with a non‐invasive parallel laser photogrammetry technique was used to non‐invasively identify individual Sphyrna mokarran over time. Based on the data collected over a duration of 59 days, 16 different S. mokarran (mean ± s.d . pre‐caudal length: 220·82 ± 13·66 cm; mean ± s.d . cephalofoil width: 71·38 ± 7·94 cm) were identified using dorsal‐fin photo‐identification, with a mean ± s.d . shark re‐sighting frequency of 4·05 ± 3·06 at‐sea days. The results illustrate a high S. mokarran sighting rate and therefore, the utilization of parallel laser photogrammetry and dorsal‐fin photo‐identification may be a plausible multi‐year approach to aid in non‐invasively determining the growth rate and inter‐annual site fidelity of these animals.     

Vulnerability to longline fisheries of three hammerhead shark Sphyrna species in the south‐western and equatorial Atlantic Ocean

Catch and effort data from 29 418 longline sets from Brazilian tuna longline vessels operating in the south‐western and equatorial Atlantic Ocean between 2004 and 2011 were analysed to investigate the distribution, catch rate and size of three species of hammerhead sharks (Sphyrna lewini, Sphyrna mokarran and Sphyrna zygaena). During that period, 6172 hammerhead sharks were caught. Among the elasmobranchs, the highest percentage of hammerhead sharks were caught in 2007, when they accounted for 3·90% of the group, while the lowest value of 0·40% was recorded in 2010. In general, the spatial distribution of the mean catch per unit effort (CPUE) by years and quarters showed a trend of higher catches near the equatorial region and in southern Brazil. The nominal mean CPUE was 0·12 Sphyrna spp. 1000⁻¹ hooks, with the highest value being recorded in 2007 (0·30 Sphyrna spp. 1000⁻¹ hooks). The standardized yearly CPUE estimated by a generalized linear model assuming a zero inflated negative binomial (ZINB) distribution were not much different from nominal values. Of the 205 sexed specimens, 117 were females and 88 were males, resulting in a sex ratio with a predominance of females (1·30:1·00), although not statistically significant. The total length of females ranged from 1200 to 2800 mm and of males from 1100 to 3100 mm. Juvenile hammerhead sharks represented 82 and 54% of the sexed female and male specimens, respectively.     

Resource use of great hammerhead sharks (Sphyrna mokarran) off eastern Australia

Great hammerhead sharks Sphyrna mokarran are the largest member of Sphyrnidae, yet the roles of these large sharks in the food webs of coastal ecosystems are still poorly understood. Here we obtained samples of muscle, liver and vertebrae from large S. mokarran (234–383 cm total length; L_T) caught as by-catch off eastern Australia and used stable-isotope analyses of δ¹⁵N, δ¹³C and δ³⁴S to infer their resource use and any associated ontogenetic patterns. The results indicated large S. mokarran are apex predators primarily relying on other sharks and rays for their diet, with a preference for benthic resources such as Australian cownose rays Rhinoperon neglecta during the austral summer. Teleosts, cephalopods and crustaceans were not significant components of S. mokarran diets, though some conspecifics appeared to rely on more diverse resources over the austral summer. Ontogenetic shifts in resource use were detected but trajectories of the increases in trophic level varied among individuals. Most S. mokarran had non-linear trajectories in ontogenetic resource-use shifts implying size was not the main explanatory factor. Stable isotope values of δ¹³C and δ³⁴S in muscle suggest S. mokarran span coastal, pelagic and benthic food webs in eastern Australia.     

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.     

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.     

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.     

Adult blacktip sharks (Carcharhinus limbatus) use shallow water as a refuge from great hammerheads (Sphyrna mokarran)

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.     

Shallow water tidal flat use and associated specialized foraging behavior of the great hammerhead shark (Sphyrna mokarran)

Evidence suggests the great hammerhead shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of shark due to its cryptic nature and wide-ranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great hammerhead shark utilizes an inshore shallow water flats environment (<1.5?m in depth), five of which involve prey capture. These observations permitted identification of two novel behaviors that may allow great hammerheads to inhabit these shallow habitats: a (1) prey-capture technique termed ‘grasp-turning’ that involves burst swimming at tight turning angles while grasping prey and (2) a post-predation recovery period whereby the shark maintains head-first orientation into the current that may facilitate respiration and prey consumption. These behavioral observations provide insights into the natural history of this species.     

Microstructural morphology in early dermal denticles of hammerhead sharks (Elasmobranchii: Sphyrnidae) and related taxa

Mello, W.C., de Carvalho, J.J., Brito, P.M.M. 2011. Microstructural morphology in early dermal denticles of hammerhead sharks (Elasmobranchii: Sphyrnidae) and related taxa. —Acta Zoologica (Stockholm) 00 : 1–7. This study uses scanning electron microscopies to investigate and describe the microstructural diversity of dermal denticles in the family Sphyrnidae, which comprises all living hammerhead shark species, comparing them to other related taxa (i.e. Carcharhinus dussumieri, Carcharhinus plumbeus, Carcharhinus acronotus, Rhizoprionodon acutus, Negaprion brevirostris and Hemigaleus microstoma). The results reveal that sphyrnids present noticeable microstructures in the dermal denticles, distinguishing them from the other related species investigated. Additionally, scale patterns are the same in three distinct body regions (i.e. cephalic, branchial and dorsal fin). Species of Sphyrnidae that reach bigger total lengths and that are widely distributed (i.e. Sphyrna lewini and Sphyrna mokarran) presented more, smaller and nearly hexagonal microstructures that do not cover the entire scale surface, unlike species reaching smaller sizes and restricted to coastal habits (i.e. Sphyrna tiburo, Sphyrna tudes, Sphyrna media and Eusphyra blochii). The sphyrnid scales are similar to R. acutus and C. dussumieri rather than to the other species, but it is not possible to identify the sphyrnid species only by scale features. It is clear that a similar morphology of scales is not necessarily related to similar life habits, and that they are candidates to provide new characters in phylogenetical studies among sphyrnids.     

Historical records reveal potential extirpation of four hammerhead sharks (Sphyrna spp.) in Mexican Pacific waters

Populations of hammerhead sharks (Sphyrna and Eusphyra) have declined in many regions of the world. Six of the eight hammerheads known to date are distributed in the Mexican Pacific: S. corona, S. lewini, S. media, S. mokarran, S. tiburo and S. zygaena. These species, with exception of S. corona, were abundant in the Gulf of California in 1960s. I analyze records from fishery-dependent and fishery-independent surveys, and records from ichthyological collections to determine the presence and frequency of hammerheads in the Mexican Pacific. The most frequent hammerheads in fishery-dependent and fishery-independent surveys were S. lewini and S. zygaena. It appears that S. media, S. mokarran and S. tiburo might have been extirpated from the Gulf of California. In the last two decades, records of S. mokarran (n = 61) were restricted to Central and Southern Mexican Pacific, and records of S. tiburo (n = 3) and S. media (n = 3) were restricted to the Southern region. Given the continued fishing pressure, inferred declines and the probable extirpation of populations, S. tiburo and S. media should be reassessed for the IUCN red list as Endangered or Critically Endangered. Sphyrna corona should be reassessed as Endangered or Critically Endangered, because it is endemic to the Eastern Pacific and recent records have been obtained only from Colombian waters. The Endangered status of S. mokarran is confirmed for this region.     

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.     

A Novel Mini-DNA Barcoding Assay to Identify Processed Fins from Internationally Protected Shark Species

There is a growing need to identify shark products in trade, in part due to the recent listing of five commercially important species on the Appendices of the Convention on International Trade in Endangered Species (CITES; porbeagle, Lamna nasus, oceanic whitetip, Carcharhinus longimanus scalloped hammerhead, Sphyrna lewini, smooth hammerhead, S. zygaena and great hammerhead S. mokarran) in addition to three species listed in the early part of this century (whale, Rhincodon typus, basking, Cetorhinus maximus, and white, Carcharodon carcharias). Shark fins are traded internationally to supply the Asian dried seafood market, in which they are used to make the luxury dish shark fin soup. Shark fins usually enter international trade with their skin still intact and can be identified using morphological characters or standard DNA-barcoding approaches. Once they reach Asia and are traded in this region the skin is removed and they are treated with chemicals that eliminate many key diagnostic characters and degrade their DNA (“processed fins”). Here, we present a validated mini-barcode assay based on partial sequences of the cytochrome oxidase I gene that can reliably identify the processed fins of seven of the eight CITES listed shark species. We also demonstrate that the assay can even frequently identify the species or genus of origin of shark fin soup (31 out of 50 samples).     

Smooth hammerhead sharks (<Emphasis Type="Italic">Sphyrna zygaena</Emphasis>) observed off the Portuguese southern coast

Despite its worldwide distribution and vulnerable status, knowledge on the biology and ecology of the smooth hammerhead Sphyrna zygaena in the temperate NE Atlantic is very scarce. Here, we reveal intra-annual fluctuations in S. zygaena abundance in the Portuguese southwestern coast, using sightings data collected on board whale watching boats over five years (2010–14; excluding winter months). Moreover, we investigated how shark abundance is related to local environmental conditions. We describe the first smooth hammerhead “hotspot” in the NE Atlantic, and we show a recurrent pattern of occurrence during the warmer summer and autumn months (from July to October) near Sagres and Martinhal Bay and islands. Intra-annual variations in abundance were significantly associated with sea surface temperature and negatively related with upwelling index and chlorophyll a, suggesting horizontal movements linked to the seasonal changes. Hence, hammerheads moved inshore during the warmer periods (with low primary productivity), due to either direct influence of temperature in their movements or indirect influence in prey distribution. This hammerhead “hotspot” may constitute a nursery ground for S. zygaena, nevertheless, our data does not allow us to prove or refute such claim. Future telemetry-based studies should be conducted to fully understand hammerhead movements and habitat preferences, and to evaluate this “hotspot” as a critical habitat for this predator.     

Population structure and cryptic speciation in bonnethead sharks Sphyrna tiburo in the south‐eastern U.S.A. and Caribbean

Population structure and lineage diversification within a small, non‐dispersive hammerhead shark species, the bonnethead shark Sphyrna tiburo, was assessed. Sphyrna tiburo is currently described as one continuously distributed species along the Atlantic continental margins of North, Central and South America, but recent genetic analysis of an insular population (Trinidad) suggests the possibility of cryptic speciation. To address this issue S. tiburo were sampled at six sites along c. 6200 km of continuous, continental coastline and from one island location (Grand Bahama) across a discontinuity in their distribution (the Straits of Florida), in order to test if they constitute a single lineage over this distribution. A total of 1030 bp of the mitochondrial control region (CR) was obtained for 239 S. tiburo, revealing 73 distinct haplotypes, high nucleotide diversity (0·01089) and a pair of highly divergent lineages estimated to have separated 3·61–5·62 million years ago. Mitochondrial cytochrome oxidase I and nuclear internal transcribed spacer loci show the same pattern. Divergence is similar within S. tiburo to that observed between established elasmobranch sister species, providing further evidence of cryptic speciation. A global AMOVA based on CR confirms that genetic diversity is primarily partitioned among populations (Φ_ST = 0·828, P < 0·001) because the divergent lineages are almost perfectly segregated between Belize and North America–The Bahamas. An AMOVA consisting solely of the North American and Bahamian samples is also significantly different from zero (Φ_ST = 0·088, P < 0·001) and pairwise F_ST is significantly different between all sites. These findings suggest that S. tiburo comprises a species complex and supports previous research indicating fine population structure, which has implications for fisheries management and biodiversity conservation.     

Possible female philopatry of the smooth hammerhead shark Sphyrna zygaena revealed by genetic structure patterns

We assessed the spatial pattern of genetic structure of smooth hammerhead shark Sphyrna zygaena in 10 localities from the Northern Mexican Pacific. A total of 35 haplotypes were identified in 129 sequences of the mtDNA control region. The results showed slight but significant genetic structure among localities (Φ_ST = 0.044, P < 0.001). In addition, the localities with highest number of juveniles were genetically different (Φ_ST = 0.058, P < 0.024), which may be representative of nursery areas. The genetic differentiation pattern can be associated to female philopatry and preference for particular birthing sites. Finally, historical demography shows that S. zygaena populations present a recent demographic expansion that occurred during glacial events in the late Pleistocene to early Holocene.     

Big catch,little sharks: Insight into Peruvian small‐scale longline fisheries

Shark take, driven by vast demand for meat and fins, is increasing. We set out to gain insights into the impact of small‐scale longline fisheries in Peru. Onboard observers were used to document catch from 145 longline fishing trips (1668 fishing days) originating from Ilo, southern Peru. Fishing effort is divided into two seasons: targeting dolphinfish (Coryphaena hippurus; December to February) and sharks (March to November). A total of 16,610 sharks were observed caught, with 11,166 identified to species level. Of these, 70.6% were blue sharks (Prionace glauca), 28.4% short‐fin mako sharks (Isurus oxyrinchus), and 1% were other species (including thresher (Alopias vulpinus), hammerhead (Sphyrna zygaena), porbeagle (Lamnus nasus), and other Carcharhinidae species (Carcharhinus brachyurus, Carcharhinus falciformis, Galeorhinus galeus). Mean ± SD catch per unit effort of 33.6 ± 10.9 sharks per 1000 hooks was calculated for the shark season and 1.9 ± 3.1 sharks per 1000 hooks were caught in the dolphinfish season. An average of 83.7% of sharks caught (74.7% blue sharks; 93.3% mako sharks) were deemed sexually immature and under the legal minimum landing size, which for species exhibiting k‐selected life history traits can result in susceptibility to over exploitation. As these growing fisheries operate along the entire Peruvian coast and may catch millions of sharks per annum, we conclude that their continued expansion, along with ineffective legislative approaches resulting in removal of immature individuals, has the potential to threaten the sustainability of the fishery, its target species, and ecosystem. There is a need for additional monitoring and research to inform novel management strategies for sharks while maintaining fisher livelihoods.     

Antioxidant defense of fish collagen peptides attenuates oxidative stress in gastric mucosa of experimentally ulcer-induced rats

The aim of the present study was to investigate the ability of fish collagen peptides (FCP) from the skin of great hammerhead shark (Sphyrna mokarran) to avert the occurrence of gastric ulcer in experimental rats. FCP treatment prevented the formation of ulcerative lesions on gastric tissues with 86% of inhibition. The histopathology analysis of gastric tissue revealed that the FCP intake prevented the occurrence of hemorrhage and erosion in gastric tissue with formation of mild edema and necrosis, as well as normalized the pH and volume of gastric juice. It also downregulated the expression of pro-inflammatory marker interferon-ɤ (IFN-ɤ) and upregulated the anti-inflammatory marker interleukin-4 (IL-4) in gastric tissue. FCP is capable to modulate the oxidative stress by enhancing the activity of antioxidant defense enzymes superoxide dismutase (SOD) and catalase and by lowering the levels of membrane lipid peroxidation.     

Residency of the scalloped hammerhead shark (<Emphasis Type="Italic">Sphyrna lewini</Emphasis>) at Malpelo Island and evidence of migration to other islands in the Eastern Tropical Pacific

Sixty nine hammerhead sharks, Sphyrna lewini, were tagged at Malpelo Island (Colombia) with ultrasonic transmitters during March 2006, 2007 and 2008, as part of a study to understand their residency at the island and their horizontal and vertical movements. Five sharks visited Cocos Island, 627 km distant from Malpelo. One of the sharks that appeared at Cocos Island also visited the Galapagos Islands, 710 km from Cocos, a month later. There is connectivity of Sphyrna lewini between Malpelo, Cocos and the Galapagos Islands, but the frequency of movements between the islands appears to be relatively low (<7% of the tagged sharks). The most common depth at which the sharks swam coincided with the thermocline (rs = 0.72, p < 0.01). The depth of the thermocline varied depending on the time of the year. Nocturnal detections of the sharks were more frequent during the cold season than during the warm season (W = 60, p < 0.01). We also found that hammerheads spent significantly more time on the up-current side of the island (Kruskal-Wallis = 31.1008; p < 0.01). This study contributes to the knowledge of hammerhead sharks not only in Malpelo Island but also at a regional level in the Eastern Tropical Pacific.     

Identification of a nursery area for the critically endangered hammerhead shark (Sphyrna lewini) amid intense fisheries in the southern Gulf of Mexico

Since the 1980s, there has been growing concern in the Mexican Atlantic regarding high catches of neonate and juvenile sharks in small-scale fisheries. Fishery-dependent data from 1993 to 1994 and 2007 to 2017 and fishers' ecological knowledge from 2017 were used to identify nursery areas for scalloped hammerhead, Sphyrna lewini, in the southern Gulf of Mexico. Catch records and fishing areas of neonates, YOYs, juveniles and adults of S. lewini (N = 1885) were obtained from calcareous and terrigenous regions in the western Yucatan Peninsula. The results suggest that a nursery for scalloped hammerhead is found in the terrigenous region, characterized by relatively shallow and turbid waters due to rivers’ discharges. Neonates and YOYs (96% and 86% of their total records, respectively) were commonly found there over the years in May–August in multiple fishing areas identified by fishers, although mainly between isobaths 10–30 m. The enforcement of management measures is necessary because the nursery is located in a region with intense fishing effort.     

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.