Sphyrna Zygaena Research Articles

Landings of Sphyrna zygaena (Linnaeus, 1758) in northern Peru indicate a lack of adult specimens

A commercial fishery for the smooth hammerhead shark (Sphyrna zygaena) exists in the waters off northern Peru. Although international and domestic norms regulate this species, adult specimens are becoming rare. Monthly visits to four ports in the La Libertad region were made to measure S. zygaena landings and understand the present state of the fishery. We found that 92% of the specimens landed were juveniles or younger and that 10% of the original biomass remains in the fishery. This highlights that stricter regulations such as protecting breeding areas, establishing a legal catch length, and limiting the catch volume and fishing season are urgently needed to maintain a sustainable fishery.

Resource partitioning in hammerhead shark species out-migrating from coastal ecosystems in the Gulf of California

Juveniles of large hammerhead shark species occupy coastal nurseries before migrating offshore to reproduce. In the central Gulf of California, artisanal elasmobranch fisheries have reported catches of juvenile scalloped Sphyrna lewini and smooth S. zygaena hammerhead sharks, but their local foraging habits are yet to be fully understood. In this study, the trophic niches of both hammerhead species as well as of sympatric Pacific sharpnose sharks Rhizoprionodon longurio were investigated using stable isotope values (δ13C, δ34S and δ15N) and fatty acid compositions in whole blood and muscle tissues. Despite interspecific similarities among trophic niches, smooth hammerheads were characterized by lower δ13C, higher δ34S and greater proportion of docosahexaenoic acid (DHA) in both tissues, suggesting they were already partly relying on offshore pelagic resources. For scalloped hammerheads, muscle reflected coastal dietary resources, while offshore trophic markers were detected in blood integrating prey signal over shorter time periods, indicating their more recent initiation of ontogenetic migration. Multidimensional niche calculation revealed low overlap between hammerhead shark trophic niches, implying that potential fine-scale differences in habitat use could reduce competition between these morphologically and ecologically similar species. In the meantime, the isotopic niches of juvenile scalloped and smooth hammerheads were smaller than that of Pacific sharpnose sharks, suggesting they could be more specialized consumers. Overall, the identification of foraging grounds for juvenile hammerhead sharks calls for a future characterization of their residency time in coastal ecosystems to further understand their interactions with fishing pressure in the Gulf of California.

Local adaptive variation in a highly migratory fish: The smooth hammerhead shark Sphyrna zygaena

Populations of highly mobile species that undertake long distance migrations are typically considered to be panmictic. Nonetheless, mechanisms related to behavior or local environmental conditions promote genetic isolation in the absence of physical barriers. Highly migratory shark species exhibit varying levels of fidelity to specific regions, shaping the genetic architecture of different populations and resulting in geographically based genetic variation with potential adaptive value. An understanding of the genetic variation of highly migratory species is needed to develop effective conservation strategies. This study aimed to assess the neutral and adaptive variation of the smooth hammerhead shark (Sphyrna zygaena) in the northern Mexican Pacific (NMP) via single nucleotide polymorphisms (SNPs). We analyzed 1480 SNPs in 92 individuals from four geographic regions in the NMP, of which 1469 SNPs were neutral loci (n-SNP), and 11 were putatively under selection (o-SNP) using four genoma scan methods. Genetic diversity was geographically similar among regions (Ho = 0.275). The neutral variation showed panmixia (n-SNPs; FST = 0.0012, p = 0.44), which may be associated with the high dispersal capacity of S. zygaena. A pattern of adaptive variation between individuals from the Gulf of California and Pacific coast was revealed using o-SNPs FST-based methods (24 oSNPs; FST = 0.061, p < 0.001), which may be promoted by individual preferences based on physiological limitations. The estimated effective population size (Ne) of S. zygaena was 1390 individuals, which is theoretically optimal for the population to persist over time.

Trophic ecology and coastal niche partitioning of two sympatric shark species in the Azores (mid-Atlantic)

The exploitation of marine resources has caused drastic declines of many large predatory fishes. Amongst these, sharks are of major conservation concern due to their high vulnerability to overfishing and their ecological role as top predators. The 2 protected and endangered shark species tope Galeorhinus galeus and smooth hammerhead Sphyrna zygaena use overlapping coastal areas around the globe as essential fish habitats, but data to assess their trophic ecology and niche partitioning are scarce. We provide the first comparative assessment of the trophic ecology, ontogenetic shifts, and niche partitioning of the co-occurring tope and juvenile smooth hammerhead around the Azores Islands, mid-north Atlantic, based on δ13C, δ15N, and δ34S (CNS) stable isotope analysis of muscle tissue of the sharks and their putative prey species. Overall, isotopic niches of both species indicated a reliance on similar resources throughout the sampled sizes (tope: 35-190; smooth hammerhead 54-159 cm total length), with significant ontogenetic shifts. Topes displayed a gradual shift to higher trophic levels and a more generalist diet with increasing size (increasing δ15N values and isotopic niche volumes, respectively), whereas smooth hammerhead diet shifted towards prey with lower δ34S at a constant trophic level and a more specialized diet than tope of comparable body size (decreasing δ34S and constant δ15N and δ13C values, respectively). Our results indicate contrasting ontogenetic shifts in δ13C and δ34S along with pronounced differences between niche overlap of life stages pointing to intra- and interspecific niche partitioning of habitat and prey.

DNA barcoding continues to identify endangered species of shark sold as food in a globally significant shark fin trade hub.

Shark fins are a delicacy consumed throughout Southeast Asia. The life history characteristics of sharks and the challenges associated with regulating fisheries and the fin trade make sharks particularly susceptible to overfishing. Here, we used DNA barcoding techniques to investigate the composition of the shark fin trade in Singapore, a globally significant trade hub. We collected 505 shark fin samples from 25 different local seafood and Traditional Chinese Medicine shops. From this, we identified 27 species of shark, three species are listed as Critically Endangered, four as Endangered and ten as Vulnerable by the International Union for Conservation of Nature (IUCN). Six species are listed on CITES Appendix II, meaning that trade must be controlled in order to avoid utilization incompatible with their survival. All dried fins collected in this study were sold under the generic term "shark fin"; this vague labelling prevents accurate monitoring of the species involved in the trade, the effective implementation of policy and conservation strategy, and could unwittingly expose consumers to unsafe concentrations of toxic metals. The top five most frequently encountered species in this study are Rhizoprionodon acutus, Carcharhinus falciformis, Galeorhinus galeus, Sphyrna lewini and Sphyrna zygaena. Accurate labelling that indicates the species of shark that a fin came from, along with details of where it was caught, allows consumers to make an informed choice on the products they are consuming. Doing this could facilitate the avoidance of species that are endangered, and similarly the consumer can choose not to purchase species that are documented to contain elevated concentrations of toxic metals.

The Importance of Understanding the Current Status of Critically Endangered Species in Shark Fisheries in Muncar, Indonesia

One-third of all elasmobranch species are classified as globally threatened (i.e., vulnerable, endangered, or critically endangered) according to the IUCN Red List of Threatened Species, The Sphyrnidae family, once among the most abundant shark species complexes, now faces one of highest extinction risks by the IUCN in 2019. This study aimed to analyse the total catch of Sphyrnidae in Muncar, East Java, Indonesia, from 2020 to 2023, and to evaluate the proportion of Sphyrnidae catches relative to other shark during this period. The research utilized both primary and secondary data sources, with daily enumeration conducted, using guidebooks, rulers, hand scales, cameras, code tags, plastic mats, and identification books. The results revealed that most Sphyrnidae catches over the past four years were Sphyrna lewini, with 653 females and 433 males recorded. In contrast, Sphyrna mokarran and Sphyrna zygaena were only landed in minimal numbers over the entire period. Furthermore, S. lewini accounted for less than 15% of the total shark catch, with an average of 58 shark species caught annually. The use of fishing gear by fishers operating vessels under 5 Gross Tonnage (GT) with gillnets in the 10-28 GT range with longlines was identified as significant factor influencing catch composition.”

Isotopic trajectories and interspecific niche partitioning in tropical pelagic sharks

Pelagic sharks are top predators with key role in the structure and functioning of ocean ecosystems. However, little is known on their assemblage-wide trophic ecology. Specifically, fundamental data gaps exist over how trophic niches of pelagic sharks diverge both intra- and inter-specifically. To address this question, multi-tissue stable isotope analysis is a powerful tool that enables the quantification of trophic dynamics of mobile predators throughout ontogeny and across species. In this study, we utilized stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) of tissues with varying turnover rates (muscle, red blood cells, liver, and plasma) to assess individual niche trajectories (i.e., temporal isotopic variation), population isotopic niche width, and isotopic niche overlap across five shark species (n = 155) in the eastern tropical Pacific Ocean: silky (Carcharhinus falciformis), blue (Prionace glauca), smooth hammerhead (Sphyrna zygaena), bigeye thresher (Alopias superciliosus), and the pelagic thresher shark (A. pelagicus). Overall, the relationship between isotopic niche trajectory length and body size was not significant, indicating that the magnitude of ontogenetic dietary variation does not increase in larger individuals. Pelagic sharks had variable feeding strategies over short-long time scales, likely reflecting species-specific responses to seasonality of prey availability and foraging location. Observed interspecific differences in isotope values indicate a degree of trophic niche partitioning across the five pelagic shark species. These data suggest ontogenetic niche shifts in pelagic sharks potentially differ from more coastal tied species and reveal species-specific ecological roles, but further studies on the diet and fine-scale habitat use are required to verify these results.

Identification Of Bycatch Sharks In The India Ocean Based On DNA Barcoding In Conservation Effort

The most potential shark fishing area in Indonesia is the Indian Ocean. One of the fishing ports that has bycatch shark is Benoa Harbor. The purpose of this research is to identify species to determine the conservation status of bycatch shark species from body tissue samples caught in the Indian Ocean in conservation efforts. The research was conducted from January to March 2021 at Pangkalan Pengawasan Sumber Daya Kelautan dan Perikanan (PSDKP) of Benoa Harbor. This study uses an exploratory method with survey techniques. The data used in this study are primary data in the form of shark fin samples in the study area and secondary data in the form of locations where sharks are caught by fishermen based on the PSDKP database. The results showed that sharks bycatch from body tissue samples caught in the Indian Ocean based on morphological identification and DNA barcoding techniques were Prionace glauca, Isurus paucus, Sphyrna zygaena, Isurus oxyrinchus, Alopias superciliosus and Carcharhinus longimanus. Bycatch sharks from body tissue samples caught in the Indian Ocean based on morphological identification and DNA barcoding techniques have close phylogenetic relationships with the Carcharhinidae, Sphyrnidae, Alopiidae and Lamnidae families. Bycatched shark from body tissue samples caught in the Indian Ocean based on morphological identification and DNA barcoding techniques has a conservation status, near threatened for Prionace glauca species, vulnerable for Sphyrna zygaena species and Alopias superciliosus species, endangered for Isurus paucus species and Isurus oxyrinchus species, critically endangered for Carcharhinus longimanus species.

Marine megafauna interactions with the Peruvian artisanal purse-seine fleet

Bycatch is a global problem for marine megafauna. Peru is a major fishing nation known in particular for its industrial purse-seine fishery for the Peruvian anchovy (Engraulis ringens). However, Peru also has an artisanal purse-seine fishery for this same resource and other species such as Pacific bonito (Sarda chiliensis), Pacific chub mackerel (Scomber japonicus) and Chilean jack mackerel (Trachurus murphyi) used for human consumption. While there is limited documentation of bycatch of megafauna by the industrial purse-seine fishery, there is no similar information for the artisanal purse-seine fishery. Therefore, this study aimed to assess the marine megafauna (small-cetaceans, seabirds, sea turtles, and elasmobranchs) bycatch interactions of the Peruvian artisanal purse-seine fishery for consumption for the year 2019 (before the COVID-19 pandemic) through interviews with artisanal fishers in 5 landing ports (San Jose, Santa Rosa, Callao, Pucusana, and San Andres). We found that these fisheries had bycatch with all taxa groups, with dusky dolphins (Lagenorhynchus obscurus), guanay cormorants (Leucocarbo bougainvilliorum) and eagle rays (Myliobatis spp.) having the highest quantity and most frequently reported bycatch. Multiple correspondence analysis (MCA) indicated an association between the bycatch of 1–3 common dolphins (Delphinus spp.) per set from the northern ports (San Jose and Santa Rosa) and vessels of 20–36 MT. Likewise, a relationship was found between smooth hammerhead sharks (Sphyrna zygaena) and vessel storage capacity, with a similar result reported for the bycatch of humpback smoothhounds (Mustelus whitneyi). In addition, a relationship of eagle ray (Myliobatis spp.) bycatch with a landing port was identified, and several respondents mentioned catching more than 1 MT per set. Fifty-three percent of fishers considered bycatch to be a problem, mainly because it wastes their time during fishing operations. This preliminary study is the first research that demonstrates bycatch in artisanal purse-seine in Peru and can serve as a baseline for future research. We also highlight the need to quantify bycatch rates of marine megafauna using additional methodologies, such as monitoring with onboard observers.

Estimation of the population status of smooth hammerhead shark (Sphyrna zygaena) and scalloped hammerhead shark (Sphyrna lewini) in the Northwest Pacific Ocean: A data-limited approach

While data on fisheries, in general, may be limited, demographic models provide a valuable tool for gaining insights into population dynamics when a more comprehensive understanding is not feasible. Demographic models may be used in the study of population dynamics because they only require life history parameters. We performed a quantitative population projection on the basis of expert knowledge, estimated mortality, and published information on the life history of two hammerhead shark species, smooth hammerhead (Sphyrna zygaena) and scalloped hammerhead (Sphyrna lewini), and we conducted an elasticity analysis determine the sensitivity of each life stage to the population growth rate. This study highlights the overexploitation challenges faced by these two ecologically important and vulnerable species and emphasizes the need to reduce fishing mortality is crucial to achieving population growth. To increase the accuracy of demographic estimates for these species, it is necessary to conduct further investigations into their natural mortality and reproductive traits. The approach used in this study can be applied to other shark species across a diverse range of taxa with limited data on catch and effort. Moreover, this method is easy to use and interpret and can be used to predict future population size for data-limited species.

Umbrella terms conceal the sale of threatened shark species: A DNA barcoding approach

Food fraud in the seafood industry is a growing concern, including the authenticity and provenance of seafood products that are often unable to be confidently verified along complex, and at times obscure, supply chains. Among the diverse types of seafood fraud, mislabelling and species substitution are common, and have potential implications on human health, the economy, and species conservation. In particular, shark meat can be difficult to monitor, associated with the use of an array of convoluted nomenclature or ambiguous umbrella terms. In Australia, shark meat fillets are a popular seafood item sold under the umbrella term flake in takeaways, and fish and chip shops. We collected samples of flake as sold to consumers at 104 retailers in South Australia and used DNA barcoding to determine the shark species being traded. At least nine distinct species were identified, with only 27% of all samples identified as gummy shark (Mustelus antarcticus), a species that has sustainable fisheries, is locally caught, and is one of two species that is recommended to be labelled as flake in Australia. Four species were threatened taxa, including the CITES Appendix II listed short-fin mako (Isurus oxyrinchus) and smooth hammerhead (Sphyrna zygaena). Of all the samples and shops analysed, only 11% of retailers correctly identified the species they sold, another 20% were mislabelled and the remaining only had ambiguous labelling. Ultimately, the umbrella term flake allowed for species misrepresentation but DNA barcoding was an effective tool to test ambiguous labelling in processed and cooked shark meat products, and can guide policy, management, and compliance efforts to mitigate mislabelling, empowering consumers to make informed decisions and champion sustainable seafood.

Molecular identification of sharks and rays species from Aceh waters, Indonesia

Shark is a cartilaginous fish that is widely hunted because it has high economic value. The waters of Aceh are directly adjacent to the Indian Ocean and the Malacca Strait making it a preferred habitat for pelagic fish, especially sharks. Information on shark species landed in the waters west and east of Aceh is very limited due to difficulties in identification and commonly used local names. This study aimed to determine the types of sharks landed in Banda Aceh, Meulaboh, Langsa, Southwest Aceh and Simeulu and to find out specifically what species of sharks are most often landed in Aceh waters. Primary data gathering consisted of four stages, namely sample collection, identification using identification books, molecular identification cytochrome oxidase subunit I (COI) and phylogenetic analysis. The results of the molecular analysis of 46 tissue samples from five locations identified 13 species of sharks, namely Carcharhinhus sorrah, Carcharhinhus amboinensis, Triaenodon obesus, Isurus oxyrinchus, Sphyrna zygaena, Sphyrna lewini, Loxodon macrorhinus, Hemipristis elongaria, Stagostoma fasciatum, Nebrius ferrugineus, Chilloscyllium punctatum, Isurus oxyrinchus, Alopias pelagicus, Alopias supercillosus and 1 species of rays, namely Rhynchobatus australiae. Phylogenetic tree reconstruction using the Neighbor Joining method of 610 basepairs consisting of two large clades separates the species Alopias pelagicus and Isurus oxyrichus with Carcharhinus sorrah, Sphyrna lewini, Loxodon macrorhinus and Rhyncobatus australiae with boostrap values of 87% and 64%. The haplotype diversity shown ranged from 0.667-0.889 while the nucleotide diversity ranged from 0.001-0.097. These values indicates high diversity because of the variance in the number of species found.Keywords:BarcodeCOISharks catchAlopias supercillosusSphyrna lewini

Mercury isotope clocks predict coastal residency and migration timing of hammerhead sharks

Abstract The management of migratory taxa relies on the knowledge of their movements. Among them, ontogenetic habitat shift, from nurseries to adult habitats, is a behavioural trait shared across marine taxa allowing resource partitioning between life stages and reducing predation risk. As this movement is consistent over time, characterizing its timing is critical to implement efficient management plans, notably in coastal areas to mitigate the impact of fisheries on juvenile stocks. In the Mexican Pacific, habitat use of the smooth hammerhead shark (Sphyrna zygaena) is poorly described, while the species is heavily harvested. Given the large uncertainties associated with the timing of out‐migration from coastal nursery grounds to offshore waters prior to reproductive maturity, a more precise assessment of smooth hammerhead shark movements is needed. Photochemical degradation of mercury imparts mass‐independent isotope fractionation (Δ199Hg) which can be used to discriminate between neonate coastal shallow habitats and the offshore deep foraging patterns of late juveniles. Here, we present the application of muscle Δ199Hg as molecular clocks to predict the timing of ontogenetic habitat shifts by smooth hammerhead sharks, based on their isotopic compositions at the initial and arrival habitats and on muscle isotopic turnover rate. We observed decreases in Δ199Hg values with shark body length, reflecting increasing reliance on offshore mesopelagic prey with age. Coastal residency estimates indicated that smooth hammerhead sharks utilize coastal resources for 2 years prior to offshore migration, suggesting a prolonged residency in these ecosystems. Policy implications. This study demonstrates how mercury stable isotopes and isotopic clocks can be implemented as a complementary tool for stock management by predicting the timing of animal migration—a key aspect in the conservation of marine taxa. In the Mexican Pacific, fishing pressure on shark species occurs in coastal habitats depleting juvenile stocks. Consequently, management decision support tools are imperative for effectively maintaining early life stage population levels over time. The finding that smooth hammerhead sharks extensively rely on highly fished habitats for 2 years after parturition supports the relevance of establishing a size limit in coastal fisheries and demonstrates how the current temporal shark fishing closure could lack efficiency for the species.

Acoustic tracking of a threatened juvenile shark species, the smooth hammerhead (Sphyrna zygaena), reveals vulnerability to exploitation at the boundary of a marine reserve

The coastal waters of South Africa are habitat to a diverse composition of sharks that are vulnerable to exploitation, many of which are endemic and/or classified by the International Union for Conservation of Nature (IUCN) Red List as Threatened or Data Deficient. Accordingly, this region has been identified as a global research and conservation priority for elasmobranchs. The De Hoop Marine Protected Area (MPA), in the Western Cape Province of South Africa, provides 288 km2 of no-take protection within its boundaries. However, the region experiences heavy commercial fishing, with two vessels actively operating as dedicated shark longliners (as of 2022). When crossing MPA boundaries, sharks are susceptible to capture by these vessels. Utilizing passive acoustic telemetry, the present study evaluated the movements of a threatened juvenile shark species, the smooth hammerhead (Sphyrna zygaena), both inside and adjacent to the De Hoop MPA, and along the greater coastline. Movement data from 20 tagged sharks were used to explore the effects of spatial, environmental, and management variables on their residency and movement patterns. Results indicate a high reliance of sharks on unprotected waters immediately adjacent to the MPA’s eastern boundary, an area of high biological productivity due to its proximity to the mouth of an estuary. Although some tagged sharks did move regionally along the South African coastline, individuals spent 95% of their days detected just outside the eastern boundary of the MPA, rendering them vulnerable to commercial shark longlining occurring there. These findings have conservation implications for smooth hammerhead sharks in South Africa and present an opportunity to revisit management practices that may optimize spatial protection for an important life stage of this threatened species.

Phylogenetic placement and molecular dating of hammerhead sharks (Sphyrnidae) based on whole mitogenomes

ABSTRACT Due to continued overexploitation and anthropogenic change, hammerhead sharks (Carcharhiniformes: Sphyrnidae) have experienced drastic declines over most of their geographic range. Owing to the K-selected life histories of these sharks, their population resilience and persistence, remain severely strained, further compromising ecosystem stability. Moreover, some species are largely understudied e.g. the cryptic congener, the Carolina hammerhead shark (Sphyrna gilberti), whilst specific regions, such as the South-West Indian Ocean (SWIO), remain relatively devoid of data, risking the eventual extirpation of unique hammerhead shark lineages. The aim of the present study was to verify the phylogenetic placement of the cryptic S. gilberti within the family Sphyrnidae through the inclusion of underrepresented species sequences in order to provide a more comprehensive phylogenetic perspective for understanding historical drivers of Sphyrnidae biodiversity. The present study describes the first complete mitochondrial genome of the cryptic S. gilberti originating from the US Atlantic, as well as the mitogenomes of smooth hammerhead shark (Sphyrna zygaena) and scalloped hammerhead shark (Sphyrna lewini) samples originating from the data deficient South-West Indian Ocean (SWIO). Furthermore, we estimate the phylogenetic interrelationships of the Sphyrnidae family using mitochondrial protein-coding (PCG) and rRNA genes, reaffirming the placement of S. gilberti as a sister lineage to S. lewini. The resulting phylogenetic estimate is further used to evaluate the most likely age of the first occurrence of S. gilberti, corresponding to the Late Miocene to Early Pleiocene Epoch (3.8–10.8 million years ago). Comparative analysis of these Sphyrnids between ocean basins, as well as preliminary divergence estimates for S. lewini and S. gilberti has contributed towards resolving the global hammerhead phylogeny. This has provided unique insights into the evolution of the genus, thereby aiding future efforts directed towards effective conservation and management of hammerhead populations over a larger spatial scale.

Trophic niche partitioning of five sympatric shark species in the tropical eastern Pacific Ocean revealed by multi-tissue fatty acid analysis

Fatty acid (FA) analysis of consumer tissues has recently shown utility in drawing further inferences about trophic niche dynamics of marine predators such as sharks. In this study, we examined liver, plasma, and muscle FAs in five coexisting pelagic sharks (blue (Prionace glauca), silky (Carcharhinus falciformis), bigeye thresher (Alopias superciliosus), pelagic thresher (Alopias pelagicus), and smooth hammerhead (Sphyrna zygaena)) inhabiting the tropical eastern Pacific Ocean. Results showed complex inter- and intra-individual and tissue variation among the five shark species. Based on multivariate analysis of the muscle FAs, P. glauca and C. falciformis have the largest FA niche widths, indicating diverse feeding habits or habitat isolation, whereas A. pelagicus and S. zygaena occupied a narrower niche width, reflecting increased trophic specialization. High percentages of muscle FA niche overlap indicated strong resource competition between S.zygaena and C. falciformis and a degree of dietary isolation by P. glauca. Interpretations of feeding ecology differed based on the analysis of plasma FAs, which could be attributed to higher dietary FA turnover rates. The liver was deemed unsuitable to examine FA niche metrics based on high and unexplained intra-specific variance in liver FAs as well as the unique lipid metabolism in chondrichthyans. Overall, our multi-tissue approach revealed the magnitude of potential competitive interactions among coexisting tropical shark species. It also expanded our understanding of inter-tissue variability and best practices when using FA analysis to estimate trophic niche metrics of sharks.

The Multi-Annual Residency of Juvenile Smooth Hammerhead Shark in an Oceanic Island Nursery

The increased risk of local extinction becomes critical for sharks depending on the narrow and isolated coastal habitats of oceanic islands. This includes large pelagic oceanic sharks that use such habitats as nurseries, as previously hypothesized for the smooth hammerhead Sphyrna zygaena, the least known of cosmopolitan large hammerhead sharks. We used a combination of acoustic and satellite telemetry in a juvenile population of Faial and Pico islands, Azores, mid-north Atlantic, to confirm if this isolated archipelago holds nurseries, and to answer questions related to their function and spatial–temporal stability. Our long-term acoustic tracking data showed a cluster of individual core home ranges in specific areas of north shore Faial, and surface positions from five Argos-linked tagged individuals also showed a clustering overlap in those areas for up to 1 year. These patterns seem to reveal a true habitat preference within the Faial-Pico island (sub) population of juvenile smooth hammerhead shark, and thus constitute strong evidence for this area to be considered a nursery. Some individuals remained in this nursery for up to 4 years, especially during summers. Sharks also showed a strong diel behavior, typically using the inshore nurseries during the day and moving further offshore during the night, during which they increased activity and dove deeper, most possibly to feed. We speculate that a combination of increased feeding opportunities, expanded trophic niche, and reduced predatory pressure may be a key evolutionary driver for the existence, prolonged use, and even preference of coastal nurseries at oceanic islands by juvenile smooth hammerhead shark. Given that these nurseries may constitute essential fish habitat for this species, they should be explicitly included in spatial management measures at the local and regional scales, as they may also play a role of greater importance to the north Atlantic population of this oceanic species.

Gillnet selectivity for non‐targeted shark species in temperate Australia

AbstractThe use of size‐selective fishing gear has been fundamental for the successful management of shark populations. For the main Australian shark fisheries, available data sets on gillnet selectivity experiments conducted since the 1990s were used to estimate gillnet selectivity parameters for nine commonly caught non‐target species: broadnose, draughtboard, Port Jackson and school sharks, common and southern sawsharks, smooth hammerhead and spikey and whitespotted dogfish. Size at selection increased with mesh size, but it varied with species, with some species having broader selectivity curves due to their particular morphological features. In particular, smooth hammerhead had much broader selectivity curves and larger length at maximum selection than other species of comparable size such as the broadnose shark. The selectivity curves derived in this study will allow a more accurate interpretation of catch size composition and model‐based assessments of stock status of these species

Preliminary study on spatio-temporal variations of five giant and 17 large fish species around the Korean peninsula from 2011 to 2016

Although giant and large fish species are highly important as a keystone species in the marine ecosystem, there have been no or few studies on their spatio-temporal variations around the Korean peninsula. For this, we analyzed daily reports made by observers at 57 fishery landing sites in Korea over 6 years, from 2011 to 2016. In total, 153 fish species were re-identified based on photos and descriptions recorded by Korean observers, of which five species were classified as a giant fish over 5 m in maximum total length (MTL) and 17 species as a large fish from 3 m to 5 m MTL according to the data presented by Froese &amp; Pauly (2021). Among the giant and large fish species, Mola mola was the most abundant species, with 75 individuals landed as by-catch. The second most abundant species was Isurus oxyrinchus (31), followed by Mobula mobular (23), Lamna ditropis (17), Masturus lanceolatus (16), Sphyrna zygaena (14), and Prionace glauca (12). As a result of cluster analysis based on the number of individuals of giant and large fish species by year and sea, six years were separated into two clusters (2011–2013 vs. 2014–2016), with high contribution of M. mola, I. oxyrinchus, and M. lanceolatus; and three seas were separated into two clusters (eastern + southern seas vs. western sea), with high contribution of M. lanceolatus, L. ditropis, and I. oxyrinchus. The largest number of M. mola accounted for 64% of the total in 2014 and 2016, and 71% in summer (June–August). It is assumed to have a correlation between seawater temperature fluctuation and the occurrence of giant and large fish species. Our study highlights importance of longterm monitoring of giant and large fish species, and can help to understand the life cycle such as natal or nursery migration of giant and large fish species around the Korean peninsula.

Unreported discards of internationally protected pelagic sharks in a global fishing hotspot are potentially large

Global abundances of oceanic pelagic sharks have declined due to overfishing. Internationally protected shark species remain at risk due to indiscriminate bycatch in longline fisheries with under-reported catches affecting reliability of population assessments for management. However, the scale of under-reporting remains poorly understood. Here we use detailed shark species catch data in a global fishing hotspot to show that the discards of three globally or regionally ‘Endangered’ or ‘Critically Endangered’ species (bigeye thresher Alopias superciliosus; oceanic whitetip Carcharhinus longimanus; smooth hammerhead Sphyrna zygaena) are potentially under-reported on a large scale: the total discards made by a single observed vessel in April–June 2018 in the eastern tropical Atlantic exceeded by 1.3–11.0 times the discards reported officially for these species Atlantic-wide for all of 2018. Scaling up observed catches (discards) of a single vessel to potential discards made by a single nation's fleet in the region, we estimate a mean annual total of 1526.2 t (±1 S.D. range: 415.3–2637.0 t), which exceeds by 89.2 times (±1 S.D. range: 24.3–154.2 times) the official reported discards for these three species. Without reducing bycatch mortality, which at present appears obscured by substantial under-reporting, Atlantic populations remain at serious risk.