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Hammerhead sharks
Introduces readers to facts about hammerhead sharks, including physical features, habitat, life cycle, food, and more.
Book
Population structure and genetic connectivity of the scalloped hammerhead shark
Defining demographically independent units and understanding patterns of gene flow between them is essential for managing and conserving exploited populations. The critically endangered scalloped hammerhead shark, Sphyrna lewini, is a coastal semi-oceanic species found worldwide in tropical and subtropical waters. Pregnant females give birth in shallow coastal estuarine habitats that serve as nursery grounds for neonates and small juveniles, whereas adults move offshore and become highly migratory. We evaluated the population structure and connectivity of S. lewini in coastal areas and one oceanic island (Cocos Island) across the Eastern Tropical Pacific (ETP) using both sequences of the mitochondrial DNA control region (mtCR) and 9 nuclear-encoded microsatellite loci. The mtCR defined two genetically discrete groups: one in the Mexican Pacific and another one in the central-southern Eastern Tropical Pacific (Guatemala, Costa Rica, Panama, and Colombia). Overall, the mtCR data showed low levels of haplotype diversity ranging from 0.000 to 0.608, while nucleotide diversity ranged from 0.000 to 0.0015. More fine-grade population structure was detected using microsatellite loci where Guatemala, Costa Rica, and Panama differed significantly. Relatedness analysis revealed that individuals within nursery areas were more closely related than expected by chance, suggesting that S. lewini may exhibit reproductive philopatric behaviour within the ETP. Findings of at least two different management units, and evidence of philopatric behaviour call for intensive conservation actions for this highly threatened species in the ETP.
Journal Article
Discover hammerhead sharks
\"Introduces basic facts about hammerhead sharks, including their physical characteristics, diet, and habitat.\"--Provided by publisher.
Book
Stomach Content Analysis for Juvenile Great Hammerhead Sharks ISphyrna mokarran/I from the Arabian Gulf
The stomach contents of 30 male and 43 female (age < 3 years; 74-236 cm total length) juvenile great hammerhead sharks (Sphyrna mokarran (Rüppell, 1837)) obtained from commercial fisheries operating in Saudi Arabian waters of the Arabian Gulf were analyzed for the first time. After exclusion of parasites and abiotics, a total of 31 prey items, including the remains of cephalopods, fish, crustaceans, and bivalve mollusks, were identified in the stomachs of 59 great hammerheads. Based on the index of relative importance, teleosts were their main prey, and Platycephalus indicus (Linnaeus, 1758) was the most important prey at the species level. Significant age-related dietary differences were noted (F = 1.57, p = 0.026), indicating that the prey of the hammerheads aged 0-3 years shifted from Platycephalidae to Myliobatidae. Levin's niche overlap index was low (0.05-0.21), indicating that <3-year-old juvenile great hammerheads are specialized predators. The estimated trophic level was 4.40-5.01 (mean ± SD, 4.66 ± 0.45), indicating that the great hammerhead is a tertiary consumer.
Journal Article
The hammerhead shark
\"Engaging images accompany information about the hammerhead shark. The combination of high-interest subject matter and narrative text is intended for students in grades 3 through 7\" --Provided by publisher.
Book
Using stable isotopes analysis to understand ontogenetic trophic variations of the scalloped hammerhead shark at the Galapagos Marine Reserve
Changes in life-history requirements drive trophic variations, particularly in large marine predators. The life history of many shark species is still poorly known and understanding their dietary ontogeny is a challenging task, especially for highly migratory species. Stable isotope analysis has proven as a useful method for examining the foraging strategies of sharks and other marine predators. We assessed the foraging strategies and ontogenetic changes of scalloped hammerhead sharks, Sphyrna lewini , at Galapagos Marine Reserve (GMR), by analysing δ 13 C and δ 15 N signatures in different maturity stages. Our isotopic results suggest ontogenetic shifts in resource use between sub-adult and adult stages, but not between adult and juvenile stages. Carbon isotopic signatures found in the juvenile stage were enriched in contrast to sub-adults (~0.73‰) suggesting a combination of the maternal input and the use of coastal resources around the Galapagos Islands. Adult female sharks also showed enrichment in δ 13 C (~0.53‰) in comparison to sub-adult stages that suggest feeding in high primary productivity areas, such as the GMR. This study improves the understanding of the trophic ecology and ontogenetic changes of a highly migratory shark that moves across the protected and unprotected waters of the Eastern Tropical Pacific.
Journal Article
Hammerhead sharks
\"Hammerhead sharks are unique for their strange head shape, their great vision, and their ability to find their prey with special organs. Find out how this amazing fish catches its meals\"--Back cover.
Book
Population structure and genetic connectivity of the scalloped hammerhead shark (Sphyrna lewini) across nursery grounds from the Eastern Tropical Pacific: Implications for management and conservation
Defining demographically independent units and understanding patterns of gene flow between them is essential for managing and conserving exploited populations. The critically endangered scalloped hammerhead shark, Sphyrna lewini , is a coastal semi-oceanic species found worldwide in tropical and subtropical waters. Pregnant females give birth in shallow coastal estuarine habitats that serve as nursery grounds for neonates and small juveniles, whereas adults move offshore and become highly migratory. We evaluated the population structure and connectivity of S . lewini in coastal areas and one oceanic island (Cocos Island) across the Eastern Tropical Pacific (ETP) using both sequences of the mitochondrial DNA control region (mtCR) and 9 nuclear-encoded microsatellite loci. The mtCR defined two genetically discrete groups: one in the Mexican Pacific and another one in the central-southern Eastern Tropical Pacific (Guatemala, Costa Rica, Panama, and Colombia). Overall, the mtCR data showed low levels of haplotype diversity ranging from 0.000 to 0.608, while nucleotide diversity ranged from 0.000 to 0.0015. More fine-grade population structure was detected using microsatellite loci where Guatemala, Costa Rica, and Panama differed significantly. Relatedness analysis revealed that individuals within nursery areas were more closely related than expected by chance, suggesting that S . lewini may exhibit reproductive philopatric behaviour within the ETP. Findings of at least two different management units, and evidence of philopatric behaviour call for intensive conservation actions for this highly threatened species in the ETP.
Journal Article
Shifts in the habitat suitability for large hammerhead sharks under climate change
One of the chief consequences of climate change is the worldwide redistribution of species in the pursuit of physiologically and ecologically favourable conditions. As part of one of the most threatened groups of vertebrates, assessing how climate change may affect the distribution patterns of key shark species is essential for their long-term conservation and management. The present study aims to assess how climate change projections (based on the representative concentration pathways 2.6, 4.5, 6.0, and 8.5) for the middle and end of the century may affect the global patterns of habitat suitability (HS) for large hammerhead sharks – a unique and particularly threatened group of elasmobranchs. Here, a decline in the global average HS is projected for both
Sphyrna lewini
and
Sphyrna zygaena
, with the scale of HS decline generally increasing with time and RCP severity, while a global increase in HS is generally projected for
Sphyrna mokarran
, albeit reduced over the long-term and overturned under long-term RCP8.5. Meanwhile, poleward shifts are projected for all three species, with considerable tropical declines for both
S. lewini
and
S. zygaena
. Additionally, regional shifts in suitability have the potential to affect population connectivity, the access to key habitats, and levels of exposure to other anthropogenic pressures, along with the effectiveness of conservation and management efforts. Taken together, these results showcase the importance of climate change for species’ extinction risk assessments and the urgency of the consideration of climate change within the design and implementation of conservation measures.
Journal Article