Shark Research Articles

Epigonal Conditioned Media from Bonnethead Shark, Sphyrna tiburo, Induces Apoptosis in a T-Cell Leukemia Cell Line, Jurkat E6-1

Representatives of Subclass Elasmobranchii are cartilaginous fish whose members include sharks, skates, and rays. Because of their unique phylogenetic position of being the most primitive group of vertebrates to possess all the components necessary for an adaptive immune system, the immune regulatory compounds they possess may represent the earliest evolutionary forms of novel compounds with the potential for innovative therapeutic applications. Conditioned medium, generated from short term culture of cells from the epigonal organ of bonnethead sharks (Sphyrna tiburo), has been shown to have potent reproducible cytotoxic activity against a variety of human tumor cell lines in vitro. Existing data suggest that epigonal conditioned medium (ECM) exerts this cytotoxic activity through induction of apoptosis in target cells. This manuscript describes apoptosis induction in a representative tumor cell line, Jurkat E6-1, in response to treatment with ECM at concentrations of 1 and 2 mg/mL. Data indicate that ECM exposure initiates the mitochondrial pathway of apoptosis through activation of caspase enzymes. Future purification of ECM components may result in the isolation of an immune-regulatory compound with potential therapeutic benefit for treatment of human cancer.

THE CIRCULATING BLOOD CELLS OF TORPEDOES (TORPEDO MARMORATA RISSO AND TORPEDO OCELLATA RAFINESQUE)

SUMMARY The literature on elasmobranch peripheral blood cells is reviewed and the results of light and electron microscope studies of 15 specimens of Torpedo marmorata Risso and 8 specimens of Torpedo ocellata Rafinesque (Pisces Torpedinidae) are presented. The haematological mean values observed were: haemoglobin 3.22 g/100 ml; haematocrit 24.54; red cells 201160/mm3; white cells 43870/mm3; thrombocytes 19530/mm3; MCV 1039μm3; MCH 149 pg; MCHC 13%. On blood smears stained with M.G.G. and peroxidase-benzidine reaction, the following cells were identified and described: mature erythrocytes, acidophilic erythroblasts (17.5%), basophilic erythroblasts (1.7%), lymphocytes, monocytes, eosinophilic granulocytes, neutrophilic granulocytes and thrombocytes. An ultrastructural study of these cells and their specific granules is included.

RE-DESCRIPTION OF THE EXTERNAL MORPHOLOGY OF SOMNIOSUS ROSTRATUS (RISSO, 1826), WITH SPECIAL REFERENCE TO ITS SQUAMATION AND CUTANEOUS SENSORY ORGANS, AND ASPECTS OF THEIR FUNCTIONAL MORPHOLOGY (PISCES SELACHII SQUALIDAE)

SUMMARY The availability of a new S. rostratus (Risso, 1826) specimen (Pisces Selachii Squalidae), the re-examination of two museum collections and a survey of literature on the subject has provided the opportunity to clarify some problems concerning this shark and other species of the genus Somniosus. The main topics investigated were morphometric characters, squamation morphogenesis, distribution of cutaneous sensory organs and modified scales. Morpho-functional problems are discussed, with special reference to hydrodynamic aspects. The little sleeper, S. rostratus, has a typical squaloid morphology. In all ontogenetic stages, a peculiar short keel occurs in the caudal peduncle, above the ventral hypochordal lobe. The function of the keel could be to improve turning ability and/or to act as a stabilizer. The caudal morphology belongs to the squaloid type (THOMSON & SIMANEK, 1977) and differs from that of the strictly benthic species. On this basis we therefore believe that S. rostratus is a benthopelagi...

Sharks whip their tails to stun prey

Sharks whip their tails to stun prey

The effects of cage-diving activities on the fine-scale swimming behaviour and space use of white sharks

Wildlife tourism has become increasingly popular and is one of the fastest growing sectors of the tourism industry. A radio-acoustic positioning system was deployed to monitor the fine-scale movements of 21 white sharks (Carcharodon carcharias) and investigate the effects of shark cage-diving activities on their swimming behaviour and space use. This study contributes towards improving our understanding of the complex relationship between wildlife tourism and its effects on sharks, and assesses how tourism targeting sharks affects behaviour at a finer spatial scale than previously investigated. Our study demonstrated that shark cage-diving operators (SCDO) influenced the fine-scale three-dimensional spatial distribution and the rate of movement of white sharks at the Neptune Islands. White sharks stayed more than 30 m away from the SCDO on 21 % of the days detected, but spent a significant amount of time in close proximity to the SCDO on the remaining days. Individual variation was detected, with some sharks behaviourally responding to SCDO more than others. The degree of variation between individual sharks and the different levels of interaction (e.g. presence, proximity to SCDO, and consumption of tethered bait) highlights the complexity of the relationships between SCDO and the effects on sharks. To improve our understanding of these relationships, future monitoring of shark cage-diving operations requires proximity to SCDO to be recorded in addition to the presence within the area. Further work is needed to assess whether the observed behavioural changes would affect individual fitness and ultimately population viability, which are critical information to unambiguously assess the potential impacts of wildlife tourism targeting sharks.

A NEAR-FATAL SHARK ATTACK BY A MAKO IN THE NORTHERN RED SEA

ABSTRACT On 7 September 1974 a girl swimmer, aged 20, and a male companion swam about 500 m offshore from North Beach, Hat, Red Sea. At about 5 p.m. the girl was attacked by a shark of about 2 m length. She was bitten approximately 12 times by the shark before being rescued. Most of the wounds were on the distal half of the limbs; surprisingly, almost no tissue was removed by the shark. The girl barely survived; ultimately it was necessary to amputate her lower left arm. Two days later a shortfin mako shark (Isurus oxyrinchus), 2.33 m total length, was caught in a wier at Elat. Mako teeth are long and prong-like without serrations. Comparison of an imprint of the shark's teeth in plastic to the tooth marks from a bite on the victim's right thigh revealed that a mako of the same size, very possibly the same shark, had bitten her. Three shark attacks which had been attributed to makos are shown to involve other species. Two other incidents in which mako identity seems certain resulted in contact with humans...

THE CHALLENGES OF PISCINE VIVIPARITY

ABSTRACT Viviparity in vertebrates first appeared among fishes where it had independently evolved at least 42 times in five of the nine major groups. It is the dominant mode of reproduction among sharks and rays, but less prevalent among bony fishes. The evolution of viviparity from oviparity involves: (1) a shift from external to internal fertilization, (2) retention of embryos in the female reproductive system, (3) utilization of the ovary or oviduct as sites of gestation, (4) structural and functional modification of the embryo and the female reproductive system, and (5) modification of extant endocrine systems controlling reproduction. Retention of developing young to term in the maternal reproductive system poses a series of physiological challenges. The challenges are reflected in the new maternal-embryonic relationships that evolved in viviparous fishes, namely: (1) trophic, (2) osmoregulatory and excretory, (3) respiratory, (4) endocrinological, and (5) immunological. In sharks, rays, and the coel...

ON DEEP-WATER SHARKS CAUGHT OFF THE MEDITERRANEAN COAST OF ISRAEL

ABSTRACT Four species of sharks were recently collected at depths of 1330–1440 m off the eastern Mediterranean coast of Israel. The occurrence of Somniosus rostratus is a first record, while Centrophorus granulosus and Dalatias licha are the first substantiated records in this region. The record of Galeus melastomus at the depth of 1440 m increases its bathymetrie range.

The complete mitochondrial genome of the grey bamboo shark (Chiloscyllium griseum) (Orectolobiformes: Hemiscylliidae): genomic characterization and phylogenetic application

The complete mitochondrial genome of the grey bamboo shark, Chiloscyllium griseum (Orectolobiformes: Hemiscylliidae) was obtained, with a total of 16 755 base pairs (bp). The mitogenome encoded 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs and a noncoding control region, a gene arrangement identical to the most common type found in vertebrates. All tRNA sequences were folded into typical cloverleaf secondary structure with the exception of tRNA-Ser2, in which the DHU arm stem was replaced with 12 unpaired nucleotides and formed a simple loop. In the control region, the putative termination-associated sequences (TAS) with hairpin-loop structure and the conserved sequence blocks (CSB) I-III were identified and considered to be associated with the replication and transcription of mtDNA. No repeat motifs were found in the mitogenome of C. griseum. On the basis of the mitogenomic data available in the Class Chondrichthyes from both Genbank and this study, and the phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) methods, the results strongly support the basal division between batoids and sharks and the monophyly of the Superorder Galeomorphii, and confirm the phylogenetic position of C. griseum in the Subclass Elasmobranchii. This study suggests that the mitogenomic data are more robust for reconstructing phylogenetic relationships than individual genes in the Elasmobranchii.

A Rapid Assessment Technique to Assist Management of the White Shark (Carcharodon Carcharias) Cage Dive Industry, South Australia

Port Lincoln, South Australia is the departure port for the only white shark, Carcharodon carcharias, cage dive industry in Australia. Established in the early 1960’s as a niche tourism venture, the industry has recently undergone a rapid expansion to accommodate greater passenger numbers, more tourism operators, and additional infrastructure aimed at capturing a greater proportion of the tourist dollar. However, to date, there has been no assessment of growth in the industry. We have used the operator logbook system, introduced in 2000, as the basis for a rapid assessment of the maturity as well as a conservative estimate of the economic value of the industry, with a focus on 2011. From the logbook system the number of days on-site has increased from an average of 67 days per year prior to 2007 to 287 days on-site in 2011. In 2011 the industry accommodated approximately 5200 passengers with a direct domestic expenditure estimated to be in excess of 6 million AUD. Changes in shark behaviour have been observed following the increase in days on-site. The white shark cage dive industry has reached a stage in its development where increased management is required in order to ensure a viable industry into the future. The rapid assessment technique described herein will allow managers to track changes in cage dive participation rates and quickly respond to changes in the industry.

Changing relative abundance and behaviour of silky and grey reef sharks baited over 12 years on a Red Sea reef

There is a lack of studies on how provisioning may influence shark numbers and behaviour. The effects of long-term provisioning were investigated at a Red Sea reef, where both grey reef shark (Carcharhinus amblyrhynchos) and silky shark (Carcharhinus falciformis) occurred. Initially, grey reef sharks outnumbered silky sharks, but over 6 years, silky shark numbers increased almost 20-fold, whereas grey-reef sightings decreased >90%. Following this, silky-shark sightings also declined considerably (>80%). It is suggested that these declines could relate to local overfishing. Many silky sharks were identified individually through distinctive markings or conventional tagging. Some individual silky sharks were recorded regularly over 2 years or more, but most appeared to be transient visitors. Sighting records indicated that provisioning extended the residency of transient individuals. If visiting silky sharks were drawn from a larger regional population, this would explain both their initial accumulation and why, to begin with, sightings were sustained despite local fishing pressure. Conversely, the site fidelity typical of grey reef sharks would have made them more susceptible to local depletion. Silky sharks were recorded as behaving more boldly when present in greater numbers, but the decline in grey reef sharks appears to be unrelated to the initial increase in the numbers of silky shark.

The effects of shark cage-diving operations on the behaviour and movements of white sharks, Carcharodon carcharias, at the Neptune Islands, South Australia

The attraction or provisioning of sharks for the purpose of tourism is a lucrative and popular industry that remains controversial regarding its possible risks to target species and impacts on local ecosystems. The long-term impacts of such activities on the behaviour and movement patterns of sharks have typically been difficult to establish as most studies investigate contemporary behaviour concurrent with existing operations and thus have no comparative base from which to compare effects. We compared patterns of residency and behaviour of acoustic-tagged white sharks at the Neptune Islands in South Australia between periods before and after an abrupt and sustained doubling of cage-diving effort that occurred in 2007. The number of sharks reported by cage-dive operators significantly increased after 2007. Comparisons also revealed there were significant increases in sharks’ periods of residency, the periods spent within areas where shark cage-diving operations occur and changes in sharks’ diel pattern of habitat use. Changes were site-specific with no significant differences in shark behaviour revealed over the same period at an island group 12 km from regular shark cage-dive sites. The results suggest that cage-diving operations can lead to long-term changes in the site-specific behaviour of a highly vagile shark species which may need to be considered in the context of their conservation and in managing the impacts of the industry.

Surface behaviour of bait-attracted white sharks at Dyer Island (South Africa)

Six research expeditions were conducted at Dyer Island to observe the surface behaviour of white sharks in the presence of bait. Observations were made from a commercial cage-diving boat. We observed 140 white sharks that exhibited 9 different types of behaviour: parading, bait following, visual inspection, breach, tail slap, tail stand, spy hop, repetitive aerial gaping, and head-up vertical emerging. Breach and tail slap were most often performed by male sharks, and tail slap and tail stand were more often performed by mature animals. The ethogram consisted of an average of 20 behavioural units, with a significant transitional pattern from bait follow to parading and from parading to bait follow. The individual surface behaviour of white sharks is not a simple stimulus–response reflex, but rather a complex tactical situation in which animals show plastic responses. Many aspects of white shark surface behaviour resemble those of other predator species that spend time at the surface.

The Effect of Processing Conditions on the Extraction Yield and Melting Point of Whitecheek Shark (Carcharhinus dussumieri) Skin Gelatin

To investigate the optimum conditions for extracting gelatin from whitecheek shark (Carcharhinus dussumieri (skin, response surface methodology (RSM) has been adopted. In this research, the effect of NaOH concentration (0.01-1 N), HCl concentration (0.01-1 N), and extraction time (3-8 h) on dependent variables, yield and melting point of the skin gelatin have been studied using central composite design. Based on the individual regression models, predict values of multiple response at optimal condition were %23.222 (yield), and 32.224 °C (melting point). The best pretreatment conditions to get to the optimum properties were 0.01 N NaOH, 0.135 N HCl and 3 h extraction time. The results showed that, NaOH and HCl concentrations had significant effects, but extraction time had no significant effect on gelatin extraction yield and its melting point.

Eating or Meeting? Cluster Analysis Reveals Intricacies of White Shark (Carcharodon carcharias) Migration and Offshore Behavior

Elucidating how mobile ocean predators utilize the pelagic environment is vital to understanding the dynamics of oceanic species and ecosystems. Pop-up archival transmitting (PAT) tags have emerged as an important tool to describe animal migrations in oceanic environments where direct observation is not feasible. Available PAT tag data, however, are for the most part limited to geographic position, swimming depth and environmental temperature, making effective behavioral observation challenging. However, novel analysis approaches have the potential to extend the interpretive power of these limited observations. Here we developed an approach based on clustering analysis of PAT daily time-at-depth histogram records to distinguish behavioral modes in white sharks (Carcharodon carcharias). We found four dominant and distinctive behavioral clusters matching previously described behavioral patterns, including two distinctive offshore diving modes. Once validated, we mapped behavior mode occurrence in space and time. Our results demonstrate spatial, temporal and sex-based structure in the diving behavior of white sharks in the northeastern Pacific previously unrecognized including behavioral and migratory patterns resembling those of species with lek mating systems. We discuss our findings, in combination with available life history and environmental data, and propose specific testable hypotheses to distinguish between mating and foraging in northeastern Pacific white sharks that can provide a framework for future work. Our methodology can be applied to similar datasets from other species to further define behaviors during unobservable phases.

The effect of familiarity on aggregation and social behaviour in juvenile small spotted catsharksScyliorhinus canicula

This study was designed to address whether juvenile small spotted catsharks Scyliorhinus canicula aggregate and to determine whether potential aggregation is underpinned by social preferences for conspecifics. Using controlled and replicated experiments, the role of familiarity as a potential mechanism driving aggregation and social behaviour in this species was considered. Observed S. canicula association data compared to null model simulations of random distributions revealed differences in aggregation under different social contexts. Only familiar juvenile S. canicula aggregated more than would be expected from random distribution across their habitat. Familiarity increased the mean number of groups but did not significantly affect mean group size. Significant preference and avoidance behaviour across all groups were also observed. Furthermore, the strength of social attraction, quantified by the mean association index, was significantly higher in groups containing familiar individuals. Mixed familiar and unfamiliar treatments were also conducted to test for within- and between-group effects, finding high variation across replicates with some groups assorting by familiarity and others not. It is believed that this study is the first to examine experimentally the influence of conspecific familiarity on aggregation behaviour in sharks. These results not only imply a functional benefit to aggregation, but also suggest that persistent social affiliation is likely to influence dispersal following hatching in this small benthic elasmobranch.

Feeding chronology of six species of carcharhinid sharks in the western North Atlantic Ocean as inferred from longline capture data

Time-at-capture data for 6 species of carcharhinid sharks were collected during 2692 fishery-independent longline sets conducted in the western North Atlantic Ocean from 1995 through 2009. As operations occurred continuously throughout the diel cycle, time-at-capture data were used as a proxy for natural feeding behavior to examine the diel feeding chronology of blacknose Carcharhinus acronotus, spinner C. brevipinna, bull C. leucas, blacktip C. limbatus, sandbar C. plumbeus, and Atlantic sharpnose Rhizoprionodon terraenovae sharks. All 6 species were collected during all hours of the diel cycle; however, application of circular statistics revealed that spinner, bull, blacktip and sandbar sharks increased their feeding activity during nocturnal hours. Atlantic sharpnose and blacknose sharks exhibited no significant directedness in time-of- capture, indicating that these 2 species lack distinct feeding patterns. The species-specific differ- ences in feeding chronologies of the sharks examined demonstrate that broad generalizations concerning the feeding behavior of sharks are not appropriate.

Consistent movement traits indicative of innate behavior in neonate sharks

Breaking down animal movements into quantifiable metrics provides an opportunity to define patterns within movement. Here, long-term telemetry data of blacktip sharks (Carcharhinus limbatus) from 1999 to 2002 were used to define movement patterns of neonate individuals. Movement was described by measures of central tendency and dispersion in distance moved, linearity of movement, bearing of movement and activity space size. These metrics were considered to define the movements on which behavior of juvenile blacktip sharks were built. Distance moved, bearing variance and activity space metrics revealed a significant increase among months suggesting longer movement steps and more variable movement over time. Movement patterns were consistent and non significant between years and there was little correlation with length (R2<0.06) or sex of individuals. There was no significant effect of fate of the individual (survival, fished or natural mortality) on movement metrics. Results indicated similarity among the movement metrics of individuals and across naive cohorts, indicating innate behavior. Individuals in all years increased use of space through time suggesting an ontogenetic shift in behavior and habitat use. The results of this study demonstrated that examining movement metrics provides a useful approach to examining behavior in mobile species.

What is an ‘elasmobranch’? The impact of palaeontology in understanding elasmobranch phylogeny and evolution

The Subclass Elasmobranchii is widely considered nowadays to be the sister group of the Subclass Holocephali, although chimaeroid fishes were originally classified as elasmobranchs along with modern sharks and rays. While this modern systematic treatment provides an accurate reflection of the phylogenetic relationships among extant taxa, the classification of many extinct non-holocephalan shark-like chondrichthyans as elasmobranchs is challenged. A revised, apomorphy-based definition of elasmobranchs is presented in which they are considered the equivalent of neoselachians, i.e. a monophyletic group of modern sharks and rays which not only excludes all stem and crown holocephalans, but also many Palaeozoic shark-like chondrichthyans and even close extinct relatives of neoselachians such as hybodonts. The fossil record of elasmobranchs (i.e. neoselachians) is reviewed, focusing not only on their earliest records but also on their subsequent distribution patterns through time. The value and limitations of the fossil record in answering questions about elasmobranch phylogeny are discussed. Extinction is seen as a major factor in shaping early elasmobranch history, especially during the Triassic. Extinctions may also have helped shape modern lamniform diversity, despite uncertainties surrounding the phylogenetic affinities of supposedly extinct clades such as cretoxyrhinids, anacoracids and odontids. Apart from these examples, and the supposed Cretaceous extinction of 'sclerorhynchids', elasmobranch evolution since the Jurassic has mostly involved increased diversification (especially during the Cretaceous). The biogeographical distribution of early elasmobranchs may be obscured by sampling bias, but the earliest records of numerous groups are located within the Tethyan realm. The break-up of Gondwana, and particularly the opening of the South Atlantic Ocean (together with the development of epicontinental seaways across Brazil and Africa during the Cretaceous), provided repeated opportunities for dispersal from both eastern (European) and western (Caribbean) Tethys into newly formed ocean basins.

Effect of Human Body Position on the Swimming Behavior of Bull Sharks, Carcharhinus leucas

AbstractThis study tested whether human body orientation can influence the behavior of bull sharks by examining sharks’ approach distances from a person positioned vertically or horizontally in the water. Results showed that bull sharks,Carcharhinus leucas, kept a significantly greater distance when the test subject was standing in chest-deep water with his head above water versus lying on the ocean floor. Furthermore, larger bull sharks in the immediate area withdrew when the subject entered the water.