Surfactants as Chemical Shark Repellents: Past, Present, and Future

The development of Shark Chaser by the U.S. Navy during World War II was the first serious effort to develop a chemical shark repellent. In the decade following the war reports of Shark Chaser ineffectiveness led the Office of Naval Research to search for a more efficacious shark repellent. After years without success, ONR eventually canceled the use of Shark Chaser and abandoned the search for a chemical shark repellent. In the early 1970s, interest in chemical shark repellents was renewed by the discovery of pardaxin, a natural shark repellent secreted by the Red Sea Moses sole, Pardachirus marmoratus. The surfactant-like nature of pardaxin led investigators to test the potential of various surfactants as repellents. Subsequent studies indicated that the shark repellent efficacy of the effective alkyl sulfate surfactants was due to their hydrophobic nature. Here we report tests conducted on juvenile swell sharks, Cephaloscyllium ventriosum, to determine if the noxious quality of alkyl sulfates is affected by surfactant hydrophobicity [carbon chain length and ethylene oxide (EO) groups] and counterions. Our results indicate that the aversive response of sharks to alkyl sulfate surfactants increases with carbon chain length from octyl to dodecyl, decreases with the addition of EO groups and is not affected by counterions. This study confirms that dodecyl sulfate is the most effective surfactant shark repellent, but it does not meet the Navy's potency requirement for a nondirectional surrounding-cloud type repellent of 100 parts per billion (0.1ugml^–1). Thus, dodecyl sulfate is only practical as a directional repellent such as in a squirt application. Future research should test the action of alkyl sulfates on cell membranes, the potential of other biotoxic agents, and semiochemicals in the search for an effective chemical shark repellent.     

应用脂肪酸组成研究热带东太平洋同域中上层鲨鱼营养生态位分化

物种对食物资源利用方式的差异,即营养生态位分化是物种共存的先决条件之一,对种间营养生态位的比较研究有助于了解同域分布物种的共存机制。脂肪酸组成可反映生物较长时间尺度的摄食信息,对探讨物种间营养生态位分化具有重要指示作用。热带东太平洋主要栖息有8种大型中上层鲨鱼,大青鲨(Prionace glauca)、大眼长尾鲨(Alopias superciliosus)、镰状真鲨(Carcharhinus falciformis)、长鳍真鲨(Carcharhinus longimanus)、浅海长尾鲨(Alopias pelagicus)、尖吻鲭鲨(Isurus oxyrinchus)、路氏双髻鲨(Sphyrna lewini)和锤头双髻鲨(Sphyrna zygaena),通过比较其肌肉脂肪酸组成,分析种间食性差异,营养关系及营养生态位分化。结果表明,尖吻鲭鲨营养级相对较高,大青鲨相对较低。3种鼠鲨与5种真鲨存在食性差异或栖息地隔离。浅海长尾鲨与大眼长尾鲨营养生态位重叠程度较高,存在激烈的资源竞争。大青鲨与镰状真鲨生态位宽度较大,表征其对环境的可塑性较强;尖吻鲭鲨和路氏双髻鲨生态位宽度较小,表现为其食性的特化。本研究解释了脂肪酸组成分析在鲨鱼摄食研究中的潜在应用,对分析大洋性鲨鱼的营养生态位分化,资源分配方式及同域共存机制有一定的应用价值。     

Structure of chondroitin sulfates analyses of the products formed from chondroitin sulfates A and C by the action of the chondroitinases C and AC from Flavobacterium heparinum

The structures of chondroitin sulfate A from whale cartilage and chondroitin sulfate C from shark cartilage have been examined with the aid of the chondroitinases AC and C from Flavobacterium heparinum. The analyses of the products formed from the chondroitin sulfates by the action of the chondroitinases have shown that three types of oligosaccharides compose the structure of chondroitin sulfate A, namely, a dodeca-, hexa- and a tetra-saccharide, containing five, two and one 4-sulfated disaccharides per 6-sulfated disaccharide residue, respectively. The polymer contains an average of 3 mol of each oligosaccharide per mol of chondroitin sulfate A. Each mol of chondroitin sulfate C contains an average of 5 mol of 4-sulfated disaccharide units. A tetra-saccharide containing one 4-sulfated disaccharide and one 6-sulfated disaccharide was isolated from this mucopolysaccharide by the action of the chondroitinase C, indicating that the 4-sulfated disaccharides are not linked together in one specific region but spaced in the molecule.     

Predicting current and future global distributions of whale sharks

The Vulnerable (IUCN) whale shark spans warm and temperate waters around the globe. However, their present‐day and possible future global distribution has never been predicted. Using 30 years (1980–2010) of whale shark observations recorded by tuna purse‐seiners fishing in the Atlantic, Indian and Pacific Oceans, we applied generalized linear mixed‐effects models to test the hypothesis that similar environmental covariates predict whale shark occurrence in all major ocean basins. We derived global predictors from satellite images for chlorophyll a and sea surface temperature, and bathymetric charts for depth, bottom slope and distance to shore. We randomly generated pseudo‐absences within the area covered by the fisheries, and included fishing effort as an offset to account for potential sampling bias. We predicted sea surface temperatures for 2070 using an ensemble of five global circulation models under a no climate‐policy reference scenario, and used these to predict changes in distribution. The full model (excluding standard deviation of sea surface temperature) had the highest relative statistical support (wAIC_c = 0.99) and explained ca. 60% of the deviance. Habitat suitability was mainly driven by spatial variation in bathymetry and sea surface temperature among oceans, although these effects differed slightly among oceans. Predicted changes in sea surface temperature resulted in a slight shift of suitable habitat towards the poles in both the Atlantic and Indian Oceans (ca. 5°N and 3–8°S, respectively) accompanied by an overall range contraction (2.5–7.4% and 1.1–6.3%, respectively). Predicted changes in the Pacific Ocean were small. Assuming that whale shark environmental requirements and human disturbances (i.e. no stabilization of greenhouse gas emissions) remain similar, we show that warming sea surface temperatures might promote a net retreat from current aggregation areas and an overall redistribution of the species.     

Evolutionary Divergence in the Structure of Myelin Basic Protein: Comparison of Chondrichthye Basic Proteins with Those from Higher Vertebrates

Abstract: A basic protein has been purified from the CNS myelin of the gummy shark (Mustelus antarticus). Electroblotting was used to examine the capacity of rabbit antisera raised against this electrophoretically pure protein to recognize myelin basic protein from higher vertebrates. The antisera bound to two shark proteins including the original polypeptide antigen and to chicken, bovine, and human myelin basic proteins. Thus, the shark protein appeared to possess antigenic determinants that have been retained through evolutionary divergence of these proteins. Whereas bovine basic protein caused experimental allergic encephalomyelitis in guinea pigs, animals that received injections of the shark protein showed neither clinical nor histological signs of this disease. However, tests for delayed-type hypersensitivity and for Arthus reaction following injection with the shark protein revealed a T-cell-mediated response to this antigen and substantial cross-reactivity with higher vertebrate basic proteins. Analysis of the amino acid composition of the shark protein, and comparison of its tryptic peptide map with that of the bovine protein, revealed substantial changes in the amino acid sequence. Although the shark protein has some antigenic determinants in common with the proteins from higher vertebrates, it appears that much of the structure differs.     

Insights into Young of the Year White Shark, Carcharodon carcharias, Behavior in the Southern California Bight

A young of the year female white shark, Carcharodon carcharias, was tagged with a pop-up satellite archival tag off Southern California in early June of 2000. The tag was recovered after 28 days, and records of temperature, depth and light intensity were extracted. Depth and temperature records indicate a number of interesting behaviors, including a strong diurnal pattern. At night the shark remained in the top 50 m, often making shallow repetitive vertical excursions. Most dives below the mixed layer were observed during the day, 91% of which occurred from 05:00 to 21:00 h, with depths extending to 240 m. Many of the dives exhibited secondary vertical movements that were consistent with the shark swimming at the bottom (at depths from 9 to 165 m) where it was most likely foraging. The white shark experienced dramatic and rapid changes in temperature, and demonstrated a considerable tolerance for cold waters. Temperatures ranged from 9°C to 22°C, and although 89% of the total time was spent in waters 16–22°C, on some days the small shark spent as much as 32% of the time in 12°C waters. The deep dives into cold waters separate the white sharks from mako sharks, which share the California Bight nursery ground but appear to remain primarily in the mixed layer and thermocline. Movement information (derived from light-based geolocation, bottom depths and sea surface temperatures) indicated that the white shark spent the 28 days in the Southern California Bight, possibly moving as far south as San Diego, California. While the abundance and diversity of prey, warm water and separation from adults make this region an ideal nursery ground, the potential for interaction with the local fisheries should be examined.     

Physicochemical properties of chondroitin sulfate. II. Molecular weight dependence of intrinsic viscosity and sedimentation coefficient, and analysis as a semi-flexible coil

1. The relation between intrinsic viscosity in 0.2 M NaCl and molecular weight for samples of chondroitin sulfate isolated from shark cartilage could be expressed by [eeta] = 6.5 X 10(-6) Mr114. 2. Their sedimentation coefficients were linear with respect to the square root of molecular weight, and the intercept was not zero but definitely positive, indicating that chondroitin sulfate in solution can be represented by a semi-flexible coil with a molecular diameter of about 1.2 nm. This value was consistent with the results of X-ray analysis. 3. The molecular weight dependence of the sedimentation coefficient for chondroitin sulfate from ox nasal septa cartilage was similar to that for chondroitin sulfate isolated from shark cartilage.     

Spatial and temporal analysis of juvenile blacktip reef shark (Carcharhinus melanopterus) demographies identifies critical habitats

Reef shark species have undergone sharp declines in recent decades, as they inhabit coastal areas, making them an easy target in fisheries (i.e., sharks are exploited globally for their fins, meat, and liver oil) and exposing them to other threats (e.g., being part of by-catch, pollution, and climate change). Reef sharks play a critical role in coral reef ecosystems, where they control populations of smaller predators and herbivorous fishes either directly via predation or indirectly via behavior, thus protecting biodiversity and preventing potential overgrazing of corals. The urgent need to conserve reef shark populations necessitates a multifaceted approach to policy at local, federal, and global levels. However, monitoring programmes to evaluate the efficiency of such policies are lacking due to the difficulty in repeatedly sampling free-ranging, wild shark populations. Over nine consecutive years, we monitored juveniles of the blacktip reef shark (Carcharhinus melanopterus) population around Moorea, French Polynesia, and within the largest shark sanctuary globally, to date. We investigated the roles of spatial (i.e., sampling sites) and temporal variables (i.e., sampling year, season, and month), water temperature, and interspecific competition on shark density across 10 coastal nursery areas. Juvenile C. melanopterus density was found to be stable over 9 years, which may highlight the effectiveness of local and likely federal policies. Two of the 10 nursery areas exhibited higher juvenile shark densities over time, which may have been related to changes in female reproductive behavior or changes in habitat type and resources. Water temperatures did not affect juvenile shark density over time as extreme temperatures proven lethal (i.e., 33°C) in juvenile C. melanopterus might have been tempered by daily variation. The proven efficiency of time-series datasets for reef sharks to identify critical habitats (having the highest juvenile shark densities over time) should be extended to other populations to significantly contribute to the conservation of reef shark species.     

Ultrastructure of irregular collagen fibrils of shark mandible

Sawada T. and Inoue S. 2011. Ultrastructure of irregular collagen fibrils of shark mandible. —Acta Zoologica (Stockholm) 92 : 62–66. Collagen fibrillogenesis was investigated in developing fibrous connective tissue (tooth band) in shark mandible by transmission electron microscopy. Fibrils varied considerably in shape and size. Both thin and thick fibrils 40–200 and 400–500 nm in width, respectively, were observed, with the latter showing irregular contours. Examination of both transverse and longitudinal sections of fibril suggested that the irregular, thick fibrils were formed by fusion of the thin fibrils. This was in agreement with a previously proposed mechanism of collagen fibrillogenesis in a variety of tissues, in which formation of thin fibrils is followed by their coalescence into thicker fibrils. Detailed high resolution ultrastructural examination revealed decorin‐like, 4.5‐ to 5.5‐nm‐wide polygonal frames and 3‐nm‐wide ribbon‐like structures previously identified as chondroitin sulfate proteoglycan ‘double tracks’ localized within the interfibrillar spaces. These structures may be closely involved in collagen fibrillogenesis.     

Selective removal of keratan sulfate in chondroitin sulfate samples by sequential precipitation with ethanol

Keratan sulfate (KS) is present as a contaminant in chondroitin sulfate (CS) mainly extracted from shark cartilage. We report a selective removal procedure of KS in CS samples by means of sequential precipitation with ethanol. Purified shark CS containing approximately 10% to 15% KS was subjected to a precipitation procedure in the presence of increasing percentages of saturated ethanol. In contrast to other solvents, 1.0 volume of ethanol was able to selectively purify CS, with a purity of approximately 100%, from KS. The current selective and simple procedure appears to be a reliable industrial preparation of CS devoid of large amounts of the residual KS.     

Tonic immobility in 12 elasmobranchs: Use as an aid in captive husbandry

Tonic immobility (TI), also known as animal hypnosis, has been observed in a wide variety of taxa and reported in all vertebrate classes with the exception of Agnatha. To date, TI has been reported in six species of elasmobranchs. Preliminary results are presented here for five species of galeomorph sharks, one species of squalomorph shark, and six species of batoids. Tonic immobility was induced in the leopard shark. Triakis semifasciata; the whitetip reef shark, Triaenodon obesus; the blacktip reef shark, Carcharhinus melanopterus; the Caribbean reef shark, Carcharhinus perezi; the swellshark, Cephaloscyllium ventriosum; the California round ray, Urolophus halleri; the shovelnose guitarfish, Rhinobatos productus; the clearnose skate. Raja eglanteria; the cownose ray, Rhinoptera bonasus; and the southern stingray, Dasyatis americana. The broadnose sevengill shark, Notorynchus cepedianus and the yellow stingray, Urolophus jamaicensis failed to exhibit the tonic immobility response, but only one individual of each species was tested. The average induction time ranged from 16.7 sec in the shovelnose guitarfish to 45.7 sec in the clearnose skate. Average duration times ranged from 34.3 sec in the clearnose skate to 274.0 sec in the Caribbean reef shark. Depending upon the species involved, TI has been used as an aid in a few husbandry and medical procedures in captive elasmobranches at the National Aquarium in Baltimore. These procedures have included gross examination, measuring lengths, tube feeding, and drawing blood via caudal venipuncture. Using tonic immobility during these procedures is beneficial as once induced, the subject's struggling is minimal and usually requires little restraint. © 1994 Wiley-Liss, Inc.     

Shark bite injuries on three inshore dolphin species in tropical northwestern Australia

Predation risk has a profound influence on the behavior of marine mammals, affecting grouping patterns and habitat use. Dolphins frequently bear evidence of shark bites, which can provide an indirect measure of predation pressure. Using photo‐identification data, we investigated the prevalence of shark bites on three sympatric species of inshore dolphin, the Australian snubfin (Orcaella heinsohni), Australian humpback (Sousa sahulensis), and Indo‐Pacific bottlenose dolphin (Tursiops aduncus), among four study sites in northwestern Australia. Bite prevalence varied markedly between species, with 72% of snubfin, 46% of humpback, and 18% of bottlenose dolphins exhibiting evidence of shark bites. Binomial logistic regression confirmed a high likelihood of bite presence on snubfin dolphins, and at one particular site for snubfin and bottlenose dolphins. The prevalence of tiger shark (Galeocerdo cuvier) bites on snubfin dolphins was high, and bites attributed to other carcharhinid sharks were observed on all species. While acknowledging methodological differences with other studies, the prevalence of shark bites on snubfin dolphins is among the highest reported for any dolphins, suggesting predation risk represents an important but varying influence thereon. This study provides a baseline for future investigations into the affect of predation risk on the behavioral ecology of these sympatric species.     

Acetate Production from Oil under Sulfate-Reducing Conditions in Bioreactors Injected with Sulfate and Nitrate

Oil production by water injection can cause souring in which sulfate in the injection water is reduced to sulfide by resident sulfate-reducing bacteria (SRB). Sulfate (2 mM) in medium injected at a rate of 1 pore volume per day into upflow bioreactors containing residual heavy oil from the Medicine Hat Glauconitic C field was nearly completely reduced to sulfide, and this was associated with the generation of 3 to 4 mM acetate. Inclusion of 4 mM nitrate inhibited souring for 60 days, after which complete sulfate reduction and associated acetate production were once again observed. Sulfate reduction was permanently inhibited when 100 mM nitrate was injected by the nitrite formed under these conditions. Pulsed injection of 4 or 100 mM nitrate inhibited sulfate reduction temporarily. Sulfate reduction resumed once nitrate injection was stopped and was associated with the production of acetate in all cases. The stoichiometry of acetate formation (3 to 4 mM formed per 2 mM sulfate reduced) is consistent with a mechanism in which oil alkanes and water are metabolized to acetate and hydrogen by fermentative and syntrophic bacteria (K. Zengler et al., Nature 401:266–269, 1999), with the hydrogen being used by SRB to reduce sulfate to sulfide. In support of this model, microbial community analyses by pyrosequencing indicated SRB of the genus Desulfovibrio, which use hydrogen but not acetate as an electron donor for sulfate reduction, to be a major community component. The model explains the high concentrations of acetate that are sometimes found in waters produced from water-injected oil fields.     

Killing in the Pliocene: shark attack on a dolphin from Italy

Abstract: Shark bite marks, including striae, sulci and abrasions, in a well‐preserved fossil dolphin skeleton referred to Astadelphis gastaldii (Cetacea, Delphinidae) from Pliocene sediments of Piedmont (northern Italy), are described in detail. The exceptional combination of a fossil dolphin having a significant part of the skeleton preserved and a large number of bite marks on the bones represents one of the few detailed documentations of shark attack in the past. Most bite marks have been referred to a shark about 4 m long with unserrated teeth, belonging to Cosmopolitodus hastalis, on the basis of their shape and their general disposition on the dolphin skeleton. According to our hypothesis, the shark attacked the dolphin with an initial mortal bite to the abdomen from the rear and right, in a similar way as observed for the living white shark when attacking pinnipeds. A second, less strong, bite was given on the dorsal area when the dolphin, mortally injured, probably rolled to the left. The shark probably released the prey, dead or dying, and other sharks or fishes probably scavenged the torn body of the dolphin.     

Assessment of multiple paternity in single litters from three species of carcharhinid sharks in Hawaii

We tested for presence or absence of multiple paternity in single litters from each of three congeneric shark species in Hawaii: the sandbar shark, Carcharhinus plumbeus, bignose shark, Carcharhinus altimus, and Galapagos shark, Carcharhinus galapagensis. Based on eight polymorphic microsatellite loci, we excluded paternity by a single sire in sandbar and bignose sharks, but could not exclude a single sire for the litter from the Galapagos shark. This study doubles the number of shark species tested for multiple paternity, and is the first demonstration of multiple paternity in sandbar and bignose sharks.     

Resource-use dynamics of co-occurring chondrichthyans from the First Coast,North Florida,USA

Recent studies on shark assemblages on the northeast Florida and southeast Georgia coast (hereafter referred to collectively as the “First Coast”) have demonstrated differences in species and age-class composition of catch from previously characterized estuaries and newly surveyed area beaches, demonstrating that these regions may provide a critical habitat to different segments (i.e., life stages) of local shark populations. In this study, carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) from muscle tissue and blood plasma were used to examine trophic dynamics (and temporal variability thereof) of the three dominant co-occurring species found along First Coast beaches (the Atlantic Sharpnose shark Rhizoprionodon terraenovae, Blacknose shark Carcharhinus acronotus and Blacktip shark Carcharhinus limbatus) to determine if they exhibit overlap in resource use along with spatial and temporal habitat use. Although considered spatially segregated from the beach species, a dominant, age-class species found in First Coast estuaries (juvenile Sandbar sharks Carcharhinus plumbeus) was also included in this analysis for comparison. Temporal variability of resource-use characteristics was detected at the species level. Resource-use overlap among species varied by tissue type and was generally higher for blood plasma, suggesting greater resource sharing over more recent time periods. Over longer time periods Atlantic Sharpnose and Blacktip sharks exhibited resource-use expansion, whereas Blacknose sharks exhibited a narrowing in resource use, suggesting a more specialized foraging strategy compared to the other species. The resource-use breadth of Sandbar sharks also expanded between blood plasma and muscle tissue. Significant size relationships were detected in Blacktip and Sandbar sharks, indicating ontogenetic resource shifts for both species. A diversity of highly productive resource pools likely support shark populations along the First Coast such that resource-use differentiation is not required to facilitate species co-occurrence. This work may shed light on understanding patterns of species co-occurrence as well as aid in future conservation efforts.     

Dramatic increase in sea otter mortality from white sharks in California

Although southern sea otters (Enhydra lutris nereis) are not considered prey for white sharks (Carcharodon carcharias), sharks do nonetheless bite sea otters. We analyzed spatial and temporal trends in shark bites on sea otters in California, assessing the frequency of shark bite wounds in 1,870 carcasses collected since 1985. The proportion of stranded sea otters having shark bites has increased sharply since 2003, and white shark bites now account for >50% of recovered carcasses. The trend was most pronounced in the southern part of the range, from Estero Bay to Point Conception, where shark bite frequency has increased eightfold. Seasonal trends were also evident: most shark‐bitten carcasses are recovered in late summer and fall; however, the period of elevated shark bite frequency has lengthened. The causes of these trends are unclear, but possible contributing factors include increased white shark abundance and/or changes in white shark behavior and distribution. In particular, the spatiotemporal patterns of shark‐bitten sea otters match increases in pinniped populations, and the increased availability of marine mammal prey for white sharks may have led to more sharks spending more time in nearshore waters utilized by both sea otters and pinnipeds.     

First report of a sleeper shark (Somniosus sp.) in the southern Colombian Caribbean

A sleeper shark, genus Somniosus, was observed in the Colombian Caribbean. A Remote Operated Vehicle (ROV) recorded a sleeper shark specimen during an inspection while drilling a hydrocarbon exploratory well at 1,820 m water depth. This is the first record of a sleeper shark for the southern Colombian Caribbean. The previous most southern records of Somniosid sharks in the tropical and subtropical western Atlantic came from the western and northern Gulf of Mexico, and from Cuba.     

Microbial community succession in a bioreactor modeling a souring low-temperature oil reservoir subjected to nitrate injection

Injection of up-flow packed-bed bioreactors with excess volatile fatty acids and limiting concentrations of nitrate and sulfate gave complete reduction of nitrate from 0 to 5.5 cm and complete or near-complete reduction of sulfate from 3.2 to 11.5 cm along the bioreactor flow path. Most of the biomass (85%) and most of the genes for nitrate reduction (narG, 96%; napA, 99%) and for sulfate reduction (dsrB, 91%) were present near the inlet (0–5.5 cm) of the 37-cm-long bioreactor. Microbial community analysis by a combination of denaturing gradient gel electrophoresis and pyrosequencing of 16S rRNA amplicons indicated that nitrate-reducing Arcobacter and Pseudomonas species were located from 0 to 3.2 cm and throughout, respectively. Desulfobulbus species were the main sulfate reducers present and acetotrophic methanogens of the genus Methanosaeta predominated at 20–37 cm. Overall, the results indicated a succession of microbial communities along the bioreactor flow path. In the absence of nitrate, the sulfate reduction zone moved nearer to the bioreactor inlet. The sulfide concentration in the bioreactor effluent was temporarily lowered after nitrate injection was re-started. Hence, the bioreactor sulfide output could be disrupted by pulsed, not by constant nitrate injection, as demonstrated also previously in a low-temperature oil field.     

Population structure,connectivity, and demographic history of an apex marine predator,the bull shark Carcharhinus leucas

Knowledge of population structure, connectivity, and effective population size remains limited for many marine apex predators, including the bull shark Carcharhinus leucas. This large‐bodied coastal shark is distributed worldwide in warm temperate and tropical waters, and uses estuaries and rivers as nurseries. As an apex predator, the bull shark likely plays a vital ecological role within marine food webs, but is at risk due to inshore habitat degradation and various fishing pressures. We investigated the bull shark's global population structure and demographic history by analyzing the genetic diversity of 370 individuals from 11 different locations using 25 microsatellite loci and three mitochondrial genes (CR, nd4, and cytb). Both types of markers revealed clustering between sharks from the Western Atlantic and those from the Western Pacific and the Western Indian Ocean, with no contemporary gene flow. Microsatellite data suggested low differentiation between the Western Indian Ocean and the Western Pacific, but substantial differentiation was found using mitochondrial DNA. Integrating information from both types of markers and using Bayesian computation with a random forest procedure (ABC‐RF), this discordance was found to be due to a complete lack of contemporary gene flow. High genetic connectivity was found both within the Western Indian Ocean and within the Western Pacific. In conclusion, these results suggest important structuring of bull shark populations globally with important gene flow occurring along coastlines, highlighting the need for management and conservation plans on regional scales rather than oceanic basin scale.