Bonnethead Research Articles

Mitochondrial DNA patterns describe the evolutionary history of the bonnethead shark Sphyrna tiburo (Linneus 1758) complex in the western Atlantic Ocean.

The apparent lack of physical barriers in the marine realm has created the conception that many groups have a constant gene flow. However, changes in ocean circulation patterns, glacial cycles, temperature, and salinity gradients are responsible for vicariant events in many fish species, including sharks. The bonnethead shark, Sphyrna tiburo, is an endangered small coastal shark species. Although considerable efforts have recently been undertaken, little remains known about the possible biogeographic scenario that can explain its actual distribution within the western Atlantic (WA). Here, we used 599 mitochondrial sequences to assess the phylogeographic structure and implement Bayesian phylogenetic analyses to obtain divergence times and reconstruct the ancestral geographic range. This allowed us to infer processes responsible for the diversification of S. tiburo into major divergent lineages. Our results indicated that S. tiburo in the WA represents three independent lineages, with Brazilian samples differentiated into a distinct genetic cluster. The posterior probability of ancestral range analysis indicated that the species likely originated in the northern region (Carolina Province and the southern Gulf of Mexico), where it colonized southward through the uplifting of the Central American Isthmus (CAI). The Northern and Caribbean genetic clusters appear to have arisen from the intensification of the Loop Current, which currently flows northward passing the Yucatan Peninsula, Gulf of Mexico, and east Florida. Following initial colonization, the Northeastern Brazil group differentiated from the Caribbean region due to the sediment and freshwater discharge of the Amazon-Orinoco Plume. Thus, the evolutionary history of the S. tiburo complex can be explained by a combination of dispersal and vicariance events that occurred over the last ~5 million years (MY). We established and confirmed the species and population limits, demonstrating that the Amazon-Orinoco Plume constitutes a significant dispersal barrier for coastal sharks. Finally, we discuss some recommendations for the conservation of the bonnethead shark.

Evidence for gene flow from the Gulf of Mexico to the Atlantic Ocean in bonnethead sharks (Sphyrna tiburo).

Gene flow is important for maintaining the genetic diversity required for adaptation to environmental disturbances, though gene flow may be limited by site fidelity in small coastal sharks. Bonnethead sharks (Sphyrna tiburo)-a small coastal hammerhead species-demonstrate site fidelity, as females are philopatric while males migrate to mediate gene flow. Consequently, bonnetheads demonstrate population divergence with distance, and Atlantic populations are genetically distinct from those of the Gulf of Mexico. Indeed, Florida forms a vicariant zone between these two bodies of water for many marine species, including some sharks. However, while bonnetheads are expected to have limited dispersal, the extent and rate of bonnethead migration remain uncertain. Thus, we aimed to determine their dispersal capacity by evaluating connectivity between disparate populations from the Gulf of Mexico and Atlantic Ocean. Using 10,733 SNPs derived from 2bRAD sequences, we evaluated genetic connectivity between Tampa Bay on the Gulf Coast of Florida and Biscayne Bay on the Atlantic coast of Florida. While standard analyses of genetic structure revealed slight but significant differentiation between Tampa Bay and Biscayne Bay populations, demographic history inference based on the site frequency spectrum favored a model without divergence. However, we also estimate that if population divergence occurred, it would have been recent (between 1500 and 4500 years ago), with continuous unidirectional gene flow from Tampa Bay to Biscayne Bay. Our findings support the hypothesis that bonnetheads can migrate over relatively large distances (>300 miles) to find mates. Together, these results provide optimism that under proper management, a small-bodied globally endangered shark can undergo long migrations to sustain genetic diversity.

First stable isotope and mercury assessment of bonnethead and Caribbean sharpnose sharks from a potential nursery ground in the Archipelago of Bocas del Toro, Panamanian Caribbean

Bonnethead and Caribbean sharpnose sharks frequent coastal waters, rendering them vulnerable to overexploitation, with the bonnethead shark listed as endangered by the IUCN. Marine Protected Areas (MPAs) have been suggested as a management strategy to regulate shark-exploitation. Moreover, it’s essential to identify key areas where nursery grounds (NG) and adult habitats overlap to prioritize conservation zones within MPAs. Along the Caribbean Sea, several NG have been identified for larger shark species, but little is known for smaller sharks. In Bocas del Toro (BDT-Panamanian Caribbean), both bonnethead and Caribbean sharpnose sharks are distributed, with the former appearing to be genetically isolated. The local MPA in BDT doesn't include a NG identified near Solarte Island. In this study, to provide ecological information on bonnethead and Caribbean sharpnose sharks within this potential NG, we evaluated stable isotopes (δ13C and δ15N) and total-mercury (THg) values in their fins. The results revealed a higher proportion of small-adult sharks in the NG, emphasizing the necessity of conducting a comprehensive study to further characterize this area. Moreover, there was no niche-partitioning between the two species and their diets primarily consisted of small prey-items, as evidenced by the significant and negative relationship between isotopic values. Both species exhibited low THg levels in their fins. Based on these initial results and previous genetic data, it appears that BDT plays a critical role as a habitat for sharks. Thus, extending the local MPA to cover the potential NG could effectively ensure conservation of bonnethead and Caribbean sharpnose sharks in BDT.

Species-specific profiles of per- and polyfluoroalkyl substances (PFAS) in small coastal sharks along the South Atlantic Bight of the United States

Per- and polyfluoroalkyl substances (PFAS) have gained widespread commercial use across the globe in various industrial and consumer products, such as textiles, firefighting foams, and surface coating materials. Studies have shown that PFAS exhibit a strong tendency to accumulate within aquatic food webs, primarily due to their high bioaccumulation potential and resistance to degradation. Despite such concerns, their impact on marine predators like sharks remains underexplored. This study aimed to investigate the presence of 34 PFAS in the plasma (n = 315) of four small coastal sharks inhabiting the South Atlantic Bight of the United States (U.S). Among the sharks studied, bonnetheads (Sphyrna tiburo) had the highest ∑PFAS concentration (3031 ± 1674 pg g − 1 plasma, n = 103), followed by the Atlantic sharpnose shark (Rhizoprionodon terraenovae, 2407 ± 969 pg g − 1, n = 101), blacknose shark (Carcharhinus acronotus, 1713 ± 662 pg g − 1, n = 83) and finetooth shark (Carcharhinus isodon, 1431 ± 891 pg g − 1, n = 28). Despite declines in the manufacturing of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), the long-chain (C8 – C13) perfluoroalkyl acids (PFAAs) were frequently detected, with PFOS, perfluorodecanoic acid (PFDA), and perfluorotridecanoic acid (PFTrDA) present as the most dominant PFAS. Furthermore, males exhibited significantly higher ∑PFAS concentrations than females in bonnetheads (p < 0.01), suggesting possible sex-specific PFAS accumulation or maternal offloading in some species. The results of this study underscore the urgency for more extensive biomonitoring of PFAS in aquatic/marine environments to obtain a comprehensive understanding of the impact and fate of these emerging pollutants on marine fauna.

Embryonic development in the bonnethead (Sphyrna tiburo), a viviparous hammerhead shark.

The hammerhead sharks (family Sphyrnidae) are an immediately recognizable group of sharks due to their unique head shape. Though there has long been an interest in hammerhead development, there are currently no explicit staging tables published for any members of the group. The bonnethead Sphyrna tiburo is the smallest member of Sphyrnidae and is abundant in estuarine and nearshore waters in the Gulf of Mexico and Western North Atlantic Ocean. Due to their relative abundance, close proximity to shore, and brief gestation period, it has been possible to collect and document multiple embryonic specimens at progressive stages of development. We present the first comprehensive embryonic staging series for the Bonnethead, a viviparous hammerhead shark. Our stage series covers a period of development from stages that match the vertebrate phylotypic period, from Stage 23, through stages of morphological divergence to complete development at birth-Stage 35). Notably, we use a variety of techniques to document crucial stages that lead to their extreme craniofacial diversity, resulting in the formation of one of the most distinctive characters of any shark species, the cephalofoil or hammer-like head. Documenting the development of hard-to-access vertebrates, like this viviparous shark species, offers important information about how new and diverse morphologies arise that otherwise may remain poorly studied. This work will serve as a platform for future comparative developmental research both within sharks and across the phylogeny of vertebrates, underpinning the extreme potential of craniofacial development and morphological diversity in vertebrate animals.

Relationships in Shark Skin: Mechanical and Morphological Properties Vary between Sexes and among Species.

Shark skin is a composite of mineralized dermal denticles embedded in an internal collagen fiber network and is sexually dimorphic. Female shark skin is thicker, has greater denticle density and denticle overlap compared to male shark skin, and denticle morphology differs between sexes. The skin behaves with mechanical anisotropy, extending farther when tested along the longitudinal (anteroposterior) axis but increasing in stiffness along the hoop (dorsoventral or circumferential) axis. As a result, shark skin has been hypothesized to function as an exotendon. This study aims to quantify sex differences in the mechanical properties and morphology of shark skin. We tested skin from two immature male and two immature female sharks from three species (bonnethead shark, Sphyrna tiburo; bull shark, Carcharhinus leucas; silky shark, Carcharhinus falciformis) along two orientations (longitudinal and hoop) in uniaxial tension with an Instron E1000 at a 2 mm s-1 strain rate. We found that male shark skin was significantly tougher than female skin, although females had significantly greater skin thickness compared to males. We found skin in the hoop direction was significantly stiffer than the longitudinal direction across sexes and species, while skin in the longitudinal direction was significantly more extensible than in the hoop direction. We found that shark skin mechanical behavior was impacted by sex, species, and direction, and related to morphological features of the skin.

Age, Growth and Maturity of the Bonnethead Sphyrna tiburo in the U.S. Gulf of Mexico

Age, Growth and Maturity of the Bonnethead Sphyrna tiburo in the U.S. Gulf of Mexico

Fisher Ethnotaxonomy for Elasmobranchs Captured Along the Brazilian Amazon Coast

The diversity of popular names used in fish nomenclature off the Brazilian coast makes it difficult to identify species, and many names have their origins in Indigenous languages, mainly Tupi-Guarani. This study sought to understand and update the list of the most popular names and assess some ethnotaxonomic patterns employed by artisanal fishers from the Brazilian Amazon Coast in naming elasmobranchs. Interviews with 314 fishermen from 17 coastal municipalities were carried out employing a semi-structured form, banners, and photographic records of local elasmobranch species, addressing characteristics applied to species identification. A total of 130 ethnospecies were identified (113 names in Portuguese and 17 of Tupi-Guarani origin) for the identification of 22 and 18 species of sharks and rays, respectively. The highest degree of homonyms occurs interspecifically for the Dasyatidae, Mobulidae, Pristidae, Urotrygonidae, Carcharhinidae, Sphyrnidae and Triakidae families. Sphyrna tiburo and Hypanus guttatus comprised the taxa with the highest diversity of common names. Morphological characteristics such as shape, colors, texture, and size of certain body parts are the ethnotaxonomic patterns most applied in shark and ray identification. We conclude that the use of common names for elasmofauna facilitates communication between fishers and that the scientific approach to this local ecological knowledge is fundamental for the management and sustainability of fisheries in the long term.

Using a multimodel approach to determine the age and growth of an endangered small shark species in the southern Gulf of Mexico

The bonnethead shark (Sphyrna tiburo), recently upgraded to endangered by the IUCN red list, is frequent in artisanal fisheries’ catches of the southern Gulf of Mexico (GOM). The age and growth parameters were determined from 162 vertebral centra collected from bonnethead sharks (28.2–112.1 cm total length; TL) between 2010 and 2019 in the southern GOM. Two readers determined age estimates using two rounds of independent band pair counts (opaque and translucent). The average percent error (APE) and coefficient of variation (CV) were estimated to assess count precision, and a Bowker test of symmetry was performed to determine potential bias between readers’ counts. The edge and marginal increment analyses were conducted to validate the band pair deposition periodicity, and a multimodel approach was used to select the best growth model. The reading precision was good because APE and CV values were 7.9% and 5.6%, respectively, and the Bowker’s symmetry test indicated no systematic differences between readers. The validation analyses did not provide evidence to determine the band pair deposition periodicity; thus, it was assumed that one band pair is deposited yearly. The oldest male and female were five (95.4 cm TL) and eight (112.1 cm TL) years. The Gompertz growth function provided the best statistical fit and best describes the growth of bonnethead sharks. The parameters were L∞=113 cm, k2=0.49/year, L0=39 cm for females, and L∞=83.6 cm, k2=0.79/year, L0=40.2 cm for males. These are the first age and growth parameters estimated for the bonnethead shark in the southern GOM, which is the second most landed shark and needs a population assessment for proper management.

Is restricting catch to young sharks only more sustainable? Exploring a controversial management strategy for bull, tiger, blue and bonnethead sharks

AbstractProper management of shark populations is an immediate concern due to their high vulnerability. In this study, we applied stochastic demographic models for four shark species (bull shark Carcharhinus leucas, tiger shark Galeocerdo cuvier, blue shark Prionace glauca and bonnethead Sphyrna tiburo) to test how population growth behaved under different exploitation scenarios, such as the exclusion of older sharks from fisheries. Populations grew at considerably slow rates when unfished, except for P. glauca. When fisheries targeted all individuals, populations started to decline at generally very low fishing mortality and harvest rates. Conversely, when adult individuals were excluded from fisheries, population resiliency increased despite higher fishing pressures, with no negative growth rates even if harvest levels were doubled. This study indicates that conservation of these species may benefit from protecting adult stocks.

Diet of the bonnethead (Sphyrna tiburo) along the northern Gulf of Mexico and southeastern Atlantic coast of the United States

The diet of a potentially omnivorous coastal shark species, the bonnethead (Sphyrna tiburo), was examined in the western Atlantic along the coast of the southeastern United States. A total of 423 stomachs collected from Texas, Alabama, Florida and South Carolina were analyzed using standardized stomach content analysis methods. The diet was dominated by crabs, primarily portunids (Callinectes spp.), across the geographical range analyzed, though the relative importance of crabs varied between regions. Ontogenetic shifts in diet were not observed throughout the region studied. Female and male bonnetheads in South Carolina displayed different diets, particularly in the amount of portunid crabs consumed, with a higher proportion ingested by females. Bonnetheads consumed limited amounts of seagrasses in all regions except in South Carolina, where they occupy habitats without seagrasses in marsh dominated bays and estuaries. This finding indicates that, at least seasonally, seagrasses are not an essential part of the diet of this shark species and may only occur in stomachs as accidental ingestion.

Microstructure of the Bonnethead Shark (Sphyrna tiburo) Olfactory Rosette.

Microstructure of the Bonnethead Shark (Sphyrna tiburo) Olfactory Rosette.

Multi-channel feeding by migratory sharks in a fluvial-dominated estuary

Rivers can transport a substantial amount of allochthonous nutrients into coastal marine ecosystems. These nutrients are a significant contributor to estuarine productivity, resulting in increased fishery production. However, for migratory marine predators, the importance of nutrients from fluvial-dominated estuaries is unclear. We used carbon (δ 13C) and sulfur (δ 34S) stable isotope mixing models to identify the contribution of prey sources in fluvial-dominated estuarine habitat relative to nearby seagrass and offshore reef habitats to five species of migratory shark: finetooth shark Carcharhinus isodon, blacktip shark Carcharhinus limbatus, bull shark Carcharhinus leucas, Atlantic sharpnose shark Rhizoprionodon terraenovae, and bonnethead shark Sphyrna tiburo. We explored how the contribution of these sources varied as a function of shark length. Sharks generally exhibited a strong reliance on prey from fluvial-estuarine energy channels, with the youngest individuals displaying the highest reliance relative to larger individuals. Models suggested that sharks rely increasingly on nutrient sources from nearby seagrass or offshore reef habitats with age, potentially acting as vectors of nutrient transport across systems. These findings illustrate the importance of a fluvial-dominated estuarine system to migratory marine predators and suggest that these individuals may connect inshore and offshore food-webs. Estuarine systems with high fluvial-influence offer important nutrient subsidies for migratory species, which can transport that energy to adjacent, nutrient-limited systems. Changes to river-flow regimes could disrupt the channeling of nutrients to coastal marine systems, affecting migratory predator populations and their role in transporting these nutrients across the seascape.

Modeling the Individual Growth of the Bonnethead Shark Sphyrna tiburo of the Western Gulf of Mexico Using the Multimodel Approach

To describe the growth pattern of the bonnethead shark (Sphyrna tiburo) in the Gulf of Mexico, a von Bertalanffy (VB) model has been automatically fit, which indicated a single−phase continuous growth without oscillations, though this would generate biases if this hypothesis is not confirmed. The objective of this research was to describe the growth pattern of S. tiburo under a multimodel approach based on information theory and contrasting single−phase models (VB, Gompertz, logistic models, and variants) and biphasic models (Soriano model and variants). The VB model was not supported. The Soriano model, with the variant in growth rate (k) and including length at birth (L0), was selected with 100% supporting evidence. The hypothesis of the two−phase growth of S. tiburo with an increase in k, more than L∞, fitted to L0, is confirmed, and a correspondence was identified between growth−phase change sizes and the sizes reported in the literature for change in the juvenile–adult stages in females and for onset of reproductive maturity in males and both sexes.

Location, Location, Location! Evaluating Space Use of Captive Aquatic Species—A Case Study with Elasmobranchs

The space use of captive animals has been reliably used as a tool to measure animal welfare in recent years. However, most analyses of space use focus primarily on terrestrial animals, with very little emphasis placed on the space use of aquatic animals. By comparing the space use of these animals to their natural histories and what would be expected of them physiologically, a general assessment of their overall welfare can be obtained. Using the Zoomonitor program, this study investigated the space use of five elasmobranch species housed in a captive aquatic environment: a blacktip reef shark (Carcharhinus melanopterus), a nurse shark (Ginglymostoma cirratum), a smooth dogfish (Musteluscanis), a bonnethead shark (Sphyrna tiburo), and a blacknose shark (Carcharhinus acronotus). The exhibit was delineated into five different zones: three represented the animal locations along the X/Y axis (‘Exhibit Use’), and two zones were related to the Z-axis (‘Depth Use’). The location of each individual on both the X/Y and Z axes was recorded during each observation. Heat maps generated from the Zoomonitor program were used in conjunction with the Spread of Participation Index (SPI) to interpret the data. It was found that while all the individuals used their given space differently, the Exhibit Use was relatively even overall (the SPI values ranged from 0.0378 to 0.367), while the Depth Use was more uneven (the SPI ranged from 0.679 to 0.922). These results mostly reflected what would be expected based on the species’ natural histories. However, for the smooth dogfish, the observed Exhibit Use and activity patterns revealed a mismatch between the anticipated and the actual results, leading to further interventions. As demonstrated here, space use results can be utilized to make positive changes to husbandry routines and enclosure designs for aquatic individuals; they are thus an important additional welfare measure to consider for aquatic species.

Bulk and amino acid nitrogen isotopes suggest shifting nitrogen balance of pregnant sharks across gestation.

Nitrogen isotope (δ15N) analysis of bulk tissues and individual amino acids (AA) can be used to assess how consumers maintain nitrogen balance with broad implications for predicting individual fitness. For elasmobranchs, a ureotelic taxa thought to be constantly nitrogen limited, the isotopic effects associated with nitrogen-demanding events such as prolonged gestation remain unknown. Given the linkages between nitrogen isotope variation and consumer nitrogen balance, we used AA δ15N analysis of muscle and liver tissue collected from female bonnethead sharks (Sphyrna tiburo, n = 16) and their embryos (n = 14) to explore how nitrogen balance may vary across gestation. Gestational stage was a strong predictor of bulk tissue and AA δ15N values in pregnant shark tissues, decreasing as individuals neared parturition. This trend was observed in trophic (e.g., Glx, Ala, Val), source (e.g., Lys), and physiological (e.g., Gly) AAs. Several potential mechanisms may explain these results including nitrogen conservation, scavenging, and bacterially mediated breakdown of urea to free ammonia that is used to synthesize AAs. We observed contrasting patterns of isotopic discrimination in embryo tissues, which generally became enriched in 15N throughout development. This was attributed to greater excretion of nitrogenous waste in more developed embryos, and the role of physiologically sensitive AAs (i.e., Gly and Ser) to molecular processes such as nucleotide synthesis. These findings underscore how AA isotopes can quantify shifts in nitrogen balance, providing unequivocal evidence for the role of physiological condition in driving δ15N variation in both bulk tissues and individual AAs.

Tidal and diel effects on the movement and space use of bull sharks (Carcharhinus leucas) and bonnetheads (Sphyrna tiburo) in a Florida Estuary

Tidal and diel effects on the movement and space use of bull sharks (Carcharhinus leucas) and bonnetheads (Sphyrna tiburo) in a Florida Estuary

Mercury concentrations and trophic relations in sharks of the Pacific Ocean of Colombia

Sharks are fished for human consumption in Colombia, and fins are exported illegally to international markets. The goal was to identify differences in total mercury (THg) concentrations in fins and muscles of shark species seized in the Buenaventura port (Colombian Pacific), and to assess potential human health risks related to shark consumption. Seven species were considered in this study: Pelagic Thresher (Alopias pelagicus), Pacific Smalltail Shark (Carcharhinus cerdale), Brown Smoothhound (Mustelus henlei), Sicklefin Smoothhound (Mustelus lunulatus), Scalloped Bonnethead (Sphyrna corona), Scalloped Hammerhead (Sphyrna lewini), and Bonnethead Shark (Sphyrna tiburo), and THg was analyzed in shark tissues. 24% muscle samples concentrations were above international recommended limits for human consumption, especially for A. pelagicus and S. lewini. Stable isotopes (δ13C and δ15N) analysis showed a foraging overlapping in coastal habitats, where overfishing usually occurs. This study provides useful scientific information to develop management plans for sharks in Colombia and neighboring countries.

Defining distribution and habitat use of west-central Florida's coastal sharks through a research and education program.

Identifying critical habitat for highly mobile species such as sharks is difficult, but essential for effective management and conservation. In regions where baseline data are lacking, non‐traditional data sources have the potential to increase observational capacity for species distribution and habitat studies. In this study, a research and education organization conducted a 5‐year (2013–2018) survey of shark populations in the coastal waters of west‐central Florida, an area where a diverse shark assemblage has been observed but no formal population analyses have been conducted. The objectives of this study were to use boosted regression tree (BRT) modeling to quantify environmental factors impacting the distribution of the shark assemblage, create species distribution maps from the model outputs, and identify spatially explicit hot spots of high shark abundance. A total of 1036 sharks were captured, encompassing eleven species. Abundance hot spots for four species and for immature sharks (collectively) were most often located in areas designated as “No Internal Combustion Engine” zones and seagrass bottom cover, suggesting these environments may be fostering more diverse and abundant populations. The BRT models were fitted for immature sharks and five species where n > 100: the nurse shark (Ginglymostoma cirratum), blacktip shark (Carcharhinus limbatus), blacknose shark (C. acronotus), Atlantic sharpnose shark (Rhizoprionodon terraenovae), and bonnethead (Sphyrna tiburo). Capture data were paired with environmental variables: depth (m), sea surface temperature (°C), surface, middle, and bottom salinity (psu), dissolved oxygen (mg/L), and bottom type (seagrass, artificial reef, or sand). Depth, temperature, and bottom type were most frequently identified as predictors with the greatest marginal effect on shark distribution, underscoring the importance of nearshore seagrass and barrier island habitats to the shark assemblage in this region. This approach demonstrates the potential contribution of unconventional science to effective management and conservation of coastal sharks.

Phylogeography and population genetics of the cryptic bonnethead shark Sphyrna aff. tiburo in Brazil and the Caribbean inferred from mtDNA markers.

Resolving the identity, phylogeny and distribution of cryptic species within species complexes is an essential precursor to management. The bonnethead shark, Sphyrna tiburo, is a small coastal shark distributed in the Western Atlantic from North Carolina (U.S.A.) to southern Brazil. Genetic analyses based on mitochondrial markers revealed that bonnethead sharks comprise a species complex with at least two lineages in the Northwestern Atlantic and the Caribbean (S. tiburo and Sphyrna aff. tiburo, respectively). The phylogeographic and phylogenetic analysis of two mitochondrial markers [control region (mtCR) and cytochrome oxidase I (COI)] showed that bonnethead sharks from southeastern Brazil correspond to S. aff. tiburo, extending the distribution of this cryptic species >5000 km. Bonnethead shark populations are only managed in the U.S.A. and in the 2000s were considered to be regionally extinct or collapsed in southeast Brazil. The results indicate that there is significant genetic differentiation between S. aff. tiburo from Brazil and other populations from the Caribbean (ΦST =0.9053, P < 0.000), which means that collapsed populations in the former are unlikely to be replenished from Caribbean immigration. The species identity of bonnethead sharks in the Southwest Atlantic and their relationship to North Atlantic and Caribbean populations still remains unresolved. Taxonomic revision and further sampling are required to reevaluate the status of the bonnethead shark complex through its distribution range.