Rhizoprionodon Terraenovae Research Articles

Seasonality and relative abundance within an elasmobranch assemblage near a major biogeographic divide.

Nearshore waters are utilized by elasmobranchs in various ways, including foraging, reproduction, and migration. Multiple elasmobranch species have been previously documented in the nearshore waters of North Carolina, USA, which has a biogeographic break at Cape Hatteras on the Atlantic coast. However, comprehensive understanding of the elasmobranch community in this region is still lacking. Monthly year-round trawling conducted along two ocean transects (near Cape Lookout and Masonboro Inlet in 5 to 18 m depth) in Onslow Bay, North Carolina provided the opportunity to examine the dynamics and seasonal patterns of this community using a multivariate approach, including permutational multivariate analysis of variance and nonparametric BIO-ENV analysis. From November 2004 to April 2008, 21,149 elasmobranchs comprised of 20 species were caught, dominated by spiny dogfish (Squalus acanthias) and clearnose skate (Rostroraja eglanteria). All species exhibited seasonal variation in abundance, but several key species contributed the most to seasonal differences in species composition within each transect. Spiny dogfish was most abundant in the winter at both locations, comprised mainly of mature females. Although clearnose skate was caught in all seasons, the species was most abundant during the spring and fall. Atlantic sharpnose (Rhizoprionodon terraenovae) was one of the most abundant species in the summer, and two distinct size cohorts were documented. Temperature appeared to be the main abiotic factor driving the community assemblage. The extensive year-round sampling provided the ability to better understand the dramatic seasonal variation in species composition and provides new information on the relative abundance of several understudied elasmobranch species that may be of significant ecological importance. Our results underscore the importance of inner continental shelf waters as important elasmobranch habitat and provide baseline data to examine for future shifts in timing and community structure at the northern portion of the biogeographic break at Cape Hatteras.

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.

Sharks associated with a large sand shoal complex: Community insights from longline and acoustic telemetry surveys.

Offshore sand shoals are a coveted sand source for coastal restoration projects and as sites for wind energy development. Shoals often support unique fish assemblages but their habitat value to sharks is largely unknown due to the high mobility of most species in the open ocean. This study pairs multi-year longline and acoustic telemetry surveys to reveal depth-related and seasonal patterns in a shark community associated with the largest sand shoal complex in east Florida, USA. Monthly longline sampling from 2012-2017 yielded 2,595 sharks from 16 species with Atlantic sharpnose (Rhizoprionodon terraenovae), blacknose (Carcharhinus acronotus), and blacktip (C. limbatus) sharks being the most abundant species. A contemporaneous acoustic telemetry array detected 567 sharks from 16 species (14 in common with longlines) tagged locally and by researchers elsewhere along the US East Coast and Bahamas. PERMANOVA modeling of both datasets indicate that the shark species assemblage differed more across seasons than water depth although both factors were important. Moreover, the shark assemblage detected at an active sand dredge site was similar to that at nearby undisturbed sites. Water temperature, water clarity, and distance from shore were habitat factors that most strongly correlated to community composition. Both sampling approaches documented similar single-species and community trends but longlines underestimated the shark nursery value of the region while telemetry-based community assessments are inherently biased by the number of species under active study. Overall, this study confirms that sharks can be an important component of sand shoal fish communities but suggests that deeper water immediately adjacent to shoals (as opposed to shallow shoal ridges) is more valuable to some species. Potential impacts to these nearby habitats should be considered when planning for sand extraction and offshore wind infrastructure.

Observations on heterodonty within the dentition of the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), from the north-central Gulf of Mexico, USA, with implications on the fossil record.

The Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (Richardson, 1836), is the most common small coastal requiem shark in the north-central Gulf of Mexico, USA. Despite this fact, little is known about the dental variation within this taxon. To help rectify this shortcoming, we examined 126 male and female R. terraenovae jaws sets across all maturity stages to document the various types of heterodonty occurring in the dentition of this taxon. Quantitative data gathered from a subset of our sample allowed for us to place teeth within the dentition of R. terraenovae into standardized upper and lower parasymphyseal/symphyseal, anterior lateral, and posterior tooth groups. As with all carcharhinid sharks, the dentition of R. terraenovae exhibits monognathic and dignathic heterodonty. We also observed significant ontogenetic heterodonty in the species, as the teeth and dentition progress through five generalized developmental stages as the shark matures. The ontogenetic development of serrations on the teeth appears to be closely related to documented dietary changes as the shark matures. Initial diets are comprised of high percentages of invertebrate prey like shrimp, crabs, and squid, but this transitions through ontogeny to a diet that is more reliant on fishes. We also provide the first documentation of gynandric heterodonty in mature male R. terraenovae, with development of these seasonal teeth likely enabling a male to grasp female sharks during copulation. Our analysis revealed a tremendous amount of variation in the dentition of R. terraenovae, which has direct implications on the taxonomy of fossil Rhizoprionodon. A comparison of the jaws in our sample to those of the extant species of Rhizoprionodon and the morphologically similar Loxodon, Scoliodon, and Sphyrna allowed us to formulate a list of generic-level characteristics to assist with the identification of isolated teeth. When applied to the fossil record, it is shown that some species previously assigned to Rhizoprionodon likely belong to one of the other aforementioned genera. The earliest occurrence of unequivocal Rhizoprionodon teeth in the fossil record are those of the Eocene †R. ganntourensis (Arambourg, 1952), the oldest records of which occur in early Ypresian deposits in Alabama and Mississippi, USA. The early Eocene occurrence of unequivocal fossil Rhizoprionodon teeth in Alabama predates the first occurrence of Negaprion, Galeocerdo, and Carcharhinus teeth in the state, supporting published molecular and morphological phylogenies positing a basal position for Rhizoprionodon within the Carcharhinidae.

Ontogenetic habitat partitioning among four shark species within a nursery ground

Context Nursery areas provide refuge from predators, rich foraging grounds, and physical conditions conducive to growth and development of juvenile inhabitants. Specifically, the Mississippi Sound in the northern Gulf of Mexico is likely a nursery ground for multiple large and small coastal sharks. Aims and methods Using over a decade of shark survey catch data, we employed habitat modelling approaches to identify preferred environmental conditions and spatial distribution, and quantify core habitat overlap within the Mississippi Sound for young-of-year (YOY), juvenile and adult life stages of four coastal shark species. Results YOY Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus) and finetooth (Carcharhinus isodon) sharks showed a preference for a combination of shallow, warm, low salinity, low dissolved oxygen and turbid waters. Corresponding to shared environmental preferences, spatial distributions of YOY sharks showed a high degree of overlap, particularly in the northern portion of the Mississippi Sound where few adult sharks were observed, suggesting that these life stages partition themselves to avoid predation. Conclusion and implications With a continued rise in US coastal shark populations, we hope this study can help further refine essential fish habitat for these coastal species and provide a framework analysis that can be used to understand habitat partitioning in other regions.

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.

Assessing the catch efficiency of predators in the presence of prey using experimental gillnets in a temperate estuary

Fishery-independent sampling is designed to representatively sample faunal communities based on the effort-standardized catch rates of individual gears. In estuaries, experimental gillnets are widely used due to their ability to passively sample mobile fish communities with multiple panels of decreasing mesh sizes. To test if concurrently collected prey in experimental gillnets create a trophic-related sampling bias for predatory or scavenging (hereafter, predators) species, we set large mesh gillnets comprising two treatments, baited (n = 80) and unbaited (n = 78), using a paired design in Back Sound, North Carolina. Furthermore, we analyzed data from the North Carolina Division of Marine Fisheries (NC DMF) estuarine gillnet monitoring program with boosted regression tree models to correlate estuarine predator occurrence with environmental factors (salinity, temperature), habitat presence, and families of common prey species as predictor variables. In our experimental manipulation, neither total catch nor community composition statistically varied between treatments, determined using permutational multivariate analysis of variance (PERMANOVA). However, species richness estimated using species accumulation curves was higher in baited gillnets, with one frequently caught species (Atlantic sharpnose sharks) collected exclusively in baited gillnets. In NC DMF surveys, prey group variables were more important (average model importance; 10% ± 8.8% SD) than habitat composition (2% ± 1.7%) to the presence of predators, but less than abiotic environmental variables (21.1% ± 13.1%). This combined manipulative and mensurative study revealed mixed evidence towards increased catch efficiency of predatory fish collected in widely used experimental gillnets. These results should be considered in refining abundance estimations for estuarine predators, as catch efficiency for some piscivorous predators may vary in relation to the abundance and catch efficiency of prey.

Environmental correlates of elasmobranch and large fish distribution in a river-dominated estuary

Coastal areas serve as vital habitat for many marine fishes and often host broad gradients of environmental conditions that result in diverse species assemblages. Understanding the influence of environmental variables on the distribution and abundance of fishes is especially important for devising appropriate management strategies. We documented large fish community structure in the Apalachicola Bay system from 2018 to 2021 using fishery-independent longline and gillnet surveys. Spatiotemporal variation in fish assemblages was evaluated with permutational multivariate ANOVA, while community- and species-level habitat relationships were described across gradients of environmental variables with non-metric multidimensional scaling and generalized additive models. We captured 5085 fishes from 17 elasmobranch and 33 bony fish species, with gafftopsail catfish Bagre marinus, blacktip shark Carcharhinus limbatus, Atlantic sharpnose shark Rhizoprionodon terraenovae, and hardhead catfish Ariopsis felis comprising 82.1% of the total catch. Fish communities varied spatially throughout the system, and changes in these communities were most strongly correlated with gradients in salinity, clarity, and depth. We documented higher species richness and density of young elasmobranchs in our surveys compared to adjacent systems, supporting past suggestions that this area serves as important juvenile shark habitat. We suggest that flow from the Apalachicola River, transporting nutrients to the system and supporting numerous environmental niches across spatiotemporal scales, plays an influential role in maintaining the elevated diversity and density of elasmobranchs observed in this study.

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.

REDESCRIPTION OF CATHARIOTREMA SELACHII (MACCALLUM, 1916) JOHNSTON AND TIEGS, 1922 (MONOGENOIDEA: MONOCOTYLIDAE), EMENDATION OF MONOTYPIC CATHARIOTREMA JOHNSTON AND TIEGS, 1922, AND PROPOSAL OF CATHARIOTREMATINAE N. SUBFAM. BASED ON MORPHOLOGICAL AND NUCLEOTIDE EVIDENCE.

We herein redescribe the enigmatic Cathariotrema selachii (MacCallum, 1916) Johnston and Tiegs, 1922 based on the holotype, paratypes, and newly collected specimens infecting the olfactory organ of 5 shark species from the Gulf of Mexico (all new host records): scalloped hammerhead shark, Sphyrna lewini (Griffith and Smith, 1834) (Carcharhiniformes: Sphyrnidae); great hammerhead shark, Sphyrna mokarran (Rüppell, 1837); blacktip shark, Carcharhinus limbatus (Müller and Henle, 1839) (Carcharhiniformes: Carcharhinidae); spinner shark, Carcharhinus brevipinna (Müller and Henle, 1839); and Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson, 1836) (Carcharhinidae). These specimens were morphologically indistinguishable from each other and from MacCallum's holotype and paratypes. Those sequenced had identical first internal transcribed spacer (ITS1) and large subunit ribosomal DNA (28S) nucleotide sequences. As such, C. selachii infects sharks of 2 orders (Carcharhiniformes, Lamniformes) and 3 families (Carcharhinidae, Sphyrnidae, Lamnidae) in the Northwestern Atlantic Ocean (type locality) and Gulf of Mexico (new records herein). This report is the first of new specimens of C. selachii in the Atlantic Ocean Basin in 95 yr and corrects long-standing error cascades and ambiguities concerning the morphology and systematic placement of C. selachii. Considering morphology and nucleotide-based phylogenetic evidence (28S, Bayesian analysis), we herein emend monotypic CathariotremaJohnston and Tiegs, 1922 and propose Cathariotrematinae Bullard n. subfam. for it and 4 other genera (all formerly assigned to Merizocotylinae Johnston and Tiegs, 1922). These genera comprise species infecting only the nose of sharks (monotypic Cathariotrema, SqualotremaKearn and Green, 1983 and SeptitremaKheddam, Chisholm, and Tazerouti, 2020 plus 3 species of TriloculotremaKearn, 1993) and nose of a chimaera (monotypic HolocephalocotyleDerouiche, Neifar, Gey, Justine, and Tazerouti, 2019). Cathariotrematinae differs from Merizocotylinae by having a 3-part attachment organ and by lacking open loculi that symmetrically encircle a cluster of >2 loculi in the center of the haptor. Monophyletic Cathariotrematinae (with sequences representing species of Cathariotrema, Triloculotrema, and Holocephalocotyle only) was sister to monophyletic Merizocotylinae, which together were sister to monophyletic Calicotylinae Monticelli, 1903. These subfamilies comprise a monophyletic group of monocotylids that have a double vagina and infect extrabranchial, enclosed niches (urogenital system, body cavity, olfactory chamber/nose) on their shark, ray, and chimaera hosts (all other monocotylids have a single vagina and infect the gill or body surfaces of rays only). Monocotylinae Taschenberg, 1879 and Decacotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 were recovered as monophyletic. Heterocotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 remained paraphyletic. We accept ParacalicotyleSzidat, 1970.

An ecological assessment of large coastal shark communities in South Florida

Given population declines of many shark species, coupled with increasing conservation efforts and recoveries, there is a need for baseline assessments and continued monitoring of shark populations to support management. The waters of South Florida, USA, are used by a diverse array of sharks that occur among a mosaic of habitats and management zones. Here we conducted standardized drumline surveys from Miami through the middle Florida Keys to examine spatial, seasonal and environmental patterns in shark occurrence, catch per unit effort, composition, and demographic structure. Between 2009 and 2021, a total of 21,755 drumlines were deployed, capturing 3398 sharks, comprising fifteen species. Ginglymostoma cirratum, (n = 1335), Carcharhinus limbatus, (n = 650), Negaprion brevirostris, (n = 314), C. leucas, (n = 253), and Sphyrna mokarran, (n = 238) were the most common species encountered. Overall, the largest shark surveyed was a 450 cm S. mokarran and the smallest shark was a 50 cm Rhizoprionodon terraenovae. At the assemblage level, relative abundance among regions and seasons were generally similar; however clear species-specific patterns of abundance, size structure, and sex-composition were detected by season, region, habitat, and management zones. Of the physical conditions evaluated, habitat type and depth emerged as the most influential parameters affecting abundances and sizes of species captured. While few species exhibited significant differences in catches by management zone, areas with the most restrictive fisheries regulations generally supported higher abundances for which differences were detected. These data serve as a baseline for future monitoring of shark populations in South Florida and assessing their response to environmental change.

Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018

AbstractHarvest may have myriad effects on target species, including a change in population size structure. To assess whether size shifts have occurred among managed coastal species of shark (superorder Selachimorpha), we examined the population size structure of 12 species caught during a nearly five‐decade‐long fishery‐independent survey conducted in Onslow Bay, North Carolina, using standardized longline gear. We evaluated trends in mean fork length (FL), median FL, and index of maximum FL (L90%) for each species separately across time using linear regression models. We also examined trends in size‐classes (200‐mm bins) and catch per unit effort for each species over time. For 10 of the 12 species (excluding sample‐size‐constrained Tiger Shark Galeocerdo cuvier and Bull Shark Carcharhinus leucas), size structure metrics indicated decreasing sizes over time, although statistical confidence for these patterns varied across species and metrics. Strongest statistical support for declining sizes was observed for Blacknose Shark Carcharhinus acronotus (mean FL, median FL, L90%), Dusky Shark Carcharhinus obscurus (L90%), Smooth Dogfish Mustelus canis (L90%), and Atlantic Sharpnose Shark Rhizoprionodon terraenovae (L90%). Magnitude of decreases in L90% among these 10 species during the survey ranged from roughly 9% (Silky Shark Carcharhinus falciformis; 83‐mm decrease) to 35% (Sandbar Shark Carcharhinus plumbeus; 541‐mm decrease). Our findings indicate a potential for fishing pressure to exert directional selection on these coastal shark species, although further research is needed regarding the nature of size‐dependent catchability and species‐specific vital rates to adequately evaluate these dynamics. Furthermore, in addition to the removal of “great sharks,” decreasing sizes of small coastal sharks, such as Blacknose Shark, Smooth Dogfish, and Atlantic Sharpnose Shark (i.e., “mesopredators”), suggest that harvest may have pervasive effects on species throughout this assemblage.

Less Soak Time Saves Those upon the Line: Capture Times and Hooking Mortality of Sharks Caught on Bottom Longlines

AbstractThe National Marine Fisheries Service is mandated by the Magnuson–Stevens Fishery Conservation and Management Act to implement effective annual catch limits and accountability measures to prevent overfishing. These requirements compel further research into alternative fishing practices that could reduce mortality of sharks (class Chondrichthyes) and allow fishers to release unwanted sharks to the water alive, while still effectively catching targeted species. We used hook timers and temperature–depth recorders aboard contracted vessels and participants in the National Marine Fisheries Service’s Shark Research Fishery to collect hooking time and time‐on‐the‐line data for 10 species of sharks that were commonly encountered in the fishery. A subset of standardized fishing sets compared the most popular circle hook and J‐hook models. Over 60% of sharks were hooked within 4 h of hook soak time. The fastest to bite the hook was the Atlantic Sharpnose Shark Rhizoprionodon terraenovae and the slowest was the Dusky Shark Carcharhinus obscurus. Shark resilience to time on the longline varied among species, with Sandbar Shark C. plumbeus exhibiting the most resilience and Atlantic Sharpnose Shark the least. Shorter set soak times, approximately 2 h, would still maximize catch, while minimizing at‐vessel mortality. The most frequently used circle hook model did not significantly reduce at‐vessel mortality over large J‐style hooks. The recent circle hook requirement will have little effect for fishers that previously used 12/0 J‐hooks, but it may be beneficial by preventing the use of smaller J‐hooks that are more likely to cause at‐vessel mortality.

Using fisher-contributed secondary fins to fill critical shark-fisheries data gaps.

Developing-world shark fisheries are typically not assessed or actively managed for sustainability; one fundamental obstacle is the lack of species and size-composition catch data. We tested and implemented a new and potentially widely applicable approach for collecting these data: mandatory submission of low-value secondary fins (anal fins) from landed sharks by fishers and use of the fins to reconstruct catch species and size. Visual and low-cost genetic identification were used to determine species composition, and linear regression was applied to total length and anal fin base length for catch-size reconstruction. We tested the feasibility of this approach in Belize, first in a local proof-of-concept study and then scaling it up to the national level for the 2017-2018 shark-fishing season (1,786 fins analyzed). Sixteen species occurred in this fishery. The most common were the Caribbean reef (Carcharhinus perezi), blacktip (C. limbatus), sharpnose (Atlantic [Rhizoprionodon terraenovae] and Caribbean [R. porosus] considered as a group), and bonnethead (Sphyrna cf. tiburo). Sharpnose and bonnethead sharks were landed primarily above size at maturity, whereas Caribbean reef and blacktip sharks were primarily landed below size at maturity. Our approach proved effective in obtaining critical data for managing the shark fishery, and we suggest the tools developed as part of this program could be exported to other nations in this region and applied almost immediately if there were means to communicate with fishers and incentivize them to provide anal fins. Outside the tropical Western Atlantic, we recommend further investigation of the feasibility of sampling of secondary fins, including considerations of time, effort, and cost of species identification from these fins, what secondary fin type to use, and the means with which to communicate with fishers and incentivize participation. This program could be a model for collecting urgently needed data for developing-world shark fisheries globally. Article impact statement: Shark fins collected from fishers yield data critical to shark fisheries management in developing nations.

Ontogenetic Shifts in Brain Size and Brain Organization of the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae

Throughout an animal’s life, species may occupy different environments and exhibit distinct life stages, known as ontogenetic shifts. The life histories of most sharks (class: Chondrichthyes) are characterized by these ontogenetic shifts, which can be defined by changes in habitat and diet as well as behavioral changes at the onset of sexual maturity. In addition, fishes experience indeterminate growth, whereby the brain and body grow throughout the organism’s life. Despite a presupposed lifelong neurogenesis in sharks, very little work has been done on ontogenetic changes in the brain, which may be informative about functional shifts in sensory and behavioral specializations. This study quantified changes in brain-body scaling and the scaling of six major brain regions (olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and medulla oblongata) throughout ontogeny in the Atlantic sharpnose shark, Rhizoprio­nodon terraenovae. As documented in other fishes, brain size increased significantly with body mass throughout ontogeny in this species, with the steepest period of growth in early life. The telencephalon, diencephalon, optic tectum, and medulla oblongata scaled with negative allometry against the rest of the brain throughout ontogeny. However, notably, the olfactory bulbs and cerebellum scaled hyperallometrically to the rest of the brain, whereby these structures enlarged disproportionately as this species matured. Changes in the relative size of the olfactory bulbs throughout ontogeny may reflect an increased reliance on olfaction at later life history stages in R. terraenovae, while changes in the relative size of the cerebellum throughout ontogeny may be indicative of the ability to capture faster prey or an increase in migratory nature as this species moves to offshore habitats, associated with the onset of sexual maturity.

Analysis of Trace Element Concentrations and Antioxidant Enzyme Activity in Muscle Tissue of the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae.

Metals occur naturally in the environment; however, anthropogenic practices have greatly increased metal concentrations in waterways, sediments, and biota. Metals pose health risks to marine organisms and have been associated with oxidative stress, which can lead to protein denaturation, DNA mutations, and cellular apoptosis. Sharks are important species ecologically, recreationally, and commercially. Because they occupy a high trophic level, assessing muscle tissue metal concentrations in sharks may reflect metal transfer in marine food webs. In this study, concentrations of cadmium, copper, lead, nickel, selenium, silver, and zinc were measured in the muscle of Rhizoprionodon terraenovae (Atlantic sharpnose shark) from 12 sites along the coast of the southeastern United States. Activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) also were examined in the muscle tissue of R. terraenovae. A total of 165 samples were analyzed, and differences in trace element bioaccumulation and enzyme activity were observed across sites. R. terraenovae samples collected from South Florida and South Carolina had the highest cumulative trace element concentrations whereas those collected from North Carolina and Alabama had the lowest cumulative concentrations. Trace element concentrations in shark muscle tissue were significantly correlated to antioxidant enzyme activity, particularly with glutathione peroxidase, suggesting that this enzyme may serve as a non-lethal, biomarker of metal exposure in R. terraenovae. This is one of the most extensive studies providing reference levels of trace elements and oxidative stress enzymes in a single elasmobranch species within the U.S.

Diet shifts of Rhizoprionodon terraenovae from the southern Gulf of Mexico: possible scenario by temperature changes

The current study examined the stomach contents of the Atlantic sharpnose shark (Rhizoprionodon terraenovae) in the southern Gulf of Mexico during 2015 to understand the relationship between diet and changes in sea surface temperature (SST). Prey-specific index of relative importance (%PSIRI), diet breadth (Bi), trophic level (TrL), and trophic overlap (PERMANOVA) were calculated between sexes, body size, and climatic seasons (dry, rainy and winter storm). The lowest temperature recorded in the area was during February (23.9°C), and the highest was during August (29.1°C). A total of 124 stomachs were analyzed, with 54.84% containing food. The trophic spectrum was composed of 32 identified prey, with demersal fish (Haemulon plumierii; %PSIRI = 22.82) and pelagic fish (Sardinella aurita; %PSIRI = 12.83) being the most important. According to the diet breadth (Bi = 0.002), Costello's graph, and trophic level (TrL = 4.2), R. terraenovae is a specialist tertiary consumer. PERMANOVA indicated significant trophic differences between sexes (F = 32.22; P &lt; 0.05), body size (F = 13.68; P &lt; 0.05), and among climatic seasons (F = 23.86; P &lt; 0.05). Spearman's correlation indicated a negative relationship between the diversity of prey consumed by R. terraenovae and sea surface temperature (r = -0.75; P &lt; 0.05). Therefore, diet for R. terraenovae is associated with SST, allowing for the development of possible scenarios related to climatic phenomena like climate change.

Spatial variability in the fecundity of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) in the northern Gulf of Mexico

Spatial variability in the fecundity of Atlantic sharpnose sharks (Rhizoprionodon terraenovae) in the northern Gulf of Mexico

Distribution and abundance of elasmobranchs and large teleost fishes in a subtropical seagrass ecosystem: community structure along environmental and spatial gradients

We used fishery-independent gillnet and longline surveys to document the elasmobranch and large teleost assemblages in the Florida Big Bend seagrass system and examine how ichthyofaunal assemblages were related to environmental factors across the region. A total of 159 paired gillnet sets were conducted in June through August from 2009 to 2012. The Big Bend, an expansive system nearly 300 km in length with seagrass from nearshore up to 20 km offshore, is inhabited by at least 13 species of elasmobranch and 56 species of larger teleost fishes during the summer. Five species dominate, including three species of sharks, two carcharhinids (Atlantic sharpnose sharks, Rhizoprionodon terraenovae Richardson, and blacktip sharks, Carcharhinus limbatus Mueller and Henle) and one sphyrnid (bonnethead sharks, Sphyrna tiburo Linnaeus), and two species of ariid catfishes (hardhead catfish, Ariopsis felis Linnaeus, and gafftopsail catfish, Bagre marinus Mitchill). We used a tiered community analysis approach which included hierarchical cluster analysis, indicator species analysis, and non-metric multidimensional scaling with environmental fitting using a Bray-Curtis dissimilarity matrix. Abiotic variables correlated with community structure included salinity, water clarity, and depth. Summer ichthyofaunal assemblages were spatially variable with a distinct southern zone where salinity and water clarity are consistently high relative to the rest of the system, and we hypothesize the observed patterns in community structure are related to a gradient of river influence in the Big Bend.

Four New Species of Paraorygmatobothrium (Eucestoda: Phyllobothriidea) from Sharks of the Gulf of Mexico and the Atlantic Ocean, with Comments on Their Host Specificity

Four new species of Paraorygmatobothrium are described from carcharhinid shark species from the Gulf of Mexico and the U.S. coast of the northwestern Atlantic Ocean. Paraorygmatobothrium bullardi n. sp. is described from Carcharhinus brevipinna as its type host, and from Carcharhinus acronotus and Carcharhinus limbatus. Paraorygmatobothrium campbelli n. sp. is described from Rhizoprionodon terraenovae. Paraorygmatobothrium deburonae n. sp. is described from Carcharhinus isodon as its type host, as well as from C. brevipinna, C. limbatus, and R. terraenovae. Paraorygmatobothrium mattisi n. sp. is described from R. terraenovae as its type host, and from C. brevipinna and C. limbatus. These 4 species differ from other species of Paraorygmatobothrium and from each other in bothridial microthrix shape, and in various combinations of features such as the total length of the worm, apical sucker size, bothridial musculature, proglottid number, testes number, and genital pore position. Difficulty in differentiating these 4 species from one another, and from other species of Paraorygmatobothrium, points to limitations in the use of morphology alone to recognize species diversity in this genus. A phylogenetic analysis of Paraorygmatobothrium and related genera, based on partial (D1-D3) 28S rDNA sequence data, confirms that the genus is not monophyletic. Genetic distances of COI revealed that sequence divergence between species of Paraorygmatobothrium is generally at least an order of magnitude larger than COI divergence within a species. Patterns of host use for 3 of the new species are consistent with previous findings that point to a lack of host specificity in Paraorygmatobothrium.