Matthew Ajemian, Gregory Stunz
Harte Research Institute for Gulf of Mexico Studies, Texas A&M University-Corpus Christi, Corpus Christi, TX, USA
Migratory Behavior and Habitat Use of Large Sharks in the Western Gulf of Mexico
Large sharks serve as critical apex predators in many marine ecosystems around the world, yet the habitat requirements and migration patterns of these species remain poorly understood throughout much of their ranges. The growing demand for shark habitat use information has supported a proliferation of satellite biotelemetry studies. Despite the multitude of anthropogenic pressures in the region, few data exist on large shark movement patterns in the western Gulf of Mexico. In summer of 2014, four large sharks (2 Scalloped Hammerhead, Sphyrna lewini; 2 Tigers, Galeocerdo cuvier) were tagged and released near an offshore production platform and tracked with Smart Position or Temperature transmitters. Sharks were tracked for thousands of miles, and demonstrated some important ecosystem connections between nearshore locales and open waters of the Gulf of Mexico. While Scalloped Hammerheads provided more frequent reports and fidelity to the Texas continental shelf, Tiger Sharks exhibited larger dispersal patterns, including a cross-basin venture towards the Campeche escarpment (Mexico) as shelf waters cooled in December and a subsequent return to the Texas shelf. Tiger Sharks also demonstrated use of NOAA-designated Habitats Areas of Particular Concern such as the south Texas hard banks and the Flower Gardens National Marine Sanctuary. Our work highlights the connected nature of many seemingly disparate habitats within the Gulf of Mexico by large sharks and the importance of establishing satellite tagging programs for conservation and management purposes. Continued tagging efforts in 2015 will assess potential year-to-year variability in the movement and habitat use patterns observed to date.
Csilla Ari1, 2, 3, Dominic D`Agostino1
1University of South Florida, FL, USA, 2Foundation for Oceans of the Future, Budapest, Hungary, 3Manta Pacific Research Foundation, HI, USA
Melanosome Aggregations Might Cause Manta Ray Skin Change Color
Natural body coloration and spot markings of giant manta rays are used to identify individuals and to distinguish species. However, recent observations revealed rapid and long-term coloration changes of giant manta rays, suggesting that their body pigmentation is not permanent over their lifespan as assumed before. The rapid coloration changes happened within a few minutes, while such rapid changes were not described in other elasmobranch species yet. In order to reveal the mechanism of these changes, histological studies were performed on giant manta ray skin. The results suggest that changes of the degree of melanophore and melanosome aggregations might contribute to coloration changes in the manta ray skin. Further studies are needed to determine what regulates the changes in melanosome aggregations and to understand the role of such changes in giant manta rays.
Amanda Barker, John Gold, David Portnoy
Texas A&M University Corpus Christi, Corpus Christi, TX, USA
Identification, Stock Assessment, and Habitat Usage of Cryptic Hammerhead Sharks
The scalloped hammerhead (Sphyrna lewini) and the recently discovered Carolina hammerhead (Sphyrna gilberti) are cryptic species that are sympatrically distributed in the southeastern United States. Differing only in the number of precaudal vertebrae, scalloped and Carolina hammerheads are morphologically conserved; a way to distinguish them in situ has yet to be determined. Due to its recent discovery and lack of morphological differentiation Carolina hammerheads have likely been included in previous stock assessment for scalloped hammerheads, leading to an overestimation of scalloped hammerhead abundance. We will use double digest restriction-site associated DNA (ddRAD) sequencing to genotype individuals at thousands of single nucleotide polymorphisms (SNPs), and a panel of SNPs will be identified that can be used to reliably identify each species. Genetic and ecological data will be used to estimate relative abundance and habitat utilization of each species within known nurseries off the east coast of the United States. Because nursery utilization may not be equivalent between the species, one or more nurseries may be critical to one or both individual species persistence. For both species we will also generate estimates of baseline genetic diversity and conduct a preliminary assessment of stock structure to provide information useful for future species-specific management.
Andrea Bernard1, Cassandra Ruck1, Vincent Richards2, Jim Gelsleichter3, Kevin Feldheim4, Mahmood Shivji1
1Save Our Seas Shark Research Center, Nova Southeastern University, Dania Beach, FL, USA, 2Clemson University, Clemson, SC, USA, 3University of North Florida, Jacksonville, FL, USA, 4Field Museum, Pritzker Laboratory for Molecular Systematics and Evolution, Chicago, IL, USA
The Genetic Connectivity of a Euryhaline Elasmobranch, the Atlantic Stingray (Dasyatis sabina)
Identifying the genetic connectivity of elasmobranchs inhabiting coastal waters remains an important global priority, as these species are particularly susceptible to human mediated impacts and declines given their close proximity to highly populated areas. The Atlantic stingray (Dasyatis sabina), a small, coastal species whose range spans the western North Atlantic (Florida to Chesapeake Bay) and Gulf of Mexico, is one of the few elasmobranchs capable of occupying both estuarine and freshwater habitats. Within Florida waters, a putative ‘resident’ population inhabits the freshwater St. Johns River System (SJRS); however, the extent of this population’s connectivity to the remainder of its distribution remains unknown. To examine the genetic connectivity of the Atlantic stingray across its southern US distribution, including the SJRS, a total of 312 individuals from 11 sampling locations were genotyped at nine species-specific microsatellite loci. Population- and individual-level analyses identified high levels of genetic population structure among collections, with coastal populations within the Gulf of Mexico showing high genetic structure (FST = 0.011 – 0.034; P <0.05) and a signal of isolation by distance (R2 = 0.957; P = 0.041). Interestingly, individual-based analyses showed that freshwater SJRS animals were differentiated from other locations, suggesting that these individuals may truly represent a ‘resident’ freshwater population. The presence of high genetic population structure, coupled with what may be locally adapted populations, suggests that care must be taken to conserve this species, as the extinction of even a single population may result in the irreversible loss of genetic diversity and adaptive potential.
Beth Bowers, Stephen Kajiura
Florida Atlantic University, Boca Raton, FL, USA
Migratory Behavior of the Blacktip Shark (Carcharhinus limbatus)
The migratory behavior of the blacktip shark (Carcharhinus limbatus) in the Western Atlantic has been anecdotally described but not empirically studied. The sharks are thought to migrate from nursery areas along the southeastern coast of the United States in the summer, to South Florida, where they remain in large aggregations (up to 800 sharks km-2) from January to April before returning northward. The first recorded description of the blacktip shark migration states that they occur north of Cape Hatteras, NC “only as a rare stray.” Given that this description was published over 70 years ago, their range might have shifted poleward in response to warming ocean temperatures, as has been demonstrated in many other marine species. To investigate the current migratory pattern of this population, ten blacktip sharks were instrumented with acoustic transmitters, while they overwintered in South Florida, and passively tracked along the eastern coast in cooperation with the Florida Atlantic Coast Telemetry (FACT) and the Atlantic Cooperative Telemetry (ACT) networks. Seven of the ten individuals were detected after instrumentation. Three of those seven individuals were detected far north of the previously reported NC limit, off Delaware Bay, NJ (1) and Long Island, NY (2). Five individuals were detected at the original capture location in South Florida the following winter, including two of the sharks that were detected in Delaware Bay and Long Island. This study provides the first empirical evidence of blacktip sharks completing a full migration cycle and suggests that their northern limit may have expanded poleward.
Darcy Bradley1, Yannis P. Papastamatiou2, Steven D. Gaines1, Jennifer E. Caselle3
1Bren School of Environmental Science & Management, University of California Santa Barbara, Santa Barbara, CA, USA, 2School of Biology, Scottish Oceans Institute, University of St Andrews, St Andrews, Scotland, UK, 3Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA, USA
Do Non-extractive Human Impacts have Quantifiable Behavioral Effects on Palmyra’s Reef Sharks?
Shark behavior can bias abundance estimates from diver-based visual surveys, thereby leading to a flawed understanding of population trends through time. The presence of this bias in diver-based visual surveys is ubiquitous in reef shark abundance estimates generated for Palmyra and the greater central Pacific. Failing to account for behavioral effects may be problematic as in most places it is impossible to differentiate changes in estimated population abundance due to behavioral modifications and those resulting from fishing. In Palmyra, we can isolate and quantify the behavioral response of reef sharks to human activities as human use of the waters surrounding Palmyra has not been constant: from 2001 to the present scientific diving, boating, and provisioning activities have significantly increased on Palmyra’s reefs. We quantified each activity to create a spatially and temporally explicit human use map of Palmyra. We then used paired baited remote underwater visual surveys (BRUVS) in research (heavy-use) and non-research (no-use) sites to assess the impact of human presence on the behavior of three species of reef shark. We found significant differences in time of first arrival in frame (p<0.05) but not maximum number of individuals in frame (maxN) for all reef shark species between heavy-use and no-use sites. In sites with minimal human impact, sharks arrived sooner, indicating greater attraction to human activity in no-use sites. By quantifying reef sharks’ responses to human activities, we can correct biased population estimates produced from existing visual survey data throughout the central Pacific.
Justin Cordova, David Ebert
Moss Landing Marine laboratories, Moss Landing, CA, USA
Species Grouping Within the Genus Apristurus Garman, 1913 Using Dermal Denticles
Apristurus is one of the largest shark genera, which encompasses 48 nominal species. Multiple morphological and molecular studies have shown the genus can be subdivided into three distinct subgroups: the A. brunneus subgroup, A. spongiceps subgroup, and A. longicephalus subgroup. This study examines the dermal denticles of three Apristurus species, one representative of each subgroup; specimens were collected off the coast of Monterey Bay CA, and Tai-chi, Taiwan. The three-species used for this study includes A. kampae for the spongiceps group; A. brunneus for the brunneus group; A. herklotsi for the longicephalus group. Dermal denticles were taken from four different locations on the specimens and observed under a dissecting microscope. Morphological features including cuspid counts, denticle size, and spacings are compared in order to find any noticeable differences. Observations reveal that the denticles of A. kampae are widely spaced and have a unicuspid structure, where the other specimens exhibited a tricuspid structure with overlapping denticles. These differences will be further examined as a means of further organizing the genus taxonomically, and to investigate whether these differences may have ecomorphological significance relative to their preferred associated habitats.
Matthew Davis, Toby Daly-Engel
University of West Florida, Pensacola, FL, USA
Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) Rangewide Genetic Stock Structure
The Atlantic Sharpnose shark is a small coastal species in the family Carcharhinidae that is common throughout the Gulf of Mexico and the Western Atlantic from Maine to Honduras. This species is regularly fished, representing as much as 45.9% of the artisanal elasmobranch fishery in the Gulf of Mexico. However, little is known about its population size, range, and movement patterns. We seek to delineate the stock structure and dispersal of this species using mixed marker molecular analysis. To date we have accumulated R. terraenovae tissue samples from a variety of locations in the Atlantic and northern Gulf of Mexico, and collections are ongoing. Connectivity will be assessed through statistical comparison of DNA sequences from both the mitochondrial and nuclear genome, including the control region and microsatellites. With these data we will delineate detailed patterns of gene flow and dispersal in R. terraenovae throughout its range, information that will enable managers and conservationists to better protect this species in the future.
Simon Dedman1, Rick Officer1, Deirdre Brophy1, Maurice Clarke2, David Reid2
1Galway-Mayo Institute of Technology, Galway, Co. Galway, Ireland, 2Marine Institute, Rinville, Co. Galway, Ireland
Modelling Abundance Hotspots for Data-poor Irish Sea Rays
Skates and rays represent one of the most vulnerable components of the fish community in temperate demersal fisheries such as the Irish Sea. They also tend to be data poor in comparison to commercially exploited teleost fish. Spatial management has been suggested as an important tool in protecting these species, but requires an understanding of the abundance distribution, and its relationship with the environment at both adult and juvenile life history stages. In this analysis, delta log-normal boosted regression tree models were used with bottom trawl survey data to derive rays’ spatial abundance, and environmental links. The modelling approach allowed the development of detailed predictive maps of abundance of four common and rare skate and ray species implicated in the fishery: thornback, spotted, cuckoo and blonde rays. The distributions were driven by a general preference for sand and courser substrates, higher salinities, temperatures and currents speeds. The abundance distribution maps were examined together with maps of skate and ray commercial landings, suggesting that the main hotspots for the species were away from the main commercial fishing areas. The maps were also compared to potential MPAs proposed for wider ecosystem protection, and the main hotspots were well covered by the proposed MPAs. This combination of the main abundance hotspots in areas of low fishing, and wider potential ecosystem protection, suggests good potential for spatial management measures to protect these species in the Irish Sea.
Hayley DeHart, Gavin Naylor
College of Charleston, Charleston, SC, USA
Comparing Demographic and Genetic Estimates of Population Sizes in Three Coastal Shark Species
Sharks are widely held by the scientific community to be threatened with extinction, and yet they remain some of the most poorly understood marine vertebrate organisms. There is belief among marine conservation biologists that population genetics based approaches can be used to distinguish species, populations, and even population sizes for these threatened animals. Estimating population sizes using multiple estimates, as well as multiple species, is critical to understanding true population sizes and life history traits that affect these estimates. This study aims to estimate census population size (Nc) and compare this demographic value to the genetically determined effective number of breeders (Nb). Census size will be estimated from an on-going demographic mark and recapture study conducted by South Carolina Department of Natural Resources and estimated using the program MARK. Effective number of breeders will be estimated using a cross-species gene capture method and variability will detected in these data to estimate effective number of breeders using the program NeEstimator. These methods will be deployed on three separate shark species: bonnetheads (Sphyrna tiburo), finetooth sharks (Carcharhinus isodon), and sandbar sharks (Carcharhinus plumbeus). These species all exhibit different population structure, life history, and recapture rates, which may in turn affect their Nb/Nc ratio, a value that may be used for future conservation regulation. It is believed that the comparisons between these estimates and species may be used for population assessment and management of coastal shark species.
Pavel Dimens, David Portnoy
Texas A&M University Corpus Christi, Corpus Christi, TX, USA
Structural Ambiguity: Population Demography of the Blacknose Shark in the Florida Keys
For marine species existing along seemingly continuous habitats, identifying regional groups poses challenges because it limits the ability to define a priori hypotheses with respect to population structure. Further, in species that feature large migrations, individuals from independent populations may co-occur seasonally on feeding grounds. A recent study using microsatellite markers identified five distinct populations spread across an area from South Carolina to the Yucatan and the Bahamas but found ambiguity in the Florida Keys, an area that spans the divide between the U.S. Atlantic and eastern Gulf of Mexico populations, as well as their management units. This study aims to use double-digest restriction associated DNA sequencing (ddRAD-seq) to identify single nucleotide polymorphisms (SNPs) and provide high-resolution population genetic data for blacknose shark in the Florida Keys. The goal is to distinguish between three possible scenarios of population structure and gene flow in the region: 1) the Keys are a zone of admixture between Atlantic and east Gulf of Mexico populations, 2) individuals from both populations are seasonally present in the keys but there is no gene flow, 3) the Keys are a unique population, separate from Atlantic and Gulf of Mexico populations.
Robert Edman1, Gorka Sancho1, Bryan Frazier2, John Kucklick3, Walter Bubley2
1College of Charleston, Charleston, SC, USA, 2South Carolina Department of Natural Resources, Charleston, SC, USA, 3National Institute of Standards and Technology, Charleston, SC, USA
Movement Patterns and Trophic Ecology of Tiger Sharks (Galeocerdo cuvier) Caught off the Southeast Coast of the United States
Exploitation of sharks has markedly increased in the past three decades, and this exploitation, coupled with degradation of essential habitats, can contribute to declining species abundance. Understanding the movement patterns and diet composition of sharks is central to creating and enacting appropriate management actions to preserve these animals and their habitats. Despite the large number of Tiger Sharks (Galeocerdo cuvier) in the western North Atlantic Ocean, the majority of research on Tiger Shark movement and diet has been concentrated in the Pacific and Indian Oceans. The present study seeks to fill these gaps of knowledge through analyses of the movement and diet of Tiger Sharks caught in coastal waters of the southeast United States. A multi-tag approach, utilizing passive acoustic telemetry and satellite telemetry, will provide insight into the movement patterns of Tiger Sharks both inshore along the coast and offshore throughout the Atlantic Ocean. Stable isotope analysis will be used to determine the trophic position of Tiger Sharks and estimate diet composition. Captured Tiger Sharks were sampled for skin, blood, and muscle to use in stable isotope analysis. Select sharks were surgically implanted with acoustic tags, and a number of these sharks were dual tagged with Smart Position or Temperature Transmitting (SPOT) tags as well. Preliminary data indicate that these Tiger Sharks repeatedly visit inshore areas but do not venture offshore of the continental shelf. Stable isotope analyses are ongoing and monitoring of tagged sharks will continue with additional sharks tagged and sampled this summer.
Samantha Ehnert, Jim Gelsleichter
University of North Florida, Jacksonville, FL, USA
Mercury Accumulation and Effects in the Brain of Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)
Studies have shown that sharks often bio-accumulate mercury concentrations that threaten the health of human consumers. However, few studies have examined mercury in the central nervous system of sharks or how mercury affects shark neurophysiology. This study’s goal is to determine if elevated levels of mercury often found in shark muscle also occur in the brain, and if mercury accumulation is associated with damage to the shark’s nervous system. Muscle and brain mercury concentrations in the Atlantic sharpnose shark (Rhizoprionodon terraenovae) are being measured and compared. Brain mercury concentrations with S100b concentrations, bioindicator of mercury-induced neurodegeneration, in shark cerebrospinal fluid (CSF) are being compared. Sharks were collected along the U.S. Southeastern coast. Total mercury concentrations in dried muscle and brain samples were measured using a Direct Mercury Analyzer. Levels of S100b were measured in shark CSF using an ELISA. Preliminary results show strong correlations between mercury in the muscle and brain. Brain mercury levels were significantly lower than the muscle and most known thresholds for biological effects; suggesting limited potential for neurological impacts. Data on S100b concentrations in CSF support this premise, as increased brain mercury levels were not correlated with increased S100b, suggesting mercury levels are below the threshold needed for release of S100b as a function of neurotoxicity. Measurements of oxidative stress, another marker of mercury-induced neurotoxicity, are being analyzed. This study will be one of the first to examine the direct impacts of mercury uptake in sharks, and therefore contribute significantly to the field of shark ecotoxicology.
Sarah Hoffmann, Steven Warren, Andrea Hernandez, Marianne Porter
Florida Atlantic University, Boca Raton, FL, USA
Swimming Kinematics of Juvenile Sphyrna lewini
Hammerhead sharks (Sphyrnidae) have a unique, dorso-ventrally compressed head that may act as a hydrofoil, generating lift and increasing maneuverability in the horizontal plane during swimming. Previously, researchers hypothesized that the cephalofoil acts as a stabilizer during swimming to maintain the shark’s position parallel to the substrate. This is different than more streamlined sharks, which use whole body rolling during swimming. Furthermore, hammerheads have greater hypaxial musculature allowing for a larger range of motion of the head. As a result, a slight change in the angle of attack of the cephalofoil could produce a significant change in pitch angle of the shark with limited energy expenditure. Our goal is to examine the whole-body swimming kinematics of juvenile scalloped hammerhead sharks, Sphyrna lewini, to better understand how head morphology has shaped swimming performance. From previous kinematics data on lift generation in elasmobranchs, we predict that the cephalofoil is generating lift. Kinematic data was assessed using synched dorsal and lateral video of S. lewini. We measured volitional straight swimming performance variables by tracking the movements of anatomical landmarks through time. These landmarks included points on the body midline, cephalofoil, pectoral fins, and caudal fin. The movements of these points were correlated with performance variables such as whole body velocity, body curvature, tailbeat frequency, tailbeat amplitude, head yaw, and cephalofoil and pectoral fin angles of attack. From these data, we are able to quantify swimming performance and better understand how the cephalofoil of hammerhead sharks may be increasing maneuverability and generating lift.
Hua Hsun Hsu1, David A. Ebert2, Shoou Jeng Joung1, Kwang Ming Liu1, Chia Yen Lin1
1National Taiwan Ocean University, Keelung City, Taiwan, 2Moss Landing Marine Laboratories, Moss Landing, CA, USA
Catch and Preliminary Fishery Biological Information of Megamouth Sharks Megachasma pelagios in Eastern Waters off Taiwan
Megamouth shark Megachasma pelagios is rare and one of three filter-feeding shark species. Prior to this study, only 65 megamouth sharks have been recorded during 19762015; 6 from the Atlantic Ocean, 6 from the Indian Ocean, and 53 individuals from the Pacific Ocean. In fact, an additional 32 megamouth sharks were caught by gill nets off Hualien, eastern Taiwan between 2013 and 2014. All sharks were caught at night before dawn from April to August, with most of them caught with ocean sunfish (Molidae), the primary target species of drift net fishery. Of the 32 specimens, body weights (BW) ranged from 210-1147 kg, and lengths measured from 220-560 cm in precaudal length, 250-710 cm in total length (TL); sexes were 20 females (250-710 cm TL), 11 males (363-484 cm TL), and sex was unknown for one individual (500 cm TL). Reproductive condition was determined for 17 sharks, two females were determined to be mature, 11 (5 females 6 males) were maturing, and 4 other females were immature. Stomach contents of 12 individuals examined, indicated that 5 were vacuous, 6 were with partial prey, and 1 was full of prey. Parasites were collected from pectoral fins, mouth, gill slits, stomach, and intestine of 14 individuals. The BW-TL relationships were estimated to be BW=2.316 TL – 524.06 (r2=0.72, n=11) for male, and BW =0.198 TL1.286 (r2=0.42, n=20) for female, respectively. Eastern waters of Taiwan may be a very important feeding ground for juvenile and subadult megamouth sharks.
Daniel Huber1, Bethany Loya1, Summer Decker2, Jonathan Ford2
1The University of Tampa, Tampa, FL, USA, 2University of South Florida, Tampa, FL, USA
Structural Mechanics of Sixgill and Mako Shark Jaws: Evolutionary Considerations
Jaw morphology has changed dramatically over the course of shark evolutionary history, and this diversity of morphology has been postulated to reflect variability in feeding mechanism, behavior, and ecology. The purposes of this study were to 1) compare the structural mechanics of the jaws of the bluntnose sixgill shark Hexanchus griseus and longfin mako shark Isurus paucus, which approximate relatively ancestral and derived jaw morphologies respectively, and 2) investigate the mechanical consequences of the transition from bone to cartilaginous jaws, which occurred early in the evolutionary history of chondrichthyan fishes. Jaws were CT scanned, segmented, and modeled to represent various character states of skeletal composition (unmineralized cartilage, composite mineralized/unmineralized cartilage, bone). Stress, strain, and strain energy density were determined using finite element analysis. Isurus paucus exhibited comparable stress, but less strain and strain energy density than H. griseus, indicating that the material and morphology of jaws have become more efficient at handling stress and strain. The heterogeneous model (composite mineralized, unmineralized cartilage) resulted in low stress, intermediate strain, and intermediate strain energy density for all jaws. These results suggest that shark jaws may have been structurally modified over time to better resist stress and strain by virtue of changes in their geometry and that emergent mechanical properties derive from the combination of mineralized and unmineralized cartilage.
Jessica Jang, Catarina Pien, David Ebert
Moss Landing Marine Laboratories, Moss Landing, CA, USA
Unlocking the Mystery of Western Indian Ocean Electric Rays (Torpedinidae: Torpedo, Duméril 1806)
The Torpedinidae consists of two genera, Torpedo Duméril 1806, consisting of 15 species, and Tetronarce Gill 1862 that consists of 12 species. Torpedo species although morphologically similar, typically exhibits an ornate coloration, with distinct dorsal surface markings, and by the presence of spiracular papillae. Tetronarce species on the other hand are drably colored, and lack these distinctive papillae. As part of a broader investigation into the ecology, life history and taxonomy of southwestern Indian Ocean (SWIO) Chondrichthyans we are currently investigating the electric ray genus Torpedo. Three species are represented in the SWIO: Torpedo fuscomaculata, Peters 1855, Torpedo panthera, von Olfers 1831, and Torpedo sinuspersici, von Olfers 1831, but these may each involve species complexes given the striking color variation of specimens collected from different island groups within the region. Regional species each have distinctly different markings and patterning, orbital papillae/protrusions, and life history characteristics suggesting some of these island groups be home to regionally endemic electric rays. Here we present our findings to date on the mysterious electric rays of the SWIO.
Dovi Kacev1, Shannon Corrigan3, Rebecca Lewison1, John Hyde2
1San Diego State University, San Diego, CA, USA, 2Southwest Fisheries Science Center, La Jolla, CA, USA, 3College of Charleston, Hollings Marine Lab, Charleston, SC, USA
Identifying Multiple Paternity in Two Species of Pelagic Shark
Polyandry is common throughout kingdom Animalia. There are several evolutionary explanations for the rise of this reproductive strategy including increasing genetic diversity, allowing for sperm competition as a proxy for male fitness, or high cost to females of mating avoidance. Several recent studies have found that multiple paternity is common among coastal and benthic shark species but to date, pelagic shark litters remain unstudied. Due to lower expected rates of conspecific interaction and higher opportunity costs, pelagic sharks may be less likely to have multiple matings than their coastal counterparts. In this study we opportunistically sampled single litters from shortfin mako (Isurus oxyrinchus) and common thresher (Alopius vulpinus) sharks (eight and four pups respectively). We used microsatellite markers to test for the possibility of multiple paternity in these species and discuss the possible implications. In the litters for both species, multiple paternity was detected. The mako litter was found to have at least two but more likely three sires, while the thresher litter has most likely two sires.
Kady Lyons1, Douglas H. Adams2
1University of Calgary, Calgary, Alberta, Canada, 2Florida Fish and Wildlife Conservation Commission, Melbourne, FL, USA
Maternal Offloading of Organochlorine Contaminants in the Pseudoplacental Scalloped Hammerhead
Elasmobranchs have a propensity to accumulate high contaminant levels, especially in species that occupy upper trophic levels. However, contaminant concentrations and the types of contaminants that marine fishes accumulate can vary with species, age, sex and environmental parameters. In addition, females have the ability to transfer contaminant to their young through reproductive processes. Therefore, contaminant concentrations and signatures can be used a tool for examining elasmobranch ecology. Organic contaminants (PCBs and chlorinated pesticides) were measured in livers of both female and male scalloped hammerheads (Sphyrna lewini) from several age classes that were collected from U.S. Atlantic waters, including two near-term pregnant females and their embryos. Adult female hammerheads were found to have lower levels of PCBs compared to the younger, adult male (mean ± SD, 11.1 ± 1.0 versus 22.8 μg g-1 lw), but had substantially higher concentrations of pesticides (4.1 ± 0.9 versus 1.9 μg g-1 lw). While females were found to offload substantial contaminants to their offspring, females were only able to depurate their total hepatic load by approximately 0.03 to 2.3%. Differences in standardized contaminant concentrations were observed between the adult male and females, with males having greater proportions of more chlorinated PCB congeners. These differences could be due to the ability of females to offload contaminants to offspring as well as sexual segregation in habitat use. Results from future contaminant studies with increased sample sizes from different localities will further our understanding of scalloped hammerhead health and ecology and aid in effective conservation.
Breanna Machuca1, Kelley van Hees2, David Ebert2
1California State University, Monterey Bay, Seaside, CA, USA, 2Moss Landing Marine Laboratories, Moss Landing, CA, USA
Trophic Ecology of Coastal Elasmobranchs Using Stomach Content and Stable Isotope Analysis
Sharks and rays are apex predators that inhabit Elkhorn Slough, a tidally influenced estuary in Central California. These elasmobranchs use the Slough as a seasonal habitat and food source. These are upper trophic level predators that may be threatened by changes in their habitat, especially to their food source. Leopard sharks (Triakis semifasciata), bat rays (Myliobatis californicus), and thornback rays (Platyrhinoidis triseriata) were used to evaluate how trophic positions and food web relationships have changed over time, using a study by Barry et al. (1996) as a comparison. Stomach-gut Content Analysis (SCA) was used to visually analyze the stomach contents and ten replicates per species of liver and white muscle tissue were analyzed for trophic position using Stable Isotope Analysis (SIA). Additionally, whole frozen prey items underwent SIA for trophic position to provide a basis for the food web. Comparing the results from SIA and SCA identified whether the elasmobranchs were benthic or pelagic feeders and what percentage of their diet is dependent on prey items available within Elkhorn Slough. The results will determine if and how trophic relationships are changing in a key estuarine habitat, and assist with management decisions and conservation of these elasmobranch species.
Melissa C. Nehmens, David A. Ebert
Moss Landing Marine Laboratories, Pacific Shark Research Center, Moss Landing, CA, USA
Age and Growth of Deep-Sea Sharks on Seamounts in the Southwestern Indian Ocean
Knowledge of deep-sea Chondrichthyan life histories is relatively limited given the difficulties in obtaining adequate sample sizes. Life history characteristics that are known of deep-sea Chondrichthyans include slow growth, increased longevity, and late maturation. Ageing studies on deep-sea sharks, such as Squaliformes, are limited and necessitate further investigation as fisheries expand to deeper waters. During a series of surveys in the spring of 2012 and 2014 on the Madagascar Ridge in the Southwestern Indian Ocean, vertebrae and dorsal fin spines were collected from a suite of deep-sea sharks for age and growth analysis. The species collected were Centroscymnus coelolepis, C. owstoni, Centroselachus crepidater, Centrophorus granulosus, Dalatias licha, Deania calcea, D. profundum, Etmopterus granulosus, and Scymnodom plunketi. These species will be aged using their vertebrae and spines. This study will provide crucial information as part of a broader project to characterize the Chondrichthyan fauna on this remote chain of seamounts and may be useful in developing better management plans for this and other remote seamounts around the world.
University of North Carolina at Wilmington, Wilmington, NC, USA
Genetic Diversity, Population Structure and Movements of the Bonnethead (Sphyrna tiburo) in North Carolina
The bonnethead shark (Sphyrna tiburo) inhabits coastal ecosystems and estuaries from North Carolina to Brazil. Some aspects of the genetic population structure of this species have been documented, including substantial variation between the Atlantic Ocean and Gulf of Mexico. S. tiburo that migrate to NC are primarily found in specific estuaries each year, yet genetic variances related to their site fidelity are unknown. This study will quantify genetic heterogeneity and detail population structure of bonnetheads along the NC coast. We are particularly interested in whether site fidelity reported previously for this species is associated with genetic population structure. Tagging efforts will help to reveal bonnethead migratory routes leaving NC estuaries and to identify overwintering grounds to the south. In conjunction with studying genetic differences, the mating system of this species will also be studied. Bonnetheads have been shown to exhibit a high percentage of genetic monogamy in Florida, contradictory to the expectation of polyandry seen in most shark species. Female specimens and their embryos collected as incidental bycatch from NC estuaries will be studied using microsatellite DNA profiling to determine numbers of males contributing to each litter. The oviducal gland will also be sampled for remaining sperm and profiled for number of paternal genotypes. Implications of this study include determining susceptibility of local populations to loss of genetic diversity in the event of population declines. Furthermore, a better understanding of the movement patterns of this highly migratory shark may lead to a reevaluation of conservation status.
Catarina Pien, David Ebert, Jessica Jang, Paul Clerkin, Justin Cordova, Matthew Jew, Breanna Machuca, Melissa Nehmens, Amber Reichert, Victoria Vasquez, Kristin Walovich
Moss Landing Marine Laboratories, Moss Landing, CA, USA
Looking for “Lost Sharks”
Sharks, and their relatives the batoids and chimaeras, come in a variety of sizes and shapes, from the whale shark (Rhincodon typus), the world’s largest fish, to the dwarf pygmy sharks (Squaliolus spp.), and occupy most marine, and some freshwater, habitats. There are more than 500 species of sharks, along with nearly 650 batoid and 50 chimaera species, bringing the overall total to about 1200 species of sharks and shark-like fishes. The diversity of sharks and their relatives has increased exponentially over the past decade with more than 230 new species having been described over the past decade. This represents nearly 20% of all shark species that have been described. Most of these new discoveries have come from the Indo-Australian region, followed by the western Indian Ocean and western North Pacific regions. However, a review of the Red List status of Chondrichthyans indicates that 17.4% are threatened and nearly half (46.8%) are Data Deficient or have not been assessed. Despite such a rich and diverse fauna, the majority of sharks and their relatives have largely been “lost”, having been overshadowed by a few large charismatic media mega-stars, such the Great White Shark (Carcharodon carcharias). In an effort to highlight and assess these little known, or unknown, species we have initiated a global program “Looking for Lost Sharks” to find and discover these lost sharks.
Bianca Prohaska, R. Dean Grubbs
Florida State University, Tallahassee, FL, USA
Stress Physiology of Deep Demersal Sharks in the Gulf of Mexico
Prior to the Deep Water Horizon oil spill, little research effort was focused on studying the physiology of deep demersal sharks inhabiting the Gulf of Mexico. While the physiology of these fishes remains virtually unknown, they are still routinely captured in commercial fisheries, both as targeted catch and as bycatch. In the absence of basic biological data, effective management plans cannot be formulated, making populations highly susceptible to declines. Potential effects the oil spill has had and will continue to have on these organisms are also unknown. Blood chemistry analysis can be used as a method of assessing physiological stress in elasmobranchs, and using this method three main questions will be addressed in the present study: 1) What are the baseline blood chemical parameters in deep demersal elasmobranchs? 2) Are the stress responses in these species ecologically-mediated or taxonomically-mediated? 3) Are there significant differences in blood chemical profiles between elasmobranchs potentially affected by the oil spill and those captured in less affected areas? Preliminary results suggest that stress responses are relatively similar among seven elasmobranch species sampled thus far, including Mustelus sinusmexicanis, M. canis, Squalus cubensis, S. c.f. mitsukurii, Centrophorous c.f. uyato, C. granulosus, and Hexanchus griseus. However, lactate and pCO2 concentrations in M. sinusmexicanis, M. canis, and S. cubensis are relatively higher than that of the other species sampled, potentially suggesting a depth mediated stress response.
Jillian Sawyna, Kelly Radecki, Weston Spivia, Marika Gotschall, Deborah Fraser, Christopher Lowe
California State University, Long Beach, Long Beach, CA, USA
Establishing Baseline Parameters for Assessment of Immunological Effects of Organochlorine Exposure in Elasmobranchs
To evaluate the effects of chronic organochlorine (OC) exposure on elasmobranch immunity, a baseline of immunological parameters including complete blood counts, leukocyte counts, and phagocytosis was established. Round stingrays (Urobatis halleri) were collected from Santa Catalina Island, CA, which is considered a low contamination reference site for toxicology research off California. The genetically isolated population of rays from Catalina exhibit a low mean summed OC tissue concentration of 0.90 ± 0.98ng/standardized liver sample compared to the mainland population, 15.7 ± 11 ng/standardized liver sample. Leukocytes obtained from lymphomyeloid tissues and peripheral blood were assayed for phagocytic activity in vitro. Using flow cytometry, % phagocytosis and phagocytic activity were evaluated by assessing % leukocytes positive for, and relative amounts of ingested fluorescent E. coli BioParticles. Cells isolated from splenic tissue, had a higher percentage of phagocytes in the sample cell population, with a mean % (±SE) phagocytosis of 18.85 ± 4.59, compared to peripheral blood, 8.58 ± 1.53, and epigonal tissue, 13.11 ± 4.93. Blood demonstrated a higher measure of the phagocytes’ activities, with a mean fluorescence intensity (±SE) of 2244.90 ± 265.63, whereas cells isolated from spleen and epigonal were calculated as 1568.65 ± 211.87 and 796.15 ± 174.27, respectively. Using microscopy, the same trend in % phagocytosis was found, but percentage values were higher, suggesting flow cytometry was a more conservative approach. These values can now be compared to those from the heavily OC contaminated southern California coastal mainland to determine if immunosuppression is correlated with OC exposure.
College of Charleston, Charleston, SC, USA
The Chondrichthyan Fauna from the Upper Eocene, Upper Oligocene, and Lower Oligocene Formations in the Coastal Plain of South Carolina
The coastal plain in southeastern South Carolina is composed of the Eocene, Miocene, and Oligocene strata, which are characterized based on sedimentary deposits. These stratigraphic layers contain the isolated remains of Chondrichthyan teeth. While the stratigraphy of the coastal plain of South Carolina has been studied extensively, a detailed study of Chondrichthyan fauna distribution and abundance present in these strata has been neglected. Here, I intend to identify and report a detailed taxonomic study of the Chondrichthyan fauna and distribution using isolated teeth present in the southeastern formations in South Carolina. Teeth of identified Chondrichthyan fauna and the presence of other microfossils in these stratigraphical layers can suggest certain ecological niches, species diversity, and marine systems from these time periods. Not only is this study vital to understanding South Carolina marine history, it is also useful for recreational fossil collectors interested in properly identifying Chondrichthyan teeth.
Katherine Vaccaro1, Rebecca Varney1, Dean Grubbs2, Toby Daly-Engel1
1University of West Florida, Pensacola, FL, USA, 2Florida State University, Tallahassee, FL, USA
Microsatellite Applications for Multiple Paternity in Squalus clarkae, a Novel Shark Species from the Gulf of Mexico
Squalus (Squalidae) is a genus of small, slow-growing sharks with long gestation periods. A new species, Squalus clarkae, was recently described from the Gulf of Mexico after being genetically and morphologically distinguished from Japanese Squalus mitsukurii. As a newly described species, little is known of S. clarkae‘s reproductive behavior. Thus far, multiple paternity in members of the genus Squalus has been understudied, and the degree to which shark species exhibit this behavior varies greatly. Eight species-specific microsatellite loci previously developed for congeners S. mitsukurii and S. acanthias and are being cross-amplified with S. clarkae to assess for their suitability in testing for paternity and kinship. These microsatellites will be applied to litters of S. clarkae to determine the presence and frequency of multiple paternity in this species using 13 litters with an average of 6.7 pups per litter. This study will offer the first genetic insight into the reproductive behavior of this species, and will provide life-history data necessary for future conservation efforts.
Liz Vinyard1, Walter Bubley2, Bryan Frazier2
1University of Charleston, South Carolina, Charleston, SC, USA, 2South Carolina Department of Natural Resources, Charleston, SC, USA
Age, Growth, and Maturation of the Finetooth Shark, Carcharhinus isodon, in Coastal Waters of the Western North Atlantic Ocean
Age, growth, and maturation are crucial fishery dynamics to understand, as they provide vital information that can be used for stock assessments of fishes. Because ontogenetic changes occur across the life history of many marine organisms, including elasmobranchs, an effort should be made to obtain specimens across entire size ranges for both sexes to accurately represent a given population structure. This study proposes three main objectives: 1) examine size at age while validating seasonal periodicity of increment formation used in age estimation, 2) estimate size and age of sexual maturation and 3) compare growth models to published growth models from the western North Atlantic and Gulf of Mexico. Samples will be collected from April 2014 through October 2015 from estuaries and nearshore waters off of South Carolina. Additional vertebral samples from a 2003 study and ongoing sampling with South Carolina Department of Natural Resources (SCDNR) will increase the sample size to approximately 500 vertebrae. Results of this study will provide accurate information regarding growth and maturation for the Finetooth Shark population along the southeastern United States.
Kristin A. Walovich, David A. Ebert
Moss Landing Marine Laboratories, Pacific Shark Research Center, Moss Landing, CA, USA
‘SPOT A BASKING SHARK’: How Citizen Scientists Can Help Save an Enigmatic Shark
The distribution and trans-equatorial migrations of the basking shark (Cetorhinus maximus) have been well documented in the Northern Atlantic, yet seasonal patterns of distribution have not been fully elucidated in the eastern North Pacific. Filling in vital knowledge gaps will help inform the best recovery plan to rebuild the basking shark population in this region, which has been designated a ‘Species of Concern’ by NOAA’s National Marine Fisheries Service and ‘Endangered’ by the International Union for the Conservation of Nature (IUCN). The ‘Spot a Basking Shark’ Project, ongoing since 2010, is a collaborative effort to investigate the abundance, distribution, and population status of basking sharks in the eastern North Pacific. The project employs a web-based reporting system for the public to record sightings, utilizes satellite tags to improve understanding of essential habitat and geographic range, and obtains additional information on life history and patterns of occurrence by data–mining existing records. Have you seen a basking shark? Report your sighting on our website: http://psrc.mlml.calstate.edu/current-research/basking-shark/
John Whalen, Jim Gelsleichter
University of North Florida, Jacksonville, FL, USA
Multibiomarker Evaluation of Pollutant Effects in Atlantic Stingray (Dasyatis sabina) Populations in Florida’s St. Johns River
The goal of this study was to examine the potential health effects of polychlorinated biphenyl (PCB) and polycyclic aromatic hydrocarbon (PAH) exposure on Atlantic stingray (Dasyatis sabina) populations in Florida’s St. Johns River (SJR). Special emphasis was placed on identifying PAH- and/or PCB-related effects in stingrays from areas of the lower SJR basin that have been shown to possess elevated levels of these compounds, as well as characterizing baseline levels of pollutant exposure in other areas that may be subjected to dredging in the near future, potentially re-suspending contaminated sediments and increasing pollutant associated effects. To accomplish this, we measured PCB and PAH biomarker levels in D. sabina collected from contaminated sites and reference locations. Animals were collected using seine nets and trotlines. We specifically examined the biomarkers cytochrome P4501a1 (CYP1a1), a Phase I detoxification enzyme; Glutathione-S-Transferase (GST), a Phase II detoxification enzyme; and fluorescent aromatic compounds (FACs), PAH bile metabolites. Enzymatic activity of CYP1a1 and GST was measured using the EROD assay and a commercially available GST Assay Kit, whereas FACs were measured using fixed wavelength fluorescence. Biomarker levels of individuals collected from contaminated sites were compared to individuals collected from reference sites. Previous research in our lab has detected elevated biomarker levels in D. sabina and bony fish from known contaminated areas in the St. Johns River. Expecting parallel results, we anticipate that the pollutants in the St. Johns River are negatively affecting D. sabina, and that dredging has the possibility to create a broader source of contamination.