Urobatis Halleri Research Articles

Automated segmentation of complex patterns in biological tissues: Lessons from stingray tessellated cartilage.

IntroductionMany biological structures show recurring tiling patterns on one structural level or the other. Current image acquisition techniques are able to resolve those tiling patterns to allow quantitative analyses. The resulting image data, however, may contain an enormous number of elements. This renders manual image analysis infeasible, in particular when statistical analysis is to be conducted, requiring a larger number of image data to be analyzed. As a consequence, the analysis process needs to be automated to a large degree. In this paper, we describe a multi-step image segmentation pipeline for the automated segmentation of the calcified cartilage into individual tesserae from computed tomography images of skeletal elements of stingrays.MethodsBesides applying state-of-the-art algorithms like anisotropic diffusion smoothing, local thresholding for foreground segmentation, distance map calculation, and hierarchical watershed, we exploit a graph-based representation for fast correction of the segmentation. In addition, we propose a new distance map that is computed only in the plane that locally best approximates the calcified cartilage. This distance map drastically improves the separation of individual tesserae. We apply our segmentation pipeline to hyomandibulae from three individuals of the round stingray (Urobatis halleri), varying both in age and size.ResultsEach of the hyomandibula datasets contains approximately 3000 tesserae. To evaluate the quality of the automated segmentation, four expert users manually generated ground truth segmentations of small parts of one hyomandibula. These ground truth segmentations allowed us to compare the segmentation quality w.r.t. individual tesserae. Additionally, to investigate the segmentation quality of whole skeletal elements, landmarks were manually placed on all tesserae and their positions were then compared to the segmented tesserae. With the proposed segmentation pipeline, we sped up the processing of a single skeletal element from days or weeks to a few hours.

Calcified cartilage or bone? Collagens in the tessellated endoskeletons of cartilaginous fish (sharks and rays)

The primary skeletal tissue in elasmobranchs -sharks, rays and relatives- is cartilage, forming both embryonic and adult endoskeletons. Only the skeletal surface calcifies, exhibiting mineralized tiles (tesserae) sandwiched between a cartilage core and overlying fibrous perichondrium. These two tissues are based on different collagens (Coll II and I, respectively), fueling a long-standing debate as to whether tesserae are more like calcified cartilage or bone (Coll 1-based) in their matrix composition. We demonstrate that stingray (Urobatis halleri) tesserae are bipartite, having an upper Coll I-based 'cap' that merges into a lower Coll II-based 'body' zone, although tesserae are surrounded by cartilage. We identify a 'supratesseral' unmineralized cartilage layer, between tesserae and perichondrium, distinguished from the cartilage core in containing Coll I and X (a common marker for mammalian mineralization), in addition to Coll II. Chondrocytes within tesserae appear intact and sit in lacunae filled with Coll II-based matrix, suggesting tesserae originate in cartilage, despite comprising a diversity of collagens. Intertesseral joints are also complex in their collagenous composition, being similar to supratesseral cartilage closer to the perichondrium, but containing unidentified fibrils nearer the cartilage core. Our results indicate a unique potential for tessellated cartilage in skeletal biology research, since it lacks features believed diagnostic for vertebrate cartilage mineralization (e.g. hypertrophic and apoptotic chondrocytes), while offering morphologies amenable for investigating the regulation of complex mineralized ultrastructure and tissues patterned on multiple collagens.

Species diversity of Rhinebothrium Linton, 1890 (Eucestoda: Rhinebothriidea) from Styracura (Myliobatiformes: Potamotrygonidae), including the description of a new species

The present study contributes to the knowledge of the cestode fauna of species of Styracura de Carvalho, Loboda & da Silva, which is the putative sister taxon of freshwater potamotrygonids—a unique group of batoids restricted to Neotropical freshwater systems. We document species of Rhinebothrium Linton, 1890 as a result of the examination of newly collected specimens of Styracura from five different localities representing the eastern Pacific Ocean and the Caribbean Sea. Overall, we examined 33 spiral intestines, 11 from the eastern Pacific species Styracura pacifica (Beebe & Tee-Van) and 22 from the Caribbean species S. schmardae (Werner). However, only samples from the Caribbean were infected with members of Rhinebothrium. Rhinebothrium tetralobatum Brooks, 1977, originally described from S. schmardae—as Himantura schmardae (Werner)—off the Caribbean coast of Colombia based on six specimens is redescribed. This redescription provides the first data on the microthriches pattern, more details of internal anatomy (i.e., inclusion of histological sections) and expands the ranges for the counts and measurements of several features. We describe a new species of Rhinebothrium from S. schmardae collected off the Caribbean coast of Panama. Rhinebothrium reydai n. sp. is diagnosed by possessing four testes per proglottid, acraspedote proglottids, single anterior-most and porterior-most loculi, and bothridia divided into 34–44 loculi. Collectively, these features distinguish the new species from all 41 species of Rhinebothrium currently recognized as valid, with the exception of R. chollaensis Friggens & Duszynski, 2005. The latter species, a parasite of Urobatis halleri (Cooper) from the eastern Pacific Ocean, has a similar morphology in comparison to R. reydai n. sp., but can be distinguished by being apolytic instead of euapolytic and by the morphology of the aporal lobe of the ovary, which reaches the mid-lateral margin of the cirrus sac, whereas in R. reydai n. sp. the aporal lobe only reaches the posterior margin, since the cirrus sac takes approximately ¾ of the proglottid in width. Also, in R. reydai n. sp., the first square proglottid occurs within the anterior third of the strobila (13–30%), whereas in R. chollaensis it occurs near the middle of the strobila (42–62%). Further, we discuss the patterns of infection and biogeographical distribution for species of Rhinebothrium in species of Styracura. The apparent disjunctive distribution of R. tetralobatum and R. reydai n. sp. in the Caribbean Sea throughout their host distribution, S. schmardae, and the absence of species of Rhinebothrium in the eastern Pacific sister-host, S. pacifica, reveal the importance of sample size and biogeographical representation for documenting the parasite fauna of host lineages.

Influence of ontogeny and environmental exposure on mercury accumulation in muscle and liver of male Round Stingrays

Mercury tissue distribution and its dynamics are poorly understood in elasmobranchs. Total mercury was measured in liver and muscle of male Round Stingrays (Urobatis halleri) from Seal Beach, California, an anthropogenically impacted site, and from the offshore island of Santa Catalina, a less impacted site. Stable isotope analysis was also performed on the muscle and red blood cells (RBCs) of a subset of rays over a range of age classes to investigate mercury accumulation with respect to trophic ecology. Mercury in both tissues was found to be significantly greater in adults than juveniles in mainland rays; however, liver mercury accumulation drastically increased after maturity and was significantly greater in mainland adult rays than Catalina rays. There were no patterns in δ15N or δ13C with size in muscle; however, there were indications of seasonal changes in RBC δ15N, suggesting short term shifts in diet or behavior is likely linked to reproductive status as is mercury accumulation.

Who's My Daddy? Considerations for the influence of sexual selection on multiple paternity in elasmobranch mating systems.

Polyandry resulting in multiply‐sired litters has been documented in the majority of elasmobranch species examined to date. Although commonly observed, reasons for this mating system remain relatively obscure, especially in batoids. The round stingray (Urobatis halleri) is an abundant, well‐studied elasmobranch distributed throughout the northeastern Pacific that we used to explore hypotheses regarding multiple paternity in elasmobranchs. Twenty mid‐ to late‐term pregnant females were sampled off the coast of southern California and their litters analyzed for the occurrence of multiple paternity using five nuclear microsatellite loci. In addition, embryo sizes and their position within the female reproductive system (i.e., right or left uterus) were recorded and used to make inferences for patterns of ovulation. Multiple paternity was observed in 90% of litters and male reproductive success within litters was relatively even among sires. High variability in testes mass was observed suggesting that sperm competition is high in this species, although male reproductive success per litter appeared to be relatively even. Using embryo size as a proxy for fertilization, females were found to exhibit a variety of ovulation patterns that could function to limit a male's access to eggs and possibly promote high rates of multiple paternity. Our study highlights that elasmobranch mating systems may be more varied and complex than presumed and further investigation is warranted.

Association between chronic organochlorine exposure and immunotoxicity in the round stingray (Urobatis halleri)

Chronic organochlorine (OC) exposure has been shown to cause immune impairment in numerous vertebrate species. To determine if elasmobranchs exhibited compromised immunity due to high OC contamination along the coastal mainland of southern California, innate immune function was compared in round stingrays (Urobatis halleri) collected from the mainland and Santa Catalina Island. Proliferation and phagocytosis of peripheral blood, splenic, and epigonal leukocytes were assessed. Percent phagocytosis and mean fluorescence intensity (MFI) were evaluated by quantifying % leukocytes positive for, and relative amounts of ingested fluorescent E. coli BioParticles. Total cell proliferation differed between sites, with mainland rays having a higher cell concentration in whole blood. ∑PCB load explained significantly higher % phagocytosis in blood of mainland rays, while ∑PCB and ∑pesticide loads described increased splenic % phagocytosis and MFI in the mainland population. Data provides evidence of strong OC-correlated immunostimulation; however, other site-specific environmental variables may be contributing to the observed effects.

Ultrastructural and developmental features of the tessellated endoskeleton of elasmobranchs (sharks and rays).

The endoskeleton of elasmobranchs (sharks and rays) is comprised largely of unmineralized cartilage, differing fundamentally from the bony skeletons of other vertebrates. Elasmobranch skeletons are further distinguished by a tessellated surface mineralization, a layer of minute, polygonal, mineralized tiles called tesserae. This 'tessellation' has defined the elasmobranch group for more than 400 million years, yet the limited data on development and ultrastructure of elasmobranch skeletons (e.g. how tesserae change in shape and mineral density with age) have restricted our abilities to develop hypotheses for tessellated cartilage growth. Using high-resolution, two-dimensional and three-dimensional materials and structural characterization techniques, we investigate an ontogenetic series of tessellated cartilage from round stingray Urobatis halleri, allowing us to define a series of distinct phases for skeletal mineralization and previously unrecognized features of tesseral anatomy. We show that the distinct tiled morphology of elasmobranch calcified cartilage is established early in U.halleri development, with tesserae forming first in histotroph embryos as isolated, globular islets of mineralized tissue. By the sub-adult stage, tesserae have increased in size and grown into contact with one another. The intertesseral contact results in the formation of more geometric (straight-edged) tesseral shapes and the development of two important features of tesseral anatomy, which we describe here for the first time. The first, the intertesseral joint, where neighboring tesserae abut without appreciable overlapping or interlocking, is far more complex than previously realized, comprised of a convoluted bearing surface surrounded by areas of fibrous attachment. The second, tesseral spokes, are lamellated, high-mineral density features radiating outward, like spokes on a wheel, from the center of each tessera to its joints with its neighbors, likely acting as structural reinforcements of the articulations between tesserae. As tesserae increase in size during ontogeny, spokes are lengthened via the addition of new lamellae, resulting in a visually striking mineralization pattern in the larger tesserae of older adult skeletons when viewed with scanning electron microscopy (SEM) in backscatter mode. Backscatter SEM also revealed that the cell lacunae in the center of larger tesserae are often filled with high mineral density material, suggesting that when intratesseral cells die, cell-regulated inhibition of mineralization is interrupted. Many of the defining ultrastructural details we describe relate to local variation in tissue mineral density and support previously proposed accretive growth mechanisms for tesserae. High-resolution micro-computed tomography data indicate that some tesseral anatomical features we describe for U.halleri are common among species of all major elasmobranch groups despite large variation in tesseral shape and size. We discuss hypotheses about how these features develop, and compare them with other vertebrate skeletal tissue types and their growth mechanisms.

First record of spine malformation of the round stingray Urobatis halleri off the Western Coast of Baja California Sur, México

Malformations of the Round stingray Urobatis hallerii, Cooper 1863 captured off the southwestern coast of Baja California Sur, Mexico are reported in this study. The ray was an adult male captured by artisanal fishery in the area of Estero Banderitas. Size measurements of total length and disk width were taken; the organism could be photographed when captured. Malformations of U. hallerii were found in the posterior part of the spine, a distortion in the upper part of the tail and in the left fin close to the tail. The specimen was considered able to reach the adult size usually reported in other specimens of this species despite the spine malformations because of its benthic habits and not losing its mobility completely. The observed malformations were likely due to genetic alterations although other studies are needed to see if other environmental factors could cause malformations in marine organisms mainly in fish and elasmobranchs.

Soluble adenylyl cyclase is an acid-base sensor in epithelial base-secreting cells.

Blood acid-base regulation by specialized epithelia, such as gills and kidney, requires the ability to sense blood acid-base status. Here, we developed primary cultures of ray (Urolophus halleri) gill cells to study mechanisms for acid-base sensing without the interference of whole animal hormonal regulation. Ray gills have abundant base-secreting cells, identified by their noticeable expression of vacuolar-type H(+)-ATPase (VHA), and also express the evolutionarily conserved acid-base sensor soluble adenylyl cyclase (sAC). Exposure of cultured cells to extracellular alkalosis (pH 8.0, 40 mM HCO3 (-)) triggered VHA translocation to the cell membrane, similar to previous reports in live animals experiencing blood alkalosis. VHA translocation was dependent on sAC, as it was blocked by the sAC-specific inhibitor KH7. Ray gill base-secreting cells also express transmembrane adenylyl cyclases (tmACs); however, tmAC inhibition by 2',5'-dideoxyadenosine did not prevent alkalosis-dependent VHA translocation, and tmAC activation by forskolin reduced the abundance of VHA at the cell membrane. This study demonstrates that sAC is a necessary and sufficient sensor of extracellular alkalosis in ray gill base-secreting cells. In addition, this study indicates that different sources of cAMP differentially modulate cell biology.

Pararhinebothroides-Neither the Sister-Taxon of Rhinebothroides Nor a Valid Genus.

The genus Pararhinebothroides was established for a species of cestode (Parahinebothroides hobergi) found parasitizing the Tumbes round stingray, Urobatis tumbesensis (McEachran & Chirichigno), in the inshore Pacific waters in the Gulf of Guayaquil, Ecuador. Its apparent affinities with the freshwater endemic genus Rhinebothroides were considered evidence to support the long-standing, yet controversial, biogeographical hypothesis that freshwater stingrays of the family Potamotrygonidae derived from a Pacific marine ancestor during the Cretaceous Period before the uplifting of the Andes. Here, we re-evaluate the phylogenetic and taxonomic status of P. hobergi based on examination of the available type material and newly collected material from the type host near the type locality. The new material allowed the description of tegumental structures using scanning electron microscopy and the generation of a hypothesis for the phylogenetic position of the species based on molecular data for the first time. Morphological investigations revealed that P. hobergi shares all the diagnostic features of the most recent concept of Anthocephalum, including the previously overlooked presence of bothridial apical suckers. Phylogenetic analyses based on partial 28S rDNA (D1-D3) and complete 18S rDNA sequence data for 4 specimens of P. hobergi, 45 species of other rhinebothriideans, and 5 non-rhinebothriidean outgroup species provided unequivocal support for the transfer of P. hobergi to Anthocephalum. Since this is the type and only species of the genus, Pararhinebothroides is considered a junior synonym of Anthocephalum, and Anthocephalum hobergi n. comb. is redescribed. Furthermore, our results reveal Rhinebothroides and Anthocephalum to be only distantly related among the Rhinebothriidea. Not only do our results confirm reservations expressed earlier about the affinities of P. hobergi, but they also substantially challenge inferences drawn previously about the biogeographical history of potamotrygonid stingrays based on parasitological data.

REPRODUCTIVE BIOLOGY OF THE VENEZUELA ROUND STINGRAY Urotrygon venezuelae SCHULTZ FROM THE COLOMBIAN CARIBBEAN

<p>As for most batoid species, little is known about the basic biology of the Venezuela round stingray Urotrygon venezuelae (Urotrygonidae). This study presents information about the reproductive biology of the species, including fecundity, embryonic development stage, relationship between maternal size and fecundity, gonadosomatic (GSI) and hepatosomatic (HSI) indices, sex ratios, maturity size and size at birth. With all this information, a preliminary reproductive cycle is proposed. A total of 269 specimens were caught with beach seine in Salguero beach, Colombian Caribbean Sea, between August 2005 and October 2006. We propose for U. venezuelae a biological cycle with three reproductive peaks: November-December, March-April and August. Median sexual maturity size was calculated in 176 mm (total length) for females and 227 mm for males; fecundity ranged between one and six embryos per female. We found that cloacal diameter and liver weight were better predictors for fecundity than total length for U. venezuelae.</p>

Nueva especie del género Urobatis (Myliobatiformes: Urotrygonidae) del Pacífico oriental tropical

Una nueva especie de raya redonda con espina, Urobatis pardalis sp. nov., es descrita a partir de material recolectado en las costas del Pacífico de Costa Rica. Esta nueva especie difiere de sus congéneres por el patrón de la coloración dorsal del disco y por varias relaciones de medidas. Se presenta una clave para la determinación taxonómica de las especies del género.

Stingray Envenomation Treatment Recommendations

INTRODUCTION ach year, millions pursue work and leisure activities in the ocean. Thousands of people Eunknowingly step into the ocean for wading or swimming and receive a barbed sting from a normally docile, frightened stingray. This wellcamouflaged creature from the Chondrichthyes class, which includes sharks and skates, lives in temperate oceans around the world. Stingrays are also found in freshwater river systems. In the coastal waters of the United States there are approximately 11 species of stingrays and about 150 worldwide, which are divided into 2 superfamilies, the Dasytoidea, or true stingrays, and the Myliobatoidea. Their sizes range from the size one’s palm to 6.5 feet (2 meters) and weigh up to 800 pounds (350 kg). The longer the stingray spine and the more distally located the spine is on the whiplike tail, the greater the danger to humans from stingray spine injuries. Stingrays are not to be confused with the Manta Ray, which is harmless and does not have a barbed tail. Of these 2 families, the majority of venomous marine stings are from 2 species. From the West Coast there is the Urolophus halleri, also commonly known as the round stingray, with an average length of up to 24 inches, and along the South-East coast there is the southern stingray, Dasyatis Americana, with lengths up to 79 inches. Scuba divers and snorkelers are fortunate when they come across the beautiful stingray. This creature is easily identifiable as it glides through the water while gently moving its dorsoventrally flattened body to feed on shrimp and small fish. Well adapted to its habitat, the stingray can blend easily into the sand. When the stingray is stepped on or encounters danger, it raises its tail, and “strikes” with its sharp pointed spine. This spine is composed of a bonelike cartilaginous material with unique histologic architecture and a venom-delivery system that can be seen on X-ray (Figure 1). On the underside of the spine are venom-secreting glandular cells. The stingray’s sheath covering breaks apart as it enters the

Stingrays as possible facilitators for foraging trevallies in a nearshore sandflat

Mixed-species associations are temporary aggregations of individuals of different species that are driven by improved foraging, anti-predator benefits, and host/ cleaner relationships (Morse 1977). Host/cleaner relationships are common among fishes, including between elasmobranchs and teleosts (Papastamatiou et al. 2007). However, the function of associations between teleosts and elasmobranchs for other purposes is poorly described (Heithaus et al. 2010). On 27 April 2013, in the waters of Petite-Terre, along the north shore of Terre de Bas (Guadeloupe archipelago, 16°10’23.10”N, 61°06’32.41”W), a ∼90 cm (disk width) southern stingray (Dasyatis americana) was observed (∼15 min) and filmed (102 s) in association with a ∼40 cm bar jack (Caranx ruber). The observation occurred at 340 pm in shallow waters (<1.5 m) over a sandflat that is adjacent to a coral reef ecosystem. Video footage shows the jack swimming above the ray and actively maintaining the association during periods when the ray stopped to forage or changed headings (Fig. 1a, see supplementary material). During extractive foraging by the ray, the jack was observed inspecting the sand plume expelled by the ray and striking at prey that were dislodged (Fig. 1b). It therefore appears that the jack was associated to the stingray to forage and may have been able to access otherwise unavailable resources. Similar commensal associations were observed in the Pacific Ocean by two of the authors (JJK and JPQ), where trevallies were associated with stingrays for foraging purposes : a t Cocos Is land (5°31 ’08 ’N, 87°04’18”W), involving the bluefin trevally (Caranx melampygus) and the black-spotted stingray (Taeniurops meyeni), and in the lagoon of Tetiaroa, French Polynesia (17°0’S, 149°33”W), where several associations between pink whiprays (Himantura fai) and both bluefin and giant trevallies (Caranx ignobilis) were observed. Stingrays were always alone, but up to three trevallies could be observed with a single ray. In several of these cases, trevallies were seen lunging in plumes created by rays. Although other benefits to trevallies (e.g. reduced predation risk) cannot be discounted, we hypothesize that rays constitute facilitators for foraging trevallies. As documented for other batoids such as bat rays (Myliobatus californica) and round stingrays (Urobatis halleri) (VanBaricom 1982; Heithaus et al. 2010), stingrays in coral reef ecosystems may facilitate other predators that take advantage of prey that are disturbed or excavated during ray foraging. Electronic supplementary material The online version of this article (doi:10.1007/s12526-014-0304-6) contains supplementary material, which is available to authorized users.

Clarifying the Northern Extent of the Diamond Stingray (Dasyatis dipterura) in Southern California

Accurate records of biogeographic distributions (latitude and elevation) are becoming increasingly important as species shift their distribution in response to global climate change (Walther et al. 2002). The Southern California Bight is a transition zone between the Oregonian and San Diegan biogeographic zones (Horn et al. 2006). Therefore, range extensions are commonly documented in the area (Pondella 1997; Lea and Rosenblatt 2000; Miller and Curtis 2008; Moore et al. 2011; among others). On 27 October 2011, a single Diamond Stingray (Dasyatis dipterura) was taken in Marina del Rey harbor (33u 58.9739N 118u 27.2459W) in Marina del Rey, California during an environmental survey using a 7.6-m otter trawl at a depth of 4.3 m. The individual weighed 1.65 kg and measured 247 mm disc width (Figure 1). Key characters used in the identification to differentiate it from other common species, such as Round Stingray (Urobatis halleri) and Bat Ray (Myliobatis californica), include the disc shape and the presence of a keel on the tail. The tail keel is unique to Diamond Stingray in comparison to both Round Stingray and Bat Ray. Being alive and in apparently good health, the animal was photographed and released. Diamond Stingray nomenclature has a multifaceted history. Originally described in a May 1880 publication by Jordan and Gilbert (1880) and again by Jordan and Gilbert (1882) as Dasybatis dipterurus, the current nomenclatural combination first appeared in Jordan and Evermann (1896). Garman (1880) described Tygon brevis in his October 1880 review of collections at the Harvard University Museum of Comparative Zoology. Garman (1913) synonymized all prior names, including T. brevis, under Dasybatus brevis, but lacked any reference to Jordan and Gilbert (1880). Instead, Garman (1913) included Jordan and Gilbert (1881), which introduced the name Dasybatus dipterurus. Nishida and Nakaya (1990) followed Garman (1913) and treated Dasyatis dipterurus (Jordan & Gilbert, 1880) with Dasybatus brevis. Eschmeyer (1998) noted dipterurus predated brevis (May and October 1880, respectively) and therefore synonymized brevis under dipterurus and recognized dipterura as the correct species name. Accordingly, Nelson et al. (2004) removed reference to brevis from North American waters in recognition of Eschmeyer’s clarification of the species’ nomenclature. We utilize the presently accepted Dasyatis dipterura (Page et al. 2013). The Diamond Stingray northern range limit is no less enigmatic than its nomenclature. Current literature (Love et al. 2005) lists the northern range endpoint as central California (Grove and Lavenberg 1997 as Dasyatis brevis), although the true northern extent is unsubstantiated by a voucher specimen collected north of 33.7uN latitude, or Long Beach, California [LACM 48829.001; Fishnet2 (www.fishnet2.net); SIO (http:// collections.ucsd.edu); MCZbase (http://mczbase.mcz.harvard.edu)]. Prior work recorded a range to southern California and ‘‘possibly British Columbia’’ (Hart 1973). The Hart reference was founded on records of a Dasyatis sp. being caught in Kyuquot on Bull. Southern California Acad. Sci. 113(3), 2014, pp. 232–235 E Southern California Academy of Sciences, 2014

Bioaccumulation of organochlorine contaminants and ethoxyresorufin‐o‐deethylase activity in southern California round stingrays (Urobatis halleri) exposed to planar aromatic compounds

While contaminant concentrations have been reported for elasmobranchs around the world, no studies have examined bioaccumulation patterns across male and female age classes. The round stingray (Urobatis halleri) is a local benthic species that forages near areas of high organochlorine contamination and represents a good elasmobranch model. Polychlorinated biphenyls (PCBs), DDT, and chlordanes were measured in juvenile and adult male and female stingrays from areas in southern California, USA (n = 208), and a nearby offshore island, Santa Catalina (n = 34). Both mainland juvenile male and female stingrays showed a significant dilution effect. After maturity, summed contaminant concentrations significantly increased with size for adult males (median 11.1 µg/g lipid wt) and females (5.2 µg/g lipid wt). However, the rate of bioaccumulation was substantially greater in male stingrays than in females, likely a result of the females' ability to offload contaminants to offspring during pregnancy. In addition, males and females showed significant differences in their contaminant profiles, suggesting differential habitat use. Male and female stingrays collected from Santa Catalina Island had significantly lower concentrations (0.51 µg/g and 0.66 µg/g lipid wt, respectively), approximately 5 times less than those of mainland animals. Potential toxicity effects mediated through activation of the aryl hydrocarbon receptor were explored through ethoxyresorufin-O-deethylase (EROD) activity assays. Mainland male stingrays exhibited significantly greater EROD activities than Catalina males (481 pmol/min/mg protein and 55 pmol/min/mg protein, respectively); however, activity levels in female stingrays from both locations were comparable (297 pmol/min/mg protein and 234 pmol/min/mg protein, respectively) and lower than those in mainland males. The results suggest that PCBs and/or other structurally related contaminants may be inducing a biological response in mainland males but not females, possibly the result of a dampening effect of estradiol; however, the exact physiological repercussions of exposure remain to be determined.

Age and growth of the round stingray Urotrygon rogersi, a particularly fast-growing and short-lived elasmobranch.

We examined the age and growth of Urotrygon rogersi on the Colombian coast of the Eastern Tropical Pacific Ocean by directly estimating age using vertebral centra. We verified annual deposition of growth increments with marginal increment analysis. Eight growth curves were fitted to four data sets defined on the basis of the reproductive cycle (unadjusted or adjusted for age at first band) and size variables (disc width or total length). Model performance was evaluated using Akaike's Information Criterion (AIC), AIC weights and multi-model inference criteria. A two-phase growth function with adjusted age provided the best description of growth for females (based on five parameters, DW∞ = 20.1 cm, k = 0.22 yr–1) and males (based on four and five parameters, DW∞ = 15.5 cm, k = 0.65 yr–1). Median maturity of female and male U. rogersi is reached very fast (mean ± SE = 1.0 ± 0.1 year). This is the first age and growth study for a species of the genus Urotrygon and results indicate that U. rogersi attains a smaller maximum size and has a shorter lifespan and lower median age at maturity than species of closely related genera. These life history traits are in contrast with those typically reported for other elasmobranchs.

Zoogeographic Analysis of the Fish Fauna Associated with Soft Bottoms during El Niño - La Niña (98-99) In San Ignacio Lagoon, Baja California Sur, Mexico

Abstract The San Ignacio Lagoon is part of the Vizcaino Biosphere Reserve, a location that has been declared a critical area for the conservation of marine mammals and fish that use it for breeding, feeding and refuge. The present paper has as its main focus to determine the impact of a large-scale oceanographic phenomenon (El Nino/La Nina) on the zoogeographic composition of the community of soft-bottom fish of the San Ignacio Lagoon. During the warm El Nino period of spring and fall 1998, the average water temperatures in San Ignacio Lagoon were between 20.9 and 21.1°C (± 0.2°C), while during the summer of 1998 average temperatures were higher (24.3°C), and during the cold La Nina period of the 1999 winter a 13.4°C average temperature was recorded. Eight species were present during all seasons: Eucinostomus dowii, Hippocampus ingens, Hypsopsetta guttulata, Paralabrax maculatofasciatus, Paralichthys californicus, Sphoeroides annulatus, Sphoeroides lispus and Urobatis halleri. The species with the highest abundance during El Nino were: Paralabrax maculatofasciatus, Eucinostomus dowii; whereas during La Nina the most abundant species were: Sphoeroides lispus, Paralabrax auroguttatus and Sphoeroides annulatus. The recorded fishes had zoogeographic affinity for the following provinces: Panamic (36%), Californian (32%), Eastern Pacific (18%) and Mexican (11%). Eleven fish species of tropical affinity that were recorded during El Nino event of 1997-1998.

Quantification of Maternal Offloading of Organic Contaminants in Elasmobranchs Using the Histotrophic Round Stingray (Urobatis halleri) as a Model

Maternal offloading is one route by which young animals may accumulate persistent organic pollutants, such as dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs), but has not been well documented in elasmobranchs despite their propensity to accumulate high concentrations of contaminants. Using the round stingray (Urobatis halleri) as a coastal elasmobranch model, we examined maternal offloading processes at two stages in the stingray's entire reproductive cycle. Post-ovulated and near-term pregnant female stingrays were sampled from southern California, and organic contaminants were measured in the ova and embryonic tissues and compared to concentrations measured in corresponding female livers to determine route and extent of transfer. Total organic contaminant loads measured in ovulated eggs were about two times lower than loads measured in embryos (p < 0.001) indicating mothers have the ability to transfer contaminants throughout pregnancy. Contaminant loads measured in pups showed a positive relationship with mother's contaminant concentrations (p < 0.001); however, mothers offloaded relatively low percentages (1.5 ± 1.7%) of their total contaminant load using contaminants measured in the liver as a proxy. However, histotrophy is only one form of supplemental provisioning utilized by elasmobranchs and variation in reproductive modes likely influences the extent to which female elasmobranchs may maternally offload contaminants.

Elemental Markers in Elasmobranchs: Effects of Environmental History and Growth on Vertebral Chemistry

Differences in the chemical composition of calcified skeletal structures (e.g. shells, otoliths) have proven useful for reconstructing the environmental history of many marine species. However, the extent to which ambient environmental conditions can be inferred from the elemental signatures within the vertebrae of elasmobranchs (sharks, skates, rays) has not been evaluated. To assess the relationship between water and vertebral elemental composition, we conducted two laboratory studies using round stingrays, Urobatis halleri, as a model species. First, we examined the effects of temperature (16°, 18°, 24°C) on vertebral elemental incorporation (Li/Ca, Mg/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca). Second, we tested the relationship between water and subsequent vertebral elemental composition by manipulating dissolved barium concentrations (1x, 3x, 6x). We also evaluated the influence of natural variation in growth rate on elemental incorporation for both experiments. Finally, we examined the accuracy of classifying individuals to known environmental histories (temperature and barium treatments) using vertebral elemental composition. Temperature had strong, negative effects on the uptake of magnesium (DMg) and barium (DBa) and positively influenced manganese (DMn) incorporation. Temperature-dependent responses were not observed for lithium and strontium. Vertebral Ba/Ca was positively correlated with ambient Ba/Ca. Partition coefficients (DBa) revealed increased discrimination of barium in response to increased dissolved barium concentrations. There were no significant relationships between elemental incorporation and somatic growth or vertebral precipitation rates for any elements except Zn. Relationships between somatic growth rate and DZn were, however, inconsistent and inconclusive. Variation in the vertebral elemental signatures of U. halleri reliably distinguished individual rays from each treatment based on temperature (85%) and Ba exposure (96%) history. These results support the assumption that vertebral elemental composition reflects the environmental conditions during deposition and validates the use of vertebral elemental signatures as natural markers in an elasmobranch. Vertebral elemental analysis is a promising tool for the study of elasmobranch population structure, movement, and habitat use.