AES Poster Presentation Abstracts
(*Presenter; C=Carrier Best Student Poster Award Candidate)
(EA) Depto. de Biología Marina, Universidad Católica del Norte, Casilla 117 Coquimbo, Chile; (MA, JP, RR) Depto Ciencias del Mar, Universidad Arturo Prat, Casilla 121, Iquique, Chile
Age and growth of the porbeagle shark Lamna nasus (Bonnaterre, 1788)
The age and growth of the porbeagle shark captured outside the Chilean EEZ in international waters off the central and northern Chilean coast. The study period was between November 2000 and August 2001 and the study area covered from 24°07¢ S to 37°13¢ S, onboard artisanal and industrial longline.boats. The age was determined by counting age rings in the vertebrae, using X-rays. The maximal age found was for a 11 years old specimen. From the fitting of several growth in length models the best fit is derived with a modification of the von Bertalanffy model, that considers the Soriano growth in two steps model. The parameters were estimated for sexes combined and the results were: Linf = 243.13 cm TL, K = 0.149/ year, t0 = – 1.738 year, h = 0.1142, th = 6.13 year. For the age – total weight relationship it was not possible to fit a parametric model, and we obtained non significant fits with the models explored. Therefore, in order to explain the growth in weight generalized additive models (GAM). Our study confirms the low growth rate of the porbeagle shark, in length and weight, during the first 5-6 years as it was found in studies in the north occidental Atlantic Ocean. Financed by Fisheries Research Fund, Chile, (Proyecto FIP 2000-23).
Museu Paraense Emílio Goeldi, Coordenação de Zoologia, Setor de Ictiologia, Avenida Perimetral 1901, Terra Firme 66077-530, Belém, Pará, Brazil
Polychromatic and morphometric aspects of the freshwater stingray Potamotrygon Scobina (Chondrichthyes: Potamotrygonidae) (Pará, Brazil)
The potamotrygonid stingrays are the only elasmobranchs completely adapted for living in freshwater environments and are restricted to some Neotropical river basins. Dorsal color patterns have been widely used as important criteria in the identification of freshwater stingrays. The intraespecific dorsal color variability (polychromatism) that occurs in the Potamotrygonidae Family almost always results in misidentifications or the use of different designations for a same species. A total of 385 specimens was capture in the Marajó Bay region during the years of 2000, 2001 and 2002. All of them were previously identified as Potamotrygon scobina. These specimens were separated into two size groups that included 80 neonates / juveniles and 305 sub adults / adults. A dorsal color pattern characterization study was carried out considering the shape, distribution and presence / absence of previously defined figures. Three dorsal color patterns were observed for neonate / juveniles individuals and four patterns were verified for sub adults / adults specimens. The sub adults and adults.specimens had 31 external morphometric measurements taken that were submitted to multivariated statistical analysis. Principal Component and Discriminant Function Analysis were used to verify the existence of differentiated groups. The results obtained indicated that all four color patterns overlap and that no particular group was formed. Results also indicated that the P. scobina specimens sampled formed a single group independent of the variations among the dorsal color patterns. Conclusively, two new color patterns were described for neonate / juvenile specimens and three new patterns were included for sub adult / adults. Extreme care is recommended when using uniquely dorsal color patterns to identify potamotrygonid freshwater stingrays.
Semmelweis University, Dept. Anatomy, Histology and Embryology, Budapest, Hungary
Supposed sexual dimorphism on the cerebellum of the ray Mobula japanica (order Myliobatiformes)
In the most advanced forms of Chondrichthyes the brain/body weight ratio (relative brain weight) matches those found in birds and mammals, and surpass those of other vertebrates. According to the recent studies the largest relative brain weights belong to the species of the Myliobatiformes order, e.g. the Mobula japanica. The determinants of this conspicuous brain size are the telencephalon and cerebellum. Size and outer structure of the cerebellum extremely diverges among Chondrichthyes (Northcutt, 1978), in several groups (Isurus, Dasyatis, Mobula) the gyrification matches the mammalian and avian cerebella. Intraspecific variations of cerebellar morphology can be considerable, but the investigation in a Dasyatis sp. could not found it to be correlated to size or sex. The neuronal structure of cerebellum is similar in all Chondrichthyes (actually, in all Vertebrates), as we also found in Raja erinacea, Dasyatis americana and pastinaca, and Mobula japanica. Immunostaining against GFAP revealed astrocytes in the molecular layer, similar to birds and mammals, whereas it detected no Bergmann-glia. The size of the cerebellum did not differ significantly between males and females, but in the latter ones a leftward prominence caught the eye, suggesting a sexual dimorphism. Although the female cerebella were recognizable by their asymmetry, even a series of measurements performed on 5-5 male and female cerebella, could not found a parameter to prove the difference significantly. The investigation continues in the analysis of the surface pattern, to reveal its regularities and coin a terminology for its description. In this analysis the gyrification index is to be determined, like in the cortex of mammals (see e.g., Zilles et al., 1988, 1989), and a higher number of specimens are to be investigated.
(ACA, PNW) School of Aquaculture, University of Tasmania, locked bag 1- 370, Launceston, Tasmania 7250, Australia; (FS) Tasmania Aquaculture and Fisheries Institute, University of Tasmania, Marine Research Laboratories, Nubeena, Crescent Taroona, Tasmania 7053, Australia; (SJD) CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania 7001, Australia
Preliminary investigation into the biology and movements of the draughtboard shark (Cephaloscyllium laticeps)
The draughtboard shark Cephaloscyllium laticeps is the most common catshark in the coastal waters off Southern Australia where it is a major higher trophic level predator of temperate reef ecosystems. It is caught as bycatch in lobster traps, demersal trawls, long-line and gillnets. There is currently no targeted commercial fishery for draughtboard sharks, although recently a small number of commercial gill net fishers are trialing the species on the local market. Because draughtboard sharks have a high catchability in traps and gillnets they are potentially vulnerable to population reduction through fishing. Assessing the potential impact of fishing mortality is currently hindered by the lack of knowledge of draughtboard shark biology. The purpose of this study is to investigate specific aspects of life history and biology of draughtboard sharks that will help future management decisions. In addition to collecting reproductive data from dead specimens, hormonal levels have been analysed from blood samples as a means of describing reproductive condition in live animals. Plasma levels of 32 progesterone, testosterone (T) and 17-bestradiol in females, and T in males were obtained measured by RIA. Stomach content analysis is being used to quantify prey items and biases associated with different fishing gears (gillnets and traps). Preliminary attempts to age the sharks using vertebral ring counts have been problematic. Local movement patterns are being investigated using traditional fin tags and acoustic tags. The fin tags have confirmed that proportions of sharks are recaptured in the same area each year. The acoustic tagged sharks are being caught, tagged and released within an array of acoustic receivers that will enable us to follow their daily movements on and adjacent to the reef system.
California State University, Fullerton Department of Biological Science 800 N State College Blvd. Fullerton, CA., USA 92831
A comparison of lactate processing in endothermic and ectothermic sharks
When compared with ectothermic shark species, lamnid sharks have higher activities of lactate dehydrogenase (LDH) in the fast, glycolytic myotomal muscle (white muscle, WM) used to power high-speed bursts. Lamnid sharks produce large amounts of lactate from WM glycogen, which may subsequently be oxidized or used to resynthesize glycogen. In fishes, it is believed that gluconeogenesis occurs within the WM, yet the gluconeogenic potential of lamnid shark tissues has not been reported. To assess this, we measured the activity of four enzymes required for gluconeogenesis (pyruvate carboxylase, malic enzyme, phosphoenolpyruvate carboxykinase, and fructose-1,6-bisphosphatase) in the WM, liver, red muscle (slow, oxidative muscle), and heart ventricle of the short-fin mako shark (Isurus oxyrinchus). Pyruvate carboxylase was not detected in any tissue samples. Malic enzyme activity was highest in the heart and red muscle of the mako shark. Fructose-1,6-bisphosphate activity was greatest in the liver and white muscle tissues. Phosphoenolpyruvate carboxykinase activity was greatest in the liver tissue and was not detected in WM. Because pyruvate carboxylase was not detected, it appears that none of the four tissues studied can carry out gluconeogenesis using the pathway known to occur in other vertebrates. However, if the reaction catalyzed by pyruvate kinase (PK) can be reversed, as has been suggested for teleosts, then gluconeogenesis may be possible. Because the PK activity is high in mako shark WM, we are currently investigating if the WM PK can catalyze the conversion of pyruvate to phosphoenolpyruvate for gluconeogenesis.
(JB, SMK, APS) Ecology & Evolutionary Biology, 321 Steinhaus Hall, University of California – Irvine, Irvine, CA 92697-2525, US
A Collagen and proteoglycan content in skeletal cartilage
In most vertebrates, cartilage plays just two functional roles – a low friction bearing surface (as in your knees) and contour filler (your nose and ears). However, a successful group of vertebrates, the class Chondrichthyes (sharks, ratfish and rays), has an entirely cartilaginous skeleton implying a far broader range of function for this connective tissue than in other animals. Whereas tetrapod cartilage is quite homogeneous in its response to load and in biochemical composition (within a functional group: bearing surface or contour filler), we have found the cartilage of sharks to be highly variable in material properties. Here we report on the biochemical variation that underlies the large differences that we have found in material properties. Cartilage is a fiber-reinforced composite material, with a network of crosslinked collagen fibers suspended in an aqueous gel of proteoglycans. In four species of shark and one hard-prey crushing stingray we have found four-fold differences in proteoglycan (PG) content and twofold differences in collagen content. The PG content is very tightly correlated with the resilience of the cartilage from these species. Collagen content also appears to have a significant effect on stiffness and strength. The extreme variation in collagen content raises the possibility of non-collagenous fibrous material in the cartilage.
(AC, DL, PM) University of South Florida, Dept. of Biology, Tampa, FL, 33620, USA; (BD, GB) Florida Museum of Natural History, Division of Fishes, University of Florida, Gainseville, FL, 32611, USA
Inter-tooth distance as a predictor of body length in sharks
The dental morphology and patterning in sharks has long been used to predict both species and body size, with somewhat limited success. The lack of fit between dental patterns and body size is partially due to monognathic and dignathic heterodonty, as well as varying tooth size along the jaw margins. The ability to accurately predict body size from bite patterns is important for better understanding shark attack on humans and even submarine equipment, both civilian and military. To this end, we measured inter-tooth distance and tooth size for the two anterior and first four lateral teeth on both the upper and lower jaws, as well as jaw circumference, in a variety of carcharhinid and lamnid sharks, and regressed these against total length. Tooth gap distance is an accurate predictor of body size (upper jaw R2 = 0.83) (lower jaw R2 = 0.82) for twelve carcharhinid species as a group. More triangular upper jaw tooth spacing is isometric (m = 1.05) whereas the narrow and more pointed lower teeth (m = 0.89) display negative allometry. Taken individually different carcharhinid species display somewhat variable spacing patterns. Tooth bearing circumference is also isometric and predictive (R2 = 0.94) of total length. White and mako sharks display greater tooth gap spacing for a given length than carcharhinids with high regression coefficients and low variability. These simple measures taken from bitten submarine equipment and organisms allow quick assessments of shark size. This research continues with collection of additional data on potentially hazardous or commercially destructive species and identification of species specific damage patterns.
(PC-A) Universidade Federal da Paraiba, Dept. Sistematica e Ecologia, Lab. Ictiologia, Joao Pessoa, PB, Brazil; (MPA) Museu Paraense Emilio Goeldi, Coord. Zoologia, Setor Ictiologia, Belem, PA, Brazil
Fishery, uses and conservation of freshwater stingrays (Chondrichthyes: Potamotrygonidae) in the Marajó Bay (Brazil)
Freshwater stingrays present unique but poorly known biological characteristics and belong to the only group of elasmobranchs completely restricted to freshwater habitats. The Marajó Bay is located in the mouth of the Amazon River and the present study observed aspects related to the fishery and uses of potamotrygonids in this region. Direct field observations, analysis of captures / landings and interviews with local habitants were carried out since 1999. Results indicated that there are 2 types of fisheries and several folklore uses attributed to freshwater stingrays. The captures take place in fishing areas that are predominantly located in islands and involve mainly the use of hook and line, nets and long lines. One of the fisheries is directed to newborn and juvenile specimens that are captured for ornamental purposes and at least 4 species are illegally being explored. These captures are very specific since the rays have to be kept alive / healthy and also depend directly on the market demand. The second type of fishery is practiced by artisanal fishermen and involves the capture of adult specimens as a food source. In this case, occasionally the freshwater stingrays are considered bycatch but in some localities there is a directed fishery. The use of potamotrygonids as edible fish is apparently uncommon in other parts of the Brazilian Amazon basin. Freshwater stingrays are locally also used for unusual / bizarre purposes that range from the preparation of folklore medicine to the use of stings in religious rituals. A quota system should be established in the State of Pará in order to try to regulate the fishery for the ornamental trade and the artisanal fishery for consumption should be kept at sustainable levels. Fisheries and other uses of potamotrygonid species require the observation of specific consevation recommendations and adequate management.
James Cook University, School of Marine Biology and Aquaculture, Townsville, QLD, 4811, Australia/Western Australian Marine Research Laboratory, WA, 6920, Australia
Age and growth of the Western Wobbegong shark (Orectolobus sp. A) based on wild and captive animals
Age and growth of Orectolobus sp. A was studied using micro-radiographs of sectioned vertebrae and laboratory growth studies with two fluorochrome marker dyes, calcein and oxytetracycline. Vertebrae from 182 individuals were examined for length at growth band formation. The relationship between total length (cm, TL) and centrum radius (mm, CR) was linear: TL = 15.92CR + 10.65 (R2 = 0.9, n = 68). Growth bands were difficult to interpret and final counts were obtained from 98 (53%) individuals with a size range of 63 to 146cm total length. The formation time of growth bands in the vertebrae of captive animals varied, with no predictable pattern, indicating that these bands may not form annually. Growth band formation is thought to be influenced by non-periodic changes in centrum or somatic growth rather than with time. Von Bertalanffy growth parameters estimated from vertebral analysis for both sexes combined were L = 146.5, K = 0.12, t0 = -1.45. Growth parameters estimated from backcalculated length at growth band formation did not agree with those estimated from observed length at growth band formation. Individual growth rates/year of Orectolobus sp. A for the period of captivity (423-472 days) varied considerably, ranging from 3.5cm/year to 13.8cm/year in total length (mean = 7.03cm/year ± 1.15cm SE) and from 0.42kg/year to 3.07kg/year in weight (mean = 1.81kg/year ± 0.25kg SE). The rates of growth in total length/year for captive animals were similar to growth rates estimated from the von Bertalanffy growth curve.
Instituto Nacional de Investigación y Desarrollo Pesquero, Casilla de Correo 82, Correo Central, Mar del Plata 7600, Argentina
Ontogenetic dietary shift in the Rio skate, Rioraja agassizi
The Rio skate is an endemic species from the Southwest Atlantic. It is abundant off Argentina and Uruguay, which may make it an important benthic predator. However, the feeding habits of Rioraja Agassizi are unknown in the region. We analyzed the feeding habits of the Rio skate from two areas: the La Plata River estuary (LP, 34-37° S) and off Blanca Bay (BB, 39-41° S). We examined 140 specimens, of which 114 had prey into the stomach. The specimens were sorted into four groups: juveniles from LP (15), juveniles from BB (42), adults from LP (18), and adults from BB (39). Cumulative prey curves as a function of sample size were constructed in order to estimate the minimum sample size for describing accurately the diet of each group. All curves showed that the sample size was large enough as to describe the diet of each group. Prey importance was quantified through the percent index of relative importance (IRI). Also, the prey-specific importance index (Pi) was calculated. The IRI gives information about the population feeding habits, while Pi brings individual-based information on foraging strategy. In general, decapod crustaceans were the most common prey (IRI = 55.5%). The diet of juveniles from both areas was composed mainly of amphipods (IRILP = 65.1%, IRIBB = 42.5%). Adults of both areas were mostly specialized in the consumption of decapod crustaceans (IRILP = 88.6%, IRIBB = 64.8%). Polychaetes and cephalochordates were consumed more often in BB than in LP. Pi showed that most juvenile individuals (43.1%) were specialized in the consumption of amphipods (Pi = 66.5). In contrast most adults (58.9%) consumed mainly decapod crustaceans (Pi = 76.3). This ontogenetic shift in diet could be due to several causes such as changes in mouth structure and dentition, changes in energetic requirements and/or prey availability.
(OTFC, MLGA, WLPD) Federal University of Amazonas State, Dept. Morphology, Cytology Lab, 3000 Rodrigo O. J. Ramos Road, Manaus, AM, 69700-000, Brazil; (MNF) Federal University of São Carlos, Dept. Physiological Sciences, São Carlos, SP, 13565-905, Brazil
Stereological analysis on the gills of freshwater stingray Potamotrygon motoro
The stingray Potamotrygon motoro (Chondrichthyies, Potamotrygonidae) occurs in the Amazon and Plata Basin. Although this species is intensively exported as ornamental fish, no information exists about the morphometry of the respiratory system, which can be used as base for future programs of specie conservation or comparative studies of gas exchanges systems in lower vertebrates. The stereological morphometry of vertical sections profiles in fish gill enables the functional capacity for.O2 transport to be established. Following this method, the harmonic mean thickness (tht) of the lamellar diffusion barrier and the total lamellar surface area at gills are related to produce the morphometric diffusing capacity of O2 and CO2 and the anatomical diffusing factor. To avoid technical artifacts, the fish gills were fixed in situ in flowing 2.5% glutaraldehyde in 0.1M phosphate buffer followed by immersion in the same fixative. Trimmed arches were orientated for embedding in glycol methacrylate, exhaustively sectioned and 15 analyzed in a light microscope coupled with a drawing tube. The gills of P. motoro are composed of five arches, the first of which bears only a hemibranch. The gases must pass through two epithelial cells, the basement membrane, and the flange of the pillar cell, as they move between the blood and the water at lamella. The tht of the lamellar barrier was estimated in 4.75 mm (2/3 tht = 3.17 mm). This value (reflecting the efficacy of gaseous exchange) is comparable with that of trout but exceeds three times that of tuna, remaining within the range waiting for water-breathing fish. Ours results indicate a good agreement between smallest diffusion distance and most active fish, particularly in view of the fact that P. motoro is one of the more active freshwater stingrays. This study discusses the implications of the gill morphometry for gas-exchange function in Amazonian elasmobranches fish.
(MND, DRH) University of South Florida, 4202 East Fowler Ave., SCA 110, Tampa, FL, 33620, USA; (HAN) The University of Texas at Austin, Jackson School of Geosciences, Mail Code C1140, Austin, TX, 78712, USA
Functional morphology of jaw trabeculation in Narcine brasiliensis: an application of high-resolution X-ray computed tomography
The design of efficient, yet durable structures that retain their integrity under dynamic loading regimes has long challenged engineers and functional morphologists alike. The trade-off between weight and strength can be optimized by hollowing a structure and replacing its inner core with support struts. In animals, this design is observed in sea urchin test, avian beak and wing bone, and the cancellous bone of tetrapod limbs. Additionally, within the elasmobranch fishes, mineralized trabeculae have been reported singularly in durophagous myliobatid stingrays (Elasmobranchii: Batoidea), and are believed to be absent in basal members of the batoid clade. However, this study presents a secondary case of batoid trabeculation in the lesser electric ray, Narcine brasiliensis, a small, benthic member of the electrogenic Torpediniformes. While orientation of myliobatid trabeculae is perpendicular to the crushing plane of the jaws, high-resolution X-ray images reveal that the trabeculae of N. brasiliensis are arranged in the frontal plane, normal to the long-axis of the jaws. This morphological difference might be 30 explained functionally. Stingrays use their reinforced jaws to crush bivalves, yet N. brasiliensis feeds by ballistically protruding its jaws into the sediment to retrieve polychaete prey. At peak protrusion, the jaw arch is medially compressed such that the trabeculae are positioned to resist the forces resulting from this excavation mechanism. These struts are localized to specific areas most likely to experience the highest load: the medial quadratomandibular jaw joint and the thinnest section of the jaw immediately caudal to the tooth plates. In this way, these supports are positioned to resist both compression at the jaw joint, and local buckling of the jaws as they contact the sediment. Thus, trabeculation in batoids appears to perform strikingly different ecological functions, and was either independently derived in two taxa or was secondarily lost by intermediate members of this clade.
(JMDA) Departamento de Ciencias Marinas, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3350, B7602AYL, Mar del Plata, Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); (EM) Museo del Mar, Mar del Plata, Argentina
Bathyraja cousseaui sp.n., a new softnose skate from the southwestern Atlantic (Rajiformes, Rajidae)
A new species of the rajid genus Bathyraja Ishiyama is described from the southwestern Atlantic. The description was based on 20 specimens collected from off northern Patagonia and southern Malvinas Islands. Methods for making measurements and counts followed standard procedures. One mature male and one mature female were dissected in order to examine the skeletal structures (neurocranium, scapulocoracoids and claspers). The specimens exhibit a rhomboid-shaped disc, its length 0.5 times in total length. Preorbital length 2.41 – 2.93 times interorbital distance. A large and more distinct round pale area ocellus-like, margined with dark brown on posterior part of each pectoral base of the upper side of disc. Lower surface of the disc largely creamy- white, with posterior margins of pectoral fins, and edges of posterior lobes of pelvic fins narrowly edged dusky brown. Underside of tail almost entirely dark-brown. Upper surface of disc completly covered with numerous small spinules, also placed on interorbital area, tail, dorsal fins and posterior pelvic lobes. No ocular thorns. A row of 7 to 9 strong thorns in a median dorsal line (two of them set on the nuchal and 1 to 2 thorns on the suprascapular regions). No gap between nuchal-suprascapular and the anterior median thorns. Tail with 16 to 18 strong midrow thorns extending from axil of pelvic fins to the first dorsal fin. Males with elongated, slender rod-shaped claspers. Dorsal fins densely spinulose, close to the end of tail and with no space between them. Ventral surface of disc, pelvics, claspers and tail without of dermal denticles. Besides the external morphological features, skeletal characteristics are also analysed, and are compared with those of other congeneric species. Bathyraja cousseaui n. sp. was named in honor of Prof. Dr. María Berta Cousseau who has been contributing greatly to the marine fishes of Argentina.
(MLD, MJS) Port Elizabeth Museum, PO Box 13147, Humewood, Port Elizabeth 6013, South Africa; (TB) Rhodes University, Department of Ichthyology and Fisheries Science, Grahamstown, 6410, South Africa
An initial estimate of the population size of the juvenile Spotted ragged tooth shark (Carcharias taurus) in Eastern Cape nursery areas off South Africa<
A maximum likelihood model is developed using mark-recapture data to estimate the population size of immature, juvenile Spotted ragged tooth sharks in the Eastern Cape of South Africa. The model is composed of 4 major components: (1) A population dynamics model, which describes the number of tagged animals surviving to the next time interval. (2) An Observation model, which describes how the tags are recovered and reported. (3) A likelihood function that specifies the likelihood of observing a specific number of recoveries as a function of the number expected according to a specific set of parameters of the population dynamics and observation models. (4) A bootstrapping program to estimate variances for the parameters F (Fishing mortality), Z (Total mortality) and N (Population size). There was insufficient contrast in the data to estimate all model parameters consequently an instantaneous tag shedding rate, non-reporting rate and M (natural mortality) had to be fixed while allowing free estimation of F (Fishing mortality), Z (Total mortality) and N (population size). In this study fishing mortality was estimated to be 0.127 year -1 , with a 95% confidence level ranging from 0.089 and 0.158. Total mortality Z was estimated to be 0.327 year -1 , with a 95% confidence level ranging from 0.289 and 0.358. The mean annual population estimate for juveniles from 1994/95 to 2001/2 was 5540 with a 95% confidence level ranging from 4583 and 6306.
California State University, Fullerton, Department of Biological Science, 800 N. State College, Fullerton, CA 92834, USA
The contribution of mitochondrial proton leak to heat production in lamnid sharks
Endothermic fishes can elevate the temperature of certain tissues above water temperature through adaptations in the circulatory system (counter-current heat exchangers) that conserve metabolically generated heat. Although adaptations for heat retention in endothermic fishes have been well studied, sources of heat production in endothermic tissues are not well understood. Proton leak is an intrinsic, non-enzymatic property of the inner mitochondrial membrane that may serve as a heat source in endothermic fishes. This study involves comparing mitochondrial proton leak rates of two endothermic tissues in the short-fin mako 50 shark (Isurus oxyrinchus): red muscle and liver. The rate of proton leak across the mitochondrial membrane is a non-linear function of membrane potential and is measured by titration of respiration rate with inhibitors of the electron transport chain. The respiration rate and membrane potential in isolated mitochondria was measured simultaneously using.a Clark-type polarographic oxygen electrode and a lipophilic probe (TPMP+), respectively. Based on preliminary measurements, mitochondrial proton leak rates are similar in the red muscle and liver of the mako shark. Ongoing experiments include measuring mitochondrial proton leak rates of red muscle and liver in ectothermic sharks for a comparative study, as well as determining mitochondrial densities of these endothermic tissues.
(NAF) University of British Columbia, Dept. Zoology, Vancouver, BC, V6T 1Z4, Canada; (JLR, WAB) University of West Florida, Dept. Biology, Pensacola, FL, 32514, USA
Comparative batoid thermal tolerance
Most of what is known about temperature’s affects on distribution and activity of elasmobranchs comes from anecdotal field descriptions. The purpose of our study was to empirically model the relationship of acclimation temperature on upper and lower thermal tolerance of three batoid species from different thermal habitats and use these data to construct ecological thermal tolerance polygons defining each species’ thermal niche as an aerial measure (°C2 ). The Atlantic stingray, Dasyatis sabina, was the most eurythermic species with a polygon area of 978 °C2 . Conversely, the blue spotted ribbontail stingray, Taeniura lymma, and big skate, Raja binoculata, from equatorial Indonesia, and the cold California coast, respectively, were stenothermic species with polygon areas of 350 and 216 °C2 . The Atlantic stingray encounters a wide range of seasonal temperatures from nearly freezing to over 35 °C, and demonstrated marked gains in cold or heat tolerance as acclimation temperatures change. Conversely, the big skate, limited to deep, cold, stable waters off the Pacific west coast, exhibited almost no change in thermal tolerance as acclimation temperatures changed. Stenothermic blue spotted ribbontail stingrays showed a hyperthermal polygon pattern with moderate changes in polygon area relative to changing environmental temperature. The three species tested in our experiments clearly demonstrate that elasmobranchs have evolved sophisticated thermal strategies to exploit a wide range of thermal habitats.
(VVF, JAR, LFL, GJN) Iowa State University, Dept. of Zoology and Genetics, Ames, IA, 50011, USA; (TW, CS) Center for Shark Research, Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL, 34236, USA
Florida sawfish (Pristis pectinata) genetic variability: preliminary analyses
Sawfish abundance has been dramatically reduced throughout the past century by fishing and habitat degradation. This lower abundance may reduce the genetic variability of these populations, compromising their capacity to respond to changing selection pressures and thereby increasing their vulnerability to extinction. In the present study we assess the genetic diversity of P. pectinata by sequencing the mitochondrial NADH-2 and D-loop regions from individuals sampled at four locations on the Florida coastline. Genetic variability inferences based on our results are discussed in the context of sawfish conservation.
Pacific Shark Research Center, Moss Landing Marine Laboratories, 8272 Moss Landing Rd, Moss Landing, CA, 95039-9647, USA
Preliminary findings on the distribution, abundance, and reproductive biology of deepsea scyliorhinids off central California
These findings are part of a broad-based ecological investigation into the life history of three deep-sea catsharks (Scyliorhinidae), Apristurus brunneus, A. kampae and Parmaturus xaniurus, in the eastern North Pacific. Preliminary results on the distribution, abundance, and reproductive biology of these species off central California will be presented. Specimens were collected from trawl and longline survey cruises by the National Marine Fisheries Service (NMFS) from June 2002 through May 2003 from Año Nuevo to Point Sur, California. Distribution, occurrence, and abundance of specimens were analyzed to identify trends associated with season, depth, maturity, sex, and species. On average, longline hauls were mainly comprised of P. xaniurus, with an occasional catch of gravid female A. brunneus. Parmaturus xaniurus were usually found 72 less than 485 m deep. Conversely, trawl cruises were primarily comprised of Apristurus spp. Apristurus brunneus were typically found between 300-942 m, while A. kampae occurred deeper than 1,005 m. The total lengths at first reproductive maturity were determined for all species using nidamental gland width, egg diameter,.and outer clasper length measurements, as well as gonadosomatic indices (GSI) for males and females. Size at first reproductive maturity as determined by GSI is being compared to the maturation of other sexual organs to determine if development is synchronous. Initial analyses are attempting to determine if reproductive seasonality is evident by associated changes in the GSI and hepatosomatic index (HSI).
Ecology & Evolutionary Biology, University of California, Irvine, CA 92697, USA.
Stereo olfaction in hammerhead sharks – smells like a red herring
The evolution of the hammerhead shark cephalofoil has been the subject of much speculation. The ‘enhanced olfaction’ hypothesis persists as one of the most popular explanations for the evolution of this peculiar structure despite the lack of empirical evidence. It has been suggested that the widely separated nares provide sphyrnid sharks with better directional localization of odors and that the accompanying lateral expansion of the nasal capsules provides them with a larger volume in which to accommodate a larger nasal organ. We tested these hypotheses by comparing the morphology of the peripheral olfactory system for representatives of all eight sphyrnid shark species and two closely related carcharhinids. Although the maximum narial separation distance is greater for sphyrnids than carcharhinids, a prenarial groove along the anterior edge of the cephalofoil of most sphyrnid species channels water into the nares, effectively reducing the separation distance. Therefore, whereas sphyrnids sample a greater volume of water, they are not able to resolve odor direction any better than carcharhinids. To address the question of olfactory acuity, the surface area of the individual lamellae, which comprise the olfactory rosette, was compared among species. Although sphyrnids possess a significantly greater number of lamellae than carcharhinids, the total lamellar surface area did not differ among the species. Therefore, the inability of the sphyrnids to spatially resolve odors any better than the carcharhinids, coupled with the similar lamellar area among the species, combine to suggest that the ‘enhanced olfaction’ hypothesis is not strongly supported as a mechanism for the evolution of the hammerhead shark cephalofoil.
(MFN) Universidade Federal do Ceara, Departamento de Engenharia de Pesca, Rua Joao Cordeiro 638, Fortaleza, CE, 60110-300, Brazil; (SC) Department of Biology, Memorial University of Newfoundland, NF, A1B3X9, Canada
Molecular phylogeny of angel sharks (Squatinidae, Elasmobranchii) from Brazil
Angel sharks (Squatinidae; Elasmobranchii) comprise a single genus that includes fifteen extant species. Three species of the genus Squatina are endemic to the continental shelf of southeastern South America, between latitudes 24°S and 42°S: Squatina argentina, S. guggenheim, S. occulta. In 1991, Squatina occulta was described and S. guggenheim was redescribed. Before that, only one species was thought to occur in the southern coast of South America whereas S. occulta and S. guggenheim were misidentified as S. argentina in some studies. PCR (polymerase chain reaction) was used to amplify 401-base pair sequences of the mitochondrial DNA cytochrome b gene from each species. Sequences of this gene from the three species of Squatina were obtained. Phylogenetic analyses were performed with the PAUP computer program of Swofford. Maximum parsimony tree was obtained with the heuristic search algorithm. The phylogenetic analyses indicate that the three species from southern Brazil constitute a monophyletic group, with the newly described species S. occulta more closely related to S. guggenheim than to S. argentina. This result suggests that evolution of the genus Squatina in southeastern South America waters occurred from deeper to shallower waters. Probably, S. argentina was the first species to occupy the continental shelf in depths of 200m or more. Fossil records suggest that this genus has existed since the Upper Jurassic. S. occulta and S. guggenheim may have evolved more recently and speciation probably occurred as an adaptation to life.in shallower waters on different types of sea bottom. If this suggestion is true, S. guggenheim that lives from 0 to 80m, is the most recent species among the three Squatina from southern Brazil.
(VBG) Universidad Nacional de Mar del Plata, Casilla de Correo 82, Correo Central, Mar del Plata 7600, Argentina; (LOL) Instituto Nacional de Investigación y Desarrollo Pesquero, Casilla de Correo 82, Correo Central, Mar del Plata 7600, Argentina
Predation on eggcases of skates (Rajidae) in the Southwestern Atlantic: quantification and life history implications
Mean predation rates (± SD) on eggcases of four skate species, Bathyraja macloviana, B. Albomaculata, Amblyraja doellojuradoi, and Psammobatis spp., from the Southwestern Atlantic were estimated to be 0.151 (± 0.230), 0.423 (± 0.344), 0.254 (± 0.390), 0.150 (± 0.288), respectively. These 90 estimates are within the ranges reported elsewhere (14-40%). Eggcases of B. albomaculata were preyed on in higher proportion than expected from their abundance, and suffer a heavier predation rate where the snail Trophon acanthodes was present. Predation rates were not correlated with the thickness of the eggcase wall, which indicates that other factors (ecological or chemical) could explain this pattern. Five types of boreholes were found in the eggcases, one was attributable to muricid gastropods, one to naticid gastropods, a third type to an unknown gastropod (probably Fusitriton magellanicus), and the remaining were of unknown origin. Published cladistic analyses showed that skates are secondarily oviparous and maximized adaptations for a living in deep water. We suggest that oviparity in skates appeared as an adaptation to maximize fecundity (45-150 eggs per year, as compared to 2-18 pups annually or biannually in viviparous guitarfishes, the plesiomorphic sister clade of skates). If a predation rate of 24% (the mean of predation rate of all skate species studied to date) is applied to the range of fecundities reported for skates, the result is that 18-114 viable pups are produced annually per female skate. Even with a high mortality rate of 64% (the only direct estimate of natural mortality for any elasmobranch), each female skate produces 17-54 eggs annually. These values are higher than most elasmobranch fecundities. This maximization of fecundity is possible mainly because the fecundity of oviparous species is not limited by body size, as in viviparity. The protracted egg-laying season (4-12 months) of most skates (like in many other deep-sea fishes) maximizes the number of eggs laid.
University of California, Irvine Ecology & Evolutionary Biology, Irvine, CA 92697-2525, 195 Cornell, Irvine, CA 92612, USA
Bioenergetics of the little skate (Raja erinacea)
The Rajidae is a speciose clade (245 species) of dorsoventrally flattened cartilaginous fishes that are all oviparous. They lay a flat, rectangular egg capsules with a pair of posterior and anterior horns emanating from the corners that generally contains a single embryo. The little skate (Raja erinacea) is a common species of the Eastern North Atlantic with a development time of 12 to 18 months. We measured the metabolic rate of the little skate using two approaches: respirometry, and calorimetry. Oxygen consumption was measured in increments of 15 or 30 minutes for ten individuals at various developmental stages. The mean recorded metabolic rate was 0.0543 mg O2 /hr.g. Oxygen consumption over the nine month development period was calculated to be 0.352 g O2 /g. Homogenized skate tissue (n = 20) was processed with micro-bomb calorimetry. The mean caloric content among the individuals was 4.25 kcal/g and 4.22 kcal/g in yolk samples. Regression analysis of yolk conversion efficiency in the embryo was found to be over 100%, suggesting that there is an alternate route for energy input other than the yolk.
Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, Apartado Postal 592, La Paz, Baja California Sur, 23000, México
Pelagic shark catch in Baja California Sur, Mexico, and its relationship with environmental factors
Within the top predators of marine food chains, sharks are in a key position for its place of hunters and scavenging animals. Environmental factors associated to their abundance location would be use for shark management. Catch of 6 pelagic shark species in the western coast of Baja California Sur, Mexico, and its relationship with environmental factors were analyzed. Logs data were from two fishing boats that operated from September 1996 to June 2001. The fishing method was a multifilament gillnet of 2000 m lenght. A total capture of 289 tons was registered. 71 % corresponded to the blue shark, Prionace glauca; 12 % to silky shark, Carcharhinus falciformis; 10% to mako shark, Isurus oxyrinchus; 3 % to pelagic thresher Alopias pelagicus; 2 % to smooth hammerhead shark, Sphyrna zygaena; 1 % to oceanic whitetip shark 23 Carcharhinus longimanus and the rest (> 1 %) to non identified organisms. The capture by unit effort (CPUE) was defined as kilograms/fishing effective hours. The higher abundance was registered in front of Bahia Magdalena. Images of sea surface temperature (SST) were obtained from the NOAA-AVHRR and photosynthetic pigment images from SeaWiFS project, NASA/Goddard Space Flight Center. The shark distribution and the CPUE were related to these oceanographic satellite images. Pigment concentrations have significant effect in the abundance of Prionace glauca and Carcharhinus falciformis perhaps for its prey aggregation. Water temperature had its most significant effect for two species: Carcharhinus falciformis showed higher abundance and preference for 27-30 °C, whereas Alopias pelagicus showed preference for 23 – 25 °C.
Southern Illinois University, Fisheries and Illinois Aquaculture Center, Department of Zoology, Carbondale, IL, 62901, USA
Microsatellite loci isolated from the blacktip shark with cross-species amplification in Carcharhinidae and Sphyrnidae
The conservation and sustainable exploitation of the world’s shark populations has been a concern among marine fisheries biologists for decades. However, highly variable molecular markers suitable for investigating population structure and other aspects of molecular ecology are available for few shark species. In this study, we characterize 1 monomorphic and 15 polymorphic microsatellite loci isolated from the blacktip shark, Carcharhinus limbatus, and 33 present results of cross-species amplification in 11 Carcharhinus species, 4 additional genera from the family Carcharhinidae, and 2 species from the genus Sphyrna. An unenriched library of 2,304 cloned fragments produced only 36 (1.6%) colonies positive for dinucleotide repeat motifs, indicating microsatellite loci are relatively scarce in blacktip sharks as in other carcharhinid species. We subsequently produced an enriched library with a much higher (48%) fraction of positive clones. Heterozygosities of polymorphic loci ranged from 0.04 to 0.96 with 2 to 22 alleles per locus in 28 blacktip sharks tested. Amplification products were observed at 9 to 13 loci in 10 Carcharhinus species with 5 to 11 loci polymorphic per.species. All of the other species examined were polymorphic at 1 to 8 loci. The range of variation and widespread cross-species amplification of these microsatellite loci demonstrate their potential utility for investigating the population structure and molecular ecology of numerous shark species.
Marine Biomedicine & Environmental Sciences Center, Medical University of South Carolina, Charleston, SC, USA
Acid-base and osmo-regulation in the Atlantic stingray: possible role for coelomic fluid
Elasmobranch fish maintain solute and acid/base balance by regulating transepithelial transport across the epithelia of the gill, kidney and rectal gland. Another possible regulatory site is the epithelium surrounding the coelomic cavity that secretes fluid into that space. Coelomic fluid in many lower vertebrates including elasmobranch fish can exit the body via paired abdominal pores, two slit-like openings adjacent to the cloaca. Analyses were made of solutes (Na+, K+, Cl-, protein, urea) and pH in coelomic fluid (CF), plasma (PL), and in surrounding seawater of male and female euryhaline, Atlantic stingrays, Dasyatis sabina, adapted to full-strength and dilute Charleston, SC Harbor seawater. The PL and CF osmolality values were nearly at unity with the full-strength (» 900 mOsm) seawater. Concentrations of cations and anions in CF and PL were approximately 25-50% less than in the surrounding fullstrength seawater. Urea concentrations in CF and PL were nearly at unity. CF pH was acidic (5.1-5.4) compared to PL (7.1-7.3) and seawater (7.6-7.7). Transfer of rays to diluted seawater (451 mOsm) for 24 hrs reduced CF and PL osmolality (17% and 20%, respectively), and concentrations of Na+, Cl-, and K+ in PL and CF. Urea, a major osmolyte in marine elasmobranchs, decreased only 5% and 8% in PL and CF, respectively. The CF pH remained markedly acidic (pH 5.7) in dilute seawater conditions. These results suggest that the coelomic epithelium may act as a selective transport site of solutes and hydrogen/bicarbonate ions to maintain the acid base and solute homeostasis in stingrays in concert with coelomic fluid excretion through the abdominal pores.
(LEL, SPC) School of Biomedical Sciences, Department of Anatomy and Developmental Biology, University of Queensland, St Lucia 4072, Australia
Visual ecology in elasmobranchs: photoreceptor and ganglion cell distributions predict interspecific variation in lifestyle and feeding strategy
The importance of vision remains unknown in many species of elasmobranchs. Here, we examine the morphology and distribution of both photoreceptor and ganglion cell populations in the retina of a range of species, in order to assess their spatial resolving power and strategies for localising both prey and predator. The retinae of five species (the ornate wobbegong, Orectolobus ornatus, the white tip reef shark, Triaenodon obesus, the great white shark, Charcharodon carcharias, the epaulette shark, Hemiscyllium ocellatum, and the eastern shovelnose ray, Aptychotrema rostrata) representing a range of lifestyles (benthic, pelagic, diurnal, nocturnal) were investigated and morphological and topographic characterization of both cell populations revealed marked variation. Anatomical measures of visual acuity ranged from 2.5 to 4.5 cycles per degree in regional specialisations (areae and horizontal streaks) mediating acute vision. The retinal location of these acute zones varied, emphasizing the relative importance of vision in different parts of each species’ visual field. The distribution of both ganglion and photoreceptor cell populations were analysed in the same eye in each species and specialised areas of increased density were found to lie in register. However, differential analyses of rod and cone densities revealed localized differences in distribution suggesting different parts of the visual field may be more important during diurnal (cone-dominated) and nocturnal (rod-dominated) vision. Two and three localized retinal regions mediate acute vision in the frontal and lateral parts of the visual field in O. ornatus and T. obesus, respectively, while an elongated region of increased cell density extends horizontally across the retinal meridian mediating acute vision across a much larger and panoramic part of the visual field in H. ocellatum and A. rostrata. The retina in C. carcharias is unique and possesses a single and localized area for mediating increased visual acuity.
Iowa State University, Dept. Zoology and Genetics, Ames, IA, 50011, USA
Two independent partial duplications of cytochrome b in the mitochondrial genome of triakid sharks
In the course of a study aimed at determining the phylogenetic relationships of the sharks of the family Triakidae, we discovered a partial duplication of the cytochrome b gene in the mitochondrial genome of members of two different triakid genera: Mustelus and Hemitriakis. In both cases, the duplicated sequences are located downstream of the cytochrome b gene and upstream of the control region. The large amount of change evident in the region immediately downstream of the functional cytochrome b gene indicate that the Threonine and Proline transfer RNAs normally occupying this position are no longer encoded at this site. Phylogenetic 64 analyses of the duplicated sequences and the functional cytochrome b gene strongly support two different origins for the duplicated sequences. The two duplication events show remarkable similarities in location and gene region affected. The duplicated regions begin 51 and 59 bases downstream of the cytochrome b gene and include sequences that would encode the last 166 and 184 amino acid residues of cytochrome b. The duplicated region of Hemitriakis has acquired a considerably greater number of mutations than that of Mustelus when each is compared to its putative parent sequence. This disparity may be due to differences in the rate of substitution or in the time of origin. Documented cases of changes in the organization and content of mitochondrial genomes of vertebrates remain relatively uncommon; however, the few reports on mitochondrial sequence duplication reveal interesting commonalities. The characteristics of the duplication events we have discovered in triakid sharks correspond well with many of those common features and thus strengthen the case for a common mechanism of origin.
(LOL) Instituto Nacional de Investigación y Desarrollo Pesquero, Casilla de Correo 82, Correo Central, Mar del Plata 7600, Argentina; (RCM) Museo de La Plata, Departamento Científico Zoología Vertebrados, Paseo del Bosque s/n, La Plata 1900, Argentina; (AHE) Universidad Nacional de Mar del Plata, Departamento de Biología, Funes 3250 segundo piso, Mar del Plata 7600, Argentina
Reproduction of the shark Galeorhinus galeus from Argentina: support for a single Southwestern Atlantic population
It has been hypothesized that Southwest Atlantic school sharks Galeorhinus galeus migrate seasonally between southern Brazil and northern Argentina for mating and pupping. Lack of data on life history of school sharks from Argentinean waters precluded the test of this hypothesis. In this study, the reproductive biology, seasonal occurrence, and embryo growth of school sharks from off Argentina are described. A total of 411 school sharks (123 males and 288 females) were examined. Female size at 50% maturity was 124.72 mm total length (TL). Fertility was, on average, 1.77 pups smaller than fecundity. Differences between fecundity and fertility were not dependent on mother size. The largest embryos were found in late October and November in coincidence with ovulation. This indicates that gestation lasts about 12 months. Embryo growth was described by the Gompertz model (with Linf = 29.77, k = 0.021, and a = – 1.171). Four groups of females were recognized: juveniles up to 129 cm.TL, with translucent-towhite ovarian follicles (<19 mm wide); mature non-ovulating females with yellow ovarian follicles (17.5-27.5 mm wide), low gonadosomatic index (GSI), and empty uteri; mature ovulating females with larger yellow ovarian follicles (42-57.5 mm wide), high GSI, and uteri empty or with recently ovulated eggs; and pregnant females carrying term embryos, with minute ovarian follicles. These observations give support to the 3-year-long reproductive cycle proposed earlier. Males dominated the catches in October and April (63-71% of examined specimens). Females were more abundant than males from November to March (67-100%). The pattern of occurrence and reproductive condition of school sharks in northern Argentina are complementary to that from southern Brazil. This supports the hypothesis that there is a single large population of school sharks in the Southwestern Atlantic that performs reproductive migrations between southern Brazil and northern Argentina.
Universidade Estadual Paulista, UNESP, Instituto de Biociências, Departamento de Zoologia, Av. 24-A, 1515, Rio Claro, SP, 13506- 900, Brazil.
Fishery biology of bigeye thresher shark, Alopias superciliosus, caught by Santos longliners off Brazil
The bigeye thresher shark analyzed in this paper were caught by longliners settled in Natal city, Rio Grande do Norte State and Santos city, Sao Paulo State. The individuals from Santos were caught from North and South/Southeast of Brazil. Observing Natal longliners data (1986-2000), in number of fish, it increased from 1986 (41 fish) to 1988 (103 fish) following a decreasing in 1994 (7 fish) and 1999 (15 fish). The Santos data (1971-2001) suggest that it was probably rejected in the beginning of the period. Yield tendency increased from 1971 (1 ton) to 1989 (85 ton) and decreased until 2001 (20t on). The average CPUE and weight have shown light increasing trend for the all period with 18 kg/10,000 hooks and 120 kg respectively. Based on Santos Fishing Terminal (2002/2003 period) 35 individuals from North (N) were examined, and 82 from South/Southeast (S/SE). The sex ratio was 0,4/1 in N and 1/1 in S/SE. The length and weight range from 137cm (42kg) to 157cm (86kg) with average of 147cm (66kg) for male in N and the length and weight range from 97cm (21kg) to 164cm (98kg) with average of 133cm (67kg) for male in S/SE. The length and weight range from 112cm (40kg) to 136cm (133kg) with average of 157cm (86kg) for female in N and the length and weight range from 88cm (23kg) to 191cm (259kg) with average of 131cm (77kg) for female in S/SE. The length-weight relationship (N to S/SE) was: W = 28.46 L 3.01 and R2 = 0.89 for females (n = 67); W = 28.76 L 2.92 and R2 = 0.94 for males (n = 50); W = 28.53 L 2.91 and R2 = 0.89 for grouped sexes (n = 117).
(JWM) Northeastern University, Dept. of Biology, Boston, MA, 02115, USA; (MAF) New England Aquarium, Research Dept. Central Wharf, Boston, MA, 02110, USA
The physiological effects of commercial fishing on the spiny dogfish (Squalus acanthias)
Despite the wealth of current literature related to the physiological responses of teleosts (primarily salmonids) to exhaustive activity and the typical stressors associated with commercial-fishing, little.study in this realm has addressed the responses and resulting fitness of elasmobranches, namely those harvested directly. The spiny dogfish (Squalus acanthias) is currently an extremely controversial NW Atlantic ground-fishery, whose actual population calculations are heavily debated among regulators and fisherman. It is highly established that female spiny dogfish possess incredibly long gestation periods and very small liters. Robust females are the larger of the two sexes and most coveted by fishermen when the fishery is directed. Of particular interest is the (discarded) bycatch mortality of the spiny dogfish and the associated stress indicators due to commercial-fishing. These findings will enable the derivation of more accurate population figures while arming regulators with data to help implement appropriate measures in the best interest of maintaining the maximum sustainable yield of the species. Concurrently quantifying the stress indicators allows one to speculate and pinpoint the physiological causes (in addition to physical causes) of post-release discard mortality. Blood samples were taken via caudal peduncle puncture from 230 spiny dogfish across three separate treatments and five separate MW to NW Atlantic sampling expeditions during the course of 2002. In accordance with the conventional haematological stress parameters, deproteinized whole-blood lactate, whole-blood hematocrit, plasma protein, and serum levels of glucose, Cl- , K+ , Na+ , and osmolality were measured from blood taken immediately following normal ottertrawl, longline and relative short-term captivity. Hematocrit levels of the dogfish captured by 83 otter-trawl were significantly higher than those taken by the less exhaustive longline and the pseudo-controlled captive environments, suggesting that dogfish release a greater amount of red blood cells upon exhaustive aerobic activity associated with otter-trawl fishing.
CICIMAR-IPN, Laboratorio de Peces, Av. IPN s/n, Col. Playa Palo de Santa Rita, La Paz, Baja California Sur, 23096, México
Reproductive biology of Pacific angel shark Squatina californica at the South Western Gulf of California
Squatina californica is a body flattened shark with sandy benthonic habits. Its pectoral expanded and very developed fins seem to be wings, what gives to this shark its name. In Mexico is captured in directed fisheries or as secondary fishery at shrimp one, and is one of the most 87 important sharks for regional commerce. A description of reproductive biology of the Pacific angel shark (S. californica Ayres, 1859) is presented. 376 organisms were obtained in four fishing camps from September 2000 to May 2002. Pacific angel shark showed a sexual ratio of 1.41 F: 1 M in adults, while at embryos the proportion was 1 F: 1 M. Sizes for this region vary from 30 to 99 cm with dominant sizes between 60 y 90 cm. First sexual maturity size for both genders was at 80 cm TL. There were captured 26 gravid females, with a range from 1 to 11 embryos by female, at different stages of development, for a total count of 104 embryos. Fecundity was measured by number of embryos by female, and has its larger frequency between 5 and 6. Females with greater fecundity measured from 85 to 90 cm TL. Also histological processes are applied to testis of males in order to describe them and to know the spermatic development stages.
Instituto Nacional de Investigacion y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo Nº 1, Escollera Norte, 7600, Mar del Plata, Argentina
Exploitation of cartilaginous fishes from Argentina: current situation and needs for an effective management
In the past, cartilaginous fishes from the Argentinian shelf (34° to 55° S) were discarded, but currently they are actively exploited (due especially to the opening of new markets). We examined effort (fishing hours), catch (tons), and catch per unit of effort (CPUE, tons/fishing hours) from Argentinian official fishing statistics. From 1992 to 1998 the smallest fleet (up to 20 m length) landed chondrichthyans. Since 1994 a fleet of large boats (> 28 m length) increased its fishing pressure on chondrichthyans. Until 1994 chondrichthyan landings did not exceed 20000 tons per year. Since 1994, chondrichthyan landings exceeded 25000 tons annually in Argentinian ports. The landings peaked in 1998 with 35500 tons. This increase was due mainly to higher landings of skates (Rajidae) from 1994 onwards. From 1992 onwards a decrease in the landings of sharks (many species lumped together) was observed, while the landings of smoothhounds (mainly Mustelus schmitti) and angel sharks (Squatina spp.) were kept at 10000 and 4000 tons, respectively. The trend in CPUE was decreasing for all fleets. The maximum decrease was for the fleet > 28 m, with CPUEs of school sharks (Galeorhinus galeus), angel sharks, smoothhounds, and sharks falling more than 50%, and CPUE of skates falling by 36%, 93 which clearly indicates a negative effect of fishing on abundance. An improvement in the catch statistics for all fisheries is needed for achieving accurate population assessment and effective management. Given that elasmobranchs are poorly known in Argentina, it is also important to carry out studies on ecology, life history and biology. In Argentina there are not management strategies for chondrichthyans, only maximum sustainable quotas are established for smoothhounds, angel sharks, skates and sharks. Taking into account the vulnerability of chondrichthyans, and the growing demand of chondrichthyan products from Argentina, a management strategy should be implemented as soon as possible.
University of South Florida, Dept. of Biology, Tampa, FL, 33620, USA
Feeding kinematics and the role of jaw protrusion in the sandtiger shark Carcharhias Taurus
To date, most functional and morphological studies of shark feeding have concentrated on identifying correlations with the feeding mechanisms of coastal and benthic species relative to their ecology. Sandtiger sharks Carcharias taurus are the only species of the primarily pelagic order Lamniformes that have been successfully held in captivity, which provides an excellent opportunity to examine the feeding kinematics of a representative from this largely unstudied order. Carcharias taurus are thought to be opportunistic hunters feeding primarily on fish, squid, and small stingrays. Studying C. taurus allows us to compare and contrast its feeding mechanism and ecology with those of other elasmobranchs inhabiting coastal and benthic environments. Feeding events were filmed for five individuals using high-speed digital videography at SeaWorld Entertainment Park, Orlando over a four-month period in order to determine a general kinematic profile of prey capture. The most notable preliminary differences in the kinematic profile of C. taurus are the presence of cranial elevation an order of magnitude larger than and relatively greater upper jaw protrusion distances compared to other sharks. Cranial elevation added from 7 to 21 cm to maximum vertical gape distance. Protrusion included both an anterior and ventral component, which qualitatively differs from previous studies of jaw protrusion in sharks. Although significant differences were not found between individuals in the majority of timing variables, differences were found in duration of cranial elevation and total bite duration. As with other studies of lower vertebrate feeding, intraspecific differences apparently represent a significant source of variation. Extensive cranial elevation and upper jaw protrusion are thought to enhance the predatory ability of C. taurus by augmenting both vertical and horizontal components of its gape, thereby placing the jaws more in-line with the longitudinal axis of the body and allowing a more perpendicular occlusion of the teeth on prey items.
(JAN, BAT) Coastal Fisheries Institute, Louisiana State University, Baton Rouge, LA, 70803-7503, USA; (JKC) National Marine Fisheries Service, 3500 Delwood Beach Road, Panama City, FL, 32408, USA
Age and growth of the bull shark, Carcharhinus leucas, in the northern Gulf of Mexico
Bull sharks, Carcharhinus leucas, are a cosmopolitan species occurring in warm-temperate and tropical coastal regions, including the Gulf of Mexico. A total of 180 specimens were collected from both fishery dependent and independent surveys from Louisiana, Alabama, and Florida. Samples ranged from 555 – 2190 mm FL. Vertebrae were removed from below the first dorsal fin and processed for ageing. Samples were cleaned and a 0.3 mm section was cut and stained using crystal violet. Samples were aged by two of the authors, first independently and then after consultation for samples for which an ageing disagreement had occurred. A final age was assigned to each specimen and a von Bertalanffy growth model with Fabens adjustment was 27 fitted to the observed data. The preliminary VBGF, for combined sexes, predicted Linf : 2204 mm FL and K: 0.09, with given a size at birth of 700 mm. Growth models were also fit to the backcalculated age estimates. Preliminary results indicate differences in both parameter estimates to those previously published with our model predicting a lower Linf and a higher K value.
Russian Federal Research Institute of Fisheries & Oceanography (VNIRO), 17, V.Krasnoselskaya, Moscow, 107140, Russia
Feeding of Pacific sleeper shark and five deep-benthic skates in the western Bering Sea
Benthic skates and Pacific sleeper shark play an important role in ecosystems of the North Pacific basin. They are a significant element of food webs in benthic communities. Elasmobranchs consume commercially important fish, cephalopods and shrimps. These species themselves have some commercial importance. For example, skates are processed into fish meat jelly and dried skate wing. Pacific sleeper shark does not support a fishery now. The diets of some northern Pacific skates were described only in few papers. Feeding habits and trophic relations of elasmobranchs inhabiting the western Bering Sea were never previously considered. Stomach contents of elasmobranchs brought aboard Japanese trawler Kayomaru No. 28 during summer 1997 were analyzed. The stomach samples were selected without known bias from bottom trawl hauls carried out around the clock in the western Bering Sea between 170° E and 178° W. Stomachs examined and those with food were as follows: 125/102 Pacific sleeper shark Somniosus pacificus, 139/123 Aleutian skate Bathyraja aleutica, 19/18 Matsubara skate B. matsubarai, 68/58 whitebrow skate B. minispinosa, 113/86 Alaska skate B. Parmifera, and 189/179 Okhotsk skate B. violacea. The diet of predatory elasmobranchs (Pacific sleeper shark, Alaska skate, Aleutian skate, Matsubara skate, and whitebrow skate) consisted of large crustaceans, cephalopods and fishes. Benthophage elasmobranchs (Okhotsk skate) consumed mainly worms, amphipods and shrimp. Diets of male and female elasmobranchs differed, probably due mostly to the effect of size. The consumption of worms and crustaceans (especially small) in diets of predators declined with increasing their size, whereas proportion of cephalopods and fishes in diet increased. The consumption of worms and small crustaceans by benthophage Okhotsk skates declined with increasing skate size while consumption of crabs and squids increased. Among the species examined, three elasmobranch pairs had a medium level of dietary 37 similarity: Aleutian and Alaska skates, Alaska and whitebrow skates, and whitebrow and Okhotsk skates. Diets of other species differed considerably.
Universidade de São Paulo, Dept. Zoologia, Rua do Matão-Travessa 14, 05508-900, Cidade Universitária, São Paulo, SP, Brasil
Preliminary study – defense/attack of stingrays of Rio Javaes, Ilha do Bananal – TO, Brazil
Fluvial stingrays (Myliobatiformes: Potamotrygonidae) are known for causing accidents in humans in the rivers of the Center-west and North regions of Brazil. Previous studies on those accidents attest that the stingrays are the main cause of damages to the man in those areas. This study intends to describe the reactions of Potamotrygon stingrays to different stimuli. 29 individuals (8 youngs, 12 males, 9 female) belonging to the Potamotrygon genus were collected with a net in Rio Javaes’s sandy margins (near IIlha do Bananal), transported inside boxes with water. For the accomplishment of the stimulus, the animals were placed in a pool made with plastic blanket, with 1 m2 area and 10 cm deep. The aeration was made through battery air pumps. The disk of the animals was divided in 9 parts, 2 cranial-lateral, 1 cranial, 2 mediallateral, 1 medial, 2 caudal-lateral and 1 caudal. For animals more than 16 cm wide, stimuli were applied with a stick with 8 cm wide extremity, for animals less then 16 cm wide the stick extremity measured 2.3 cm. 29 experiments were accomplished, in each one of them the 9 sections were stimulated and the respective reactions were registered (escape after the stimulus, attack with the sting, escape visually oriented before the stimulus, no reaction). After each stimulus a recovery period was given and the normalization of the movements of ventilation of the spiracles was observed, only then a new stimulus was accomplished. The results show that in 57% of the cases escape after the stimuli occurred, in 31% attack with the sting, 10% escaped after visualizing the stick.and 2% showed no reaction. So we can say that the attack reactions happen mainly when the animal does not see that something is about to reach it, when the stimulus is given in the caudal and medium parts.
Estación Hidrobiológica de Puerto Quequén and División Ictiología, Av. Angel Gallardo 470, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires, C1405DJR, Argentina
Life-history strategies of two sympatric skates of the genus Psammobatis off Buenos Aires, Argentina
Psammobatis bergi and P. extenta are two sympatric skates commonly caught in the commercial bottom trawl fishery of Puerto Quequén (58°50¢ W; 38°37¢ S) Buenos Aires, Argentina. A sample of 224 P. bergi and 535 P. extenta was collected seasonally from the commercial fishery between June 2000 and November 2001 and March 2000 and May 2001 respectively, with the exception of Spring 2000. Both species presented sexual differences in the Total Length (TL) – Total Weight (TW) relationship and also differed in the TL50% of maturity (P.bergi females 79.1%, males 75.5%; P.extenta females 80.0%, males 84.0%). A seasonal pattern was observed in the Gonadosomatic Index (GI) of P. bergi (H = 37.97, p < 0.001) and in the Liver mass (LM) – TL relationship of P.extenta; conversely, the GI of P.extenta and the LM – TL relationship of P. bergi did not evidence a temporal pattern. Furthermore, the two skate species differed in several morphometric relationships associated with reproduction, namely Oviducal gland width (OW) – TL (P. bergi significant [S], P.extenta not significant [NS]), Egg case width (EW) – TL (P. bergi NS, P.extenta S), EW – OW (P. bergi S, P.extenta NS) and EW/OW – TW (P. bergi S, P.extenta NS). These species presented low Niche overlap (S = 0.0132) and similar Niche Width figures (P. bergi B = 0.11: Brachyura 91.64%, P. extenta B = 0.0975: Penoidea + Gammaridea 88.73%). From the evidence presented, it can be inferred that these two sympatric skates present different lifehistory strategies and occupy different niches.
Florida Museum of Natural History, University of Florida, Gainesville, FL, 32611, USA
Site fidelity and behavior of sharks at a long-term shark feeding dive site
To encourage tourism, commercial dive boat operators often offer shark feeding excursions and provide video footage of the dives to participating SCUBA divers. We conducted a longitudinal study of Caribbean reef shark (Carcharhinus perezi) feeding dives occurring at a single location off West End, The Bahamas. We analyzed video tapes of 36 dives recorded over the period of November 1992- September 2001. Data was collected on the following variables: water visibility; human activity; number of sharks and humans per dive; shark parasite load; gender of shark and male maturity; and frequency of feeding attempts, acts of antagonism, and yawning. Site fidelity of individual sharks was investigated by documenting, when possible, markings and scars on each shark. We found that the minimum number of female and male sharks per dive, as well as the parasite load on both sexes, increased temporally. Parasites were most frequently found near gill openings. Bumping of the camera, presumably an act of antagonism, was observed more often in females than in males. The frequency of shark feeding attempts was correlated with the technique of the human feeder. The number of divers and water visibility had no significant affect on the recorded shark behaviors. No seasonal trends concerning recorded behaviors, parasite load, or clasper size were observed. Females and males did not differ significantly in frequency of feeding attempts. Nine individual females and eight males were identified in more than a single dive. Although one individual had a hiatus of 4.5 years between sightings, most of the reappearing individuals were repetitively observed on site over periods of several months. Such site fidelity may be attributable to feeding-induced conditioning of the sharks.
Laboratório de Ictiologia, Depto. de Sistemática e Ecologia, CCEN, Universidade Federal da Paraíba, Cidade Universitária, João Pessoa, PB, 58051-900, Brazil
Diet of the Caribbean sharpnose shark, Rhizoprionodon porosus, on the coast of Paraiba – Brazil
The Caribbean sharpnose shark, Rhizoprionodon porosus, is the most abundant shark species in the coastal fisheries of Paraiba State, Brazil. It is a coastal shark, with size at birth between 31 and 39cm, and a maximum adult size of 110cm total length (TL). With the objective of analyzing 17 the diet composition and its variation, according to the size classes, 42 samples were obtained from the gillnet artisanal fisheries at the Paraiba coast. Stomach contents were fixed in 10% formalin and preserved in 75% ethanol. The items were counted, weighted, and identified to the lowest possible taxonomic level or category; for the assessment of the importance of prey items, the percentage Index of Relative Importance (%IRI) was used. The sample was composed of 32 males, with TL between 35.1 – 81.5 cm and 10 females with TL between 33.9 – 91.5 cm. Body weight varied from 182.0 to 2232.0g for males and from 133.3 to 3886.0g for females. Of the 42 stomachs examined, seven (16.67%) were empty, nine (21.43%) contained only amorphous substance and the remaining (61.9%) contained semi-digested prey items. The predominant item (%IRI) was teleost fish, representing 97.58%, followed by crustaceans (1.36%) and cephalopods (1.06%). The following prey groups were identified: Clupeidae, Engraulidae, Holocentridae, Ophichtidae and Pleuronectoidei (Teleostei), Penaeidae and Isopoda (Crustacea) and Cephalopoda (Mollusca). Cephalopods were onlyfound in the stomach of adult individuals. The obtained results indicate that Rhizoprionodon porosus is predominantly piscivorous, opportunistic with respect to the teleost species it preys, and supplements its diet with crustaceans and mollusks.
(TNT, LSW) Texas A&M-Corpus Christi, Physical and Life Sciences CS 242, 6300 Ocean Drive, Corpus Christi, TX 78412, USA (RW) Texas Parks and Wildlife, Perry R. Bass MRFS, HC 02, Box 385, Palacios, TX 77465, USA
Detection of genetic variation in Rhizoprionodon terraenovae and R. porosus using singlestranded conformational polymorphisms (SSCP)
The Atlantic Sharpnose Shark, Rhizoprionodon terraenovae, and the Caribbean Sharpnose Shark, R. Porosus are small coastal-temperate and tropical sharks of the continental shelves that overlap in.distribution along the Gulf of Mexico, Florida and around the Yucatan Peninsula to the Caribbean Sea. In order to properly distinguish between the two species, current methods require counting caudal and precaudal vertebrate. These species used to be highly abundant within their prospective ranges, but current fishery pressures have caused declines in landing at some locations. Assessment of population size and structure is necessary to determine future management plans for this species. Use of SSCPs is a viable method to differentiate between the two species and to measure population structure. SSCP analysis was able to detect unique haplotypes indicative to a particular species. Use of sequencing confirmed the variation between the species with an estimated nucleotide divergence as high as 1.08%. AMOVA analysis comparing Atlantic sharpnose sharks collected in the Bay of Campeche with samples obtained from four other sites throughout the Gulf of Mexico and along the Northwestern Atlantic Ocean found that the eleven haplotypes observed were evenly distributed throughout the range (fST = 0.022, p=0.191). However significant differences were observed in pairwise analysis between the Bay of Campeche and other sites. These differences disappeared when samples were examined based on temporal data suggesting that genetic bottlenecking is occurring in the R. terraenovae along the Mexican Coast.
California State University, Long Beach, Department of Biological Sciences, Long Beach, CA, 90840, USA
Round stingray (Urolophus halleri) movements and site fidelity at Seal Beach, California: a preliminary report
The round stingray, Urolophus halleri, is a common nearshore elasmobranch in southern California waters. At Seal Beach, CA, round stingrays are found in high densities and are responsible for over 300 injuries to humans each year. Little is known about their movement patterns or residence time in the Seal Beach area. Fine-scale movements and site fidelity of round stingrays at Seal Beach are being determined using acoustic telemetry techniques. To date, six rays were manually tracked continuously for up to 90.5 h, and 14 rays have been monitored using acoustic listening stations for up to 151 days..Manually tracked rays exhibited limited daily movement, with a median rate of movement of 32.0 m h-1 , which varied with tidal stage. Rate of movement was lower rate during periods of incoming tide (19.2 m h-1 , median) than high slack tide (38.6 m h-1 , median) and outgoing tide (44.4 m h-1 , median). Acoustically monitored rays typically remained off Seal Beach for weeks after they were tagged. During this time, rays were most often recorded at the mouth of a local coastal river at the west end of Seal Beach. Six rays were observed to move to neighboring beaches between 1 and 2.5 km away during the 151-day period and five of these rays later returned to Seal Beach. So far, rays monitored have showed periods of little movement followed by movement out of the area.
University of Queensland, Centre for Marine Studies, Brisbane, QLD 4072, Australia
Comparisons of ampullae of Lorenzini obtained from Carcharhinus leucas native to various habitats
Ampullae of Lorenzini were examined from Carcharhinus leucas captured in the freshwater reaches of the Brisbane River and from sharks obtained from the marine waters of Moreton Bay. On sharks from both habitats, ampullary pores (0.14 to 2.5 mm, diameter) are distributed across the head area of the shark and have a mean number of 2052, 59% of these pores appear on the 91 ventral surface of the head. There are two general forms of the canal epithelial cells, flattened squamous and ridged cells that contain a high density of vacuoles and appear to release material into the lumen of the canal. The alveolar sacs contain numerous receptor and supportive cells bound by tight junctions and desmosomes. The pear-shaped receptor cells possess a single kinocilium that extends into the ampullary lumen. Along the basal surface of the receptor cells are junctions with unmyelinated neural terminals. A central centrum stage consisting of a luminal layer of cuboidal epithelial cells overlying squamous epithelial cells lies in the center of the basal ampullary region. This overlies the primary incoming afferent nerve, which radiates from this central area to divide and connect with all receptor cells. Apically nucleated supportive cells produce a rigid ampullary wall and possess a low number of microvilli.
Utilizing Public Sightings Data to Investigate the Distribution and Habitat Use of Smalltooch Sawfish