1999 AES Annual Meeting Abstracts

The main theories of evolution, Lamarckim (adaptation) and Darwinism (natural selection), were conceived during the XIXth century from studies made at the organismal level. At present, deciphering of complete genomes and proteomes leads to a definition of the species in molecular terms. Molecular phylogenetic trees, constructed on the percentages of substitutions in nucleic acid and protein sequences, are confronted to morphological trees derived from taxonomy. However, the substitution rates greatly vary from a protein to another and, in a given protein, from a domain to another. Protein shapes, determined by aminoacid sequences through self-folding, evolve following rules different from those governing body evolutions. Molecular clocks are usually not in agreement with divergence times between lineages estimated through fossil records. Furthermore new evolutionary mechanisms, such as genetic drift (neutral evolution), genomic drive, horizontal gene transfer, have been hypothesized. Evolution of Chondrichthyes differ sharply from that of bony vertebrates by several specific features (skeleton, osmoregulatory strategy, reproduction). The osmoregulatory system implies four organs: gut, kidney, gills and rectal gland. Regulation of nephron cells involves a cascade of molecule interactions : mediators, receptors, transductors and effectors. A great diversity is found in neurohypophysial hormones when compared to those of bony vertebrates, whereas, among effectors,Squalus acanthias urea transporter and CFTR-chloride channels exhibit, respectively, 61% and 72% sequence identity with their human counterparts. Evolution of the osmoregulatory function was apparently made more by changes in the combinatorial coordination of effectors in target cells rather than modifications in the molecules themselves.

Uterine fluid and serum protein composition and serum steroid hormone concentrations during gestation in the aplacental viviparous Atlantic stingray, Dasyatis sabina

The Atlantic stingray,  Dasyatis sabina, is an aplacental viviparous elasmobranch. Embryos have an external yolk sac which is quickly depleted within the first few weeks of a 12-14 week gestation. Uterine fluid is produced shortly after ovulation, and continues to be produced until parturition. We test the hypothesis that this fluid contains unique proteins that are synthesized and secreted by the uterus, and that the changing protein composition is correlated with varying serum steroid hormone concentrations. To test this hypothesis, blood and uterine fluid samples were collected from rays during the annual reproductive cycle. Uterine fluid and serum proteins were characterized by isoelectric point (pI) and molecular weight using two dimensional gel electrophoresis. Uterine fluid from early through late gestation contained a series of basic (pI 7-8) and acidic (pI 4-5) proteins ranging from 30-220 k molecular weight. A large acidic protein (pI 5) first appeared in mid-gestation uterine fluid, and was present through late-gestation. Serum 17-ß estradiol concentrations significantly increased from 426 +/- 78 pg/ml early gestation to 8293 +/- 2165 pg/ml mid-gestation, and remained elevated through late gestation. Serum testosterone concentrations increased from 78 +/- 8 pg/ml during early gestation to 279 +/- 19 pg/ml during mid-gestation.

Morphology of the uterus during the annual reproductive cycle of the aplacental viviparous Atlantic stingray, Dasyatis sabina

The Atlantic stingray,  Dasyatis sabina, is an aplacental viviparous elasmobranch that reproduces annually. In our study population, ovulation occurred in April, and gestation lasted approximately 14 weeks. Villous extensions of the uterine mucosa line the inner wall and are present throughout the year. Prior to ovulation, during the final stages of oogenesis, the uterus was aglandular. Villus length averaged 3.7 +/- 0.7 mm. The uterine morphology transformed dramatically during gestation. Uterine villi were differentiated when encapsulated embryos were developing in the uterus. Shallow tubular glands were present in villi, and deep tubular glands were present in the uterine mucosal lining. Uteri containing unencapsulated, early gestation stage embryos were completely glandular. The uterus was fully glandular through mid- and late gestation. Villi length significantly increased to 6.9 +/- 0.6 mm during early gestation, and length remained similar through mid- and late gestation. Vascularization increased and capillaries hypertrophied during early and mid-gestation. Lipid droplets accumulated within glandular pits mid- and late gestation. The uterine mucosa and villi were aglandular in the post-partum uterus, and villus length significantly decreased to 5.2 +/- 0.6 mm.

A juvenile megamouth shark Megachasma pelagios caught off southern Brazil.

The megamouth shark Megachasma pelagios is one of the rarest elasmobranchs. Since the capture of the first megamouth known to science in 1976, only about thirteen specimens have been reported, and only four have been available for scientific study. A juvenile megamouth shark was accidentally caught by the Brazilian longline vessel Tooshin Maru 106 off southern Brazil (27o 08’S 43o 55′ W) on September 18, 1995. The specimen was hooked in the mouth at depth of 15-40 m over water approximately 1400 m deep. The specimen was recognized as unusual and donated to the Instituto de Pesca in Santos, Brazil. This is the first juvenile megamouth seen and studied by scientists. The specimen is an immature male 1800 mm TL (1448mm FL), weighing 24.4 kg. Morphologically, this specimen is very similar to other megamouth sharks described from the Pacific. The body is soft and flaccid, with poor vertebral calcification. The claspers are small and poorly developed, and the specimen is clearly a juvenile. The specimen is clearly countershaded, being black and brown above and white below. This specimen confirms the presence of megamouth in the Atlantic.

Sharks of the inshore waters of the Canaveral Bight, Florida with emphasis on the spinner shark, Carcharhinus brevipinna 

Between September, 1995 and October, 1998, the sharks of the Canaveral Bight, Florida were qualitatively sampled during the summers between the beach and approximately 10 m depth. Preliminary observations indicated that the inshore waters in this area were being used as a nursery area by the spinner shark, Carcharhinus brevipinna. The objective of this study was to ascertain if spinner sharks are using these waters as a nursery area, and if so, to better understand  C. brevipinna life history parameters. Sharks were captured via hook and line from either a 5.9 m outboard boat or the Ocean Obsession II, a 21.4 m charter boat providing nightly shark fishing trips between May and October. Four hundred eighty-nine sharks representing three families and seven species were captured during the study. The Atlantic sharpnose shark,  Rhizoprionodon terraenovae, and the spinner shark were the most common species captured and appear to use these waters as a nursery area throughout the summer months. Spinners began arriving in June and were common into September and October. There was no difference in fork length (FL) between males and females. The 1997 spinners were larger those observed in 1998. Spinner pups grew about 10 cm FL during the summers of both 1997 and 1998. The lack of adult female spinner sharks and the failure to observe any young of the year spinner sharks with fresh umbilical remains lends support to Castro’s (1993) statement that spinners appear to undergo parturition in deeper waters. Young of the year blacktip sharks, Carcharhinus limbatus,were observed but not in sufficient quantities to indicate that blacktips are selecting the inshore waters of the Canaveral Bight as a nursery area. A number of 1+ yr. juvenile  C. brevipinna  and  C.limbatus  sharks were captured in May and June of 1998.

A remarkably consistent fishery-independent measure of the relative abundance of large coastal and pelagic shark species inhabiting the northwestern Atlantic, 1976-1994.

The research vessel  Geronimo, owned and operated by St. George’s School of Newport, Rhode Island, instituted a shark-tagging program in 1976 in collaboration with Jack Casey of the National Marine Fisheries Service Laboratory in Narragansett. The boat’s longline gear, method of operation, and fishing area remained remarkably consistent through 1994, although annual fishing effort waned after the mid-1980’s. The consistency of operation provides a continuous index of CPUE for sandbar Carcharhinus plumbeus, bluePrionace glauca, and other large coastal and pelagic species inhabiting New England shelf and canyon waters. In this region from 1976 to 1994, Geronimo’s crew set a total of 37,631 hooks consistently deploying about 80 to 140 hooks per set, resulting in a total catch of 5,454 sharks. Reductions in CPUE over the nearly twenty-year period indicate the abundance of sandbar and blue sharks declined substantially during the 1980’s, declines which match those from other studies. There was no apparent decline in average length of either sandbar or blue sharks caught during the period. Sex ratios in the catch of blue sharks show an approximately four-year cycle that may be indicative of segregated migratory habits of females vs. males.

The dentition of the pelagic stingray Dasyatis violacea, its design and function. In both sexes, the pelagic stingray dentition combines high-cusped anterior files with broadly cuspidate teeth in posterior positions. The transverse ridges of these posterior teeth create a cutting edge. This is unlike the typical clutching-crushing design associated with most members of the genus. Based upon tooth and dentition design, and feeding observations at the Monterey Bay Aquarium, there appears to be sufficient evidence to characterize this as a deboning dentition.

A systematic revision of the electric ray genus  Narcine  Henle, 1834 (Chondrichthyes: Torpediniformes: Narcinidae).

The electric ray genus Narcine Henle, 1834 is revised and found to be more diverse than previously understood. Some 20 species are recognized from tropical and sub-temperate waters from all major oceans and seas of the world (except the eastern Atlantic Ocean and Mediterranean Sea), and new species are described. Species of Narcine  occur primarily in shallow to off-shore waters of continental shelf regions, but some species are known from upper continental slope areas as well. The Indo-West Pacific region is the most speciose but one of the most undersampled areas in which species of  Narcine  are known to occur. Many nominal species are placed in synonymy, some for the first time. A combination of proportional measurements, numerous counts and external and internal morphology were used to identify all valid species of Narcine . Difficulties surrounding taxonomic revisions of electric rays include the poor state of many specimens in preservative (including type-specimens), the misidentification of many nominal species by previous authors, and the great similarity among many species. Taxonomic revisions of the remaining electric ray genera are currently underway or have been completed.

A Preliminary investigation of spatial distribution of Nurse shark at Atol das Rocas, Brazil.

The nurse shark Ginglymostoma cirratum, although widely distributed along the Brazilian coast, faces possible localized population declines, especially due to artisanal fishery impact. The goal of this study is to investigate some populational aspects of this species, and its distribution in the Biological Reserve of Atol das Rocas, only atol of South Atlantic. We carried out underwater observations at different parts of the area, recognizing the individuals through natural distinctive marks, like scars on their fins. A total of 92 nurse sharks was observed, of which 29 were individually identified. Most specimens (57 %) were found in tide pools. The maximum observed period of individual permanence in the pools was 22 days; three individuals moved among different pools in intervals of five days or less. Total length of the individuals varied from 45 to 350 cm, and average length in open areas of reserve was significantly higher than the one of specimens from closed areas (t=2.3918, p<0.05). Most specimens were young and their total length did not exceed 150 cm, rendering sex determination difficult. Mature specimens were only observed in open areas (TL>235 cm).

Myths and misinformation about the nurse shark,  Ginglymostoma cirratum .

Although the nurse shark is an extremely common shallow-water species, abundant in Florida and the Caribbean, its biology is poorly known, and there are numerous myths and a great deal of misinformation about it in the literature. Although its name has been attributed to the making a “sucking sound” while feeding, it is actually derived from the name “huss”, an ancient English name for a dogfish. The size and weight attained by the nurse shark has often been exaggerated, with claims of specimens 2130-3350 mm TL being common. None of the specimens measured in this study exceeded 2680 mm TL and 110 kg. None of the specimens actually measured by other researchers ever exceeded 2800 mm TL. The size at maturity is also often stated erroneously at about 1500 mm TL. Nurse shark females begin to develop sexually at about 2200 mm TL. In late spring, maturing females measuring 2360-2380 mm TL carried ripe oocytes 55-58 mm in diameter. Mating occurs primarily from mid-June to early July. The reproductive cycle of the nurse shark encompasses a five to six-month gestation cycle and a two-year ovarian cycle. A female will mate and ovulate in June of the first year. It then gestates for about five and a half months and gives birth in November or early December of that year. It will not mate again until about eighteen months later, in June of the second year. Thus, the reproductive cycle is biennial and a female produces a brood or litter every two years. The adult population of females could be divided into two groups during most of the year based on whether they were reproducing that year (carrying ripe oocytes or embryos) or they were post-partum.

Temporal Variation of Heavy Metal Concentrations of  Galeus sauteri (Carcharhiniformes: Scyliorhinidae) in the Northeastern Waters of Taiwan

This study is to determine the concentrations of Hg, Zn , Cu , Ni , Pb and Cd in Galeus sauteri in the waters off northeastern Taiwan by flameless and flame atomic absorption spectrophotometry. The concentration of Zn was found to be abundant in vertebrae (72.29ºg.g^-1  dry.wt.) and stomach (71.85ºg.g^-1  dry wt.) samples and was the lowest in muscle samples (17.00ºg.g^-1 dry wt.). The concentration of Cu was associated with stomach samples (9.23ºg.g^-1 dry wt.) and the highest concentrations of Cd was found in liver (0.99ºg.g^-1  dry wt.) and kidney (1.13ºg.g^-1 dry wt.) samples. The concentrations of Pb (ˇ0.02ºg.g^-1  dry wt.) and Ni (ˇ0.01ºg.g^-1  dry wt.) were not detectable and that of Hg was found abundant in liver (293.60 ng.g ^-1  wet wt.) and muscle (871.42 ng.g^-1  wet wt.) samples. The Zn ranked the first place in concentration series of G. sauteri and followed by Cu. There was no significant difference on heavy metal levels between males and females except that of Zn in gonad and Cu in kidney. The concentrations of Zn and Cu in liver and vertebrae have significantly temporal variation. There was no significantly temporal variation on Cd and Hg which were not essential elements. Hence, concentrations of Cd and Hg could be resulted from biomagnification and long-term accumulation. There was an exponential positive relationship between the length of adult  G.sauteri and Hg concentration in the muscle.The concentration of Hg in elesmobranchs was higher than that in teleosts, but no significant difference on the concentrations of Zn was found between  G. Sauteri  and teleosts.

Preliminary study of discard composition of Batoids in a bottom trawl fishery at Puerto Quequéñ, Buenos Aires, Argentina.

From the 439 coastal vessels working in Argentina, 25 are at Puerto Quequéñ(38^o  37′ S, 58^o  50′ W). Bottom trawl (BT), in multispecific fishery, is the most common kind of gear used and the fishing discard is composed by invertebrates, elasmobranchs and finfishes. This work describes the by-catch composition of batoids in BT at Puerto Quequéñ, studied during 1998 winter-spring seasons by on board observed in 24 gear operations. Eleven batoid species were recognized and 599 specimens were weighted and measured disc width. The commercial species were  Raja castelnaui,  R. flavirostris  and  R. cyclophora  . Vessels worked in the same fishing area during winter and spring and each gear operation spent 2.2 ò 0.3 hours. Batoids was 56 % of the total catch with an average of 220.13 ò 156.80 kg per operation (83.6 ò 60.5 kg of commercial biomass) in winter and 309.22 ò 201.99 kg (56.9 ò 39.1 kg) in spring. Batoids was 57.2% of the discard in winter and 72% in spring. Electric ray,  Discopyge stchudii, was 78,5% of the race captured (sex ratio 1:0.9; mature males and females 87 and 90%) and all the individuals were discarded . For the electric ray populations and other diferent taxa, BT fishery impact might by important and its effect on benthonic communities has not been measured yet.

Age and growth of Blackmouth Catsharks,  Galeus melastomus, from Portuguese waters

1301 vertebrae were extracted from Blackmouth catsharks fished off the Portuguese Continental slope during five surveys held by the IPIMAR in 1994 and 1995. The vertebrae were prepared and observed following a protocol established earlier by the same authors. A growth curve was established based on vertebrae where both readers had 100% agreement (56%) and parameters were estimated using models from Von Bertallanfy, Gompertz, Richards and Schnute. The model that provided the best fit for the data was Richards’, yielding Linf = 70.0 cm, K = 0.57, T0 = 2.27. These results were verified using MULTIFAN, a length frequency analysis based on five length distributions totalling 10.361 individuals.

Life history patterns and relationships in sharks

This study examines life history patterns and correlations between traits related to body size, reproduction, age, and growth in sharks, using data from over 200 populations. Interspecifically, body size correlated positively with litter size and offspring size, and a trade-off between litter size and offspring size was found after factoring out the effects of body size. Offspring size correlated positively with growth completion rate (K) after correcting for body size effects. Parental size for males, females, and genders combined was negatively correlated with K. Parental size and size at maturity exhibited a strong positive correlation, with sexual maturity occurring at about 75% of maximum size in both genders. Males were found to be 9% smaller than females and to reach their maximum length 46% faster than females on average. Maximum size and longevity were not correlated in females, but were positively correlated in males. Principal component and cluster analyses were used to reflect similarities among traits of 40 populations and three separate life history strategies were identified. Among conspecifics, body size shows considerable geographic variability, but no clear patterns could be discerned. There is also limited evidence of clinal variation in life history traits in some species.

Diversity and taxonomy of chimaeroid fishes (Chondrichthyes, Chimaeridae)

At present there are 34 described species of chimaeroid fishes. Taxonomy of this lineage is historically problematic and many species of chimaeroids remain undetermined due to lack of useful characters for species identification. As part of a taxonomic revision of chimaeroid fishes over 1200 specimens were examined. A total of 35 measurements were taken on each specimen for morphometric analysis. At least 5 described species of chimaeroids are synonymous, 4 new species have been described, and at least 9 additional new species have been discovered. Status of each species, including several newly described species, and known geographic range, including range extensions for some species are presented. Characters for species determination and phylogenetic analysis are identified. Accurate identification of species is critical for management and preservation of chimaeroids as a bycatch and emerging fishery. This study emphasizes the instrumental role of systematics research centers, such as museums, as leaders in addressing issues of global biodiversity and conservation. Supported by NSF DEB-9510735.

Nursery areas of elasmobranch fishes in the coastal waters of the British Isles

Nursery areas are utilised by many species of elasmobranch fishes and are important habitats for neonatal and juvenile individuals. Nursery areas of coastal elamobranchs are typically in shallower waters than areas inhabited by the adults, and usually provide abundant food resources and protection from predation. Nursery areas have been documented for several species of carcharhinid and sphyrnid sharks, although there have been fewer studies on the nursery grounds of other families. Additionally, there are few records of elasmobranch nursery grounds in the coastal waters of the British Isles. Groundfish survey data (1988-1998) from the English Channel, Irish Sea and Bristol Channel were used to identify those locations where juvenile demersal elasmobranchs and the egg cases of oviparous species (e.g.  Raja  spp. and  Scyliorhinus canicula ) occur. Recent data on the macro-epibenthic assemblages within the study areas are used to describe some of the biological characteristics of these juvenile habitats.

Multiple paternity of a lemon shark litter determined by DNA microsatellite analysis

A long term field and genetic study of lemon shark mating system and breeding biology is in progress at a nursery ground in Bimini, Bahamas. In the spring of 1996 an adult female lemon shark was caught, measured, sampled for DNA analysis, and injected with a PIT tag. The female was judged to be pregnant when caught. This same female was also caught in April, 1998. At the time of her second capture, the female gave birth to 13 offspring, of which 11 were caught, tagged, and sampled. The recapture of this female provides the first definitive evidence that female lemon sharks are returning to give birth at the Bimini nursery ground, and the reproductive cycle can be no longer than biennial for some females. We used four microsatellite marker loci, developed from a genomic library of  Negaprion brevirostris, to genotype the adult female and her litter. At two of the four loci, four paternal alleles were observed among the pups, indicating that the littermates were sired by at least two males. These results suggest that lemon sharks likely have a polygamous mating system. Observation and analysis of this single female therefore provided critical new information regarding the mating and reproduction of a large coastal shark.

Isolation and characterization of microsatellite markers in the lemon shark genome

Although microsatellite loci have proven to be extremely useful for population genetic studies of many vertebrates, their application in elasmobranchs has been extremely limited. We are currently developing microsatellite markers for lemon sharks ( Negaprion brevirostris ) in order to assess the local mating system and larger-scale stock structure of this species. A size selected plasmid library was constructed from genomic DNA and screened for 10 di- and trinucleotide repeats. Screening yielded 42 positive clones, of which 35 have been sequenced. (CA)_n  and (GA)_n  dinucleotide repeats were primarily found. Primer pairs were developed for 21 loci, and these are being screened. To date, only five loci have been shown to be polymorphic, suggesting that microsatellite loci in sharks may be less variable than in other vertebrates. Two loci, LS22 and LS30, have been optimized, and at least 90 adult and juvenile lemon sharks from two populations, Bimini, Bahamas, and Marquesas Key, Florida have been genotyped at each locus. LS22 has 16 alleles and observed heterozygosity of 0.82 and LS30 has 15 alleles and observed heterozygosity of 0.70. These preliminary data suggest that although application of microsatellite markers in elasmobranchs may require additional screening, these markers can provide an important new tool for shark biologists.

Chondrichthyan calcified cartilage: chimaerid cranial tissue with reference to Squalus.

Select cartilages of the chimaerid,  Callorhinchus capensis, were processed for light microscopy, stained with hematoxylin and eosin, alizarin red, and von Kossa stains, and assessed for features of mineralization. The calcified cartilage demonstrates a tesserate-mode of mineralization which is fundamentally similar to that observed for  Squalus acanthias . Calcification exists in the form of superficial, polygonal deposits of calcium phosphate. In cross section, they appear block-like and are located subperichondrally. Viable chondrocytes and Liesegang waves could be seen throughout the bodies of calcification. Comparison of select stains permits a study of progressive mineralization. Presumptive sites of mineralization first stain positive with alizarin red then positive with von Kossa. This suggests the progression from calcium to calcium phosphate as mineralization proceeds. Fundamentally these results conform to those obtained from examination of  S. acanthias . They demonstrate similar developmental and histological characteristics of mineralization in sister taxa. However, there was no evidence of a discrete tessera cap, as has been noted in  Squalus  and other sharks and jaw tissue provided evidence of mineralization other than that found peripherally. Regional variation in the stage of mineralization was observed across the tissue. At this time these features are interpreted as architectural and stress related.

Seasonal changes in thyroid hormones in the bonnethead shark Sphyrna tiburo.

Studies among vertebrates suggest that thyroid hormones may influence, or be influenced by, the reproductive cycle. Whereas the reproductive cycle in bonnethead shark populations along the southwest coast of Florida has been described, the relationship of thyroid function to reproduction has not been characterized in this species. To determine if thyroid hormone production is activated during periods of spermatogenesis, vitellogenesis, and gestation, circulating thyroxine (T₄ ) and 3,5,3,-triiodothyronine (T₃ ) were measured in serum samples collected during discrete phases of reproduction in two southwest Florida populations. Results showed that both these populations exhibited a bimodal annual cycle in serum T₄  levels ranging from mean levels of 2 to 12 ng/ml, with peaks during the spring and again in the fall. In contrast, T₃  levels were not detectable. Seasonal changes in T₄  levels did not differ between mature and immature sharks, between males and females, or between the two populations sampled. These results suggest that seasonal changes in circulating T₄  are not directly related to reproductive condition, but may correlate instead with temperature-related feeding or migration.

The production of seasonal increments in the vertebral cartilage of the clearnose skate, Raja eglanteria : Changes in cartilage growth or mineralization?

Seasonal increments present in the vertebral cartilage of most elasmobranchs are commonly used to determine age and growth rate in these fishes. However, the physiological process(es) that gives rise to these structural phenomena are poorly understood. The goal of this study was to determine if increments present in the vertebrae of the clearnose skate, Raja eglanteria  were a consequence of seasonal changes in cartilage growth or mineralization. Changes in the appositional growth of vertebral cartilage were examined by histologic and histochemical observations. Patterns of vertebral mineralization were investigated by energy-dispersive spectrophotometry (EDS). Visible differences in matrix synthesis and cellular activity of vertebral cartilage were apparent, and indicated that growth of the vertebral margin was greatest during late spring to early fall. However, there appeared to be no changes in cartilage mineralization associated with season. In fact, concentrations of calcium and phosphorus appeared to be relatively stable throughout the entire vertebral cartilage. Additional observations using scanning electron microscopy, coupled with these studies, demonstrate that seasonal vertebral increments are directly related to changes in cartilage growth, and that differences in mineral concentration appear secondary to regional cell concentrations.

Phylogenetic relationships among the hammerhead sharks (Chondrichthyes: Carcharhiniformes: Sphyrnidae)

The hammerhead sharks are poorly know species that inhabits coastal and all oceanic waters. The unusual lateral expansion of the head or cephalofoil, is the diagnostic feature of the family. Previous phylogenetic analysis of morphology between these sharks ordered taxa according to the absolute degree of cephalofoil lateral expansion (small cephalofoil = ancestral taxa; exaggerated cephalofoil= derived taxa), this hypothesis suggests directional selection for the lateral expansion character. Phylogenetic analysis of the DNA data provided support for to claim that hammerheads constitute a monophyletic group, but that the evolution of cephalofoil was contrary to the generaly accepted hypothesis. For this reason this study research the sphyrnids interspecific relationships based on based about morphology and morphometry chondrocranium characters. The description of ontogenetic and morphological variation among species propose an hypothesis to explain the presence and different cephalofoil shapes in the hammerhead sharks. The technique of phylogeny reconstruction (cladistic method) was carried out by the maximum parsimony method (PAUP 3.1.1). The results shows phylogenetic evidence for to eliminatee the division hierarchy of genus  Eusphyra  and subgenus of  Sphyrna . The variation among specimens of the same specie is discussed from morphometric view, because certain modifications in shape of the head of sphyrnids can to provide ontogenetic transformational series.

Morphological and osteological features in the embryonic development of  Rhinobatos productus  (Girard, 1854) (Chondrichthyes:Rajiformes:Rhinobatidae)

Embryonic development of the guitarfish  Rhinobatos productus  is described in detail based on a complete series of embryos from 5.6 to 200 mm TL (total length). A total of 494 specimens were collected from Almejas bay in the west coast of Baja California and others two fisheries centers in the middle region of the Gulf of California. The development of  Rhinobatos productus  is defined by a suite of morphological characters in addition to total length including the size and shape of paired and unpaired fins, the disc wide and cephalic characters. Particular attention is given to features of the branchial arches and external branchial filaments. Apparently the embryos utilize histotrophic nutrition in the early development.
Embryological development of  Rhinobatos productus  is similar to that described previously for elasmobranchs taxa. These include sharks such as the spiny dogfish, Squalus acanthias, and other rhinobatids closely related including R. horkelii, R. hynnicephalus  and R. halavi . The external features of these specimens, in comparison with other chondrichthyans embryos, are proposed to stablish the embryonic development of Rhinobatidae. This study provides information on  Rhinobatos productus  embryonic development, determines the morphological, morphometric and osteological changes in the embryonic development and shows the relationships between corporal proportions and growth during the development of this specie.

Re-examination of  Helodus simplex  and the relationships of Carboniferous Euchondrocephalans.

Cranial morphological analyses of Paleozoic Chondrichthyes suggests division of the Class into two discrete units, elasmobranchs and euchondrocephalans (paraselachians + holocephalimorphs). The previous interpretations of the skull of Helodus have been the subject of much debate and are inconsistent with the data for all known Paleozoic chondrichthyan cranial types. Our re-interpretation of Helodus’ cranium is presented. The dorsally flaring orbitonasalis identified by Moy-Thomas is shown to be internal, not superficial. Further, the ethmoidal region is completely roofed over, in a manner consistent with all other euchondrocephalans. The shape and dimensions of the cranium approximate that of iniopterygians. These analyses result in a logical placement of Helodus within the euchondrocephalans, at or near the base of the Holocephalimorpha.

Endoskeletal Mineralization in  Squalus : types, development, and evolutionary implications.

Research on the structure and composition of  Squalus acanthias  calcified cartilage demonstrates the existence of at least three modes of endoskeletal mineralization; tesserate cap, tesserate body, and notochordal areolar. Globular (spheritic) and prismatic forms of calcification have been confirmed as the same type of mineralization and merely represent different developmental stages. Areolar mineralization, by comparison, is radically different in structure, development and chemical composition. It does not involve hyaline cartilage, but arises through direct mineralization of a centrum comprised of circumferentially arranged fibroblastic cells. Select morphological and chemical characteristics of areolar mineralizations reveal greater similarities to bone than to the calcified cartilage of terrestrial vertebrates. This, and the differential staining of the tesserae cap compared to that of the body, indicate that selachian calcified cartilage exhibits features of both endochondral and intramembranous bone. Such data suggests reconsideration of the popular paradigms for mineralized tissue development and the phylogenetic relationship of selachian calcified cartilage to the mineralized tissues of the higher vertebrate classes.

Embryological development of the cephalofoil in the bonnethead shark,  Sphyrna tiburo .

Selected embryological stages of the bonnethead shark,  Sphyrna tiburo, were examined to analyze the development of a unique morphological modification of the head that is characteristic of the sphyrnid sharks. Lateral expansion of the head, accompanied by flattening along the dorsal-ventral axis of the expansions, produces a morphological modification known as a cephalofoil. Specimens, representative of stages from early embryogenesis through parturition, were examined using macrophotography, light microscopy and electron microscopy. Measurements were made of the width of the entire cephalofoil, the length of the right and left lateral extensions, and the total fork length of each embryo. Changes in chondrocranium morphology, elongation of the optic nerve, expansion of the olfactory sacs, and general neural development were also characterized. Based on our observations, the morphogenetic events that produce the unique bonnethead cephalofoil are initiated early in embryonic development. Thus, the major morphological modifications of the head are established relatively early in development, whereas the middle and late phases of development involve growth of the cephalofoil relative to growth of the body.

DNA Microsatellite abundance, allelic diversity, and cross-species amplification in three sharks.

Subgenomic DNA libraries were prepared and screened for di-, tri-, and tetranucleotide repeat motifs in three sharks: sandbar shark  Carcharhinus plumbeus, blacktip shark  C. limbatus  and shortfin mako  Isurus oxyrinchus . DNA sequences from positive clones were used to identify and characterize microsatellite repeat motifs. PCR primers were developed and used to amplify loci and screen for allelic diversity within and among putative populations of each species. Amplification of loci in species other than those from which the loci were identified was attempted with some success. Compared to similar studies in other vertebrate taxa, microsatellite loci are relatively scarce in sandbar and blacktip sharks and only slightly more frequent in shortfin mako. Low frequencies of microsatellites occurs in the presence of large genome sizes, ranging from 5.9 to 8.5 picograms DNA per diploid nucleus as determined from flow cytometry and from published reports. Many loci averaged fewer than ten uninterrupted repeats per microsatellite motif. There is a positive correlation between the number of uninterrupted repeats per microsatellite motif and allelic diversity in microsatellite loci in sharks.

Preliminary results on the size of proteins and protein concentration in histotroph from three species of batoids.

Myliobatoid rays reproduce via aplacental viviparity. Uterine milk ,or histotroph, produced by uterine villi (trophonemata) is the sole source of embryonic nutrition once the yolk supply is exhausted through parturition. Previous studies have documented that protein is a major component of histotroph. To determine protein size and concentration, we collected histotroph from three species of myliobatoid rays: the southern stingray,  Dasyatis americana, the cownose ray  Rhinoptera bonasus, and the yellow ray  Urolophus jamaicensis . Preliminary results on the size and concentration of proteins in histotroph were obtained in all three species. Histotroph and serum collected from a gravid southern stingray on day 54 of a 138 day gestation were analyzed via gel filtration, SDS-PAGE, and protein assay. The predominant protein was ~55-61 KDa from both histotroph and serum. Fractions collected off the gel filtration column yielded a protein concentration of 39.1 mg/ml in the histotroph. SDS-PAGE of histotroph from all three species indicated the relative sizes of the predominant protein to be ~55-61, 64.6, and 53.5-64 KDa for the southern, yellow, and cownose ray, respectively. The protein concentrations in the histotroph from the three species were 20.6, 1.2, and 80.0 mg/ml, for the southern, yellow, and cownose ray, respectively.

Aspects of the life history of epaulette sharks,  Hemiscyllium ocellatum  on Heron Island Reef, Great Barrier Reef, Australia

The population of  Hemiscyllium ocellatum  on Heron Island Reef, Great Barrier Reef, Australia was examined over a three year period. The abundance of  H. ocellatum  on a 0.25 km2 site on the reef flat was examined by conducting a tag-recapture study. A total of 494 sharks were tagged during 11 sampling trips from July 1994 to August 1997. The interval between initial release and recapture of sharks ranged from 1 – 725 days. The overall recapture rate was 22% with an estimated 3% tag loss. Recaptured sharks appeared to move randomly within the study site, and distances between initial release site and recapture site ranged from 0 – 329 m. There was no obvious site attachment. Estimates of animal abundance using the Jolly-Seber method gave a range of 93 – 1359 sharks during the study period. The Peterson and Fisher-Ford methods provided ranges of 320 – 3298 and 200 – 2190 respectively. Catch per unit effort and captive observations showed  H. ocellatum  were most active at dusk/dawn hours and during night low tides. Activity patterns coincided with prey activity periods. Sharks were found to consume polychaete worms and crustaceans.

Spinal deformities in elasmobranchs

Three shark species from Australian waters, and two species from North American waters, were found with skeletal deformities. Three epaulette sharks,  Hemiscyllium ocellatum,one gummy shark,  Mustelus antarcticus, one whiskery shark,  Furgaleus macki, one bull shark,  Carcharhinus leucas  and two bonnethead sharks,  Sphyrna tiburo  were all found with similar spinal curvatures. Spinal curves consisted of large scoliotic (lateral spinal curvature), lordotic (axial spinal curvature) and kyphotic (humpback curve) bends of the vertebral column. Possible causes of these deformities are currently unknown, but may include asymmetrical stresses to the vertebral column, parasites, arthritis, injury, disease, localized tumors or malnutrition. However, all species show similar curvatures along the vertebral column, suggesting the cause of the deformity is uniform across multiple families and geographic areas.

Comparative structure and evolution of mitochondrial genome control region in sharks

The control region is the main non-coding region of vertebrate mitochondrial (mt) DNA, and contains the major regulatory elements controlling replication and transcription of this genome. In many vertebrates, the control region appears to be the fastest evolving locus in the mt genome, and portions of this locus are often used in population and phylogenetics studies. The control region has most extensively been studied in mammals, where it is partitioned into three domains: the two peripheral, highly variable domains I and III, and a central conserved domain II. To better understand the organization and evolutionary dynamics of this locus in vertebrates, we have performed a comparative analysis of control regions from divergent sharks with the mammalian control region. Our analysis reveals an overall similarity in the structure of the control region between sharks and mammals, and identifies several shared conserved elements (TAS, CSBs1-3). Like mammals, variability in shark control regions occurs mainly in peripheral domains I and III, with the central domain II exhibiting significant conservation among species. Domain II from sixteen globally distributed blue sharks reveals no sequence variation. The overall similarity in control region structure between sharks and mammals suggests strong functional constraints control evolution of this locus in vertebrates.

Comparing the dentition of the extant white shark with the fossil megatooth shark, Carcharocles megalodon 

Descriptions of fossil species of sharks are often based upon comparisons with living species. Since the cartilaginous skeletons of sharks do not fossilize well, our deductions are often limited to the examination of fossil shark teeth. This is especially true for Tertiary sharks where whole or partially preserved specimens are very few. It is difficult to identify the more recent fossil sharks and to establish relationships to other species, both living and extinct. Although fossil shark teeth are the most commonly collected fossil in the world, naturally associated sets of teeth, i.e. a group of teeth from one individual, are a very rare find. These naturally associated sets are essential for understanding the evolution of a species or family of sharks. A careful examination of a naturally associated set of 95 Carcharocles megalodon  teeth found in Central Florida shows distinct differences between  C. megalodon  and the recent  Carcharodon carcharias  and suggests that the two species are only distantly related.

Probable range extensions for several species of sharks from NMFS bottom longline survey data.

This study examined shark catch data from NMFS-SEFSC bottom longline surveys conducted between 1973 and 1997 for geographical, depth, temperature and salinity distributions by species of sharks captured. Analyses of geographical distribution using SURFER plots revealed probable range extensions for 11 species of sharks, including the night shark Carcharhinus signatus , the bignose shark Carcharhinus altimus , the sharpnose sevengill shark Heptranchias perlo , the bigeye sixgill shark Hexanchus vitulus , the spiny dogfish  Squalus acanthias , and 6 additional species of dogfish. Analyses of distribution by depth indicated probable range extensions for 6 species of benthic sharks: the Caribbean reef shark Carcharhinus perezi, the bignose sharkCarcharhinus altimus , the nurse shark Ginglymostoma cirratum, the Cuban dogfishSqualus cubensis, the smooth dogfish Mustelus canis, and the Florida smooth-houndMustelus norrisi. Temperature range extensions were indicated for the silky sharkCarcharhinus falciformis, and the night shark Carcharhinus signatus. In addition, useful information on depth, temperature, and salinity distributions were found for species for which little or no information of this type has been published.

Shark nursery areas in the major bay systems of Texas.

The Texas parks and Wildlife Department conducted gill net surveys in major Texas bay systems from 1975 – 1995. Data collected includes indentification to lowest possible taxon, length, date, location, water temperature, and salinity. Included in the catch from these surveys are a number of shark species. By using available published information on age and growth for these species, the sharks captured can be separted into age classes and this database used to identify probable shark nursery areas. The environmental data gives an indication of preferred temperature and salinity regimes and the temporal distribition for each species. Included in the species that appear to be using these bays as pupping or nursery areas are: the bull shark Carcharhinus leucas, the blacktip shark Carcharhinus limbatus, the finetooth shark Carcharhinus isodon, the spinner shark Carcharhinus brevipinna, the Atlantic sharpnose shark Rhizoprionodon terraenovae, the bonnethead shark Sphyrna tibure, the scalloped hammerhead Sphyrna lewini, and 8 other shark species. The results of this study indicate that databases of this type can be useful as a step in the identification of shark nursery areas and characterization of essential habitat.

The cestode faunas of some skates from the Bering Sea

The cestode faunas of six species of deep-water skates belonging to the genera Bathyraja  and  Rhinoraja  from the Bering Sea were identified and observations were made on the enteric distribution of the parasites. Nine cestode species were encountered, several of which are new. All except one cestode species represent new host and locality records. A relatively low degree of host specificity was observed among the parasites in this study and evidence is given to suggest that this may be the result of similarities in mucosal morphology reflecting the systematic relatedness of the hosts. Zoogeographic records indicate a bipolar distribution among  Phyllobothrium,  Onchobothrium  and possibly Echeneibothrium  in species of  Bathyraja  when compared to Antarctic hosts. Echeneibothrium  and  Phyllobothrium  species closely resemble those reported from Raja naevus  in the North Atlantic and occur in hosts with similar mucosal morphologies. Echeneibothrium  species had wide distributions within the spiral valves but cestodes were consistently absent from the posterior regions. The enteric distribution of the worms appears related to villus length in the spiral valve mucosa. The distribution of juveniles and adults of  Onchobothrium  changed significantly along the antero-posterior axis within the spiral valves of  B. parmifera .

Punting: pelvic fin locomotion in  Raja erinacea 

The pelvic fins of the little skate  Raja erinacea  resemble most other skates in that an external notch or concavity in the lateral border partially separates each fin into anterior and posterior lobes. Dissections reveal that skeletal elements and musculature of the anterior lobe are highly modified and comprise a functionally distinct appendage (walking finger or crus) with three flexible joints. Anecdotal reports have suggested that the anterior portion of the fin might assist in locomotion especially along the bottom. Video recordings of skate movements in the field and in captivity clearly show that locomotion along the bottom is frequently carried out exclusively by the crural portion of the pelvic fin. Each cycle consists of two phases: a thrust generating phase which involves the synchronous action of the crura pushing off the bottom and a gliding phase during which time the crura are re-positioned for the next cycle. This mode of locomotion is referred to as punting (Long, J.H. personal communication; Martinez, et. al., 1998). Analysis of punting cycles and a brief anatomical description of the pelvic fin will be presented. This is the first time punting has been described for any species of fish.

Lamniform phylogeny based on DNA sequence comparisons.

Representatives of each of the 14 described species of Lamniform sharks were sequenced for the mitochondrial genes NADH-2, NADH-4 and Cytochrome B, and the recombination activating single copy nuclear gene, rag1. The sequences were used in phylogenetic analyses with parsimony and likelihood optimality criteria. Spectral analyses were carried out to contrast signals derived from the different genes and to determine the relative amount of support for different nodes on the cladogram. The hypothesis of lamniform inter-relationships supported by the molecular data is discussed in the context of previous, morphology-based hypotheses, particularly those of Compagno (1990) and Maisey (1985).

Life History of the Atlantic sharpnose shark,  Rhizoprionodon terraenovae, in the South Atlantic Bight

The life history of the Atlantic sharpnose shark ( Rhizoprionodon terraenovae ), is well documented in the Gulf of Mexico, yet there are no published age and growth data available on this species in the South Atlantic Bight. A total of 1013 specimens were collected from Virginia to northern Florida during the first 22 months of a 24 month sampling schedule. Frontally sectioned vertebral centra were used to age each specimen, and the periodicity of circuli deposition was validated through marginal increment analysis. Atlantic sharpnose shark reached a maximum size of 813 mm precaudal length (PCL, or 1045 mm TL) at age ten. Sexual maturity (100%) was reached at age three and size 601 mm PCL (801 mm TL) for females, and age three and size 617 mm PCL (827 mm TL) for males. Mean back-calculated lengths at age ranged from 401 mm PCL (543 mm TL) at age one to 754 mm PCL (993 mm TL) at age ten. Back-calculated lengths from the last annulus for each age group yielded the following von Bertalanffy growth equation: L_t  = 773.5(1 – e^{-0.323(t – (-1.276)} ). The 95% confidence intervals for L_inf, K and t_0, respectively, were: 768.0-779.3, 0.331-0.334 and -1.340 to -1.215.

Endoskeletal mineralization of several Paleozoic Chondrichthyes: some observations

Histological studies of the endoskeletons of several Paleozoic chondrichthyans reveal a greater variety of types of mineralization than previously reported. The primitive vertebrate condition consists of perichondral bone alone. A successor condition, as observed in actinopterygians, reveals an underlayer of either sphaeritic calcified cartilage, trabecular bone, or both in the same fish. Sphaeritic calcification is the most primitive of the non-perichondral mineralization types. Modern prismatic calcified cartilage, as observed in Euselachii, lacks a gross perichondral cap component. Variations upon the successor condition are noted for Cladodont sharks, a petalodont, and an iniopterygian. Holocephalimorpha have several different styles of mineralization that are phylogenetically and regionally specific, but generally display acellular tesserae. Some mandibles exhibit fibrous mineralization. Other chondrichthyans of uncertain affinity display three-dimensional trabecular, tesserate mineralization. Aside from the growth of osteonal bone spines and clasper sheaths of perichondral bone, tile-like (tesserate) mineralization is common to some growth stage of all observed specimens but the types of mineralization observed within and among the tesserae are variable among the Paleozoic Chondrichthyes.

Do shark reproductive steroid hormone concentrations exhibit a diurnal cyclical pattern?

Despite the recent increased understanding of the patterns and roles of steroid hormones in elasmobranch reproduction, little is known regarding short-term cycles in these animals. Diel cycles in reproductive steroid hormones have been described in a wide variety of vertebrates including mammals, reptiles, amphibians, and teleost fishes. To determine whether the bonnethead shark,  Sphyrna tiburo, undergoes a similar diurnal cycle, blood was collected from mature females from the wild at three hour intervals over a two day period. The serum derived from this blood was then analyzed for 17-beta estradiol, progesterone, testosterone, dihydrotestosterone and corticosterone. These hormone concentrations were determined using standard radioimmunoassay techniques. Results of these analyses and implications of the findings will be presented.

Elasmobranch corticosterone concentrations: related to stress or sex or what?

The steroid 1-alpha hydroxycorticosterone is known to be the major stress hormone in elasmobranchs, but the related steroid corticosterone that serves as a stress hormone in many other groups of animals is also present in elasmobranch serum. To determine whether corticosterone might function as a secondary stress hormone, blood samples were collected from bonnethead sharks,  Sphyrna tiburo, in the wild when the exact time of first contact with the net for capture was known. Some of the sharks sampled in this way were taken into the laboratory for monitoring of hormone levels over a longer time frame as well. No change in corticosterone concentration was detected either for short term stress (acute stress) or for longer term stress (chronic stress) in these animals. To assess the possibility of a reproductive role for this steroid, samples were taken from immature and mature male and female bonnetheads in the wild, and a number held in the laboratory over a large portion of the reproductive cycle, as well as from mature male and female Atlantic stingrays, Dasyatis sabina, from the wild. There was a significant difference between male and female corticosterone concentrations, but no difference between immature and mature sharks. There were also significant differences for both mature male and female sharks and stingrays at different reproductive stages.

Development of elasmobranch transportation techniques

An overview of techniques utilized to transport elasmobranchs to the Oceanário de Lisboa is undertaken. Specifically, techniques to capture, restrain and transport elasmobranchs are examined. In addition, anaesthetic regimes and profilactic protocols are reviewed. The efficacy of different techniques is discussed.

Rates of organelle and nuclear gene evolution follow same rules: continuing lessons from sharks

Rates of nucleotide substitution for organelle and nuclear genes are thought to follow different sets of rules. Rates of nucleotide substitution for nuclear genes may be governed primarily by the number of germ line replication events (the so called “generation time” hypothesis) whereas rates of mitochondrial DNA evolution appear to be controlled primarily by DNA damage pathways of mutation mediated by mutagenic by-products of oxidative phosphorylation (the so called “metabolic rate” hypothesis). Comparison of synonymous substitution rates estimated for dlx, hsp70, and RAG-1 genes in mammals and sharks, two taxa with similar generation times but differing metabolic rates, shows that rates of molecular evolution in sharks are approximately an order of magnitude slower than mammals for both nuclear and mitochondrial genes. In addition, there is significant positive covariation of substitution rate for mitochondrial and nuclear genes within sharks. These results, interpreted in the light of differences in life history and metabolic rate between taxa, and coupled with increasing evidence for cross-genome activity of DNA repair enzymes, suggests that molecular clocks for mitochondrial and nuclear genes follow the same set of rules.

Growth parameters of the Caribean sharpnose shark  Rhizoprionodon porosus  (poey, 1861) off Pernambuco State (Brazil) continental shelf 

The Caribbean sharpnose shark,  Rhizoprionodon porosus  (Poey, 1861), is a tropical specie found in Caribbean waters, along all Brazilian coast, until Uruguay waters. The present paper aim to present a preliminary result of growth parameters of the Caribbean sharpnose shark, from specimens caught by the artisanal fishery of Pernambuco State-Brazil, relevant for the adequate resources administration. The growth curves for females as much as for males, in length and weight, demonstrate that females grow larger, but males grow faster, and that K, t₀  and L(infinite) values, are close if compared to other genus species, and even if compared with other small and medium groups size sharks. The obtained growth curves in centimeters, from von Bertalanffy (1938) mathematics equation, are:
L_t  = 87.13 [1 – e ^{-0.42 (t + 1.10)} ] (males) and
L_t  = 106.82 [1 – e ^{-0.30 (t + 1.12)} ] (females).
There was a high significant difference among the growth curves in length for males and females. For the gutted weight / total length relationship for males and females, the mathematics equations are:
W_e  = 0.0054 L_t ^2.8993  (males) and
W_e  = 0.0017 L_t ^3.1666  (females).
It was observed a significant difference among gutted weight / total length relationship for males and females. From the mathematics expression of the growth curve in length and the gutted weight / total length relationship, it was obtained the growth curve in weight in grams, for males and females:
W_e  = 2,277.9 [1 – e^{-0.42 (t + 1.10)} ]^2.8993  (males) and
W_e  = 4,512.6 [1 – e ^{-0.30 (t + 1.12)} ]^3.1666, (females).

Reproductive biology of the Caribean sahrpnose shark  Rhizoprionodon porosus  (Poey, 1861) off Pernambuco State (Brazil) Continental Shelf

The Caribbean sharpnose shark, Rhizoprionodon porosus (Poey, 1861), is a tropical specie found in the Caribbean waters, along all Brazilian coast, until the Uruguay waters. The present paper aim to describe the preliminary results on the reproductive biology of the Caribbean sharpnose shark. A total of 264 specimens were analysed, 161 been females, with total length (TL) ranging from 33.5 to 100.5 cm, and 103 been males, with TL ranging from 33.5 to 80.0 cm. The total body weight (TW) range from 128.0 to 5,010.0 g for females and from 131.5 to 1,907.0 g for males. Among the females, 80 were pregnant, with TL ranging from 63.0 to 100.5 cm. The Diameter of the largest ovarian follicle in these pregnant females showed a growth at the same rate of the embryos growth, indicating that probably they should be ready for another ovulation immediately after parturition. The sub-adult and pre-ovulatory females presented a TL near to the pregnant females. The actual data suggest that females first mature at approximately 65 cm in the Pernambuco State waters. Concerning males, the clasper length showed a sharp increase in the 60-65 cm length class, and together with the data on clasper calcification, suggest that male first mature at these length.

Preliminary Results of the 1998 Cooperative Atlantic States Shark Pupping and Nursery Survey (COASTSPAN)

Understanding coastal shark nursery habitat is critical to effective management and necessary for defining essential fish habitat (EFH). The Apex Predators Program (APP) formed the Cooperative Atlantic States Shark Pupping and Nursery Survey (COASTSPAN), an alliance of state cooperators to investigate shark nursery grounds along the east coast of the United States. Cooperative researchers in selected coastal states conducted a comprehensive and standardized investigation of putative shark nursery areas. North Carolina DMF, South Carolina DNR, Savannah State College with cooperation from Georgia DNR, Florida DEP and NMFS/University of Rhode Island in Delaware Bay all participated to sample a total of 1104 sharks in east coast waters in 1998. Seven hundred seventy three of these sharks were tagged with fin tags and released. Sharks commonly caught by these states were: sandbar,  Carcharhinus plumbeus, Atlantic sharpnose,  Rhizoprionodon terraenovae, smooth dogfish,  Mustelus canis, bonnethead, Sphyrna tiburo, finetooth,  Carcharhinus isodon, spinner,  C. brevipinna, and bull shark,  C. leucas .

Confirmation of embryonic diapause in the bluntnose stingray  Dasyatis say 

The female reproductive cycle of  Dasyatis say  has been confirmed for the Indian River Lagoon system population (Brevard County, FL).  D. say  exhibits embryonic diapause, arresting development of its embryos at the blastoderm stage. In the summer, mating activity immediately precedes ovulation and fertilization of the eggs. Encapsulated, diapausing embryos are maintained in the uterus for approximately 10 months. When embryogenesis resumes in the spring, development is rapid, lasting 10-12 weeks. Pupping is followed by ovulation and mating, then the cycle repeats. There is no period of reproductive inactivity.

Toward a molecular phylogeny for Galeomorph sharks: A progress report.

Representatives of each of the eight orders of sharks were sequenced for 3 mitochondrial and one nuclear gene in an effort to determine the evolutionary branching order among the major lineages of sharks. Comparisons between mitochondrial and nuclear inferences are presented.

Protein Analysis of the Uterine Histotrophe of Rays

Stingrays display a form of aplacental viviparity in which embryos develop  in utero without connection to maternal tissues. In most species, yolk reserves are exhausted early in development and uterine fluid, termed histotrophe, is the putative source of nutrients for the remainder of gestation. Uterine fluid from several species of stingrays was analyzed for total protein content. Fatty acid components were removed and soluble and insoluble protein was isolated. The molecular weight of the proteins was determined using SDS-PAGE. The majority of the soluble protein present in histotrophe has a molecular weight of less than 10 KD, although a substantial amount has a weight that exceeds 100KD. Quantitative and qualitative comparisons were made of protein content at different phases of the reproductive cycle. In some species, protein content is low early in gestation and increases during mid-gestation. Work continues on the identification of specific proteins in histotrophe such as immunoglobulin M, vitellogenin, albumin, and transferrin or other iron-binding proteins.

Virtual Embryology: 3D Reconstruction of Skate Embryos ( Raja erinacea )

The most notable use of 3 dimensional reconstruction of serial sections of elasmobranchs dates back to the 1911 monograph of Scammon on  Squalus acanthias  embryos. Since then few authors have attempted reconstructions because early methodologies were so labor intensive. Recent advances in computer technology, however, have made this form of morphological analysis more feasible. Our work represents one component in a comprehensive series of studies on the embryology of  Raja erinacea . Using a combination of video microscopy and computer techniques we seek to visualize development of this species in the three dimensions of space as well as the fourth dimension of time.

A comparative study of time-place learning in skates and stingrays

Few studies have been conducted on the learning abilities of elasmobranchs and fewer still have examined comparative learning abilities in these animals. Yet, distinctive differences in brain morphology and relative brain size suggest that differences in learning abilities may exist among them. The most disparate brains, in terms of relative size and morphological complexity are found in two groups of batoids – skates (Rajiformes) and stingrays (Myliobatiformes). This study compared the abilities of skates  Raja erinacea  and stingrays  Dasyatis sabina  in learning a simple time-place task. The results of four sets of experiments based upon the presence or absence of a light cue at a specific time of day provided evidence that  D. sabina  are capable of time-place learning. Under the same conditions in paired experiments,  R. erinacea  did not respond in a manner that statistically demonstrated their ability to make a time-place association.

Molecular population genetics of the Great white shark, Carcharodon carcharias 

The Great White Shark (GWS), Carcharodon carcharias, is considered a threatened species. However, the true conservation status of this predator is uncertain, due to its intractability as a research organism. Aside from the inherent problems of working in a marine environment GWS are elusive and uncommon. The difficulty of undertaking research on this species is evident from the paucity of information on most aspects of its biology, in particular population dynamics, encouraging speculation about its conservation status. Molecular based approaches are now routinely used on a variety of organisms to address previously intractable questions pertaining to their population biology. Application of these approaches to GWS research promises to significantly improve our knowledge of shark population biology and behaviour. The potential to use minute tissue samples for identification of individuals will circumvent many of the problems current in GWS research programmes on natural populations, in addition to making fragmentary museum material susceptible to robust genetic analysis.

Effect of salinity on Na,K-ATPase expression in the gills, rectal gland, and kidneys of the Atlantic stingray ( Dasyatis sabina )

The influence of environmental salinity on osmoregulatory mechanisms of elasmobranch fishes has not been well studied. One of the most important enzymes associated with ion balance is the sodium, potassium-ATPase (Na-pump). The goal of this study was to describe and/or quantify the branchial, rectal gland, and renal expression of the Na-pump, using immunocytochemistry and Wesern blotting, in the euryhaline Atlantic stingray ( Dasyatis sabina ). In fresh water, the Na-pump was localized to both filamental and lamellar cells of the branchial epithelium, but was only localized to cells of the filament in marine ( D. sabina ). Results from Western blots demonstrated that the overall branchial expression of the Na-pump was lower in sea water animals. Rectal glands from marine ( D. sabina ) were larger and expressed more overall Na-pump than those from freshwater animals. Western blots of kidney tissue showed a similar amount of expression for the Na-pump in fresh and sea water animals. We suggest that the differential expression of the Na-pump in the gills and rectal gland of ( D. sabina ) may be a key component to its euryhaline life style. Supported by American Elasmobranch Society Student Research Award (PMP), EPA STAR Grant U-915419-01-0 (PMP) and NSF Grant IBN-9604824 (DHE).

Microsatellite DNA profiling in the blue shark  Prionace glauca : development and potential application for population studies.

The world-wide increase in shark fisheries is thought to be resulting in declining population numbers of many species. The blue shark ( Prionace glauca ), possibly the most abundant of the larger pelagic sharks, is no exception. In addition to a directed fishery, large numbers of blue sharks make up the bycatch in the tuna and swordfish fishery. Increased fishing pressure and inadequate management strategies have prompted concerns about the sustainable health of blue shark populations. The main reason for inadequate management measures is the paucity of information on population genetic structure and life history strategy for this species. Traditional methods used to gather this type of information such as allozyme electrophoresis and RFLP analysis of mitochondrial DNA have proved to be only of limited use due to the apparent low rate of molecular evolution in this and other shark species. Recently, microsatellite DNA profiling techniques have been proposed as an alternative source of highly informative molecular makers. This new class of markers has not yet been fully exploited for shark population studies. Here we report on the development of blue shark microsatellite markers from an enriched library. Their potential for blue shark population genetic studies with examples is also discussed.

The Phylogenetic Importance of Fossil Shark Teeth

Since the classic work of Louis Agassiz (1835-1843), paleontologists have given much attention to the taxonomic description and interpretation of fossil shark teeth, which occur mainly as isolated teeth. Most of this work has been done without the benefit of knowledge of the great variation present in the teeth of living sharks. Although Leriche recommended reconstructing fossil shark dentitions as means of reducing the number of unneeded taxonomic names, his advice has gone unheeded. As a result of this, for fossil lamniform sharks close to 1000 names alone exist in the literature. Recently the importance of fossil shark teeth to our understanding of their phylogenetic history has been questioned. We review briefly dental variation in lamnid sharks, discuss its impact on the taxonomy of fossil forms, demonstrate the usefulness of reconstructed dentitions to taxonomic studies, and discuss their strengths and weaknesses. Finally we discuss the importance of selecting the correct outgroup for the cladistic analysis of shark dental characters.

Elasmobranch pheromones:hints from the clearnose skate,  Raja eglanteria 

The identified sex pheromones of vertebrates include a somewhat random variety of chemical compounds; lampreys utilize bile salts, while some teleost fishes employ steroid derivatives, especially progestins, and prostaglandins. Snakes, salamanders, hamsters, pigs and elephants utilize methyl ketones, a protein, a dimethyl disulfide protein complex, a steroid and an acetate, respectively. Among the various compounds employed by marine invertebrates,  Aplysia  utilizes a novel peptide. Identification of elasmobranch pheromones has potential to provide chemical, functional and evolutionary insight. Over a five-year period bioassays were conducted with isolated male skates during their active reproductive period. Three types of female-derived material (urine, ovarian extracts and serum extracts from actively mating females) and selected steroidal hormone derivatives were investigated. Significantly elevated male response was observed to urine from ?hot” females, extracts of serum from females with elevated testosterone and estradiol levels, and dichloromethane extracts of ovaries. The results from assays of nine substituted estradiols and five progestins were generally negative. There was some response observed to estradiol 17-sulfate and less to estradiol 3-sulfate. Continued research will include a placental viviparous species, the bonnethead shark, Sphyrna tiburo, and will focus on the assay of protein extracts from female urine.

Short-term movements of juvenile sandbar sharks, Carcharhinus plumbeus, in Delaware Bay using acoustic telemetry

Acoustic telemetry was used to investigate short-term movements of neonate and juvenile sandbar sharks,  Carcharhinus plumbeus, on the shark nursery grounds in Delaware Bay during the summer of 1998. A total of 12 sharks was tracked continuously for between 6-70 hours. The majority of the sharks caught and tracked in the southern region of the bay remained in this area for the entire duration of the tracks. These sharks predominantly limited their movements to within 3 km of shore and to water that was approximately 2-5 m deep. Two sharks made longer offshore movements, one into the deepest section of the bay (37 m), and the other crossed the bay from Lewes, DE to Cape May, NJ. Tidal flow appears to affect the fine-scale movements of these small sharks, however no diel patterns were observed for distance from shore, rate of movement or depth. The results of this study indicate that young sandbar sharks concentrate their movements within a restricted portion of the bay, and therefore, area closures during the summer months might prove to be an effective management technique for this species.

Agonistic display in sharks with special reference to the blacktip shark,  Carcharhinus limbatus 

Some carcharhinid show aggressive behavior patterns starting with forms of agonistic display. This display has been described in detail for the gray reef shark,  Carcharhinus amblyrhynchos . Modified or less extensive forms of this display have been described for other carcharhinid species as well. We will describe the agonistic display observed in the blacktip shark,  Carcharhinus limbatus, and discuss possible origins of these patterns.

Subordinate hierarchy between two closely related shark species, Caribbean reef shark ( Carcharhinus perezi ) and blacktip shark ( C. limbatus )

Anecdotal evidence suggests that different shark species exhibit interspecific subordinate hierarchies while feeding. Such events have never been statistically examined. This paper describes subordinate associations between two closely related carcharhinid species of similar size, the Caribbean reef shark,  Carcharhinus perezi, and the blacktip shark, Carcharhinus limbatus, during a controlled setup. A subordinate event was identified when a shark initiated a bite at the food source but then first hit, bit or pushed another approaching shark away, before taking the actual bite. After analyzing 610 biting acts, 35 interspecific subordinate events were recorded between specimens of the two species.

The relationship between home range and body size in several sharks.

The home range of an animal is an important facet of its biology and can give insight into other aspects of its lifestyle. Home range size is correlated with the energetic requirements of terrestrial organisms. The home range areas of several shark species as reported in the literature are discussed here and their relationship to shark size is examined. The home ranges of several shark species (i.e.  Heterodontus fransisci,  Sphyrna lewini, Carcharhinus amblyrhynchos ) did not regress significantly against animal size. Only the home range of the lemon shark,  Negaprion brevirostris  showed a significant, positive increase with the size of the individual. This increase was similar to that of the increase in metabolic requirements with mass; the home range increased at a greater rate than that predicted by both mammalian and elasmobranch data. It is proposed that the lemon shark has a high metabolic rate for elasmobranchs and thus requires a relatively larger area per mass from which to acquire energy.

Status of sharks and their fisheries in Central America

Shark fisheries in Central America represent an important source of labor for artisanal fishers as well as protein for local populations. The demand for shark products, especially fins and cartilage, has led to an expansion in fisheries and trade throughout the region. Limited data on landings suggest that shark populations have been declining over the past 10 years. Increased fishing effort, scant data on biological reference points, and lack of management are key factors that negatively impact this fishery. A project currently under way aims to gather basic information on population status, nursery and fishery grounds, socioeconomics of the fishery, and needed conservation measures. Twenty four commercially valuable species have been identified including  Carcharhinus falciformes and  Nasolamia velox  (Guatemala),  C. falciformis  (Nicaragua, Costa Rica),  C. obscurus  (El Salvador), and  C. limbatus  (Panama). Commercial products include the meat, fin, oil, cartilage, and skin. Shark fins are the most valuable product (e.g., dried caudal fins sell for to $US 150 – 400 per kg in Costa Rica), which are exported to Hong Kong, Taiwan, Japan, and the United States. Recommended management measures to improve the long-term viability of these sharks and the sustainability of their fisheries are discussed.

The Evolution of Batoid Locomotion

The recent integration of functional morphology with phylogenetic data is creating a renaissance in our view of functional evolution. A phylogenetic context provides the ability to distinguish between patterns that arise from similar selective pressures or constraints independently and patterns that only reflect a common ancestry. Comparative methods using current higher level phylogenies for batoids (skates, stingrays, etc.) will reveal the evolutionary patterns of locomotion within this unique and diverse group of fishes by tracing morphology and kinematic behavior. Batoids exhibit three locomotor modes related to their lifestyles including axial-based locomotion (shark-like), undulation of the pectoral fins (waves propagated down the fins), and oscillation of the pectoral fins (bird-like flapping). Some species use a combination of at least two of these, like guitarfish in the family Rhinobatidae which use both axial and pectoral fin undulation. Others, such as the dasyatids, are able to modify their locomotor style from undulation to oscillation at high velocities. The assumed evolutionary trend for these locomotor types is axial (sawfish, electric rays, guitarfish) to undulation (skates and stingrays) to oscillation (eagle and manta rays), however undulation and oscillation may have independently evolved multiple times in these fishes.

The phylogenetic relationships of carcharhinid shark: An inference based on both nuclear and mitochondrial genes.

The Carcharhinidae is one of the most diverse families of sharks, as well as one of the most commercially important. Our current understanding of carcharhinid phylogeny is based on the comparative morphological studies by Compagno (1988) and allozyme studies by Lavery (1992) and Naylor (1992). In the present study we present phylogenetic inferences based on 6kb of sequence data comprising 3 mitochondrial genes and one nuclear gene for 45 carcharhinid taxa.

The prey capture behavior and kinematics of the Atlantic cownose ray,   Rhinoptera bonasus .

This study explores the feeding behavior and mechanics of the myliobatid Atlantic cownose ray,   Rhinoptera bonasus . This species possesses a euhyostylic jaw suspension permitting extensive ventral protrusion of the jaws. Inertial suction prey capture during the preparatory phase is characterized by depression of the subrostral lobes. The expansive phase begins with the closure of the spiracle, followed by depression of the mandible and protrusion of the palatoquadrate and nasal cartilages. Throughout the feeding sequence, the subrostral lobes are fully depressed, forming a laterally enclosed chamber trapping the food. During the compressive phase, the mandible is elevated toward the palatoquadrate and nasal cartilages grasping the food. In the recovery phase, the jaws are brought back to the resting position and the spiracle is reopened. Manipulation involves repeated jaw open and closing movements such that the hard parts of the food are winnowed from the edible portions and ejected from the mouth. Total prey-capture duration is 240 ms. When excavating food from the sand, the ray repeatedly opens and closes its mouth to fluidize the sand, and suspend the food, before using suction to capture the food.

The use of PCR-RFLP and DNA sequence analysis of major histocompatibility class II alpha genes for paternity testing in the nurse shark,  Ginglymostoma cirratum .

We have developed a DNA-based paternity test with which to further our understanding of the mating behavior and reproductive biology of the nurse shark. It is hoped that this paternity test will allow us to determine if matings of female nurse sharks with multiple males can lead to multiple paternity in a single brood of offspring. We have focused our analysis on the major histocompatibility class II alpha (MHC II A) locus. Others have shown that this locus is duplicated, and that each of the duplicated loci is highly polymorphic(Kasahara et al.,1992, Eur. J. Immunol. 23: 2160-2165). We have used a PCR-RFLP strategy to determine the MHC class II A genotypes of DNA amplified from frozen shark tissue of one small family consisting of one mother and seven offspring. We were able to assign genotypes to each member of this family, but there was no evidence for multiple paternity. However, the sample size was too small to rule out this possibility. The analysis of a second family consisting of one mother and 33 offspring is underway, and the results of this analysis will be reported.

The Highly Migratory Species Fishery Management Plan

On October 21, 1998, the Highly Migratory Species (HMS) Management Division of the National Marine Fisheries Service (NMFS) announced the availability of the draft Fishery Management Plan (FMP) for Atlantic highly migratory species, including Atlantic tunas, swordfish, and sharks. The draft FMP addresses rebuilding of overfished stocks (western Atlantic bluefin tuna, Atlantic bigeye tuna, Atlantic swordfish, and large coastal sharks), managing healthy stocks at optimum yield levels, limited access, essential fish habitat, economic and social impacts, safety at sea, scientific data and research needs, and permitting and reporting requirements. NMFS released the proposed rule to implement the provisions contained in the draft HMS FMP on January 20, 1999, and is conducting numerous public hearings throughout the Atlantic, Gulf of Mexico, and Caribbean coasts.

Flushing Behavior of the Bluntnose Stingray ( Dasyatis sayii )From the Southwest Gulf Coast of Florida

This study was carried out to determine whether method of approach influenced the flushing distance of bluntnose stingrays. Juvenile bluntnose stingrays were captured, tagged with a small float, and released at the site of capture. One hour after release each ray was approached by a researcher and the flushing distance was recorded. Flushing distance was a measure of the distance between the investigator and the ray at the moment the ray “spooked”. During the first part of the study each ray was approached once by a researcher walking normally and once by a researcher doing the “stingray shuffle”. During the second part of this study each ray was approached once by a barefoot researcher and once by a researcher wearing booties. Statistical analysis showed that neither the “stingray shuffle” nor booties influenced flushing distances. Short flushing distances were observed in response to all methods of approach. While the “stingray shuffle” did not increase the flushing distances observed, it did have the benefit of reducing one’s chances of stepping directly on top of the ray and therefore one’s chances of getting stung. The results did show a significant difference in the flushing distances recorded between the beginning and end of the study period.

Species-specific markers for PCR-based identification of sharks

Since individual species of sharks respond differently to exploitation, management of the shark fishery on a species-specific basis is considered imperative for effective conservation and sustainable harvesting of this resource. The morphological similarities of many of the commercially harvested species, coupled with on-board processing methods have made it very difficult to collect accurate, species-specific catch data. As a result, many of the sharks landed are either incorrectly identified or classified as “unidentified sharks” in fishery records. Moreover, the widespread practice of shark finning in many parts of the world, and a potentially expanded list of prohibited shark fishery species in US waters will require the ability to identify sharks accurately from dried fins and other body parts for legal forensic purposes. To this end we are exploring the development of DNA sequence-based differences in sharks as markers for reliable species identification. In the quest to develop a streamlined process, we investigating the utility of multiplex PCR-based protocols for rapid identification of tissues using nucleotide differences in the ribosomal internal transcribed spacer regions. We report here on our progress to date in this endeavor.

Demography of western Atlantic sawfishes: Implications for conservation

Sawfish are a group of elasmobranchs that have been heavily impacted by humans due to targeted fishing, entanglement in fishing gear, and habitat modification. Four species are currently listed on the World Conservation Unions Red List of Threatened Animals, two as critically endangered. Two species occur in the western Atlantic: the small tooth sawfish ( Pristis pectinata ) and the large tooth sawfish ( P. perotteti ). There are limited biological and population data available. However, sufficient exists to construct preliminary demographic models for both western Atlantic species. A series of models were constructed to examine the sensitivity of demographic results to uncertainties in the biological and population data. The results of these models indicate that  P. perotteti  has an intrinsic rates of population increase of between 0.04 and 0.07, while  P. pectinata  has a rate between 0.08 and 0.13. These intrinsic rates of increase result in estimates of population doubling time of 10 – 17 years for  P. perotteti  and 5 -9 years for  P. pectinata . The implications of these results for conservation of sawfish populations are discussed.

Stock assessment and risk analysis for the whiskery shark ( Furgaleus macki ) in south-western Australia

The status of the whiskery shark population in south-western Australia was assessed using an age and sex structured model. The results from the best estimates of the model indicate that fishing prior to 1975 had a limited impact on the population, with total biomass estimated to be 97% of virgin and mature female biomass estimated to be 95% of virgin. The best estimate of total biomass in 1998 was 38.8% of virgin (95% confidence interval (CI) 22.7% to 47.2%) indicating that heavy commercial fishing had resulted in a significant decrease in the population. The best estimate of mature female biomass in 1998 was 23.0% of virgin (95% CI 13.4% to 36.4%), demonstrating that the impact of the fishery has been biased towards mature animals. Sensitivity tests indicated that uncertainty in the catch and effort data, or the way it was corrected, had the greatest effect on the biomass estimates. Uncertainty in biological and gear parameters resulted in only small changes in the biomass estimates. Risk analysis indicated that to have a greater than 60% probability of achieving biomass targets set by the management body would require annual catches to be reduced to less than 160 tonnes.

Distribution and feeding of rays in the northeastern North Sea and on the Norwegian Sea Slope

Spatial distribution and diet composition of five ray species were analysed based on data from several research vessel cruises in the period 1984-1996.
Three species were characteristic members of the demersal fish communities of the northeastern North Sea and Skagerrak and the warm upper continental slope waters of the eastern Norwegian Sea, i.e. Raja radiata, R. lintea, and R. fyllae. Within the North Sea, the southern slope of the Norwegian Deeps at the entrance to the Skagerrak had a particularly high density of rays.
In the Norwegian Sea, two species, Raja hyperborea and Bathyraja spinicauda, occurred near the slope front between the Atlantic Watermass and the cold Norwegian Sea Deep-water. R. hyperborea was the only ray inhabiting sub-zero temperature water beneath the front.
The gut contents of Raja hyperborea and Bathyraja spinicauda were dominated by fish, also epipelagic species, suggesting extensive scavenging. Also R. lintea had mainly consumed fish prey, but also deep-water shrimps. R. fyllae was the more typical benthivore, feeding mainly on polychaetes and benthic crustaceans. The diet of Raja radiata differed between the slope and North Sea-Skagerrak areas. Along the slope euphausids were the prominent prey, whereas in the North Sea, shrimp, polychaetes and, in the bigger specimens, fish were significant.

An update on elasmobranch landings in Portugal: 1986-1998

Elasmobranch Portuguese landings from 1986 until 1998 were analysed. Landings were discriminated by species, port, year, month and selling cost. All species totalled 77651 metric tonnes, where Squaliformes and Hexanchiformes accounted for 46% of the total, Charcharhiniformes and Lamniformes for 16% and Squatiniformes for 38%. A total of 36 species (some only identified by genus) were officially landed during that period of time. The most landed species were  Raja spp.  (36% of the total landed between 1986 and 1998),  Centrophorus granulosus  (11%),  Centroscymnus coelolepis  (10%), Scyliorhinus spp.  (10%),  Centrophorus squamosus  (8%),  Prionace glauca  (7%), Dalatias licha  (6%) and  Mustelus spp.  (4%). Because landings are only available for a period of 13 years, it is hard to determine accurately whether there is an increasing or decreasing trend. However, when looking at monthly values it is possible to observe that some species show high and low variations within each year. All species that showed landings greater than 250 metric tonnes and ports with landings greater than 500 metric tonnes were analysed with detail. Some species show a clear boom-and-crash pattern parallelled by an increase in value.

A preliminary assessment of the elasmobranch fishery in the northern Gulf of California, Mexico

Mexican elasmobranch fisheries have expanded to become the largest in the Americas (~30,000 MT/year), with much of the yield taken from the Gulf of California (GOC). To improve the understanding, conservation, and management of shark and ray resources in the GOC, a 2-year, multi-institutional project involving Mexican and US scientists was initiated. The extent and activity of fishing camps within the northern GOC and catch information from these camps, including species composition, sex, weight, size, and other pertinent biological information were determined during 1998 field surveys. A total of 31 elasmobranch species were encountered. Fishing effort was highly variable among seasons in both Baja California Norte (BCN) and Sonora. Landings were highest in summer and fall. Batoids numerically dominated BCN catches and were important constituents of the Sonoran fishery. Large sharks (esp.  Alopias pelagicus,  Carcharhinus falciformis, and C. limbatus )comprised a greater component of the catch in BCN than Sonora. Small sharks, juveniles of larger species, and batoids dominated landings in both locations. Females dominated the fall catch composition of  Mustelus  sp. and  Gymnura marmorata . These primary data represent an important step toward documenting fishing trends that are critical for sustainable fisheries management of elasmobranchs in the GOC.

Gastric Evacuation and Estimates of Daily Ration in the Bonnethead Shark  Sphyrna tiburo 

The rate of gastric evacuation is an integral component in estimating daily ration in fishes caught in the wild. The gastric evacuation curve for the bonnethead shark was established in a laboratory study by force feeding a pre-weighed meal of the iridescent swim crab, Portunus gibbesii . Stomach contents were removed by everting the stomachs at selected times after feeding. These data were best fit by both the exponential and Gompertz nonlinear models. Analysis of these contents was used to develop a discrete stage-of-digestion scale that then was applied to prey items from bonnethead stomach contents obtained in the wild. This allowed reconstruction of meal size which, together with feeding frequency, was used to estimate daily ration. As an alternative approach, stomach contents were collected from bonnethead sharks in the field over a 24-hr period at 3-hr intervals. Stomach content weight and stage of digestion were used to determine daily ration with this method. Daily ration also was estimated through the balanced energy equation. These and other methods of estimating daily ration will be compared for their suitability given the assumptions implicit in each method.

Age and Growth of the Pacific lesser electric ray, Narcine entemedor, from the west coast of Baja California Sur, Mexico

We describe the age and growth of the Pacific lesser electric ray, Narcine entemedor, from artisanal fisheries in two locations, Almejas Bay and San Ignacio Lagoon, along the western coast of Baja California Sur, Mexico. We removed, cleaned and sectioned vertebrae for growth zone analysis. We independently counted pairs of opaque and translucent bands and calculated the average percent error (APE) and percent error (D) and produced precision histograms that indicate precision of counts was relatively good, with among-reader APE and D values for females being 10.38 and 6.10%, while for males they were 8.25 and 4.71%, respectively. Most age estimates were within 2 years of each other. Marginal increment measurements for large females over 70 cm TL and males over 50 cm TL indicated seasonal changes, with an increase in the dimension of opaque bands during the summer months. We fit the von Bertalanffy growth (VBG) function to the data from 315 female and 79 male rays, producing growth curves that indicated that females grew faster (k = 0.313) and reached a larger size (Loo = 82.4 cm TL) than males (Loo = 79.4 cm TL; k = 0.094). The oldest female and male rays were estimated to be 15 and 11 years old, respectively. Growth characteristics, coupled with information on reproduction, indicate that this ray could be susceptible to heavy fishing pressure, especially in their nursery areas.

Characterization of group I intron-like insertion elements in shark ribosomal DNA spacers.

A set of insertion elements has been found in the ribosomal DNA (rDNA) internal transcribed spacers in four Orders of sharks (Carcharhiniformes, Hexanchiformes, Lamniformes, and Orectolobiformes). These elements are from 303 to 575 nucleotides in length, and show all the RNA folding characteristics of group I introns, with each element having nine to eleven pairing regions and a conserved core region. Each of these putative introns has been cloned into RNA expression vectors and  in vitro  splicing experiments are underway. If these elements are capable of  in vitro splicing, this will be the only group I intron within rDNA reported for any metazoan. Also, this would be the only report of a group I intron within a transcribed spacer region. If these elements are incapable of  in vitro  splicing, they may represent remnants of a very ancient insertional event by a group I intron ancestor. Aside from the biological and evolutionary importance of these elements, their sequences vary greatly and so have the potential for use as species-specific markers for shark identification.

Dexamethasone-induced apoptosis (programmed cell death) in immune cells from peripheral circulation and lymphomyeloid tissues of juvenile clearnose skates ( Raja eglanteria ).

Programmed cell death (apoptosis) plays a critical role in shaping the immune repertoire in higher vertebrate thymi. Elasmobranchs represent the earliest phylogenetic appearance of a clearly defined thymus. Apoptosis was induced in juvenile clearnose skates by IM injections of dexamethasone-21-phosphate in areas adjacent to the thymus at levels of 50, 75, and 100 mg/kg body weight. After 24 h, skates were sacrificed, and Leydig organ, spleen, and thymus were removed and frozen in liquid nitrogen. Blood was drawn via cardiac puncture, and peripheral blood leukocytes (PBL) isolated. A method to detect DNA strand breaks (TUNEL reaction) was used to assess apoptotic activity in cryostat sections of tissue and cytospin preparations of PBL, and transmission electron microscopy was utilized to examine glutaraldehyde/paraformaldehyde fixed thymi. Results show that dexamethasone treatment resulted in increased apoptotic activity in immune tissues and PBL of juvenile clearnose skates. These studies demonstrate that immune cells of elasmobranchs have the capacity for glucocorticoid-driven apoptosis, and that mechanisms of programmed cell death appear to have been well conserved during evolution. Knowledge gained from studies of these processes in primitive vertebrates such as elasmobranchs should contribute to a better understanding of the significance of apoptosis in higher vertebrates.

A series of developmental stages for the clearnose skate,  Raja eglanteria 

A series of developmental stages for the clearnose skate,  Raja eglanteria, based on external morphology has been prepared. Images were collected with macrophotography, epifluorescent microscopy, and scanning electron microscopy from more than 100 embryos. The skates were maintained at 21 C and fixed with aldehydes at regular intervals throughout their 12 week incubation period. Embryonic development was observed from early cleavage to 1 week post-hatching. The embryos were staged based on modifications of the staging systems of Ballard and Mellinger, 1993; Scammon, 1911; and Balfour, 1876. Newly laid eggs are in the blastoderm stage. The embryonic axis of the skate is established 3 days after oviposition. Fusion of the neural folds is complete 7 days after oviposition. Otic and optic vesicles are apparent 10 days after oviposition. The olfactory pit is invaginated in day 12 embryos. Thirteen days after oviposition all pharyngeal grooves are open and gill filaments protrude from the gill bars. Pectoral and pelvic fins attain their definitive shape 17 days after oviposition. The stages established for the clearnose skate will be useful for comparative and evolutionary studies of vertebrate development.

Photo-identification of individual manta rays,  Manta birostris, at the Yaeyama Islands, the Miyako Islands, and the Ogasawara Islands, Japan

The manta ray,  Manta birostris  (family Mobulidae), is the largest ray and one of the largest living fishes, reaching a disc width of at least 6.7 m and a weight of more than 1360 kg. The manta ray occurs worldwide in tropical and subtropical regions, and occasionally migrates into temperate waters. Individual mantas are recognizable on the basis of natural marks and color patterns, especially dark markings on their abdomen. In this study mantas were recorded by photographs and video tape recording around several Japanese islands. We identified 180 individuals at the Yaeyama Islands, Okinawa, from 1978 to 1998, 48 individuals at the Miyako Islands, Okinawa, from 1996 to 1998, and 42 individuals at the Ogasawara Islands, Tokyo, from 1995 to 1998. We observed that manta rays migrated between the Yaeyama Islands and the Miyako Islands. The color patterns of manta rays differed between the Yaeyama Islands/Miyako Islands populations and the Ogasawara Islands population. Seasonal abundance, migration, and swimming behavior of manta rays are reported.