Highlights d More than one-third of chondrichthyan fish species are threatened by overfishing d Disproportionate threat in tropics risk loss of ecosystem functions and services d Three species not seen in >80 years are Critically Endangered (Possibly Extinct)d The depletion of these species has been driven by continuing demand for human food

The bull shark (Carcharhinus leucas) is a widely distributed, large coastal shark species known to travel long distances. These characteristics, coupled with the species' long life span and late age of maturity, would lead one to predict significant global genetic exchange among bull shark populations. By contrast, data show localized depletion in some areas of large coastal shark fisheries, indicating some geographic isolation may exist. We examined genetic variation in the control region of mitochondrial DNA and at five nuclear microsatellite loci in bull sharks sampled from the western Atlantic to investigate the degree of population subdivision. The average per sample haplotype and nucleotide diversity in the mtDNA (0.51 ± 0.26 and 0.12% ± 0.12, respectively) and expected heterozygosity (0.84) in the microsatellite loci contrast sharply in having lower and higher values (respectively) relative to many other shark species. Significant structure exists between the Brazilian and all northern populations at the mtDNA control region (pairwise U ST [ 0.8, P \ 0.001), but not at the nuclear microsatellite loci. Adjacent northern populations show weak to no genetic differentiation for both markers. These results are congruent with restricted maternal gene flow between populations caused by female site fidelity to nursery areas. We estimate the current effective population size to be around 160,000 and 221,000 individuals for the southern and northern Atlantic populations, respectively. The philopatric habits and the relatively low levels of mtDNA genetic diversity observed in bull sharks must be considered in the conservation of this species. Our results indicate that effective bull shark management strategies will require local, regional, and international attention and cooperation.

Sawfishes are among the most endangered of all elasmobranch species, a factor fostering considerable worldwide interest in the conservation of these animals. However, conservation efforts have been hampered by the confusing taxonomy of the group and the poor state of knowledge about the family's geographical population structure. Based on historical taxonomy, external morphology, and mitochondrial DNA sequences (NADH-2), we show here that, globally, the sawfish comprise five species in two genera: Pristis pristis (circumtropical), Pristis clavata (east Indo-West Pacific), Pristis pectinata (Atlantic), Pristis zijsron (Indo-West Pacific), and Anoxypristis cuspidata (Indo-West Pacific, except for East Africa and the Red Sea). This improved understanding will have implications for the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), International Union for Conservation of Nature (IUCN) Red List assessments, and endangered species laws and regulations in several countries. Furthermore, based on both or either of NADH-2 and the number of rostral teeth per side, we show that populations of P. pristis, P. pectinata, P. zijsron, and A. cuspidata exhibit significant geographic structuring across their respective ranges, meaning that regional-level conservation will be required. Finally, the NADH-2 gene may serve as a marker for the identification of rostra and fins involved in illegal trade.

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DNA barcoding is a recently proposed global standard in taxonomy based on DNA sequences. The two main goals of DNA barcoding methodology are assignment of specimens to a species and discovery of new species. There are two main underlying assumptions: i) reciprocal monophyly of species, and ii) intraspecific divergence is always less than interspecific divergence. Here we present a phylogenetic analysis of the family Potamotrygonidae based on mitochondrial cytochrome c oxidase I gene, sampling 10 out of the 18 to 20 valid species including two non-described species. Potamotrygonidae systematics is still not fully resolved with several still-to-be-described species while some other species are difficult to delimit due to overlap in morphological characters and because of sharing a complex color patterns. Our results suggest that the family passed through a process of rapid speciation and that the species Potamotrygon motoro, P. scobina, and P. orbignyi share haplotypes extensively. Our results suggest that systems of identification of specimens based on DNA sequences, together with morphological and/or ecological characters, can aid taxonomic studies, but delimitation of new species based on threshold values of genetic distances are overly simplistic and misleading.

Freshwater stingrays (Potamotrygonidae) are the only elasmobranchs completely adapted for living in freshwater and all species studied so far presented a reproductive mode described as matrotrophic viviparity with development of trophonemata. Several specimens were collected, dissected and had their reproductive parameters studied. The following species are being studied: Potamotrygon motoro, P. orbignyi, P. schroederi, P. scobina, Potamotrygon sp., Paratrygon aiereba and Plesiotrygon iwamae. The reproductive cycle in the potamotrygonid species observed is directly related to the hydrologic cycle. All species studied have defined reproductive periods with the following sequence of events: gonadal maturation, copulation, pregnancy, birth and resting. Each species analyzed presented a different reproductive periodicity. Gonadal maturation lasts for an average of about 3 months. Copulation does not happen during the same period of the year for all species and it takes place during the rainy or dry season. The lowest average uterine fecundity observed corresponded to 1 and the highest average value was 8. The gestation period varied and lasted between 3 to 9 months. Birth season also presented variation and may last from 3 to 4 months. A resting interval was observed in the reproductive cycle of most species. It is expected that the observation of reproductive aspects of freshwater stingrays contributes to the understanding of population dynamics of these species.

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