conservation of freshwater and euryhaline elasmobranchs: a review

Abstract

Published data on the diversity, life history, ecology, and status of freshwater and euryhaline elasmobranchs was reviewed in the context of anthropogenic threats and principles of conservation biology. At least 171 species of elasmobranch, representing 68 genera and 34 families, are recorded from fresh or estuarine waters. Of these, over half are marginal in estuaries, less than one-tenth are euryhaline, and one-¢fth are obligate in fresh water. Obligate freshwater elasmobranchs are dominated by myliobatoid stingrays, of which two-thirds are potamotrygonids endemic to Atlantic drainages of South America. Freshwater and euryhaline elasmobranchs adhere to strongly K-selected life histories and feed at high trophic levels, similar to those of their marine relatives. However, freshwater and euryhaline elasmobranchs are also subject to habitat constraints, notably more limited volume and physicochemical variability than the ocean, that may render them more vulnerable than marine elasmobranchs to the e¡ects of human activities. The greatest diversity and abundance of freshwater and euryhaline elasmobranchs occur in tropical countries with enormous and rapidly increasing human populations, notably South America, West Africa, and south-east Asia. Knowledge of the biology, distribution, ecology, and status of freshwater and euryhaline elasmobranchs is frustrated by unresolved taxonomic problems, which are brie£y summarized. To clarify selected issues in the conservation of freshwater and euryhaline elasmobranchs, special attention is given to sharks of the genus Glyphis, pristids, and potamotrygonids. To foster live release when possible as well as prevent discard of specimens and loss of data, an illustrated key to di¡erentiate Carcharhinus from Glyphis sharks is provided. Obligate freshwater elasmobranchs with limited geographic ranges are deemed most vulnerable to extinction, but euryhaline elasmobranchs that require access to the sea to breed are also at signi¢cant risk. Based on the foregoing data and principles of conservation biology, suggested action plans for the conservation of freshwater and euryhaline elasmobranchs and the conservation of freshwater habitats are provided.

Phylogeography and conservation genetics of the Amazonian freshwater stingray Paratrygon aiereba Müller & Henle, 1841 (Chondrichthyes: Potamotrygonidae)

“…Using DNA barcoding one could identify putative illegal stingrays catches and exports. Although DNA barcoding cannot discriminate between the species of the Potamotrygon rosette-spot group, it can differentiate mines, dragging), persecution (Araújo et al, 2004;Martin, 2005), and climate changes which affect the events of reproductive cycle. Further, with the enormous area to be covered, protective policies in the Amazon are very difficult to be implemented and reinforced.…”

“…This distribution is probably due the ability to adjust to the diverse ionic characteristics of Amazon River and its tributaries (Duncan et al, 2009). The wide geographic range allied with low fecundity makes this species vulnerable to different environmental risks such as persecution, direct and indirect fisheries and habitat degradation (Araújo et al, 2004;Martin, 2005). Because of their wide distribution and potentially vulnerable status, understanding how populations are structured has a high value for conservation.…”

Rhinebothrium jaimei sp. n. (Eucestoda: Rhinebothriidea: Rhinebothriidae): a new species from Neotropical freshwater stingrays (Potamotrygonidae)

“…Potamotrygonids have been reported in brackish waters of the Amazon River mouth region and Potamotrygon orbignyi, the typehost of R. jaimei, seems to be one of the most tolerant potamotrygonids to brackish water, having been collected in salinities up to 12.4 psu (Almeida et al 2009). As a result of the salinity dynamics in the region, potamotrygonids and marine stingrays -many of which are known to be euryhaline (see Martin 2005 and references therein) -are found to be syntopic at the type locality of R. jaimei.…”

The spine-brush complex in symmoriiform sharks (Chondrichthyes; Symmoriiformes), with comments on dorsal fin modularity

“…However, because of extreme climatic conditions, the seasonal fluctuations in the water level of the rivers constrain the developmental time and maximum growth of P. microdon in the fluvial system. Relatively small individuals appear to use pools as refuge habitats during the dry season (Martin 2005) but the large mature or nearly mature individuals move back to the sea. Orthacanthus platypternus and other xenacanth sharks (e.g., O. texensis and B. luedersensis; Zidek et al 2004: 146) which grew very fast and reached several meters in total length, could already present such adaptive behavior migrating from one habitat to another in order to respond to the unstable palaeoenvironmental conditions of a broad, low relief coastal plain under the influence of tropical semi-arid to sub-humid climate with seasonal rainfalls (DiMichele et al 2006).…”