Conservation of freshwater and euryhaline elasmobranchs: a review
a1 Fish Museum, Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada, E-mail: firstname.lastname@example.org
a2 ReefQuest Centre for Shark Research, PO Box 48561, 595 Burrard Street, Vancouver, BC V7X 1A3, Canada, E-mail: email@example.com
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-fifth 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 effects 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 briefly 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 differentiate 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 significant 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.
(Received February 2 2005)
(Accepted July 13 2005)