Freshwater and Euryhaline Elasmobranchs

The diversity of freshwater obligate and euryhaline generalist chondrichthyans is low, yet they offer a unique insight into elasmobranchs adapted to non-marine environments. The freshwater stingrays of South America dominate the freshwater obligate fauna, and freshwater obligate stingrays of Asia and West Africa and a small diversity of euryhaline sharks, sawfish, and stingrays comprise the rest of the fauna. This chapter explores the diversity and biogeography, biology and ecology (including habitat, life history, trophic ecology, sensory biology, and physiological adaptations), relationship with humans, and the conservation status of freshwater and euryhaline elasmobranchs. Freshwater obligate elasmobranchs inhabit lowland rivers in tropical and subtropical regions, and, due to the nature of euryhaline species’ ability to tolerate wide range of salinities, these species can occupy a range of habitats, from oceanic marine waters to riverine and floodplain freshwaters. Species are subject to high levels of anthropogenic pressure as a result of overexploitation in ornamental and consumptive fisheries, bycatch, persecution, and habitat alteration. Substantial interspecific variation in life history, geographic range size, and habitat specialization does, however, result in differences in population dynamics, dispersal ability, and ultimately, extinction risk. A substantial investment is urgently required in (1) research, to acquire the information to effectively manage and conserve these species; (2) threat management, to mitigate threats; and (3) conservation planning, to secure populations and ensure the recovery of threatened and depleted species. Without direct intervention there is a risk that the status of some species will deteriorate to the point of no return.