Categorising use patterns of non-marine environments by elasmobranchs and a review of their extinction risk

摘要

As the state of non-marine aquatic environments (freshwater and estuarine environments with salinities = 30 ppt) continues to decline globally, there is increasing concern for elasmobranchs (sharks and rays) that use them at critical stages of their life history. Due to a range of impediments including unresolved taxonomy, lack of fisheries data, and poor public perception, our knowledge of elasmobranchs in non-marine environments has lagged behind marine species. Here, we refine previous categorisations of elasmobranchs that occur in non-marine environments by reviewing the timing and duration of freshwater (= 5ppt) and/or estuarine (> 5 to = 30 ppt) habitat use throughout each species' life history. We identified five categories describing elasmobranchs in non-marine environments: (1) freshwater obligates (43 spp.); (2) euryhaline generalists (10 spp.); (3) estuarine generalists (19 spp.); (4) non-marine transients; (5) non-marine vagrants. Criteria for species inclusion is provided for all categories, and species lists are presented for categories 1-3. Euryhaline and estuarine generalists had the highest number of species that are threatened with extinction on the IUCN Red List of Threatened Species (50% and 65%, respectively), and freshwater obligate species have a very high portion of Data Deficient and Not Evaluated species (77%). The refinement of non-marine elasmobranch categories will aid in our understanding of elasmobranchs that occur in non-marine environments, helping facilitate more strategic conservation and management initiatives. Research on the biology of elasmobranchs and their human interactions in non-marine environments are suggested, as this will lead to better availability of information for conservation and management.