Movement ecology and natural mortality of threatened river sharks: informing conservation planning.

Elasmobranchs (sharks and rays) represent some of the most threatened vertebrates on the planet, largely due to overexploitation and their conservative life history strategies. Euryhaline generalist elasmobranch species are among the few elasmobranchs which occur in non-marine environments and regularly utilise marine, brackish, and freshwater environments during particular life stages. These species are disproportionately threatened with extinction due to increasing human populations surrounding estuarine and freshwater habitats, exposing them to fishing pressure and habitat degradation or loss. As a result, 70% of euryhaline species are listed as at risk of extinction on the IUCN Red List, despite making up only 0.8% of all described chondrichthyan (shark, ray, and chimaera) species. The absence of detailed life history, movement ecology, and habitat use information for the majority of euryhaline and estuarine species hinders the implementation of appropriate management and conservation measures. The Northern River Shark Glyphis garricki and the Speartooth Shark Glyphis glyphis are two such rare and threatened euryhaline species requiring further information on their biology and ecology in the Northern Territory where data is currently lacking. This project will use short- and long-term acoustic telemetry to study the movement ecology, habitat use, and natural mortality of these species. As northern Australia is currently the focus of significant development, this information will inform fisheries management and sustainable development of the macrotidal rivers and marine waters utilised by these threatened species.