Sharks and Rays of Northern Australia’s Roper River, with a Range Extension for the Threatened Speartooth Shark Glyphis glyphis

Abstract

Northern Australia is considered a ‘lifeboat’ region for globally threatened shark and ray species (elasmobranchs), although much of the region is understudied. The Roper River in the Northern Territory’s Gulf of Carpentaria has been inadequately surveyed, with most elasmobranch data gained opportunistically through freshwater fish surveys. This study aimed to report the occurrence of elasmobranch species in the Roper River through targeted field surveys conducted between 2016 and 2024 and to review data from other sources. Four euryhaline species were recorded, comprising two sharks, a sawfish, and a stingray. Records of the globally Vulnerable speartooth shark (Glyphis glyphis) represented a significant range extension and the documentation of a new reproductive population. Records of the Critically Endangered largetooth sawfish (Pristis pristis) extended almost 400 km upstream, highlighting extensive use of the river system. A predominantly marine species, the Critically Endangered giant guitarfish (Glaucostegus typus) was observed in brackish estuarine waters, approximately 15 km upstream from the river mouth. Further research is required to develop a more thorough understanding of abundance, life history, and population connectivity for these species in this river system. Given the documentation of threatened species, the potential impacts of fisheries, water allocations, and climate change require assessment.