Ectoparasites of the Critically Endangered Giant Shovelnose Ray Glaucostegus typus in the Eastern Indian Ocean, with a Summary of the Known Metazoan Parasites.

ABSTRACT

PURPOSE: This study examined the metazoan ectoparasites of the Critically Endangered giant shovelnose ray, Glaucostegus typus, in the eastern Indian Ocean. METHODS: We screened 186 G. typus for ectoparasites in four coastal regions of Western Australia between 2020 and 2022 the Pilbara Region, Exmouth Gulf, Ningaloo Coast and Shark Bay. RESULTS: Five parasite taxa were encountered on 186 G. typus Caligus furcisetifer (Copepoda Caligidae), Dermopristis cairae (Monopisthocotyla Microbothriidae), Branchellion plicobranchus and Stibarobdella macrothela (Hirudinida Piscicolidae), and praniza larvae of unidentified gnathiid isopod/s (Isopoda Gnathiidae). Two of these species, B. plicobranchus and S. macrothela, are reported for the first time on G. typus. Only C. furcisetifer and S. macrothela were relatively common, encountered on 31% and 40% of G. typus, respectively. Gnathiids were observed infrequently, encountered on 13% of G. typus, and D. cairae and B. plicobranchus were scarce, encountered on 1% and 2% of G. typus, respectively. Intensity of infection for C. furcisetifer and gnathiids increased with host length. Likelihood of infection varied seasonally for C. furcisetifer, being considerably lower in summer, and regionally for gnathiids, being greatest at Shark Bay. Intensity and likelihood of infection for S. macrothela increased with host length and varied regionally, being greatest at Shark Bay. CONCLUSION: These findings improve our understanding of the downstream impacts for dependent parasites that might arise should populations of G. typus continue to decline.