Effects of coastal development on sawfish movements and the need for marine animal crossing solutions.

Although human-made barriers to animal movement are ubiquitous across many types of ecosystems, the science behind these barriers and how to ameliorate their effects lags far behind in marine environments compared with terrestrial and freshwater realms. Using juvenile sawfish in an Australian nursery habitat as a model system, we aimed to assess the effects of a major anthropogenic development on the movement behavior of coastal species. We compared catch rates and movement behavior (via acoustic telemetry) of juvenile green sawfish (Pristis zijsron) before and after a major coastal structure was built in an important nursery habitat. Acoustic tracking and catch data showed that the development did not affect levels of sawfish recruitment in the nursery, but it did constrain movements of juveniles moving throughout the nursery, demonstrating the reluctance of shoreline-associated species to travel around large or unfamiliar coastal structures. Given the current lack of information on human-made movement barriers in the marine environment, these findings highlight the need for further research in this area, and we propose the development of and experimentation with marine animal crossings as an important area of emerging research.

Efectos del desarrollo costero sobre los movimientos del pez sierra y la necesidad de soluciones para el cruce de animales marinos Resumen Mientras que las barreras construidas por humanos que limitan el movimiento de animales son ubicuas en muchos tipos de ecosistemas, la ciencia que sustenta estas barreras y la reducción de sus impactos está muy retrasada en ambientes marinos en comparación con medios terrestres y dulceacuícolas. Utilizando peces sierra juveniles en un hábitat de vivero australiano como sistema modelo, intentamos evaluar los efectos de un importante desarrollo antropogénico sobre el comportamiento de especies costeras. Comparamos las tasas de captura y el comportamiento de movimiento (mediante telemetría acústica) de peces sierra verdes juveniles (Pristis zijsron) antes y después de que se construyera infraestructura costera en un importante hábitat de vivero. El seguimiento acústico y los datos de captura mostraron que el desarrollo no afectó los niveles de reclutamiento de pez sierra en el vivero, pero sí restringió los movimientos de los juveniles desplazándose por el vivero, lo cual demuestra la renuencia de las especies asociadas a la costa a viajar alrededor de estructuras costeras grandes o desconocidas. Dada la actual falta de información sobre las barreras de movimiento creadas por el hombre en el medio marino, estos hallazgos destacan la necesidad de realizar más investigaciones en esta campo, y proponemos el desarrollo y la experimentación con cruces para animales marinos como un área importante de investigación emergente.

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

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.