Stationary video monitoring reveals habitat use of stingrays in mangroves

Abstract

Mangroves are highly productive habitats offering many elasmobranch species abundant food resources and physical refuge from predators, which can be important for survival of juveniles. However, habitat use and behavioural patterns of stingrays are poorly understood within mangrove areas, and the drivers of direct use of mangroves remain unclear. Stationary video monitoring was used to investigate fine-scale spatial use by juvenile mangrove whiprays Urogymnus granulatus and cowtail stingrays Pastinachus ater in a mangrove-fringed intertidal area in Pioneer Bay, Orpheus Island, northeast Australia. Abundance, residence time and behaviour were compared among 3 different habitats (inside mangroves, mangrove edge and sandflat) between summer and winter. Abundance of U granulatus was not significantly different between seasons, while P. ater was significantly more abundant in summer than in winter, suggesting a seasonal habitat shift. U granulatus exhibited tide-associated movement, with individuals occupying mangroves during flood tides and moving to sandflats at ebb tides. Juvenile U. granulatus were frequently observed feeding within mangrove habitats. P. ater predominantly occurred on sandflats regardless of tidal height and were observed feeding only on sandflats, confirming the possible importance of sandflats for feeding by this species. Potential predators rarely occurred in these mangrove habitats, suggesting that U. granulatus reduced predation risk by residing in flooded mangrove habitats. Mangroves can form a critical habitat for early life stages of many species, and their loss may have significant negative effects on populations of these species.