Movement patterns and habitat use of juvenile mangrove whiprays (Himantura granulata)

Abstract

Understanding the extent of movements and space use of animals is necessary to identify vital habitats and better conserve and manage vulnerable species. We used acoustic telemetry to examine movement patterns and habitat use of juvenile mangrove whiprays (Himantura granulata) in an intertidal bay at Orpheus Island, Australia. Thirteen juveniles were acoustically monitored between March and December 2012, and in July 2012, four active tracks were completed. The majority of the acoustically monitored rays remained within the intertidal bay for the entire monitoring period. Tidal changes caused rays to move from the inner-bay mangrove (high tide) habitat to coral reef in the outer bay (low tide). Actively tracked rays moved in a directed way during running tides, remaining in shallow water. During periods of high and low tide, when rays refuged in mangrove or reef habitats, movement was limited and sinuosity was high. In mangrove areas, rays were most commonly observed refuging under or close to mangrove roots, and rarely in open sand areas. Refuging behaviour in mangrove and reef habitats suggested that predation risk may be the predominant factor influencing the movement of small rays. The continuous use of intertidal habitats demonstrates their importance to Himantura granulata.