Seasonal variation in space use and residency of the southern eagle ray Myliobatis tenuicaudatus in a temperate ecosystem

Abstract

The environmental conditions determining the distribution of the southern eagle ray Myliobatis tenuicaudatus are mostly unknown. We tracked 40 southern eagle rays using a network of 28 acoustic receivers deployed in Coffin Bay and a second array of 6 receivers deployed along the Fleurieu Peninsula, both in South Australia, to investigate the spatiotemporal changes in space use and residency and the influence of biotic (disc width, sex) and abiotic (water temperature, salinity, tides, moon illumination, time of day) factors. We also assessed the efficacy of a small sanctuary zone to reduce anthropogenic pressures. Tagged southern eagle rays in Coffin Bay were semi-permanent residents (residency index ~ 0.35), with a seasonal exodus from late autumn to spring, high residency from mid-spring to mid-autumn, and selection of Kellidie Bay (located within Coffin Bay). Most (67%) rays were detected in the Kellidie Bay Sanctuary Zone, but spent <15% of their time in Coffin Bay within the sanctuary. Individual variation in the amount of time spent in the Kellidie Bay Sanctuary Zone was high, ranging 0-42%. In contrast, tagged southern eagle rays along the Fleurieu Peninsula had high site fidelity throughout the year (residency index ~ 85%). Our study provides new information on space use and movement patterns of southern eagle rays, highlighting that intraspecific variation should be accounted for in future management considerations.