Movement patterns of juvenile porcupine rays Urogymnus asperrimus at a remote atoll: a potential nursery ground within a proposed marine protected area

Abstract

Marine protected areas (MPAs) can provide distinct conservation benefits for threatened species, particularly in regions where there is a lack of population assessments. The St. Joseph Atoll, Seychelles, has been under consideration for MPA designation due to the presence of multiple threatened and important species. This study aimed to assess the nursery role of this isolated ecosystem for Vulnerable (IUCN) porcupine rays Urogymnus asperrimus. Twenty porcupine rays were tagged with VEMCO transmitters and their movements passively monitored for a 2.5-year period using an array of 88 acoustic receivers. The majority (71%) of porcupine rays displayed medium (RI: 0.34–0.66) to high (RI: 0.67–1) levels of residency and 82% of individuals were detected in the atoll for periods close to or exceeding one year. Horizontal movements were limited as small home ranges and activity spaces were identified (mean of 0.65km2 and 4.35km2 respectively). General linear mixed models highlighted that home range size increased with disc-width and that there was dispersal from the atoll over time. These results have implications for the proposed marine protected area at the St. Joseph Atoll and suggests that protecting this habitat will provide strong conservation benefits for this poorly understood species.