Movement ecology of the reef manta ray (Mobula alfredi) in southern Africa: multi-scale habitat use and implications for regional and transboundary conservation

Abstract

Reef manta rays (Mobula alfredi) are wide-ranging, vulnerable elasmobranchs experiencing global declines largely due to targeted fishing and indirect anthropogenic threats. Southern Africa is a critical yet understudied region for the species, spanning multiple national jurisdictions across a range of protected and unprotected habitats. This thesis investigates the movement ecology of reef manta rays across Mozambique and South Africa, integrating long-term sighting records, acoustic telemetry, satellite tagging, and transboundary management approaches. Together, these chapters provide the most comprehensive assessment to date of habitat use, connectivity, and conservation needs for reef manta rays in this region. First, I analyse a 15-year sightings dataset from Závora, Mozambique, revealing pronounced declines in reef manta ray encounters, alongside shifts in seasonal occurrence and spatial use. Despite declining sightings, the emergence of large seasonal aggregations suggests the site may support critical reproductive behaviours, highlighting its ecological importance and the need for strengthened local management. Second, I tag 48 reef manta rays with acoustic transmitters and track them across an array of over 300 receivers along the southeast African coastline. Results demonstrate high residency within South Africa’s iSimangaliso Wetland Park, while 30% of individuals crossed the border between South Africa and Mozambique. These findings highlight the effectiveness of well-enforced Marine Protected Areas (MPAs) such as the iSimangaliso Wetland Park, while also revealing the lack of protection in Mozambican waters and the need for improved enforcement and regulatory measures across both countries. Third, satellite telemetry (n = 15) revealed broad-scale offshore movements and previously undocumented use of pelagic habitats, including areas of potential overlap with industrial fisheries. These results identify risks and opportunities for conservation beyond coastal MPAs and emphasize the importance of regional-scale planning, including into areas beyond national jurisdiction. Lastly, a synthesis of terrestrial transboundary management strategies across southern Africa identifies lessons that could enhance governance for mobile marine species, highlighting the need for adaptive, cooperative, and community-integrated approaches to managing species that cross political borders. Collectively, this thesis advances understanding of reef manta ray spatial ecology across southern Africa and provides an evidence-based foundation for strengthening national and transboundary conservation strategies.