Spatial connectivity of reef manta rays across the Raja Ampat archipelago, Indonesia

Abstract

The reef manta ray <i>Mobula alfredi</i> is present throughout most island groups that form the Raja Ampat archipelago, Indonesia. The species is protected regionally and nationally and is currently managed as a single homogeneous population within the 6.7 million ha archipelago. However, scientific evidence is currently lacking regarding the spatial connectivity and population structure of <i>M. alfredi</i> within this archipelago. Using network analysis and an array of 34 acoustic receivers deployed throughout Raja Ampat between February 2016 and September 2021, we examined the movements of 72 subadult and adult <i>M. alfredi</i> tagged in seven regions of Raja Ampat. A total of 1094 <i>M. alfredi</i> movements were recorded and were primarily concentrated between nearby receiver stations, highlighting frequent local movements within, and limited long-distance movements between regional acoustic receiver arrays. Network analysis revealed highly connected nodes acting as hubs important for <i>M. alfredi</i> movements. A community detection algorithm further indicated clusters within the network. Our results suggest the existence of a metapopulation comprising three demographically and geographically distinct subpopulations within the archipelago. They also reveal the importance of Eagle Rock as a critical node in the <i>M. alfredi</i> movement network, justifying the urgent inclusion of this site within the Raja Ampat marine protected area network.