![]() All tags were programmed to archive light level, depth and sea temperature every 30 seconds and detach from the animal after a maximum of 180 days. These tags are equipped with a Fastloc-GPS receiver, allowing locations to be recorded even when the tag only surfaces for a brief period of time (0.2 second). This study used SPLASH10-F-321A PSAT tags (Wildlife Computers Inc., Redmond, Washington, USA) coated with Propspeed ™ silicone coating to prevent fouling during the deployment period. These data reveal an unexpected outstanding feature: the unique depths and high number of deep dives, which considerably extend the known depth range for Mobula alfredi. This short communication presents the first data collected on the diving behaviour of reef manta rays in New Caledonia. In New Caledonia, manta feeding grounds seem to be scattered, with aggregations never exceeding a dozen individuals (Lassauce, pers. Massive feeding aggregation of hundreds of reef mantas have been observed targeting such dense zooplankton aggregations in the Maldives and occasionally in the southern reaches of the Great Barrier Reef. These processes, combined with tidal currents and bathymetry can support dense zooplankton concentrations and favourable feeding grounds for filter feeders such as Mobula alfredi. Processes such as coastal upwellings and river run-off are both important sources of nutrient enrichment of coastal waters. Eutrophication benefit the development of phytoplankton upon which zooplankton feed. Nutrient enrichment is known to be the primary factor of phytoplankton proliferation, causing a subsequent increase in zooplankton abundance. Environmental processes and conditions shape the distribution and the abundance of their zooplankton prey. ![]() In New Caledonia, reef manta rays are not targeted by fishing, but have a highly fragmented distribution due to the specificity of their food resources and preferred habitat. These foraging strategies remain unclear and more detailed information on this behaviour and the associated drivers are needed. Some studies have shown that reef manta rays are also able to explore substantial depths (up to 432 m), presumably to feed on deeper zooplankton and other food resources. As opportunistic feeders, manta rays are capable of undertaking relatively large-scale movements between productive areas (up to 750 km). For instance, seasonal migrations were found to be correlated with monsoonal shifts in the Indian Ocean. Seasonal or long-term presence of the species on a particular site is often associated with enhanced local productivity and increased food availability. Manta ray aggregations have been observed and monitored in multiple locations in tropical and sub-tropical waters around the world. Satellite telemetry using pop-up satellite archival tags (PSAT tags) is one of the most effective methods to investigate fine scale horizontal and vertical movements and habitat use in manta rays, but until now there have been no such studies conducted in New Caledonian waters.Īs planktivores, manta rays spend a major part of their time feeding or searching for foraging grounds. Specifically, data on spatiotemporal dynamics and habitat use are necessary to develop concrete management plans and conservation actions to prevent further declines of reef manta rays, now listed as “vulnerable” on the IUCN Red-List. Despite significant advances in our knowledge and understanding of this species in the past decade, more detailed information on the biology and the ecology of this species throughout its range is urgently needed. Reef manta rays ( Mobula alfredi), are declining worldwide, in large part due to fishing pressure for their gill rakers. These results add new information on the habitat use of this species in a region where manta behaviour has not previously been studied, and increase the known depth range of M. We hypothesize this deep-diving behaviour is employed to access important food resources at these depths during the night and may also indicate that zooplankton abundance in the surface waters surrounding New Caledonian coral reefs is insufficient to sustain these megafauna. ![]() Diel comparisons revealed that most of the deepest dives occurred during night-time. All tagged individuals performed dives exceeding 300 m in depth, with a maximum depth recorded of 672 ± 4 m. ![]() Here we briefly report the results from nine SPLASH10-F-321A pop-off satellite archival tags (PSAT-tags) deployed in New Caledonia that recorded the world’s deepest known dives for reef manta rays. Studies have highlighted the need to further investigate the spatial ecology of this species to inform conservation and management initiatives. The interest in reef manta rays ( Mobula alfredi) from the scientific community is growing in reaction to the major decline of populations around the world.
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