Search Results (10)

Cleaning stations on seamounts play a crucial ecological role in the health and behavior of marine megafauna, yet interspecific interactions at these sites remain understudied. This study investigates potential hierarchical dynamics between reef manta rays (Mobula alfredi) and pelagic thresher sharks (Alopias pelagicus) at two cleaning stations atop a seamount in the Philippines. Using over 960 h of autonomous video recordings across 119 survey days, we examined species-specific site preferences, visitation types, and behavioral responses to interspecific encounters. Results indicate that, while manta rays used both stations equally, thresher sharks showed a strong preference for the deeper, sloped station. Interruptions during cleaning suggest a hierarchy: all manta-to-shark interactions resulted in thresher sharks vacating the station prematurely, possibly before completing cleaning. In contrast, manta–manta interactions showed more balanced outcomes, with no significant impact on cleaning duration. Shark presence decreased as the flow speed intensified and was lowest during high tide, suggesting that sharks’ decision to clean may be dictated by factors affecting the effectiveness of the cleaning process. These findings also suggest that manta rays may outcompete thresher sharks for access to cleaning services. Understanding such interspecific dynamics is vital for effective marine habitat management and the conservation of vulnerable pelagic species. Full article

In the dynamic and increasingly threatened marine environment, understanding the full spatial ecology of species like the reef manta ray (Mobula alfredi) is crucial for effective conservation. While typically considered a shallow-water species, reef manta rays in New Caledonia were investigated to explore their vertical habitat use. This study utilized satellite telemetry data from 19 tagged individuals, with three tags providing sufficiently high-resolution information on dive behaviour, to describe and quantify three-dimensional movements. We found that New Caledonian reef manta rays exhibit outstanding deep-diving capabilities, with all individuals diving below 300 m and one reaching 672 m. These deep dives occurred regularly, averaging one every 4.8 days, which is notably more frequent than in other studied populations. Dive profile analysis revealed a mixture of foraging and exploratory behaviors, supporting the hypothesis that these deep excursions are driven by the search for demersal or mesopelagic food resources. Our findings highlight the ecological plasticity of M. alfredi and demonstrate that their habitat use extends far beyond the coastal, shallow waters previously assumed, a critical consideration for developing comprehensive and effective marine protected areas. Full article

Stagnation remains a persistent challenge in optimization with metaheuristic algorithms (MAs), often leading to premature convergence and inefficient use of the remaining evaluation budget. This study introduces $MsMA$, a novel meta-level strategy that externally monitors MAs to detect stagnation and adaptively partitions computational resources. When stagnation occurs, $MsMA$ divides the optimization run into partitions, restarting the MA for each partition with function evaluations guided by solution history, enhancing efficiency without modifying the MA’s internal logic, unlike algorithm-specific stagnation controls. The experimental results on the CEC’24 benchmark suite, which includes 29 diverse test functions, and on a real-world Load Flow Analysis (LFA) optimization problem demonstrate that MsMA consistently enhances the performance of all tested algorithms. In particular, Self-Adapting Differential Evolution (jDE), Manta Ray Foraging Optimization (MRFO), and the Coral Reefs Optimization Algorithm (CRO) showed significant improvements when paired with MsMA. Although MRFO originally performed poorly on the CEC’24 suite, it achieved the best performance on the LFA problem when used with MsMA. Additionally, the combination of MsMA with Long-Term Memory Assistance (LTMA), a lookup-based approach that eliminates redundant evaluations, resulted in further performance gains and highlighted the potential of layered meta-strategies. This meta-level strategy pairing provides a versatile foundation for the development of stagnation-aware optimization techniques. Full article

Indonesia is home to significant populations of globally vulnerable reef manta rays (Mobula alfredi) in at least four key regions: Berau, Nusa Penida, Komodo, and Raja Ampat. Despite detailed population studies in each of these regions, little is known about their horizontal movement patterns. Our study used satellite telemetry to investigate reef manta rays’ habitat use and home ranges. A total of 33 manta rays were tagged with SPLASH10F-321A satellite tags across the four regions: Berau (n = 5), Nusa Penida (n = 8), Komodo (n = 6), and Raja Ampat (n = 14), yielding usable data from 25 tags. The rays were tracked for 7 to 118 days (mean ± SD = 50 ± 30) from July 2014 to July 2022. The results showed localized movements, strong residency near tagging sites, and high site fidelity as evidenced by area-restricted search (ARS) behaviors and frequent revisitations. Most manta rays showed restricted home ranges in each region, with no connectivity between regions. Across 25 individuals, the home range (95% utilization distributions) varied significantly, ranging from 19 to 48,294 km² (mean ± SD = 4667 ± 10,354). These findings offer important insights into the spatial movement patterns of reef manta rays in Indonesia, allowing the formulation of more effective management strategies. Full article

The field of bioinspired underwater robots aims to replicate the capabilities of marine animals in artificial systems. Stingrays have emerged as highly promising species to be mimicked because of their flat body morphology and size. Furthermore, they are considered high-performance species due to their maneuverability, propulsion mode, and sliding efficiency. Designing and developing mechanisms to imitate their pectoral fins is a challenge for underwater robotic researchers mainly because the locomotion characteristics depend on the coordinated movement of the fins. In the state of the art, several mechanisms were proposed with 2 active rotation degrees of freedom (DoFs) to replicate fin movement. In this paper, we propose adding an additional active DoF in order to improve the realism in the robotic manta ray movement. Therefore, in this article, we present the mechanical design, modeling, and kinematics analysis of a 3-active-and-rotational-DoF pectoral fin inspired by the Mobula Alfredi or reef manta ray. Additionally, by using the kinematics model, we were able to simulate and compare the behaviour of both mechanisms, that is, those with 2 and 3 DoFs. Our simulation results reveal an improvement in the locomotion, and we hypothesized that with the third DoF, some specific missions, such as hovering or fast emergence to the surface, will have a better performance. Full article

Though a previous study in Sudan confirmed the existence of a living hybrid of an oceanic manta ray (Mobula birostris) and a reef manta ray (M. alfredi), courtship behaviors between the two closely related species have never been documented. Here we report the first observation of courtship behaviors between two male M. birostris and a female M. alfredi at a manta ray cleaning station on a shallow coral reef seamount in Misool, Raja Ampat, Indonesia. The observed courtship event lasted for approximately 45 min and involved one male oceanic manta actively chasing the mature reef manta female around the cleaning station and repeatedly bumping her on the left wing tip with his right cephalic lobe, while the second male continuously flanked the female to seemingly prevent her retreat from the cleaning station and potential evasion of the pursuing male. Notably, the female exhibited a rapid coloration change, likely indicative of courtship-related stress, transitioning from the striking pale hue she exhibited throughout the courtship activity to a normal chevron pattern once the males departed. Full article

Over recent decades, elasmobranchs (sharks, rays, and skates) have been increasingly recognized among the world’s most threatened marine wildlife, leading to heightened scientific attention. However, batoids (rays and skates) are relatively understudied, especially in Large Ocean States of the Pacific. This synthesis compiles insights on batoid diversity and occurrence in Fiji’s waters by integrating a literature review, participatory science programs such as the Great Fiji Shark Count (GFSC) Initiative, Projects Abroad Fiji (PA), Manta Project Fiji (MPF), and iNaturalist, along with environmental DNA. Nineteen batoid species from seven families were identified: 19 species from the literature, 12 from participatory science programs, and six from eDNA analysis. Notably, this study provides the first photographic evidence for the bentfin devil ray (Mobula thurstoni, Lloyd, 1908) in Fiji. GFSC data indicated the highest species diversity in the Western Division, with spotted eagle rays (Aetobatus ocellatus, Kuhl, 1823) and maskrays (Neotrygon sp.) being observed most. In-person interviews conducted by PA provided information on the occurrence of wedgefishes and potentially sawfishes. MPF records and iNaturalist uploads were dominated by reef manta rays (M. alfredi, Krefft, 1868), while the pink whipray (Pateobatis fai, Jordan and Seale, 1906) yielded the most DNA sequences. Overall, 68.4% of the species face an elevated extinction risk based on the International Union for the Conservation of Nature Red List criteria. Although caution is warranted with older literature-based records for the giant guitarfish (Glaucostegus typus, Anonymous [Bennett], 1830), giant stingaree (Plesiobatis daviesi, Wallace, 1967), and the lack of sawfish verification, this synthesis highlights the effectiveness of a combined methodological approach in establishing a reference point for the diversity and occurrence of this understudied taxon in Fiji. Full article

The reef manta ray, Mobula alfredi (Krefft, 1868), is a highly mobile and plankton-feeding species, classified vulnerable to extinction on the IUCN Red List for Threatened Species. Knowledge on their spatial ecology and the extent of their dispersal remain incomplete, especially within island-fragmented habitats as found in New Caledonia. Satellite telemetry was used to investigate the horizontal movement ecology of reef manta rays in New Caledonia. A total of 21 reef manta rays were tagged with pop-up satellite archival transmitting tags (21 Fastloc and 2 MiniPAT) that remained deployed for a duration ranging from 3 to 180 days (mean ± SE = 76.7 ± 50.3). Rays presented a strong site fidelity and an important affinity for coastal waters. Long-distance migrations (>300 km) were also observed, mainly through coastal and shallow water paths. Horizontal movements were compared to a home range area and classified into four distinct patterns: Fidelity, Excursion, Fidelity + Relocation and Relocation. The most dominant pattern was Fidelity, where manta rays remained within their home range for the whole duration of the tag deployment. Our findings may assist in the design of more appropriate management strategies for the species in New Caledonia and other regions worldwide. Full article

This study explores the application of small, commercially available drones to determine morphometric the measurements and record key demographic parameters of reef manta rays (Mobula alfredi) in Raja Ampat, Indonesia. DJI Mavic 2 Pro drones were used to obtain videos of surface-feeding M. alfredi with a floating, known-length PVC pipe as a reference scale—thus avoiding the need to utilize altitude readings, which are known to be unreliable in small drones, in our photogrammetry approach. Three dimensions (disc length (DL), disc width (DW), and cranial width (CW)) from 86 different individuals were measured. A hierarchical multivariate model was used to estimate the true measurements of these three dimensions and their population-level multivariate distributions. The estimated true measurements of these dimensions were highly accurate and precise, with the measurement of CW more accurate than that of DL and, especially, of DW. Each pairing of these dimensions exhibited strong linear relationships, with estimated correlation coefficients ranging from 0.98–0.99. Given these, our model allows us to accurately calculate DW (as the standard measure of body size for mobulid rays) using the more accurate CW and DL measurements. We estimate that the smallest mature M. alfredi of each sex we measured were 274.8 cm (males, n = 30) and 323.5 cm DW (females, n = 8). We conclude that small drones are useful for providing an accurate “snapshot” of the size distribution of surface-feeding M. alfredi aggregations and for determining the sex and maturity of larger individuals, all with minimal impact on this vulnerable species. Full article

Manta rays are classified as Vulnerable to Extinction on the IUCN Red List for Threatened Species. In Australia, a key aggregation site for reef manta rays is Lady Elliot Island (LEI) on the Great Barrier Reef, ~7 km from the shelf edge. Here, we investigate the environmental processes that triggered the largest manta ray feeding aggregation yet observed in Australia, in early 2013. We use MODIS sea surface temperature (SST), chlorophyll-a concentration and photic depth data, together with in situ data, to show that anomalous river discharges led to high chlorophyll (anomalies: 10–15 mg∙m⁻³) and turbid (photic depth anomalies: −15 m) river plumes extending out to LEI, and that these became entrained offshore around the periphery of an active cyclonic eddy. Eddy dynamics led to cold bottom intrusions along the shelf edge (6 °C temperature decrease), and at LEI (5 °C temperature decrease). Strongest SST gradients (>1 °C∙km⁻¹) were at the convergent frontal zone between the shelf and eddy-influenced waters, directly overlying LEI. Here, the front intensified on the spring ebb tide to attract and shape the aggregation pattern of foraging manta rays. Future research could focus on mapping the probability and persistence of these ecologically significant frontal zones via remote sensing to aid the management and conservation of marine species. Full article