How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones
This study explores the application of small, commercially available drones to determine morphometric the measurements and record key demographic parameters of reef manta rays (<i>Mobula alfredi</i>) in Raja Ampat, Indonesia. DJI Mavic 2 Pro drones were used to obtain videos of surface-f...
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| Format: | Article |
| Language: | English |
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MDPI AG
2022-02-01
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| Series: | Drones |
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| Online Access: | https://www.mdpi.com/2504-446X/6/3/63 |
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| author | Edy Setyawan Ben C. Stevenson Muhamad Izuan Rochelle Constantine Mark V. Erdmann |
| author_facet | Edy Setyawan Ben C. Stevenson Muhamad Izuan Rochelle Constantine Mark V. Erdmann |
| author_sort | Edy Setyawan |
| collection | DOAJ |
| description | This study explores the application of small, commercially available drones to determine morphometric the measurements and record key demographic parameters of reef manta rays (<i>Mobula alfredi</i>) in Raja Ampat, Indonesia. DJI Mavic 2 Pro drones were used to obtain videos of surface-feeding <i>M. alfredi</i> 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 <i>M. alfredi</i> of each sex we measured were 274.8 cm (males, <i>n</i> = 30) and 323.5 cm DW (females, <i>n</i> = 8). We conclude that small drones are useful for providing an accurate “snapshot” of the size distribution of surface-feeding <i>M. alfredi</i> aggregations and for determining the sex and maturity of larger individuals, all with minimal impact on this vulnerable species. |
| first_indexed | 2024-03-09T19:55:14Z |
| format | Article |
| id | doaj.art-9a2416e598254b4c9e6d4e240436d1f9 |
| institution | Directory Open Access Journal |
| issn | 2504-446X |
| language | English |
| last_indexed | 2024-03-09T19:55:14Z |
| publishDate | 2022-02-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Drones |
| spelling | doaj.art-9a2416e598254b4c9e6d4e240436d1f92023-11-24T00:58:08ZengMDPI AGDrones2504-446X2022-02-01636310.3390/drones6030063How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small DronesEdy Setyawan0Ben C. Stevenson1Muhamad Izuan2Rochelle Constantine3Mark V. Erdmann4Institute of Marine Science, The University of Auckland, Auckland 1010, New ZealandDepartment of Statistics, The University of Auckland, Auckland 1010, New ZealandPOKJA Manta, Waisai 98471, IndonesiaInstitute of Marine Science, The University of Auckland, Auckland 1010, New ZealandConservation International Aotearoa, The University of Auckland, Auckland 1010, New ZealandThis study explores the application of small, commercially available drones to determine morphometric the measurements and record key demographic parameters of reef manta rays (<i>Mobula alfredi</i>) in Raja Ampat, Indonesia. DJI Mavic 2 Pro drones were used to obtain videos of surface-feeding <i>M. alfredi</i> 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 <i>M. alfredi</i> of each sex we measured were 274.8 cm (males, <i>n</i> = 30) and 323.5 cm DW (females, <i>n</i> = 8). We conclude that small drones are useful for providing an accurate “snapshot” of the size distribution of surface-feeding <i>M. alfredi</i> aggregations and for determining the sex and maturity of larger individuals, all with minimal impact on this vulnerable species.https://www.mdpi.com/2504-446X/6/3/63aerial photogrammetrymarine megafaunaunmanned aerial vehiclesexual dimorphismsize at maturity |
| spellingShingle | Edy Setyawan Ben C. Stevenson Muhamad Izuan Rochelle Constantine Mark V. Erdmann How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones Drones aerial photogrammetry marine megafauna unmanned aerial vehicle sexual dimorphism size at maturity |
| title | How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones |
| title_full | How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones |
| title_fullStr | How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones |
| title_full_unstemmed | How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones |
| title_short | How Big Is That Manta Ray? A Novel and Non-Invasive Method for Measuring Reef Manta Rays Using Small Drones |
| title_sort | how big is that manta ray a novel and non invasive method for measuring reef manta rays using small drones |
| topic | aerial photogrammetry marine megafauna unmanned aerial vehicle sexual dimorphism size at maturity |
| url | https://www.mdpi.com/2504-446X/6/3/63 |
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