A simple and efficient method for making a high-resolution seagrass map and quantification of dugong feeding trail distribution: A field test at Mayo Bay, Philippines Katsunori Mizuno a, ⁎, Akira Asada a , Yoshinori Matsumoto a , Kenichi Sugimoto b , Tomonori Fujii b , Masumi Yamamuro c , Miguel D. Fortes d , Monica Sarceda d , Lea A. Jimenez e a Institute of Industrial Science, The University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan b Windy Network Corporation, 6-4-25 Magarikane, Suruga-ku, Shizuoka, Shizuoka 422-8006, Japan c Department of Natural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan d Marine Science Institute, College of Science, University of the Philippines, Diliman, 1101 Quezon City, Philippines e Regional ICRM Center XI, Davao Oriental State College of Science and Technology, Guang-guang, Dahican, City of Mati, Davao Oriental, Philippines abstract article info Article history: Received 28 September 2016 Received in revised form 7 February 2017 Accepted 7 February 2017 Available online 10 February 2017 The Philippines has one of the most diverse seagrass meadows in south-east Asia, with substantial dugong pop- ulations still existing. However, the seagrass population is declining worldwide, and 30–40% of the seagrass areas in the Philippines have been lost in the last 50 years. The quadrat method by scuba diving has been widely used to study seagrass distribution and measure dugong feeding trails. However, this method is affected by observational skills of the divers and the survey time is usually limited by air capacity in the tank and effort for high-resolution sampling. In this study, a new method of seagrass mapping and quantification of dugong trail distribution is pro- posed and tested. The method produces clear and high-resolution data using acoustic and optical devices with high efficiency. The field study was conducted at Mayo Bay, southeastern Philippines. Continuous optical images were taken using a water-proof digital still camera from the sea surface by a swimmer with snorkel. Using the software PhotoScan, 3D optical images were generated from the continuous photos. The resolution of the optical image is 2.96 ± 0.17 (SD) mm per pixel so that a leaf of Halophila sp. is identifiable. By counting the pixels of du- gong trails, the feeding rates were calculated and the values were 13.5% in the survey area 1 and 7.1% in area 2. The quantification method, based on high-resolution optical image generated by continuous photos, can be use- ful for assessing the status of the seagrass meadows and the distribution of dugong trails. © 2017 Elsevier B.V. All rights reserved. Keywords: Dugong dugon High-resolution seagrass mapping Dugong feeding trail Southeastern Philippines 1. Introduction The dugong (Dugong dugon), which is listed as Vulnerable to extinc- tion at a global scale by The World. Conservation Union (IUCN), is distributed in at least 37 countries in tropical and subtropical coastal and island waters from east Africa to Vanuatu, including the Red Sea, Indian Ocean, and the Pacific Ocean (Nishiwaki and Marsh, 1985). The Philippines has one of the most di- verse seagrass meadows in south-east Asia, with substantial dugong populations still existing in northern Palawan, Guimaras, and especially in southern Mindanao, e.g. Mati, Malita; Talikud and Samal Islands, Balut and Sarangani Islands, and Pujada Bay (Marsh et al., 2002). How- ever, the seagrass population is declining worldwide (Short and Wyllie- Eciieverria, 1996), and 30–40% of the seagrass areas in the Philippines have been lost in the last 50 years (Fortes, 2001). Since the dugong is a seagrass specialists which prefers to consume seagrasses from the genera Halophila and Halodule (Marsh et al., 1999; Preen, 1995), the protection and monitoring of seagrass meadows are necessary for du- gong conservation. Measurements of the coverage and distribution of both seagrass and of dugong feeding trails are important to assess the appropriate amount of seagrass meadows for the dugong. Several remote sensing methods are often used for mapping aquatic plants with high efficiency: optical (including satellite) and acoustic re- mote sensing methods (Abukawa et al., 2013; Chunhui et al., 2013; Dekker et al., 2005; Gonzalez-Socoloske and Olivera-Gomez, 2012; Mizuno et al., 2013; Zainal et al., 1993), however, the resolution is not enough to measure the dugong trails which are mainly constructed from Halophila (which has a leaf size of less than 2 cm). Therefore, the quadrat method or transect tape measurement by diving have been widely used for the study of seagrass distribution and measurement of the dugong trails (Ame and Ayson, 2009; de Longh et al., 1995; Ecological Informatics 38 (2017) 89–94 ⁎ Corresponding author. E-mail address: kmizuno@iis.u-tokyo.ac.jp (K. Mizuno). http://dx.doi.org/10.1016/j.ecoinf.2017.02.003 1574-9541/© 2017 Elsevier B.V. All rights reserved. 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