(Dugong Dugon) Movements and Habitat Use in a Coral Reef Lagoonal Ecosystem
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Vol. 43: 167–181, 2020 ENDANGERED SPECIES RESEARCH Published September 24 https://doi.org/10.3354/esr01061 Endang Species Res OPEN ACCESS Dugong (Dugong dugon) movements and habitat use in a coral reef lagoonal ecosystem Christophe Cleguer1,2,3,4,*, Claire Garrigue3,4, Helene Marsh1 1College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia 2Harry Butler Institute, Centre for Sustainable Aquatic Ecosystems, Murdoch University, Murdoch, Western Australia 6150, Australia 3Opération Cétacés, Nouméa 98802, New Caledonia 4UMR ENTROPIE (IRD-Université de La Réunion-CNRS), 98800, New Caledonia ABSTRACT: Little is known about how the Vulnerable dugong Dugong dugon uses coral reef lagoons despite the importance of these habitats throughout much of its vast range. We used GPS satellite tracking systems to explore the space use of 12 dugongs at 3 locations in the coral reef lagoons of the main island of New Caledonia in the southwest Pacific: Cap Goulvain, Ouano and Nouméa. The movements of the tracked dugongs varied among individuals and all except one animal undertook large-scale movements (>15 km; mean [±SE] 37.7 ± 5.2 km) from their capture location (maximum waterway distance range: 13.8 to 72.9 km). The straight-line distances be - tween the furthest GPS locations during each animal’s tracking period ranged from 21.3 to 74.5 km. We identified areas used intensively by dugongs in all 3 study areas, some of which were areas where seagrass presence has not been verified, or where dugongs have not been observed during past aerial surveys. Dugongs spent most of their tracking time within the lagoons, with 99.4% of GPS locations found inside the barrier reef. Nonetheless, where the lagoon was narrow and confined, 3 tracked dugongs used the fore reef shelf outside the barrier reef in the open ocean to commute between bays. Our findings can inform conservation and management initiatives in New Caledonia as well as other countries within the dugong’s range which have similar habitat geomorphology but where dugongs occur in numbers too low to be tracked and are considered Critically Endangered. KEY WORDS: Dugong · Movement · Coral reef lagoons · GPS satellite technology · Conservation 1. INTRODUCTION cal coastal and island waters of some 40 countries from East Africa to Vanuatu. As the only strictly mar- Information on the space use of wildlife can help ine herbivorous mammal and a seagrass community their conservation (Cooke 2008, Fraser et al. 2018). specialist, the dugong is of high biodiversity value Critical habitats and space use tend to vary with the (Marsh et al. 2011). The dugong is listed as Vulnera- spatial structure of the landscape or seascape (Boyce ble to extinction at a global scale by the International et al. 2003, Mayor et al. 2007). Thus, it is important to Union for Conservation of Nature (Marsh & Sobtzick study how wildlife, particularly species with vast dis- 2019). However, its conservation prospects are vari- tribution ranges, use the various habitats within their able across its vast distribution range. Marsh et al. range (Mayor et al. 2009). (2011) consider the species to be at high risk of local The dugong Dugong dugon, the only surviving extinction in multiple parts of its range, including member of the family Dugongidae, is a broadly dis- several island groups with fringing coral reefs, such tributed species that occurs in tropical and subtropi- as Palau and the Nansei Islands south of Japan. © The authors 2020. Open Access under Creative Commons by *Corresponding author: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 168 Endang Species Res 43: 167–181, 2020 Marsh & Rathbun (1990) pioneered the use of satel- aimed to document the movement ecology of dugongs lite tracking for dugongs to document their move- in this environment to inform local management ini- ments and habitat use in North Queensland, Aus- tiatives and provide insight into how dugongs might tralia. That study and many others which followed use similar environments in other parts of their range. have shown that dugong movements in Australia are individualistic (e.g. Holley 2006, Sheppard et al. 2006, Gredzens et al. 2014, Cleguer et al. 2015a, 2. MATERIALS AND METHODS 2016a, Bayliss & Hutton 2017). For example, Shep- pard et al. (2006) found that while some of the 70 ani- 2.1. Study sites mals they tracked were sedentary (37% moved less than 15 km from their capture sites), others under- New Caledonia is located in the southwest Pacific took large scale movements (40% moved 15−100 km Ocean, some 1200 km east of Australia. The archipel- and 20% moved >100 km). ago has a subtropical climate moderated by the How dugongs use space has mostly been studied in south-easterly trade winds. The warm season is from Australia where the continental shelf is wide. In October to March, when tropical depressions and other parts of the dugong’s range such as Okinawa cyclones occur. After a brief transition, the cool sea- (Japan), Palau, Mayotte, Madagascar and New Cale- son (April to October), features cold fronts associated donia, small populations of dugongs often use nar- with polar low-pressure areas. The mean water tem- row coral reef lagoons ranging in width from a few to perature in the lagoons during this study was 26.3°C tens of kilometers. However, with the exception of a (range: 19.9−30.5°C; Varillon et al. 2020). The tides study by De Iongh et al. (1998) in Indonesia, there is are semi-diurnal and the tidal range, which reaches a lack of understanding of how dugongs use these up to 1.8 m, does not vary substantially diurnally or coral reef lagoons. In some regions the width of the seasonally (Bonvallot et al. 2012). lagoons and the tides may substantially restrict The lagoons that surround the main island of New access to seagrass habitats, especially those distrib- Caledonia sit on a shallow oceanic shelf ringed by a uted over shallow patch reefs and reef flats. barrier reef 1600 km long (Andréfouët et al. 2009), New Caledonia, a French archipelago located at one of the most diverse reef systems in the world the eastern edge of the dugong’s range in the south- (Andréfouët et al. 2004). At their widest, these west Pacific, supports a globally important dugong lagoons are up to 50 km wide, but they narrow to population (Garrigue et al. 2008, Cleguer et al. 2017). only 4 km wide on the mid-west coast. The lagoons A single baseline aerial survey of dugongs in 2003 vary from very shallow (<5 m on the mid-west coast) estimated a population of 2026 ± 553 (mean ± SE) to deep (>40 m) and channels can reach 80 m in individuals (Garrigue et al. 2008). Similar surveys depth at the reef passes near the barrier reef. conducted between 2008 and 2012 produced lower Reef diversity and known seagrass presence and estimates ranging between 426 ± 134 and 717 ± 171 extent is heterogeneous around the main island. A individuals (Cleguer et al. 2017, Hagihara et al. fore reef shelf stretches most of the length of the bar- 2018). It is impossible to determine whether the de - rier reef to the west of the main island and is gen - cline in estimates between 2003 and 2008 is due to a erally composed of spur and groove coral reef for - real decline in the population or is the result of con- mations (Andréfouët et al. 2004). Eleven species of founding effects of variation in environmental condi- seagrass from 6 genera belonging to the families tions, animal behaviour and sampling biases. Cymodoceaceae (Cymodocea, Halodule and Syrin - Using data collected from the aerial survey time se- go dium) and Hydrocharitaceae (Enhalus, Halophila ries, Cleguer et al. (2015b) identified areas of consis- and Thalassia) have been recorded (Hily et al. 2010). tently high dugong density around the main island of Georeferenced information on seagrass distribution New Caledonia. Most of these areas are not designated available at the spatial scale of our study is limited to as Marine Protected Areas, which restrict anthropogenic the maximum extent of shallow seagrasses (<5 m) activities (Cleguer et al. 2015a). The main threats to generated from Landsat imagery (Andréfouët et al. dugongs in New Caledonia include illegal take, by- 2010). Diffuse seagrasses are relatively abundant in catch in fishing gear, collisions with vessels and de - the intertidal zones of the west coast of the main gradation of seagrass habitats (Cleguer et al. 2017). island (S. Andréfouët pers. comm.). In the southwest- We explored the space use of dugongs in the coral ern lagoon, a deeper association of seagrass mead- reef lagoons of New Caledonia by deploying GPS ows (mean depth 11.2 m) represented a biomass of satellite tracking devices on 12 adult dugongs. We 31g ash-free dry weight m−2 (Garrigue 1995). Cleguer et al.: Movements of dugongs in coral reef lagoons 169 We selected 3 sites on the west coast of the main 2.2. Dugong capture and tracking unit island of New Caledonia: Cap Goulvain, Ouano and deployments Nouméa (Fig. 1). These sites were chosen because (1) they support consistently high dugong densities We used the rodeo technique developed by Marsh across seasons (Cleguer et al. 2015b) and thus pro- & Rathbun (1990) as detailed by Lanyon et al. (2006) vided the best chances to capture dugongs, and (2) to capture the dugongs. This technique requires a we wanted to investigate how dugongs use space in close pursuit of an individual dugong, preferably in a range of environments. The central western sector, clear, shallow waters to increase the likelihood of fol- which includes 2 of our sites (Cap Goulvain and lowing it as it moves through the water column.