Informing dugong conservation at several spatial and temporal scales in New Caledonia
Other Publication ResearchOnline@JCUAbstract
Comprehensive, up-to-date spatial information on species distributions and threatening processes can enhance the identification of sites for conservation and management action. Such information is often incomplete or simply unavailable at a scale that can inform real-world decision making because the cost and capacity needed for collecting reliable information are high especially when targeting species that occupy large ranges. Obtaining data to inform conservation at the appropriate spatial scale is of particular importance for species that occupy large ranges. The dugong (Dugong dugon) is a seagrass specialist and marine mammal that occurs over 130,000km of coastline in the Indo-West-Pacific. The dugong attracts global conservation attention because it is listed as vulnerable (IUCN Red List) and is increasingly exposed to multiple anthropogenic hazards in most of its range. There are many regions within the dugong's range where the likelihood of survival of the species is unknown. Collecting spatial-ecological information on the dugong in these regions can inform and optimize the effectiveness of regional and national conservation and management initiatives. The island-archipelago of New Caledonia is located in the Oceania region at the eastern edge of the dugong's range. The conservation status of the dugong in this region is unknown. The presence of the charismatic dugong in the lagoons of New Caledonia was an explicit reason for the World Heritage listing of some of the lagoons. No conservation actions have been implemented in New Caledonia to ensure the maintenance of the dugong stock except for the legislation that restricts dugong harvesting despite the species' high biodiversity, cultural and traditional value. The goal of my thesis was to build an evidence-base to enhance the conservation and management of dugongs in New Caledonia at several spatial and temporal scales and enhance understanding of dugong ecology in tropical coral reef environments by: 1. Assessing the temporal changes in the dugong population size and the capacity of the current marine protected areas (MPAs) to protect dugongs at the scale of New Caledonia. 2. Investigating the spatial ecology of dugongs in the coral reef lagoons of New Caledonia by studying their movement patterns and habitat use at local scales. 3. Integrating scientific research conducted on dugongs as part of this thesis to inform decisions relating to dugong conservation and management regionally and internationally. A single baseline aerial survey of dugongs in New Caledonia in 2003 estimated a population of 2026 (± SE = 553) individuals. A second similar survey in 2008 produced a lower estimate of 606 (± SE = 200) individuals, leading to concerns that the dugong population was experiencing a decline. I conducted four additional surveys in 2011 and 2012 with the objectives of updating information on the current size of the dugong population in New Caledonia and investigating evidence of decline in the population. The abundance estimates obtained from my four surveys ranged from 649 (± SE = 195) to 1227 (± SE = 296) dugongs. These results were not significantly different to the 2008 estimate but were significantly lower than the 2003 estimate. I concluded that the confounding effects of variation in environmental conditions, animal behaviour and sampling biases likely played a key role in the variation of the dugong population size estimates as I could not find any evidence external to the surveys that the dugong population had declined between 2003 and 2008 or that temporary migration was likely to have occurred. I used the data obtained from the time series of aerial surveys to develop a spatially-explicit model of dugong distribution and relative density. This model enabled me to determine the distribution of dugongs at the scale of the main island of New Caledonia over nearly a decade of monitoring, and to detect key dugong habitats. Dugongs were not explicitly considered in the design of the network of marine protected areas (MPAs) in New Caledonia. Thus any representation of important dugong areas in the MPA network is incidental. I used the spatially-explicit model of dugong distribution and relative density to retrospectively assess the capacity of the New Caledonia MPA network to protect dugongs from anthropogenic hazards. I quantified the amount of overlap between dugong relative density units and each type of MPA that was managed at the time of the study. I found that most of the important dugong areas in New Caledonia had a low coverage from the MPAs that provide high levels of restriction of anthropogenic activities. I identified several important dugong areas along the west and the north-east coast that were not covered by MPAs and should be considered in future conservation and management plans. The spatial mismatch between MPAs and dugong distribution was likely caused by weaknesses in the planning process. I provided guidance on how these shortcomings can be overcome for marine species of conservation concern in New Caledonia and other regions. The lack of consideration of marine mammals in conservation tools such as MPAs often stems from their highly mobile nature and dynamic movement patterns and the difficulty of defining their specific habitat needs due to lack of knowledge. Information on the dugong's use of space among key habitats and the scale of these movements has been comprehensively studied only in Australian waters where the environment differs from the lagoons of New Caledonia. I used satellite tracking technology to document the use of space by dugongs in the lagoons of New Caledonia. I developed a method of safely and quickly capturing dugongs in coral reef habitats and satellite–tracked 12 adult dugongs in three different regions of the west coast of New Caledonia. Animals displayed individualistic movement patterns. Their extent of movement was large relative to the size of the main island, and some individuals crossed jurisdictional boundaries. Three dugongs exited the lagoon and used the fore reef shelf (i.e., flattened coral reef area, located between the fore reef crest and deep open ocean waters) as corridor to transit from one bay to another. All tracked dugongs returned to their capture location. Home-range analyses showed that the range and core areas used by dugongs reflected the width of the lagoons. The home-range and core areas of dugongs did not differ between day and night. I investigated the habitat use of dugongs at a local scale at Cap Goulvain to enhance understanding of seasonal changes in abundance and habitat use of dugongs in coral reef environments and to provide spatially-explicit data to help local conservation decisions in a key dugong conservation value area. Access to seagrass resources is restricted by tides and the geomorphology of habitats and small size of the lagoon restrict dugongs' space use. I used data obtained from fine-scale dedicated dugong aerial surveys conducted every two weeks over 18 months at low and high tide to determine the seasonal and tidal changes in the number of dugongs and their use of a range of habitats in Cap Goulvain. I then compared the resultant dataset with the temporal changes in water temperature inside and outside the lagoon in this region. I found that more dugongs were sighted during the cool season than during the warm season in Cap Goulvain. At high tide, dugongs were expectedly sighted over the intertidal seagrass meadows in higher proportion than in any other monitored habitats during both seasons. As tides restricted access to the intertidal seagrass meadows there was a seasonal change in the use of other non-seagrass coral reef habitats: during the cool season, a higher proportion of dugongs was sighted outside the lagoon on the fore reef shelf than in any other habitat inside the lagoon; during the warm season the use of the fore reef shelf was less pronounced and dugongs were sighted in higher proportion inside the lagoon in the channels surrounding the intertidal seagrasses. Behavioural thermoregulation is a plausible explanation for the changes in the number of dugongs and the use of the fore reef shelf in Cap Goulvain during the cool season. Further investigation is required to assess the effect of other external factors including the temporal changes in the availability and quality of seagrass and abundance of sharks. Dugong aggregations (i.e., group of ≥ 10 animals) were observed inside the lagoon of Cap Goulvain during the warm season and outside the lagoon during the cool season. I used aerial and underwater footage of the dugong herds located outside the lagoon to explore the behaviour of dugongs in the herds. I found that the dugongs forming the aggregations were resting and no social behaviour other than calves feeding from their mother's teats was identified. The likely causes of dugong aggregations in this habitat include access to warm water, the number of dugongs present in the region at the time, the size of the fore reef shelf, the distance to inshore seagrass resources, and the risk of predation from sharks. These results demonstrated that both seagrass and non-seagrass habitats are important for dugongs and need to be included in future conservation and management programs in New Caledonia as well as other tropical coral reef regions. My thesis provided opportunities to enhance the conservation and management of dugongs in New Caledonia and new insights into the spatial ecology of dugongs in coral reef environments. Future management would be enhanced by considering the important dugong habitats and corridors identified in my research and should be coordinated at an ecological scale relevant to the dugong to be effective. Given the high cultural value of the dugong to the peoples of New Caledonia, communities should be consulted about their desire to participate in community-based management. In addition, ongoing education and communication programs should be continued especially in regions where illegal hunting may occur. Future research should be directed at understanding why illegal hunting occurs in New Caledonia and how compliance with the law could be increased. Further investigating the fine-scale interaction between seagrasses and dugongs in New Caledonia would also greatly enhance our understanding of dugong and seagrass ecology in tropical lagoons and coral reefs more generically.
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228
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10.25903/49ja-s792