Dugong dugon (Muller 1776) and Its Habitat in Coastal Areas and Small Islands of East Java Province, Indonesia

Dugong dugon, an endangered marine mammal is listed the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Dugongs are classified as herbivorous mammals that live in the shallows associated with seagrass beds. The objectives of this study are (1) to collect data on dugong encounters in East Java, both direct encounters and literature studies; and (2) to analyze seagrass meadows that are potentially dugong grazing habitats in East Java. This study was conducted from January to July 2023 in the coastal area of East Java. Dugong and seagrass data, which were descriptively analyzed, were obtained from the literature, questionnaire interview, and by direct observation. Distribution of dugongs in East Java is known to be in the southeastern side of Banyuwangi, Situbondo, Sumenep, Lamongan, and Bawean Island. Direct encounters with live and dead dugongs in East Java have been recorded in several locations, including Bawean Island. Seagrass beds in East Java can be found on the coastal area of Lamongan, Bawean Island - Gresik, Sumenep, Bangkalan, Situbondo, Banyuwangi, Malang, and Pacitan. The seagrass species found in these eight areas are: E. acoroides, T. hemprichii, C. modocea rotundata, C. serrulata, H. pinifolia, H. uninervis, H. decipiens, H. ovalis, H. minor, S. iseotifolium, and T. ciliatum. Although, dugong status is fully protected in Indonesia, and its distribution is limited, further steps are needed to protect dugongs and their food habitats. Marine Protected Area is one of the policies that could be recommended to protect dugongs and their habitat.


Introduction
Dugongs are herbivorous mammals that live scattered in the shallow waters of Indonesia.Duyung (local name in Indonesia), is one of 35 species of marine mammals that is protected in Indonesia, and is listed on the Red List of IUCN, and in Appendix 1 of the Convention on International Trade in Endangered Species of Wild Fauna and Flora or CITES [1].In Indonesia, dugongs have been protected through regulation Law No. 5 of 1990 concerning the Conservation of Biological Resources and Ecosystems, Government Regulation No. 7 of 1999 concerning the Preservation of Plant and Animal Species [2] [3].
Dugong is found in the tropical and subtropical coasts of 40 countries, including Australia, Arabian Coast, Persian Gulf, Iran, China, India, Bahrain, Thailand, and Indonesia [1], [4], [5], [6], [7], [8], [9], [10].The first rough estimate of the global population of dugong reached nearly 30,000 was published in 1979 report by the Institute of Cetacean Research [1].The IUCN, however, reports that the remaining dugong population is now decreasing.Dugongs are highly susceptible to anthropogenic disturbance due to their long lifespan of 70 years or more and a slow reproductive rate.Global populations have been subjected to overexploitation primarily due to direct fishing for their meat, skins, and oil, and also due to loss of habitat, including siltation of seagrass beds [11].
Distribution of dugongs in Indonesia can be found in several regions including Papua, North Sulawesi, South Sulawesi, Central Sulawesi, Maluku, the south coast of East Java, to Sumatra [1], [2], [9], [12].Information on distribution, number, and behavior of dugongs in Indonesia is rare, therefore the total population is uncertain.Most of the data was obtained from interviews and surveys with snorkeling and others were incidentally recorded.Dugongs, which are always in very small numbers, are scattered throughout Indonesian waters.In the 1970s, the dugong population in Indonesia was estimated at around 10,000.In 1994, the population was estimated to be only 1,000 individuals [12], [13].
One of the areas in Indonesia where dugongs are known to exist is coastal area of East Java Waters.Encounters with dugongs in East Java in the last ten years have occurred in Kepuh Teluk Village, Bangkalan Regency (2019) and Bawean Island, and Gresik Regency in 2021, 2022, and 2023 [14].These encounters with the dugong occurred alive, stranded alive, and stranded dead.This was presumably due to a decrease in environmental quality, availability of their food habitat, and human activities that threaten the existence of dugongs.These unfavorable conditions likely contributed to the population decline of dugongs in East Java waters.Hence, the purpose of this paper is (1) to collect data on dugong encounters, includes the number of individuals encountered and their morphometric morphology in the East Java region, including both direct encounters and literature studies and (2) to analyze seagrass meadows that have the opportunity to become feed habitats in East Java.

Methods
This study was conducted from January to July 2023 according to data availability in the coastal areas of East Java.Dugong's data were obtained from literature study methods, questionnaire interviews, and direct observation [13].Information on the distribution of dugongs in Indonesia was collected from several scientific literatures [12][13] [2], which described their distribution in the form of maps.Direct observation was directly conduct includes the number of individuals encountered and their morphometric morphology.Specifically on stranded and dead dugongs measurements of body length and circumference were taken.Meanwhile, data collection on the distribution of seagrass species in East Java was conducted by literature study [15].Data on dugongs and seagrasses as food habitats were descriptively analysed.

Distribution of Dugong In East Java
The distribution of dugongs in Indonesia was reported three times, in 2012, 2016, and 2019 [2], [12], [13].This map was created based on public reports regarding sighting of dugongs, died stranded dugongs, and dugongs which are entangled in nets (Figure 1).Referring to the dugong distribution map in Indonesia, which is the result of previous literature review, it is known that distribution of dugongs in East Java is on the southeastern side of Banyuwangi, Situbondo, Sumenep, Lamongan, and Bawean Island.Dugongs are marine mammals that possess a "home range" even though they also travel for instance, the dugong home range is around 4km 2 -43km 2 , on Mali Beach and Sika Island, Alor Regency, ).The length of the first stranded dugong was 220cm with a body width of 80cm, while the second one was found to have a length of 200cm and a body width of 76cm.Both were found in a pathetic condition, with many wounds all over their bodies which showed signs of swelling.Dead and almost inflated dugongs have also been reported in the Persian Gulf, which are suspected to be due to habitat degradation and climate change [10].This value of body length and circumference indicates that the stranded dead dugong is classified as an adult, as stated in some literature related to the life cycle of dugongs.

A B
Dugongs have a long life span of between 40 and 70 years, however, the female only has the opportunity to get pregnant and give birth three to seven times throughout her life.Even though the chance of a dugong baby being born alive is very high, this marine mammal only gives birth to one baby in the birth process [17].The dugong gestation period lasts 12 to 14 months, then the baby dugongs are born and can immediately swim.Newborn dugongs are pale cream in color with a body length of about 1 -1.5 meters and weigh 20 -40 kg.Furthermore, the dugong cubs will be breastfed and cared for 14-18 months until they reach adulthood [17], [18].As adults, dugong cubs will leave their mother, which gives birth again three to seven years later so a female dugong can only give birth a few times throughout her life.
Morphologically, all parts of the dugong's body are covered with short hairs, thick, hard skin with a smooth surface, and on the chest, the dugong has fins 35-45 cm long.In young dugongs, this fin functions as a propulsion while it acts as a rudder for adults.The tail of the dugong is in the form of a homo cercal that functions as a propellant [18].Male and female dugongs have the same morphology (monomorphic), hence it is difficult to distinguish between male and female dugongs.On the ventral side, from the tail to the head, three holes/slits are visible, namely the anal canal, genital slit, and the umbilicus or navel, and the distance between the slit and the anus distinguishes males from females.For example, the female dugong has a closer distance between the genital slit and the anus than the male dugong.In simple terms, the dugong cycle can be explained by the process of mating, baby, rearing, growing up, and growing old (Figure 3).

Figure 3. Life cycle of Dugong dugon
Sighting dugongs were found in April and May 2023, both of which were found in the waters between Daun Village and Noko Selayar Island.The first sighting happened while a dugong was exploring alone (Figure 4A).However, the dugong swam quickly away from the ship, which is normal behaviour of the dugong when disturbed by human activities, including ship traffic.Ship engines are known to have acoustic sound frequencies that interfere with dugong communication [19], [20].The second dugong sighting occurred in May 2023 (Figure 4B), obtained from drone camera footage, taken over the waters of Daun Village, Bawean Island.The activity that was caught on camera at that time was surfacing or staying on the surface.This dugong activity was also found in the Andaman Islands -India, but in a herd consisting of adults and children.The dugong herd was reportedly consisted of six to 13 individuals, with about one to two cubs [5].A herd of dugongs was also reported to be found in large numbers, with more than 50 individuals near Hawar Island -Bahrein [6].Dugongs are often found in groups, and communicate.These mammals communicate using acoustic signals, making sounds in their various activities.The sounds dugongs make are often used to mark and defend territory, communicate with children, or attract the opposite sex.The sounds produced by dugongs are known to consist of several types, including chirp, bark, and trill [21].These three sounds have different frequencies.Chirp sounds are similar to a bird's song, with a frequenciezy of 3000-7500 Hz, an intensity of 0.002-0.01W/m2, and a duration of 520 ms.Their bark is small with frequency of 1000-1200 Hz with an intensity of 0.001-0.004W/m2 and a duration of 108 ms.Meanwhile, The trill sounds like the resonant sound of an object, with frequenciezy 250-500 Hz, intensities 0.04-0.18W/m2, and a duration of 84 ms.
The vocalization patterns of dugongs in nature and in captivity have similarities and differences.This comparative study was conducted and showed that the transition from chirp to chirp is most often made by wild dugongs in Thailand compared to captive ones in the Philippines [22].The transition frequency of dugong calls in the wild and dugong calls in captivity is similar.Meanwhile, the trill often appears in the middle and last part of vocal patterns sequence of the two dugongs.Similarities between geographically and genetically separated areas imply converged vocalization patterns [22].The dugongs have certain preferences for spatial and temporal patterns, which are closely related to their communication patterns.This communication pattern with the acoustic signals is strongly influenced by environmental factors and human anthropogenic activities.Each region has its own threats to dugong communication patterns.However, the distribution of boat traffic poses a threat to dugongs both spatially and temporally [20].Various types of boats pass through the shallow waters where dugongs live, and it is likely that their sound frequencies overlap with the dugong's communication frequencies, which interfere with their communications.One of the dugong's responses, when a ship passes nearby, is to swim away and to a deeper place.Even dugongs that are eating will stop their activities when a ship passes near their nesting habitats [19].

Distribution of Seagrass Bed In East Java
Seagrasses play a crucial role in providing habitat and food for endangered species such as dugongs.The temporal variability in the size of the dugong population is associated with changes in the distribution of their seagrass food, indicating the significance of seagrass in their habitat.There are six known daily activities of dugongs, namely: overturning, surfacing, exploring, resting, socializing, and IOP Publishing doi:10.1088/1755-1315/1328/1/0120036 grazing [2], [11], [18], [23], [24].Overturning is a dugong activity which involves swimming by by turning its body upside down and rubbing its body on the bottom of the water, aiming to clean the parasites on its body.Surfacing is a dugong activity for respiration, mainly taking in air, for a few seconds.Exploring is the dugong's activity of moving from one place to another, which involves swimming at slow, medium, and fast speeds.
The dugong rests on the water surface and at the bottom of the substrate, often taking a break during the day at 10.00-13.00 and at night.Socialization is the activity of dugongs interacting with other dugongs, but this is difficult to observe in Indonesia because dugongs do not live in large groups.Grazing is a dugong activity that is carried out in the seagrass beds many times a day.These mammals spend up to 10 hours grazing, with a duration of time per activity of 5 minutes.[11] reported that dugongs graze in their home range, which is a seagrass bed generally composed of Halophila ovalis, Halodule uninervis, Syringodium isoetifolium and Cymodocea serrulate [11], [23], [24], [25], [26].
Seagrass ecosystems are found almost all over coastal areas and small islands in Indonesia.The status of the seagrass ecosystem in Indonesia is currently at a moderate level, with the national average cover being 34% [27].In fact, seagrass beds in Indonesia in 2015 -2021 experienced a pattern of decreasing area of around 0.4 Ha per year.A decrease in the extent and quality of the seagrass ecosystem will greatly affect its ecological function as a primary producer and habitat for organisms in shallow seas, including dugongs.The distribution of seagrass in Indonesia was last reported in 2022 by the Indonesian seagrass data guardian (Figure 5), nevertheless information on the distribution and types of seagrass on the East Java coast is limited.[15].The distribution of the types of seagrass beds in East Java is illustrated in Figure 6, which also depicts the seagrass species preferred by the dugong.Three areas with a high diversity of seagrass species are Bawean Island -Gresik, Baluran National Park -Situbondo, and Sumenep Coastal.
Dugongs generally often eat seagrass species that have smooth leaf morphology and are not too dense.However, it is possible that dugongs also consume all types of seagrass [11], [24].Types of seagrass that have high nitrogen content, low fiber, and high calories generally have pioneer characteristics with a low level of resistance (colonizing) from disturbance but can recover quickly [25], [28].Characteristics of this type are often found in the intertidal and subtidal areas of Halodule sp. and Halophila sp.Dugongs are often found in these seagrass species at a depth range of less than 5 meters during the day and at night during high tide conditions.Based on observations that have been made in several areas in Indonesia, dugongs will regularly return to the same area in search of food [25], [29].Seven types of seagrass with the potential as food for dugongs include C. rotundata, C. serrulata, E. acoroides, H. pinifolia, H. uninervis, H. ovalis, and T. hemprichii [26], [29], [30].

Conclusions & Suggestions
Dugongs are a type of marine mammal that is almost extinct but have full protected status in Indonesia.They can still be found in several Indonesian waters, including in East Java, although in small numbers.Encounters with dugongs in East Java have been reported in six districts.Furthermore, the seagrass meadow ecosystem, which is the feeding habitat for dugong feed is known to be distributed in eight districts in East Java, and it is possible to find dugongs as an association bota in the ecosystem.Although, the dugong has full protected status in Indonesia, its population continues to decline, therefore further steps are required to protect the dugong and its food habitat, including in East Java.Therefore, it is necessary to implement policies for establishing Marine Protected Areas in areas where dugong populations are detected in order to sustainably maintain anconserve dugong species and genetics.

Acknowledgment
This research could be conducted with the assistance of Ir.Sukandar, MP, who is the supervisor of the Community Monitoring Group along the coastal area of East Java.Hijau Daun Monitoring Community Group, which has assisted with monitoring activities for dugongs and seagrass, as well as handling stranded dugongs.
1328 (2024) 012003 IOP Publishing doi:10.1088/1755-1315/1328/1/012003 2 which has been updated by the Ministry of Environment and Forestry No. P20 of 2018 concerning Wild Plants and Animals in conjunction with Ministry of Environment and Forestry Regulation No. P92 of 2018

Figure 1 .
Figure 1.Distribution of dugong encounters in Indonesia Stranded dugongs were found in February and March 2023 on the southwest side of Bawean Island (Figure.2A and 2B).The length of the first stranded dugong was 220cm with a body width of 80cm, while the second one was found to have a length of 200cm and a body width of 76cm.Both were found in a pathetic condition, with many wounds all over their bodies which showed signs of swelling.Dead and almost inflated dugongs have also been reported in the Persian Gulf, which are suspected to be due to habitat degradation and climate change[10].This value of body length and circumference indicates that the stranded dead dugong is classified as an adult, as stated in some literature related to the life cycle of dugongs.