Dugongs (
Dugong dugon) are large long-lived (about 70 y) marine mammals. An adult dugong weighs around 400 kg and measures up to 3 m in length. The closest living relatives to dugongs are the three species of manatee: West Indian manatee
Manatus latirostris, the Amazonian manatee
Trichechus inunguis and the West African manatee
Trichechus senegalensis. Dugongs are also distantly related to elephants and hyraxes.
Dugongs are streamlined, fast over short distances and are superbly adapted for a fully marine pelagic lifestyle. Their dolphin-like tail flukes provide propulsion whilst their front flippers help them to steer. Female dugongs feed their calves from nipples located under their front flippers. There is no obvious sexual dimorphism in terms of body size and shape, however the sexes can be determined by looking at the distance between the genital and anal slits: in females these are almost contiguous, whilst in males these are further apart. Adult males and very old female dugongs have large emergent tusks.
For more details regarding dugongs and our research, see
Dugong Biology
Dugong Distribution, Abundance, and Status
Dugongs in Southern Queensland
Moreton Bay Dugongs
Tagging and Sampling Wild Dugongs
Dugong Resight Histories
Dugong Biology
| Dugongs are seagrass specialists feeding on only a few species of tropical seagrasses in any part of their range. When they feed, they usually dig up the entire seagrass plant if the seagrasses are small, e.g. Halophila ovalis and Halodule uninervis, leaving feeding trails through the seagrass bed. When feeding on longer-leaved seagrasses such as Syringodium isoetifolium, dugongs ingest the leaves only. |
 |
 |
| Halophila ovalis: dugong's favourite food |
Feeding trail |
 |
 |
| Feeding dugong |
| The head and mouthparts of the dugong are unusual. The strangely- shaped skull of the dugong has a prominent down-turned anterior region so that the mouth is located ventrally. External features of the mouth include a large disc-shaped rostrum and strong prehensile lips. Dugongs feel for seagrasses in muddy waters using extra-sensitive hairs on the rostral disc, and then grasp and uproot seagrasses using their lips. The cheekteeth (premolars and molars) of the dugong are small, soft and peg-like and become largely non-functional as a dugong ages. Dugongs rely on large internal mouthpads to ingest and macerate seagrasses. Dugongs are able to ingest huge quantities of seagrass during a single dive- they create feeding trails of up to 8 m in length and up to 20 cm width with removal of >70% of seagrass during dives of about 1 minute. Rather than stopping to chew, dugongs choose seagrasses that are low in fibre and break up easily as they are pulled into and through the mouth. |
 |
 |
| Dugong head showing rostral disc and prehensile lips |
| Like most other marine mammals, dugongs are long-lived, give birth to one calf at a time and the females invest a lot of time and energy into each offspring. However, the breeding cycle of the dugong is probably protracted compared to almost all other marine mammals. In most parts of their range, dugongs reach sexual maturity in their teens (13-17 y for females) and then mate and give birth every 5-7 years. In comparison, manatees have calves every 2-3 years. We think that the slow growth and low and variable breeding rate of the dugong is probably due to the dugong's narrow and nutrient-poor seagrass diet. We have evidence that the metabolic rate of the dugong may be quite high compared to a manatee so that a dugong may have high nutrient and energy requirements that are difficult to meet. |
 |
| Dugong skull |
 |
| Dissected head of dugong showing positions of cheekteeth and horny pads |
Dugong Distribution, Abundance, and Status
| Dugongs are found throughout the Indo-Pacific region in tropical and subtropical waters. Over the past century, populations of the dugong have shown marked declines throughout their range. These population declines have been attributed to seagrass habitat loss, incidental mortality in nets, traditional hunting and more recently to boat strike in urbanised waters. The dugong is currently listed as vulnerable to extinction by the World Conservation Union (IUCN 2001).
Australia is one of the last strongholds for dugongs in the world with a conservative estimate of >100,000 dugongs in the waters of northern Australia and Torres Strait. Within their Australian range there appear to be several geographically-distinct populations from Moreton Bay on the east coast through the northern waters to Shark Bay on the west coast.
|
 |
 |
| Herd of dugongs |
Dugong drowned in net |
 |
| Boat strike victim |
Dugongs In Southern Queensland
 |
In southern Queensland, it has been suggested that there may have been a 95% decline in dugong populations over the past 50 years. This decline appears to have occurred in the more developed and urbanised coast of southern Queensland. Within this area, there are three significant dugong 'populations' in Moreton, Hervey and Shoalwater Bays.
We are studying these dugong populations through mark-recapture population studies. This research yields data pertaining to individuals (including reproductive patterns and growth rates), populations (including adult survivorship, age structure, recruitment rates), and social structure (including intra-population genetics and mating strategies). Life history parameters obtained from this study will be used in management plans for sub-tropical dugong populations.
On the map at left, the arrows indicate from south to north: Moreton Bay, Hervey Bay, and Shoalwater Bay.
|
Moreton Bay Dugongs
 |
A large resident population of about 850 dugongs lives in the relatively clear waters of eastern Moreton Bay. Dugongs in this area feed in herds of 10-300 individuals, moving up onto the shallow seagrass beds at high tide and off into deeper adjacent waters as the tide ebbs. We are studying the population dynamics of this accessible population.
This is the first hands-on and long-term mark-recapture program for dugongs in the world. The UQ Dugong Team has captured more than 500 dugongs representing about 400 individual dugongs in Moreton Bay since 2001. We capture dugongs using the 'rodeo' technique which involves leaping out of a boat and grasping the dugong firmly around the peduncle region. The dugong is held at the surface for about 5 minutes whilst measurements are made, and samples and photographs taken.
|
 |
 |
| Seagrass beds in eastern Moreton Bay |
Arial shot of small dugong herd in Moreton Bay |
 |
 |
| Dugong held at surface |
Tagging and Sampling Wild Dugongs
 Because most dugongs look alike, we apply tags in order to identify them at later recaptures. We use a system of multiple tags since at this stage we are not certain how long different types of tags will last. For each captured dugong, we apply a uniquely-numbered titanium turtle tag to the tail fluke and a microchip PIT tag to the shoulder region. We also take a small notch out of the trailing edge of the fluke (a 'cookie') using a cattle ear notcher: this gives us an additional physical marker, but also a tissue sample for stable isotope analysis. A small skin scraping from the dorsum is used for genetic analysis. We are using DNA profiles at 26 microsatellite loci to routinely identify individuals, assign paternity, construct pedigrees, detect population structuring and estimate rates of physical tag loss.
A series of photographs of each dugong allows us to record any distinguishing features (e.g. scars or old injury) which may be useful in identifying an individual.
In addition to tagging a dugong, we measure it and collect a number of samples at each capture. Body measurements include body length and a series of girth measurements to assess body condition of the animal, i.e., how fat it is. We also sex the dugong then take a small faecal sample to check levels of reproductive hormones to determine reproductive status. If a dugong has unusual pathology, appropriate samples are also taken.
View a video of the team tagging and sampling a dugong.
Please note: This video file has been compressed for download viewing, and should open automatically in Windows Media Player on a PC. It is best viewed at set (100%) resolution; viewing in larger or 'full screen' resolution will result in a poor picture. To view on a Mac computer, a suitable viewing program should be installed; Windows Media Player for Mac may be downloaded from Microsoft.
This video , "Reef Dreams" was produced by Iguana Films, and they have kindly made the segment available to the website for research and educational purposes only (not for commercial use or screening).
|
 |
 |
Dugong flukes showing position of
turtle tag (LHS)and 'cookie' notch (RHS) |
Flukes with old scars |
 |
 |
 |
| |
Recaptured dugong with turtle tags |
|
 |
 |
| Tagged dugong swimming away |
 |
| Measuring a dugong |
 |
 |
| Male dugong |
Female dugong |
Dugong Resight Histories
We now have substantial numbers of dugongs that have been caught in consecutive years. All dugongs have individual ID numbers and have been named to make it easier to keep track of individuals. At recapture, dugongs are measured so that growth rates can be determined, sex is confirmed and a small skin biopsy confirms genetic identity. Although turtle tags have been retained by some dugongs since they were first applied. i.e., for 4-5 years so far, in some cases, turtle tags are lost. In these cases, a new turtle tag is applied and identity of the individual relies on combination of gene-tag and photos.
This project is a long term one which will yield data on growth and life history of wild dugongs in Moreton Bay. Recent expansion of this mark-recapture program to dugongs elsewhere in Australia (e.g. Hervey and Shoalwater Bays) will allow us to examine population structure, relatedness and migration over regional scales.
 |
| Examples of resight histories for individual dugongs |
The mark-recapture program has expanded recently to include the dugong populations in the more northern Hervey and Shoalwater Bays. These bays hold the nearest dugong populations to Moreton Bay. At this stage animals in these areas are not captured as part of the program. Instead, a small tissue sample from the dorsum of the dugong is collected remotely from the boat using a biopsy implement attached to a long pole. Through DNA analysis and genetic mark-recapture, we are examining structure and size of these populations, and relatedness and migration between populations over regional scales.
 |
 |
| Preparing to remotely biopsy a dugong from the boat |
Small skin biopsy being taken from a surfacing dugong |
 |
Sea World Research & Rescue Foundation has provided logistic support to the
Hervey and Shoalwater Bay sampling programs |
Dugong faecal samples (for DNA, hormone and microbial/diet analyses) are also collected opportunistically in Hervey and Shoalwater Bays. They can be found either free-floating amongst feeding herds of dugongs or at low tide on the exposed seagrass banks where herds were feeding during the previous high tide.
 |
| Low tide faecal collection |
 |
 |
| Collecting faeces from the water surface |
A fresh dugong poo |