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CURRENT STATE OF KNOWLEDGE April 2002

Photo: D. Yates

Dugongs live in the shallow waters of at least 37 Dugongs are not in imminent danger of disappearing but countries and territories around the world. Throughout it is likely that they will vanish from parts of their range. their range which runs from east Africa to Vanuatu The World Conservation Union (IUCN) has listed dugongs between about 26o north and south of the Equator, as vulnerable to extinction on a global scale because the dugongs are threatened by rising pollution from the land, numbers of dugongs worldwide appear to have declined coastal development, boat traffic, entanglement in fishing by at least 20% over the last 90 years (about three nets, and hunting and poaching for their meat and trophies. generations). (continued) were donated by Aboriginal or Torres Strait Newborns are about 1.2 metres long and weigh Dugongs have already disappeared from some Islander hunters from remote communities in about 30 kg. The calves suckle for 18 months or places including the waters off Mauritius,Taiwan, northern , as well as from Papua New longer. They never venture far from their mothers western Sri Lanka, the Maldives, Japan’s Guinea. From these autopsies, researchers and often ride above their backs. So far, only one Sakishima Shoto Islands, Hong Kong’s Pearl River learned about dugong anatomy, lifespan, orphaned calf has been successfully rehabilitated estuary, several islands in the Philippines and breeding and diet. in Australia. Dugongs are expensive to keep in parts of Cambodia and Vietnam. oceanaria because they suckle for so long and Dugongs grow to three metres long, can weigh their diet cannot be grown in captivity. Although dugongs are found in the waters of up to 400 kg and live for 70 years or longer. The many countries, nearly all of them except age of a dugong is estimated by counting Dugongs have few natural predators but Australia are developing nations with limited growth layers in its tusks, like measuring rings in , crocodiles and killer whales will feed capacity to contain impacts on dugongs a tree. The tusks erupt after puberty in males on young dugongs. within sustainable limits. Therefore, dugong and in a small proportion of older females. conservation world-wide is largely dependent on Australian initiatives. Their ears (which have no flaps or lobes) and Diet eyes are on the side of the head. Dugongs do Australia is home to most of the world’s dugongs not see very well but are believed to have acute Dugongs feed mainly on seagrass, but can which live in northern waters between Bay hearing within narrow sound thresholds. They supplement their vegetarian diet with in and in have sensitive bristles covering their upper lip invertebrate animals such as polychaete worms, . One of the reasons for nominating which they use to find and grasp seagrass. sea squirts and shellfish. the Great Barrier Reef as a World Heritage Area in 1981 was its importance as a feeding ground Dugongs generally surface to breathe after only for large populations of dugongs. a few minutes. Their paired nostrils are on the top of the head and have valves to stop water Dugongs are not considered under threat in most entering when they dive. parts of Australia, however, the number of dugongs has declined along the urban coast of Dugongs have flippers and tails that resemble Queensland. To protect dugongs, especially in the those of dolphins, but they lack a dorsal fin. Great Barrier Reef region, Dugong Protection Unlike dolphins which can often be individually Areas and Marine National Parks have been recognised from their physical characteristics, established along the east coast of Queensland. most dugongs are difficult to distinguish even Australia has a critical role in protecting these though they are marked by scars which are often Researchers from CRC Reef have undertaken extensive seagrass mapping surveys within unique marine mammals. made by the tusks of other dugongs. the Great Barrier Reef.

Dugong biology Breeding In the Great Barrier Reef region, dugongs feed mostly on small, delicate , especially Dugongs (Dugong dugon) are marine Groups of male dugongs follow a female when Halophila and Halodule, which are low in fibre, mammals in the Order Sirenia which are she is in oestrous (‘in heat’) and many mate high in nitrogen and easily digestible. Dugongs commonly called sea cows. There are only four with her, inflicting scars on the female’s back, can dig up whole seagrass plants including the living species of sea cow - three manatee species and on each other. roots. They do not favour lush seagrass meadows. (Trichechidae) found in the Atlantic region and one dugong (Dugongidae) in Australian tropical Females have their first calf when they are Often very little of their preferred food can be and subtropical waters. Sea cows are more closely between six and 17 years old and then produce seen on the seabed. In the Great Barrier Reef related to elephants than they are to other calves only once every 2.5–5 years. The female region, there are eight genera and 14 species of marine mammals such as whales or dolphins. will bear one calf after a pregnancy which lasts seagrass. The distribution of the seagrass about 14 months. depends on the availability of light and the type In Australia, scientists have learned a lot about of sediment. In areas of high turbidity where the the biology of dugongs by studying their water is murky, seagrasses are limited to the area carcasses. Researchers from University in Townsville collected specimens from dugongs that had been killed accidentally in fishing nets and in shark nets (set for the opp The bond between the protection of swimmers). Other dugong parts dugong cow and calf is strong. The calf suckles A, B. Cr from a nipple under each flipper. GBRMP Photo: Dugong feeding trails on the sea floor. Dugongs also use estuarine creeks and streams. sharks. Every two days, contractors check Of nine dugongs tracked by satellite in the equipment at a number of popular beaches in DPI Hinchinbrook area, six used mangrove-lined their region and record the catch, including any

Photo: creeks at some stage. The dugongs were found dugong by-catch. Analysis of the annual catch mostly within 600 metres of the creek mouth, per beach for the nets indicates that the numbers Dugongs seem to prefer but some travelled 2.7 km up creeks. Dugongs of dugongs caught declined from the inception small delicate travelled up to 10 km through one creek that of the program. The estimated rate of decline DPI Cairns seagrasses to rejoined the main channel. One dugong caught averaged about 8.7% per year. This is a decline dense older and

Photo: coarser ones. north of Cooktown travelled 15 km up a creek in of 97% of the initial catch rates over the 38-year this region. sampling period (1962–99). This decline provides an index of the change in dugong numbers from between the high and low watermark, but One dugong tracked in spent all causes in the regions where nets were seagrasses have been found more than 30 metres nearly three months in a tiny area where there deployed. The large declines reported are deep in the clear waters off the northern coast of was a strip of seagrass only a few metres wide. confirmed by anecdotal information. Aboriginal Cape York. Dugongs can dive to at least 39 metres Therefore, the total area of seagrass may not be elders consider that dugong numbers in the but spend most of their time in shallow water, a good indication of its value to dugongs. Other southern Great Barrier Reef World Heritage Area less than 10 metres deep. factors that influence seagrass quality, such as have been declining for decades. protein concentration or the ability to regenerate quickly, determine the value of a seagrass bed Since the mid 1980s, standardised aerial surveys Dugong populations to dugongs. to determine the patterns of dugong distribution and abundance have been conducted in many around Australia regions of Australia. Surveys in the Great Barrier Population changes Reef region have been conducted in two series: There appear to be two genetically distinct one along the remote coasts north of Cape groups of dugongs in Australian waters. One Historical accounts of dugong numbers off the Bedford near Cooktown and; in the more group ranges from Moreton Bay in southern Queensland coast are almost unbelievable today. populated coast south of Cooktown. Queensland to Western Australia. The other In his book ‘Queen of the Colonies’ published in lineage has a more restricted distribution ranging 1876, Ebenezer Thorne wrote: Ryan

from Moreton Bay to the Northern Territory. These G. two groups may represent separate invasions of “One of the fishermen of Wide Bay told the A, dugongs on to the Australian continental shelf. writer...he had seen a mob which appeared GBRMP to fill the water with their bodies. He

computed this school...to be half a mile Photo: Dugong movements wide and from three to four miles long...The writer’s boat once anchored in Dugongs can move large distances, travelling Hervey’s Bay, in one of those channels alone or with their calves in search of food. They through which the tide passes when appear to have a good memory of place because running off the flats. For between three and A dugong, clearly visible in shallow water satellite tracking shows that they return four hours there was a continuous stream hundreds of kilometres to specific locations. of dugong passing while the tide went out, which those in the boat could only liken to The remote coast was surveyed in 1984, 1985, Of the 29 dugongs tracked on the east coast of the rush of cattle out of a stockyard after a 1990, 1995 and 2000 using the same technique. Australia, more than half moved more than general muster...some thousands must have The number of dugongs did not change 80 km from the point of capture (and up to gone out with the tide” significantly during these surveys; this area 600 km). Aerial surveys also show large supports an estimated 10,000 dugongs and fluctuations in dugong numbers over long The best scientific indication of changes in 4,400 km2 of seagrass. This suggests that the stretches of coastline that can only be explained dugong numbers comes from data collected by dugong population is stable in the northern by movements of large numbers of dugongs. One the Queensland Shark Control Program – the Great Barrier Reef. However, the surveys showed of the suggested causes of these movements is program designed to make popular bathing changes in seagrass distribution and abundance. beaches in Queensland safe from shark attack. Nets have been deployed at popular beaches in eight locations along the Queensland coast between Cairns (17oS) and the Gold Coast (28oS) since 1962 to reduce the numbers of resident that the dugong distribution changed between or 1999, despite historical records of the region Why have dugongs surveys. The surveys in 1985, 1990 and 1995 supporting substantial Indigenous hunting in the indicated that Princess Charlotte Bay supported 1960s. Shark meshing data also indicate a huge declined in the southern between 37–56% of dugongs in the northern decline in dugong numbers in the Cairns region Great Barrier Reef? Great Barrier Reef region. The corresponding since the 1960s. proportion for 2000 was about 24%. The survey suggested that these dugongs had moved from Aerial surveys indicate that the numbers of People who lived in coastal north Queensland Princess Charlotte Bay to south of Cape Melville. dugong in the to Great Sandy Strait in the early part of the century have been region have fluctuated from about 2,200 in 1988, interviewed by researchers from James Cook In the southern Great Barrier Reef, the surveys to 800 in 1994, 1,650 in 1999 and 1,710 in 2001. University. They said that they noticed that also showed large-scale dugong movements there were fewer dugongs along the coast even and some decline. Estimates of the dugong In 1992, more than 1,000 km2 of seagrass were in the 1960s. population between Dunk Island and lost from Hervey Bay when there were two floods Bundaberg fluctuated from a and a cyclone within three weeks. The dugongs To maintain populations, at least 95% of adult minimum of 3,500 dugongs in 1986 in the region stopped breeding and many died of dugongs alive at the beginning of a year must to 1,700 animals in 1994 to about starvation (99 carcasses were recovered). Some still be alive 12 months later. The maximum 4,000 dugongs in 1999. The dugongs travelled up to 900 km and four sustainable mortality from all human impacts is numbers of dugongs counted carcasses were washed up south of Sydney. estimated to be about 1–2% of adult females between Cooktown and Dunk However, by 1993, there were more dugongs per year. If dugongs calve later and less often Island were insufficient to counted in Moreton Bay than had been seen in because they are not getting enough to eat, they estimate the population size any of the 28 previous surveys. This suggests that will produce fewer young which means that their with accuracy in 1986, 1992 some dugongs moved and survived. Studies from sustainable mortality as a result of human impact the Gulf of Carpentaria demonstrate that would be even less. seagrasses may take a decade to fully recover in areas subjected to changes caused by extreme While fishing has been blamed for dugong loss, forces of nature, such as cyclones. Most of the it is not the only, or necessarily the major seagrass in Hervey Bay has now recovered and activity to impact dugong populations. Natural dugongs have moved back into the area. dugong births and deaths, and extreme weather events can impact population movement and numbers. Hunting, modern farming practices, increasing boat traffic, and land clearing causing a change in the composition of river run-off, all have an influence.

Q UEENSLAND

Legend

Dugong Protection Area ‘A’ Dugong Protection Area ‘B’ Reefs and Shoals The boundaries on this map are indicative only. For specific details please contact the local Boating and Fisheries Patrol office. A

‘A’ Protection Areas are: ‘B’ Protection Areas are:

■ Hinchinbrook ■ Taylors Beach ■ ■ tesy of GBRMP Cleveland Bay Bowling Green Bay ■ Upstart Bay ■ Edgecumbe Bay ■ Newry Region ■ Repulse Bay ■ Ince Bay ■ Sand Bay

mation cour ■ Shoalwater Bay ■ Llewellyn Bay ■ Port Clinton ■ Clairview Region ■ Hervey Bay - Great ■ Rodds Bay

Base infor Sandy Strait Dugong Protection Aboriginal and Torres Areas provide quality seagrass Strait Islander issues Schluepmann habitat for dugongs. H.

Some Aboriginal people regard dugongs as a Photo: vital part of their Aboriginality. It is widely recognised that dugong meat and oil are among the most valuable traditional foods of coastal Most of the dugongs and their habitat on the In 1997, the Great Barrier Reef Ministerial Aborigines and Torres Strait Islanders in northern urban coasts of Queensland are in marine parks; Council decided that all nets should be replaced Australia. Hunting can be carried out under the Great Barrier Reef and the with drumlines unless the nets are preferable for permit in the Great Barrier Reef Marine Park associated Queensland Marine Parks in the Great reasons of human safety. A decision to replace all except in Preservation Zones. Barrier Reef region, the Hervey Bay Marine Park nets with baited lines may be controversial. and the Moreton Bay Marine Park. The distribution Some scientists and resource managers believe A large inshore Preservation Zone was and abundance of dugongs has also influenced that nets as well as lines are needed to keep the established by management agencies primarily to the placement of highly protected areas along numbers of inshore sharks low enough so that protect dugongs in the Far Northern Section of the remote areas of the Great Barrier Reef their risk of attacking people is acceptably low. the Park, south of Cape Melville. Following the Marine Park near Cape York. decline of the dugong in the southern Great Others consider that there is evidence that lines Barrier Reef, some traditional owners decided to In 1997, the Australian and Queensland are at least as effective as nets, and in places suspend dugong harvesting. There is also no governments agreed to several measures aimed with some species such as tiger sharks, are more hunting permitted south of Cooktown. The at arresting the decline of dugongs along the effective in minimising the risk of shark attacks Darumbal-Noolar Murree Aboriginal Corporation urban coast of Queensland. The most significant on bathers. They therefore consider that any by- for Land and Culture of Rockhampton have initiative was to establish a series of Dugong catch of marine mammals in shark nets is signed a formal agreement with the Great Barrier Protection Areas along the coastline, in which gill unacceptable in a World Heritage Area, given the Reef Marine Park Authority (GBRMPA). Other and mesh net fishing is restricted and, in the extremely low risk of a swimmer being attacked traditional owner groups have recently made Hinchinbrook Region, boat speeds are restricted. by a shark. historic declarations that it would be inappropriate for hunting to continue within their regions and Sixteen Dugong Protection Areas have now been hunting has been suspended until populations established along the Queensland coast using Future directions recover. Nonetheless, the interest of Aboriginal Queensland Nature Conservation legislation and and Torres Strait Islanders in dugongs transcends Queensland Fisheries legislation. In 1999, a ■ Dugong Protection Areas (DPAs) are an hunting and they seek involvement in all areas conservation plan for dugongs in Queensland important first step in the recovery of dugongs and aspects of their management. was implemented by the Environmental along the urban coast of Queensland. The Protection Agency. This plan further reinforced success of DPAs requires that there is no illegal the functions of Dugong Protection Areas. fishing within them. The DPAs must also Protecting dugongs continue to provide quality seagrass habitat for in Australia dugongs and be the preferred location for Shark nets most of them on the urban coast. In Australia, dugongs are not considered to be ■ Initiatives should be expanded to address all under serious threat throughout much of their Since 1962, shark nets (which have been used possible causes of dugong decline, especially range. Dugongs in Australia are not listed as at since the 1960s to protect bathers) have caught loss of habitat and habitat quality. risk of extinction under the Commonwealth at least 654 dugongs in Queensland, an average ■ Management regimes should be implemented Environment Protection and Biodiversity of 18 per year. Very few of these dugongs were for the urban coast of Queensland to minimise Conservation Act. However, the numbers of released alive. Following a review in 1992, many human impacts on dugongs in local regions. dugongs on the urban coast of Queensland have shark nets have been replaced with lines of ■ Indigenous people and commercial fishers declined as explained above and so, dugongs are baited hooks. should be encouraged to participate in the listed as vulnerable under the Nature management of dugongs throughout the Conservation Act in Queensland. Ten nets remain in the Great Barrier Reef region; coastal waters of Queensland. five at locations near Cairns and five near ■ Vessels should maintain a 25-knot speed limit Mackay. With the decline in numbers of dugongs and less than 10 knots in important dugong in the southern Great Barrier Reef and since the feeding areas (such as Hinchinbrook Dugong reorganisation of the netting program in 1992, Protection Area). fewer dugongs are being caught in Great Barrier Reef nets. Counting dugongs

One of the most efficient and reliable ways to study the distribution and abundance of dugongs in a population is to count them using aerial Ensuring the future of the surveys. These surveys were first used in the 1970s world’s reefs and an improved method established in the 1980s. CRC Reef is a knowledge-based Dugongs are counted at the same time by two Dugong aerial surveys are conducted partnership of coral reef managers, researchers seated on either side of a light along pre-defined transects. The researchers and industry. Its mission aircraft flies at a constant height and aircraft. Each observer watches a 200 metre-wide speed while two observers on either is to plan, fund and manage world- strip of sea on either side of the aircraft. The plane side search for dugongs in a defined leading science for the sustainable flies at a constant height (137 metres above sea strip of sea. use of the Great Barrier Reef World level) and speed (185 km/h) along pre-determined Heritage Area. transects which are perpendicular to the coast. CRC Reef is a joint venture between: The dugong counts are then used to estimate population sizes. The counts are corrected for perception bias (the proportion of dugongs seen in the transect but missed by observers) ■ Association of Marine Park and availability bias (the proportion of dugongs below the surface that are invisible due to Tourism Operators water turbidity). ■ Australian Institute of Researchers are working on improving the estimate of dugong numbers from aerial surveys. Marine Science Fibreglass models of dugongs have been used to measure the depths at which dugongs can be seen from the air in waters of different turbidity and sea state. Miniature computers have been ■ Great Barrier Reef Marine attached to the tails of 15 dugongs to measure the depths and times of 40,000 dives. This Park Authority allows scientists to estimate how much time dugongs are likely to be available to observers ■ during aerial surveys in waters of different turbidities, depths and sea states. Improved Great Barrier Reef information on the size of dugong populations should be available in 2002. Research Foundation

■ James Cook University

■ Queensland Department of Primary Industries

Satellite tracking ■ Queensland Seafood Industry Association Recent advances in technology, coupled with inventive science, have made it possible to track dugongs using satellites tags. The device is connected to a satellite transmitter which sends ■ Sunfish Queensland Inc. signals to polar orbiting weather satellites. With the incorporation of GPS technology, dugongs can now be located 24 hours per day to within a few metres of their actual position. This technology will provide new insights into how dugongs use seagrass beds and what For more information and constitutes good habitat for them. further reading, contact: .wwd.net.au

To tag a dugong, researchers in a small boat use the noise of the engine to move the dugong CRC Reef Research Centre Ltd to shallow water. They place a net over the dugong’s head and flippers, fit a belt-like device PO Box 772 containing a remote release to the dugong’s tail and then release the animal. When the Townsville 4810 Queensland Australia researchers want to release the belt from the dugong they have to get within 500 m of it and Email: [email protected]

then press a button on the release transmitter. The entire tagging apparatus then floats free. Website: www.reef.crc.org.au Design by WWd: www

Established and supported under the Australian Government’s This brochure was written by Dr Ivan Lawler (CRC Reef, James Cook University), Cooperative Professor Helene Marsh (CRC Reef, JCU), Ms Brenda McDonald (JCU) and Mr Tony Stokes (GBRMPA). Research Centres Program

Published by CRC Reef Research Centre Ltd