| Citation | Summary | Whales and Dolphins |

Environmental Status: Marine Mammals

The marine mammals of the Great Barrier Reef include dugongs, whales and dolphins. This chapter is divided into two sections, the first concerning dugongs and the second cetaceans (whales, dolphins and porpoises).


Dugongs

Condition

Dugongs (or sea cows) are marine mammals that are specialised for feeding on seagrasses. They inhabit shallow, tropical waters throughout the Indo-Pacific region with most of the world’s population of dugongs found in northern Australia between Shark Bay in Western Australia and Moreton Bay in Queensland. Dugongs have a very low reproductive rate having one calf at intervals of 2.5-7 years. The maximum likely rate of increase of a dugong population, if all the females in the population are breeding at their maximum potential, is estimated at 5% per year. Thus, in order for numbers to be maintained, adult survivorship must be higher than 95% each year. The maximum sustainable mortality rate of adult females killed by human activities is around 1 or 2%. For other facts on dugongs, see the Dugong Information Kit (GBRMPA 2002).

Worldwide, the dugong is listed under the 2003 IUCN - the World Conservation Union - Red List of Threatened Animals as being ‘vulnerable to extinction’ - criteria A1cd. This means that this species is at 'high risk of extinction in the medium-term future'. The Dugong Action Plan (Marsh et al. 2001b) provides an overview of dugong status, threatening processes and conservation initiatives from around the world. In Australia, dugongs are listed as ‘vulnerable to extinction’ under the Queensland Government’s Nature Conservation Act 1992 and are both a listed marine species and a listed migratory species under the Australian Government’s Environment Protection and Biodiversity Conservation Act 1999.

Aerial surveys of dugong populations commissioned by the Great Barrier Reef Marine Park Authority (GBRMPA) have been carried out by James Cook University since 1984. For the purposes of these dugong surveys, the Great Barrier Reef has been divided into the regions north of Cooktown and south of Cooktown. North of Cooktown, surveys were carried out in 1985, 1990, 1995 and 2000 (Marsh and Lawler 2002). The dugong population estimates did not vary significantly at each of the four counts, ranging from 7,843 (± 1155 standard error) to 10,176 (± 1575 standard error) dugongs.

However, surveys south of Cooktown in 1986-1987, 1992, and 1994 documented a distinct decline in the dugong population from an estimated 3,480 (± 460) to an estimated 1,680 (± 240) dugongs within eight years. The results of the 1999 surveys (3993 ± 644) showed that numbers in the southern area were back at 1986-87 levels probably as a result of dugongs moving into the survey area from other parts of their range in Australia. Nonetheless an analysis of dugongs caught unintentionally in shark nets at bathing beaches indicates that the catch per unit effort in the nets has fallen to about 3% of the initial catch rates. If the assumptions underlying this analysis are correct, it confirms anecdotal information and the beliefs of Aboriginal elders that the dugong population along the urban coast of Queensland has declined drastically since the 1960s (Marsh et al. 2001a).

More than 50 dugongs have been tracked (from 2 weeks to more than a year) using satellites on the east coast of Queensland (from Cooktown, Hinchinbrook/Cleveland Bay, Shoalwater Bay and Hervey Bay). Many of the dugongs moved greater than 80km, and some moved up to 800km.
 

For further information click on the following reports:

  • Research Publication #77 Dugong distribution and abundance in the northern Great Barrier Reef Marine Park -November 2000. [Adobe Acrobat Format 1405.42KB]
  • Research Publication #70 Shark control records hindcast serious decline in dugong numbers off the Urban Coast of Queensland; and Dugong distribution and abundance in the southern Great Barrier Reef Marine Park and Hervey Bay: results of an aerial survey in October – December 1999. [Adobe Acrobat Format 2305.91KB]
  • Research Publication #67 Dugongs, Boats, Dolphins and Turtles in the Townsville-Cardwell Region and Recommendations for a Boat Traffic Management Plan for the Hinchinbrook Dugong Protection Area.

Pressure

There are several sources of pressure on dugong populations from human related threats. These include:

  • Boat strike and disturbance from boats, ships and other motorised machines
  • Habitat loss from coastal development and declining water quality
  • Incidental catch in mesh net fishing and shark control programs
  • Traditional hunting

Pressure: boat strike and disturbance

Collisions between boats and dugongs are one of the causes of dugong deaths related to human activities. Dugongs may be seriously injured by boat hulls if struck at high speed resulting in fractures and damage to internal organs. Cuts caused by propellers may lacerate organs killing the animal outright, or lead to serious infection or disability that may also result in death. The Queensland Parks and Wildlife Service (QPWS) Strandings Database recorded three dugongs being struck in the Great Barrier Reef between 1996 and 2001. There are also concerns that frequent boat activity can displace dugongs from their preferred habitats, although this is likely to be a less serious problem than the mortality resulting from boat strikes.

Pressure: habitat loss

Habitat loss and degradation is an impact that can have disastrous effects on dugong populations. In particular, seagrass habitats are important as seagrasses are the dugong’s primary food. The most significant example of such an impact occurred just outside the Great Barrier Reef World Heritage Area (GBRWHA) in Hervey Bay. More than 1,000 km2 of seagrasses were lost in 1992-93. Although the exact cause of the seagrass death was uncertain, it is likely to have been caused by a combination of effects from a tropical cyclone and highly turbid water from flooding and coastal run-off. Population estimates indicate that the number of dugongs in the area fell from 2,200 in 1988 to 800 in 1994. 

Seagrass beds may also be affected by dredging activities and terrestrial run-off. Dredging can stir up large amounts of sediment that smother seagrasses nearby, and nutrient and sediment rich run-off can result in algal blooms and increased turbidity that can reduce the amount of light reaching seagrasses. However, it should be noted that large scale seagrass die-offs such as the Hervey Bay event have not been documented from the GBRMP since the 1970s. Indeed, repeat seagrass surveys at the two localities with the highest dugong densities in the southern Great Barrier Reef, Hinchinbrook Island and Shoalwater Bay, have indicated that seagrass areas have been stable in recent years.

Seagrass beds may also be disturbed by trawling. Trawlers generally avoid areas of dense seagrass habitat as the seagrass clogs the nets, however, areas of sparse` seagrass growth may still be affected.

For more information on seagrass status and management activities, see Environmental Status – Water quality and Environmental Status – Seagrasses.

Pressure: incidental catch

As air breathing mammals, dugongs can drown within minutes of becoming entangled in a net if they are unable to reach the surface to breath. Commercial mesh netting is considered a significant cause of dugong mortality and there is clear evidence of dugongs killed by mesh nets from the Strandings Database. However, net deaths are virtually never reported directly, and minimal information is available on the actual numbers of dugongs killed in this way. For more information about the inshore net fishery, see Management status – Fisheries.

Dugongs also risk becoming entangled in mesh nets deployed as part of the Queensland Shark Control Program. Between 1962 and 1992, 837 dugongs were killed in Shark Control Program mesh nets on the urban coast of Queensland  (Queensland Department of Primary Industries 1992). The Shark Control Program was reviewed in 1992 and 1998 and very few dugongs are now killed in shark nets in the Great Barrier Reef region (see Response).

Pressure: traditional hunting

Dugongs are an important element of the traditional diet of Australia's Indigenous peoples, particularly for celebrations and family gatherings. A recent survey of Indigenous fishing in northern Australia estimated that over a twelve month period in 2000-01, 1,293 dugongs were taken by Indigenous hunters in north Queensland waters excluding the Torres Strait. The GBRMPA  has reservations about this survey methodology because the harvest is extrapolated from a very small proportion of the catch. Recent modelling by scientists indicates that the current level of dugong hunting in some parts of the Great Barrier Reef is unsustainable.

Response

Response: protected species listings

The dugong in Australia is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES) throughout its range. This listing recognises the vulnerable status of the dugong by IUCN, the World Conservation Union at a global scale. In Australia, dugongs are a listed species under the Environment Protection and Biodiversity Conservation Act 1999 meaning that it is an offence to kill, injure, take, trade, keep, or move dugongs in the GBRMP without a permit.In Queensland, dugongs are listed as ‘Vulnerable Wildlife’ under the Nature Conservation Act 1992 which prohibits the take, use or keeping of dugongs without a permit or specific exemption. The Cairns and Whitsunday Plans of Management also prohibit interference with dugongs.

Response: boat strike and strandings

A tri-agency (Queensland Parks and Wildlife Service, Department of Primary Industries and Fisheries, GBRMPA) approach is enabling close examination of dugong carcasses to establish the causes of mortality and obtain further information. The GBRMPA website enables the general public to subscribe to an E-mail Listserver that posts notices about each stranding soon after they are investigated.

Concern over vessel impacts on dugongs resulted in voluntary transit lanes being trialled in the Hinchinbrook region and an education campaign has been launched to encourage boaters to “go slow” in areas frequented by dugongs. The GBRMPA has also released a set of Best Environmental Practices for dugong-watching

Response: habitat loss

Seagrasses are protected under the Great Barrier Reef Marine Park Act 1975 and Queensland Fisheries Act 1994. Further, under the newGreat Barrier Reef Marine Park Zoning Plan 2003, some 24% of known shallow water seagrass beds are included in highly protected ‘green zones’ that prohibit extractive activities. Outside of the GBRMP, many seagrass areas are protected as Fish Habitats Areas under the Queensland Fisheries Act 1994.

The GBRMPA is addressing the potential impacts of increased runoff of terrestrial sediments and nutrients through the Reef Water Quality Protection Plan. The Plan aims to halt and reverse the declining water quality in the Great Barrier Reef within 10 years.

Detailed information on how the GBRMPA is addressing pressure on seagrass habitats is included in the following chapters:

Response: incidental catch

Dugong Protection Areas (DPA’s) were introduced in 1997 as an initiative of the Great Barrier Reef Ministerial Council. In total, 16 Dugong Protection Areas were declared, all south of Cooktown in the region where the dugong population had declined. The Dugong Protection Areas were declared in places where there are many dugongs and/or important seagrass habitat. Mesh netting is restricted in Dugong Protection Areas and prohibited in the two most important dugong habitats south of Cooktown: Shoalwater Bay and Hinchinbrook.  The reduction in mesh netting in areas of high dugong numbers is an important step towards assisting the recovery of the dugong population south of Cooktown.

The management arrangements for the commercial net fishery are set out in the Queensland Fisheries Act 1994 and Fisheries Regulation 1995. The Queensland Fisheries Service has indicated that resources will be directed to develop an East Coast Inshore Finfish Fishery Management Plan to address a variety of issues including incidental catch of non target species.

Since 1991, the Queensland Department of Primary Industries and Fisheries has conducted research on the effectiveness of acoustic alarms or ‘pingers’ to alert marine mammals such as dugongs to the presence of nets.  These alarms have been successful in reducing the incidental capture of some species of cetaceans in gill nets in other countries. Unfortunately, experiments testing the effects of acoustic alarms on dugong behaviour indicate that they are unlikely to reduce the numbers of dugongs caught in nets.For more information on the management of the inshore gillnet fishery, see Management status – fisheries and Environmental status – fishes.

Concern over catch of dugongs, as well as dolphins and turtles, in nets set in the Queensland Shark Control Program led to a review of the program in 1992 that resulted in many nets being replaced with baited hooks known as “drum lines”. Nets are now only deployed at ten locations within the GBRWHA, five near Cairns and five near Mackay. This reduced the number of dugongs caught by the Shark Control Program to less than 4.3 dugongs per year between 1992 and 1995 (Gribble et al. 1998). Shark control contractors record incidental catch of marine mammals and turtles, and the release of live animals is now a priority. Published records show that 17% of dugongs caught between 1992 and 1995 were released alive, giving an average mortality of about four dugongs per year (Gribble et al. 1998). More recently, evidence from the QPWS stranding reports indicate generally 1 to 2 dugongs are caught and killed each year in the program.

Response: traditional hunting

The hunting of dugongs and turtles is permitted within the GBRMP, however this activity is restricted to Aboriginal peoples and Torres Strait Islanders. A new system for managing traditional use of marine resources in the GBRMP started on 1 July 2004 as part of the rezoning of the GBRMP through the Representative Areas Program. Some traditional uses of marine resources will continue to be ‘as of right’, while others will be conducted in accordance with a permit or Traditional Owner-developed and GBRMPA-accredited ‘Traditional Use of Marine Resources Agreement’ (see Management status – Indigenous connections with the Great Barrier Reef).  The intent of these Agreements is to ensure that marine resources such as dugongs are used sustainably. Some Aboriginal and Torres Strait Islander communities have made voluntary formal and informal decisions not to hunt, as a contribution to addressing the decline in dugong numbers in the southern Great Barrier Reef.

Response: research and monitoring

Because of concern over dugong populations, extensive monitoring through aerial surveys and other research is continuing. Research into the behaviour, ecology and conservation management of dugongs is also being undertaken through the Cooperative Research Centre for the Great Barrier Reef World Heritage Area. Research into the genetics of dugong populations is ongoing and in 1999 the GBRMPA collaborated with community groups, researchers, stakeholders and management agencies to develop a Dugong Research Strategy. The Strategy includes a list of research priorities organised into four categories,

  • Maintaining or enhancing dugong numbers.
  • Minimising impacts of management decisions on affected groups.
  • Development of cooperative management arrangements.
  • Enhancing the effectiveness of dugong protection measures.

Dugongs are also listed as a high priority in the GBRMPA’s Research Priorities and Species Conservation Program.
 

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