8. Resilience

Urban coast dugongs are those found along the coast of Queensland, between Cooktown and the southern Region. Dugongs are seagrass community specialists and are generally sighted in the vicinity of seagrass meadows.²¹²³ Urban dugong populations belong to two distinct breeding units, separated by a genetic break in the Whitsunday Islands region. It is not known if individuals of these populations cross between these two genetic units ⁵¹⁸ but movement has been inferred from aerial surveys.⁵¹⁹ 

Direct human impacts that kill adult animals are dugongs’ greatest threat.^141,1904 These include incidental entanglement in fishing gear, vessel strike and illegal and legal harvest. The impact of legal harvest and illegal poaching on dugong populations remains a knowledge gap. Extreme weather events, such as prolonged or heavy rain, floods, marine heat waves, algal blooms and cyclones can indirectly affect dugong populations by reducing food availability, which in turn can increase adult mortality, reduce fecundity, delay breeding and lead to changes in dugong movement habits.²¹²⁴

Dugongs feed mainly on seagrasses,²¹²³ making them susceptible to indirect impacts that affect the extent and community composition of their seagrass habitat. The frequency of extreme weather events is increasing over time due to climate change. Loss of seagrass can exacerbate the anthropogenic pressures directly affecting dugongs.²¹²⁵

Management

Dugongs are listed as Vulnerable in the IUCN Red List.¹³⁵⁴ They are recognised in the Statement of Outstanding Universal Value for the Great Barrier Reef World Heritage Area, as are seagrass meadows, which are primary feeding grounds for dugongs. Dugongs are designated a matter of national environmental significance as a migratory and a protected marine species under the EPBC Act. 

The Action Plan for Australian Mammals 2012 has a list of information needs for dugongs.²¹²⁶  Local-scale information is collected by Indigenous rangers and the Queensland Parks and Wildlife Service in the marine wildlife strandings database, StrandNet, which records numbers of stranded and injured animals through time. The Queensland Department of Agriculture and Fisheries collects data on interactions between dugongs and fishing equipment via inspection of commercial logbooks and data on incidental interactions with the Queensland Shark Control Program (Section 5.4.3). Information on bycatch, hunting and poaching is still lacking.

Further initiatives to reduce direct threats to dugongs include fishery-wide cameras being installed on boats for validation of data and scrutiny of current practices. Additionally, new and continuing agreements with Traditional Owners support sustainable traditional use, research and monitoring of the Region’s dugong populations.²¹²⁷

Despite the collective effort to monitor dugong populations in the Region, there is considerable uncertainty in spatial estimates of populations,⁵²⁰ primarily due to poor detectability by aerial surveys of dugongs in deep water and under different environmental conditions. Dugong abundance estimates in Australia were recalculated in 2019 using improved methods.^{2128 2129,2130} Using drones provides the potential to conduct repeated surveys and collect long-term information at local scales.^1904,2131 There may be increasing opportunities for involvement of First Nations rangers on vessel-based surveys. Monitoring changes in the density of dugong feeding trails can also inform population trend estimates.²¹²⁸

Evidence for recovery or decline

Declines of dugong populations along the urban coast of Queensland have been estimated based on changes in the catch per unit effort of dugong bycatch in a government shark control program since the 1960s.²¹³² Dugongs have been monitored along the coast of Queensland using standardised aerial surveys for estimating long-term distribution and abundance since the 1980s. Monitoring is also a requirement under the objectives of the Reef 2050 Plan. It is estimated that the current size of the urban coast dugong population is small compared to pre-European numbers and may never recover.²¹²⁸ 

Between 2005 and 2022, the lowest density of urban coast dugongs was recorded in 2011, following floods and cyclones in the 2010–11 summer.⁵²² Record numbers of dugong strandings occurred during that period. Numbers recovered by 2016, and fewer strandings have been reported since 2011, likely due to the recovery of the seagrass food resource. Another post-flood decline in seagrass occurred in the intertidal areas of south-east Queensland in the 2021–22 monitoring year.¹⁴⁵ The life history traits of dugongs, such as long lifespan and late maturity, contribute to their slow recovery rate even under good conditions.

The most recent aerial surveys, conducted in November and December 2022 from Mission Beach to the Queensland–New South Wales border, estimated an overall long-term decline in Great Barrier Reef urban coast dugongs of 2.3 per cent per year since 2005.⁵²² Previously, it was estimated as declining at a rate of 4 per cent per year from 2005 to 2016. The current dugong population in the urban coast of the Region is estimated to be around 2124 individuals, based on the Mission Beach to Bundaberg surveys. This is the lowest population estimate across all surveyed regions.⁵²²

There are spatial differences in reported population trends. Hervey Bay had an estimated decline of 5.7 per cent per year.⁵²² Decline is occurring throughout the southern section of the Region, corresponding to seagrass areas that were lost in the 2022 floods in the Burnett Mary region.¹⁴⁹ However, the number of dugongs in Bowling Green Bay increased, and north of Hinchinbrook near Cardwell recorded its highest numbers since 2005.⁵²² The proportion of new calves in the population is a measure of population health and resilience, and in 2022 this measure was lower for the urban coast than in previous years. Despite Australia having the largest dugong population in the world, the outlook for the southern Region is poor.²¹²⁸

Trend estimates can be confounded by temporary emigration between sites. Large-scale movements of dugongs are stochastic. Many individuals are relatively sedentary, while others may travel hundreds of kilometres. Large-scale movements may be driven by limiting foraging resources, fluctuations in water temperature or exploratory behaviour. Group movements are known to occur in response to regional loss of food.²¹²⁴ The diversity in movement patterns dugongs exhibit may be indicative of their adaptability to short-term changes, such as loss of seagrass meadows,²¹²⁴ and they highlight the importance of population connectivity. Resilience of populations following habitat loss relies on dugongs having alternative areas to forage.²¹³³

Dugong populations depend on seagrass meadows, and their recovery hinges upon reducing direct and indirect threats. Resilience continues to be influenced by interactions between anthropogenic impacts and climate change. The potential impacts of future coastal development, increases in fishing and recreational use of the Marine Park can further affect the already threatened coastal dugong populations.