GREAT BARRIER REEF
// Outlook Report 2014
dolphins in Halifax Bay in 2011 and another in 2013 means the long-term viability of this population is at risk. There are similar concerns for Indo-Pacific humpback dolphins in Keppel Bay and Port Curtis where eight died of unknown causes in 2011. 211 It is likely that changes in the population’s size will not be detectable over a short time period, unless they are very high (greater than 20 per cent per year). This could mean local populations of the two species could decrease to very low levels before a decline is detected. 248 Another inshore species, the Indo-Pacific bottlenose dolphin, has similar life history traits to the Australian snubfin and Indo-Pacific humpback dolphins. 255,256 However, the Indo-Pacific bottlenose dolphin uses a wider range of habitats and may be more abundant, 255,256,257,258 though there is limited information on the population status within the Region. The other 15 dolphin species in the Region are likely to be less susceptible to pressure. They generally occur further offshore and have less conservative life history traits. For example, the common bottlenose dolphin usually associate in large groups, display low site fidelity, and forage on large prey aggregations. Many of the species are rarely seen or only intermittently reported as stranded. 259
While the northern dugong population remains stable, the population south of Cooktown has declined substantially.
The Region is home to a globally significant population of dugongs and provides essential habitat and connectivity between populations in the Torres Strait and the waters off south-east Queensland. 260 The Region’s population is recognised as contributing to its outstanding universal value. 23 Monitoring of dugong populations in the Region began in 1985 (Figure 2.15). The dugong population in northern areas of the Region is considered in good condition and stable with no evidence of a major decline. 261,262,263,264 The southern, or urban coast, dugong population (south of Cooktown) has declined over many decades. Modelling indicates this occurred at an average rate of 8.7 per cent per year between 1962 and 1999, with most of the decline occurring in the early years. 268 The Outlook Report 2009 reported that the southern population was thought to have stabilised. However, indirect impacts of declining seagrass abundance (see Section 2.3.4 and Section 2.4.2) — the primary food resource for dugongs — combined with direct humanrelated impacts such as drowning in commercial fishing set mesh nets, boat strike, marine debris and illegal poaching has caused the southern dugong population to decline again. 267,269 In 2011, there was an estimated population of only 600 animals between the Daintree River and the Region’s southern boundary 3,267, compared with an estimate of around 2000 from the previous survey in 2005267,270. This estimate is a standardised relative index of dugong abundance and is less than the actual abundance. This is the lowest population estimate for this area since surveys began in 1987267 and coincided with significant seagrass losses (Section 2.3.4). The decline is likely to be explained by animals moving out of the survey area to seagrass meadows elsewhere and increased mortality. 266,267 In 2011, an unprecedented number of stranded dugongs were found, reported and verified along the Region’s coast (Figure 2.16).
Figure 2.15 Dugong populations, 1985–2011
In 2009, the Region’s southern dugong population was thought to have stabilised after a long history of decline. However, recent surveys indicate further decline, principally as a result of deterioration in seagrass meadows. Surveys indicate the population north of Cooktown is stable. Some of the variation between surveys is due to animals moving between and within survey regions. The error bars represent standard error. Source: Marsh et al. (various years) 3,262,264,265,266
and Sobtzick et al. 2012267
Figure 2.16 Dugong strandings, 2000–2013