Title

Long-term trends in dugong numbers — Great Barrier Reef-wide

Objective

To monitor temporal changes in the distribution and relative abundance of dugongs (and sea turtles and dolphins) in the Great Barrier Reef region at a regional scale, by continuing the aerial survey program initiated in the mid 1980s and with the aim of surveying each region at five-year intervals.

Relevance

A time series of standardised dugong population estimates is required to determine regional scale trends in distribution and abundance, the status of populations and whether or not management is working.

Feasibility

Methods to estimate the distribution and abundance of dugongs at regional scales using aerial survey have been developed by researchers at James Cook University and extensively applied in the Great Barrier Reef, other parts of the dugong's range in Australia, and overseas.

Methodology

Aerial surveys are the only technique available to obtain quantitative information on dugong population size. Correction factors have been developed to standardise for availability bias (dugongs that are not available due to water turbidity) and correct for perception bias (dugongs that are visible but missed by observers). Trend analysis indicates that the optimum time between regional surveys is five years. The value of aerial surveys will increase as the time series gets longer.

Previous surveys of the Great Barrier Reef region have been conducted in two series: (a) Cape Bedford to Cape York (next survey scheduled for 2000), and (b) Hervey Bay to Cape Bedford (next survey scheduled for 1999). In future, it would be advantageous to use two aerial survey crews in two aircraft simultaneously for each survey to maximise the likelihood of completing the survey in excellent weather conditions. There would also be some merit in overlapping the survey areas to provide information on the likelihood of mass movement of dugongs between the survey regions. (Genetic information suggests that such mass movement is unlikely). The suggested new regions are: (a) Bowen to Cape York; (b) Hervey Bay to Cape Bedford. This would mean that the Bowen–Cape Bedford region was surveyed in successive years.

Approximate cost

$80 000 per survey assuming survey regions are: (a) Cape Bedford to Cape York, and (b) Hervey Bay to Cape Bedford. If the survey regions are altered as suggested above the cost of each survey would increase by an estimated 40%.

Time required

Ongoing. Additional information every five years within six months of survey.