Two James Cook University studies commissioned by the Great Barrier Reef Marine Park Authority shed new light on historical and current dugong numbers on the southern Great Barrier Reef and southeast Queensland coast. The studies complement each other with the first report providing a long-term context for interpretation of the second.

In the first report, a 38-year data set (1962-1999) collected by the Queensland Shark Control Program (QSCP) , administered by the Queensland Department of Primary Industries and Fisheries, was analysed to assess trends in dugong numbers between Cairns and the Gold Coast. Because regular aerial surveys of dugong numbers in the area only commenced in 1986/1987, it was important to take advantage of the information provided by the QSCP records.

The QSCP analysis showed that the number of dugongs caught in shark nets at shark contract areas between latitudes 17^o (near Cairns) and 28^o S (near the Gold Coast) has declined significantly since the inception of the QSCP in 1962. The estimated rate of decline averaged 8.7 per cent each year for dugongs caught per beach per year from the 31 beaches in six localities. Thus, by 1999 the bycatch of dugong in the nets was 3.1 per cent of the initial catch rate in 1962, over the 38 year sampling period (1962-99). If dugong catches in shark nets are a reliable index of dugong numbers, and if the depletions occurred at regional rather than local scales, the dugong population in the Great Barrier Reef would have been only a small fraction of current population estimates for the area.

The reliability of the analysis as an estimate of a general decline in the dugong populations from Cairns south, depends upon assumptions that: (1) the catch of dugongs was dependent on dugong population density in the contract area, (2) dugongs did not learn to avoid the nets, and (3) dugongs had not been alienated from the contract areas by increased human use of the beaches. The first two potentially confounding factors are likely and there is no data to reject or support the third factor. At the very least, the netting data suggest a substantial depletion in dugong numbers from Cooktown south since the early 1960s. This result accords with anecdotal reports by long-term residents including Indigenous peoples of a decline in dugong numbers.

Dugong numbers in the Great Barrier Reef along the urban coast of Queensland have fallen by 97 per cent since the 1960s. The results of aerial surveys indicate that the dugong population south of Cooktown is fluctuating at a level much lower than in the 1960s. It is too soon to say whether dugong numbers south of Cooktown are still declining, or increasing, or what rate these declines or increases may be occurring.

Dugong numbers in the Great Barrier Reef along the urban coast of Queensland have fallen by 97 per cent since the 1960s. The results of aerial surveys indicate that the dugong population south of Cooktown is fluctuating at a level much lower than in the 1960s. It is too soon to say whether dugong numbers south of Cooktown are still declining, or increasing, or what rate these declines or increases may be occurring.

Aerial surveys have been conducted since mid 1986/87 at approximately five year intervals (1992,1994,1999,2005) to monitor the status of the dugong on the Queensland coast south of Cooktown. The interim results of the 2005 aerial survey to estimate dugong population level have been received. The results of this survey show that the numbers of dugongs along the urban coast of the Great Barrier Reef have stabilised, but at a level (3700 ± 400) that is still less than five per cent of the estimated population size in the 1960s. The greatest proportion of dugongs sighted in the 2005 survey occurred in Dugong Protection Areas, in particular in the Shoalwater Bay, Cardwell/Hinchinbrook, and Cleveland to Upstart Bay areas. Because the current population remains a fraction of its estimated size in the 1960s, the implications of these latest aerial survey results for future management include the need to continue to reduce human-related mortality to as close to zero as possible, particularly in the area south of Cooktown.

The increase is unlikely to be explainable solely by changes in dugong sighting conditions. It is also not possible for the increase since 1994 to be solely the result of reproduction because the species cannot breed that rapidly (see Marsh and Lawler 2001 report). The most plausible explanation for most of the increase observed is movement of substantial numbers of dugongs into the survey area, probably from the area north of Cooktown.