Dugong distribution and abundance in the northern Great Barrier Reef Marine Park - November 2000

The waters of northern Australia are internationally recognised as the stronghold of the dugong (Dugong dugon) which is listed as vulnerable to extinction by the IUCN (2000). Significant populations persist in Australian waters, and dugongs are specifically cited as one of the World Heritage values of the Great Barrier Reef World Heritage Area. Much of the information used to manage dugong populations in this region has been provided by aerial surveys using standardised techniques. We report here on aerial surveys conducted in the following regions in November 2000 to assess the status of the dugong: (1) the Northern Great Barrier Reef Region between Hunter Point (11°15’S — south of Cape York) and Cape Bedford (15°30’S — near Cooktown); and, (2) the region between Cape Bedford and 17°25’S (near Innisfail)

The status of the dugong in the southern Great Barrier Reef Marine Park

Australia has international responsibilities for the management of dugongs in the Great Barrier Reef Region. One of the World Heritage values of the Region is that it "provides major feeding grounds for large populations of the endangered species Dugong dugon" (Great Barrier Reef Marine Park Authority (GBRMPA) 1981, p. 7). In addition, the dugong has high biodiversity value as the only species in the Family Dugongidiae and one of only four species in the Order Sirenia. AlI four extant species of Sirenian are listed as vulnerable to extinction by the IUCN (IUCN 1990). In 1986 and 1987, Marsh and Saalfeld (1990 a) counted dugongs, dolphins and sea t1\l11es during an aerial survey over an area of some 39,000 km' in the inshore waters of the Great Barrier Reef Marine Park south of Cape Bedford. Survey-and-taxon specific correction factors were used to correct for perception bias (the proportion of animals visible in the transect which are missed by observers) and to standardise for availability bias (the prop0l1ion of animals that are invisible due to water turbidity)

Assessing the risk of boat strike on dugongs (Dugong dugon) at Burrum Heads, Queensland, Australia

The risk of mortality due to boat strike is increasingly being recognized as an important management issue for marine wildlife, including Dugongs Dugong dugan. Ameliorating the effects of boat strike requires assessment of how that risk varies over the management area. This is dependent on the distribution and movements of both Dugongs and boats and on the physical characteristics of the area, particularly depth. In this study we assess these features for a small community that is dependent on tourism centred around recreational fishing and which is home to a regionally significant Dugong population. During one of the most popular holiday times, boats accessing the favoured fishing site pass directly through the core area of Dugong activity. Our data show that boat strike risk to Dugongs can be lowered significantly with minimal imposition on boaters. Boaters can avoid the area of highest risk by travelling around it in deeper water. However, this straightforward solution is only possible because of the restricted spatial scale of Dugong activity and the proximity of a deepwater channel enabling boaters to easily avoid shallow areas where boat strike risk is highest

Diet selection in marsupial folivores of Eucalyptus: the role of plant secondary metabolites

Past efforts to explain feeding by eucalypt folivores focussed on three groups of plant secondary metabolites – phenolics, tannins and terpenes. It is yet unkownn if these compounds consistently limit the food available to marsupial folivores or whether they provide a better explanation of food choice or habitat quality than do nutrient concentrations alone. Recently, the formylated phloroglucinolc compounds were shown to defend many eucalypts against the marsupial browsers. This discovery has enhanced our understanding of the interaction between marsupial folivores and Eucalyptus while elaborating its complexity. Some informal subgenera of Eucalyptus, such as Monocalyptus, appear to lack formylated phloroglucinol compounds while others (e.g. Symphyomyrtus) contain a wide variety. Of most importance ecologically, is the huge variation in formylated phloroglucinol compounds between individual trees within species, even within a small area. This makes it impossible to generalize about “food trees” across species. The concentrations of formylated phloroglucinol compounds and terpenes in foliage are positively correlated. It appears that folivores use smell to gauge terpene concentrations and hence that of formylated phloroglucinol compounds, and thus avoid the foliage of some trees and feed from others. Thereafter, a physiological feedback mechanism, involving the emetic system, keeps the dose of formylated phloroglucinol compounds below a threshold. This understanding of formylated phloroglucinol compounds makes it pertinent to re-evaluate the roles of other plant secondary metabolites, particularly tannins, in marsupial feeding. However, the greatest challenge ahead is to extrapolate the results of feeding experiments with captive animals to predicaments of wild marsupial folivores. Near infrared spectroscopy provides a way of measuring formylated phloroglucinol compounds concentrations in samples from hundreds of trees. Preliminary research suggests that it may be possible to measure formylated phloroglucinol compounds at the landscape scale with remote sensing

Vulnerability of marine mammals in the Great Barrier Reef to climate change

Townsvill

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

This technical report consists of the reports of two of the studies commissioned by the Great Barrier Reef Marine Park Authority: 1. Shark control records hindcast serious decline in dugong numbers off the urban coast of Queensland by Helene Marsh, Glenn De'ath, Neil Gribble and Baden Lane. 2. Dugong distribution and abundance in the southern Great Barrier Reef Marine Park and Hervey Bay: results of an aerial survey in October-December 1999 by Helene Marsh and Ivan Lawler