Movement Patterns and Habitat Usage of Shark Bay Dugongs - Thesis

The 'chase and catch' procedure was used in this study to capture dugongs in Shark Bay to attach 18 remote tracking tags at locations within the Shark Bay World Heritage Property (see thumbnail). Of the 18 tags, eight were PTT satellite tags, eight were GPS data logger tags, and two were combination PTT/GPS tags capable of both transmitting and logging. All units incorporated a VHF radio transmitter on its own frequency to enable each unit to be tracked at sea.

(for full technical descriptions of the tags see Chapter 2 of thesis)

To assess fine scale habitat structure and identify the composition, density and biomass of seagrass forage species that occurred in areas preferred by dugongs (the 50% kernel contours calculated from positions obtained from the GPS tags), a total of 14 sites were sampled. Sites were chosen based upon a subset of the spatial and temporal distribution recorded from two of the GPS tags deployed on female dugongs during their autumn-winter-spring distribution pattern.

Habitat surveys were conducted during August 2002. At each site, four 50m transects were laid out on the benthos in a north, south, east and west direction respectively from a randomly located point. A video of the benthos was then taken along each individual transect at a constant speed and height of 50cm above the bottom. Seagrass percentage cover and composition were later determined from the video through consensus of three observers. In addition, eight replicate 0.5m2 quadrats were sampled by SCUBA divers at locations selected randomly over the four transects at each site. Seagrass percentage cover was estimated within each quadrat. Shoot density was determined within a 0.1 m2 sectioned corner of the quadrat after which the seagrass within that corner was harvested for above ground biomass determination. Biomass was measured for dry weight by drying samples at 600C for a 48 hour period.