Abstract
Five aerial survey transects in eastern Shark Bay, along which dugongs (Dugong dugon) had been
reported in deep water in July 1989, were flown on 3 and 14 July 1992. As in 1989, dugong sightings
were concentrated between 9- and 15-m depth contours. Thermal patterns shown on images obtained
from NOAA satellites, and direct measurement of temperatures in the water column, confirmed that
temperatures were at least 19�C where dugongs were concentrated. Although no seagrass had previously
been reported in this zone, examination of benthic communities using a remotely controlled underwater
video system revealed an apparently monospecific stand of Halophila spinulosa. Dugong behaviour,
observed from a 10-m catamaran, indicated that the animals were diving to the bottom. Long, deep
dives may be more costly in time and energy than the shorter dives characteristic of feeding in shallow
water. H. spinulosa has large fleshy rhizomes similar to those known to contain abundant starch in
other members of the genus and it is suggested that carbohydrate-rich rhizomes might compensate
for the higher costs of foraging in deep water. Previously known stands of preferred forage species
appeared inadequate to support the large dugong population of Shark Bay, but if temperatures are
favourable throughout the winter and if the H. spinulosu observed in this study is available throughout
the year, this H. spinulosa community may be an important resource for the Shark Bay dugong
population.
Subject
Management, Monitoring, Policy and Law,Ecology, Evolution, Behavior and Systematics
Cited by
20 articles.
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