dugongs in palau - C3

have been any drastic changes in calving rates over the past 25 years. The average proportion of calves
seen in Australian and Torres Straits surveys, varies from 9-14% (Anderson, 1986, Anderson, 1989,
Marsh et al. 1984, Marsh, 1986, Marsh et al., 1997). So in comparison, it appears that the proportion of
calves see in Palau is high. The groups of dugongs observed in Australia were, however, larger and calves
may be more easily overlooked when compared to the distinct lone female-calf pairs usually observed in
Palau. Smaller groups are seen around Torres Strait but even so, the proportion of calves is, on average,
much lower. It could be possible that the reproductive interval for females is on average lower for female
dugongs in Palau, when compared to those in Australia. Factors that may contribute to possible higher
calving rates in Palau might include:
• Less competition for food (abundant food resources and little competition due to low population
size)
• Relative lack of seasonality (constant warm waters throughout the year)
• Limited potential migration distances relative to Australia (10s of km versus 100s of km).
40
calves
adults
35
30
#
25
20
15
10
5
0
1977 1978 1983 1991 1998 2003
survey year
Figure 7: Numbers of adults and calves seen on each aerial surveys
All cow-calf pairs were seen on or very close to reefs in 1998 and 2003, most likely for the purpose of
sheltering the calves from strong currents and possibly to allow a quick escape to shallow waters in the
presence of predators. In 1998, three cow-calf pairs were seen in the Malakal Harbor area (I and II) three
cows with calves in north and northeast Babeldaob areas (section V and XI), and one pair in the Rock
Islands area (section VIII). In 2003, four pairs were observed close to reefs in the Malakal Harbor area (I
and II), with two pairs in north Babeldaob (IV and V), and another pair within the Rock Islands (section
VIII) ( Table 3). There has been speculation that dugongs in Palau are restricted in their feeding habits by
poaching and boat activity and thus rest by day and come into shallow waters to feed by night when these
threats
are lessened. However, cow-calf pairs are also likely to be in close proximity to high-quality
resources at all times, not only during the night, as lactation makes heavy energy demands on females.
Females with calves need to be feeding more often and/or on better quality resources than lone dugongs,
thus it is possible to infer that high quality seagrasses are likely to be present in sections I, II and V
(Malakal Harbor and the northwest lagoon). Although feeding or feeding plumes were not observed
during the 2003 aerial survey, this does not mean that dugongs were not feeding. Flying at such altitude
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