Evening temperature of natural and artificial nests
Figure 12 Temperature distributions of green turtle C. mydas artificial nests in Pangumbahan beach hatchery A open cage. Measured in the evening
at the surface sand and nest upper rim and bottom, mean: 27.4±1.0°C at upper rim nest, 29.6±1.3°C at bottom nest, and
29.7±2.7°C at surface sand.
It seems that temperature condition at hatchery was different than at its nature condition, see Figure 11 and 12. Surface sand was warmer than the nest
upper rim and bottom part. This condition was contrary to the natural condition which surface sand cooler than at natural nest.
Figure 13 Temperature comparisons of green turtle C. mydas natural nests and artificial nests in Pangumbahan beach. Measured in the evening at the
surface sand and nest upper rim and bottom. Mean: natural nests: 28.2±0.8°C at upper rim nest, 28.6±0.8°C at bottom nest,
26.7±0.8°C at surface sand; artificial nests 27.2±0.8°C at upper rim nest, 29.6±1.5°C at bottom nest and 30.3±2.5°C at surface sand.
25 26
27 28
29 30
31 32
33 34
5 10
15 20
T e
m p
e ra
tu re
° C
artificial nests
nest upper rim
nest bottom sand surface
25 26
27 28
29 30
31 32
33 34
35
25 26
27 28
29 30
31 32
33 34
35
A r
ti fi
c ial
n e
st °
C
Natural nest °C
nest upper rim
nest bottom surface sand
Temperature measurement of natural nests n = 9 and artificial nests n = 9 were compared Figure 13. The datasets were distributed normally at the level of
significance α = 0.05. Statistically, there were no significance difference between the mean of natural nests and artificial nests temperature at the level significance
of α = 0.05 and α = 0.01. Nevertheless, surface sand temperature of natural nests and artificial nests were significantly different at the level of significance α = 0.05
but were not significantly different at the level significance of α = 0.01. It inferred that temperature difference in the natural and artificial nests upper rim and
bottom were narrow. But whether it affected hatching success or hatchling sex ratio remain unclear because it was not investigated in this study.
Table 11 Sand characteristic at natural nest, artificial nest and hatchery area
Sample Sand humidity
Dominant sand grain size mm
surface bottom
note surface
bottom Natural nest n = 8
0.7 - 3.7 1.9 ± 1.2
n = 7 0.2 - 4.8
2.7 ± 1.5; n = 7
medium sand - fine sand
Artificial nest n = 7 0.3 - 6.6
2.8 ± 2.1 n = 7
0.0 - 7.1 3.0 ± 2.9
n = 7 all at open
cage hatchery
A fine sand -
very find sand
medium - fine sand
Hatchery Asbestos roof n = 9
0.2 - 11.4 1.9 ± 3.6 n
= 9 -
very fine - fine sand
Hatchery Fiber roof n = 9
0.0 - 7.1 1.5 ± 2.5
n = 9 -
very fine - fine sand
∗ Sand humidity was sampled at night. Medium sand :0.50 - 0.25 mm; fine sand: 0.25 - 0.10 mm; very fine sand: 0.10 - 0.05 mm
Nest temperature has close relation with its characteristic such as sand humidity and grain size composition. The sampling was taken at dry and wet
season. The sand was dry in all samples Table 11. It was not different significantly. Sand composition at natural nest was different to artificial and
hatchery. Sand grain provides porosity for interstitial water which can maintain humidity. In turn humidity can decrease temperature. But here we found contrast
result. Surface sand of natural nest was cooler than at bottom whereas the surface was drier than the bottom. Surface sand of artificial nest was slightly drier than the
bottom, this was in line with temperature condition where surface sand was warmer than the bottom.
Humidity is important for hatching. If the sand was too dry then the eggs will not hatch, vise versa, if the sand was to wet then the eggs will become rotten.
This is quite an issue in Pangumbahan, especially during dry season. Dry sand tends to be lighter and easy to collapse. It was observed that dry sand hampers the
adult female green turtle C. mydas in excavating body pit and eggs cavity while nesting. Dry sand also hampers the hatchlings to emerge to the surface. Thus,
Pangumbahan’s wardens gave a lot of effort to maintain the sand humidity at hatchery and beach area. They watered the beach area by seawater and the
hatchery by freshwater. The watering at the beach was done every day during dry season before the sun sets. The watering at the hatchery was done every week,
especially at the roofed hatchery fiber and asbestos. This strategy was done by experience where many green turtles C. mydas were failed to nest during dry
season Janawi, 2010, personal communication. They also experienced of 0 emerging success of green turtle C. mydas hatchlings at fiber roofed hatchery
last year. It is inferred that low humidity was the cause of this case. Hence, it is important to monitor sand humidity and temperature for future strategy.
In nature, nest depths were ranged around 45 cm until 84 cm depth with 75 of the measurement showed range of approximately 55 – 71 cm Figure 14.
Then, the same eggs with mentioned nest depth relocated into hatchery sites. However, all the eggs were not treated resembling the natural condition, regarding
the original nest depth. The eggs were reburied into shallower depth nest. The artificial nests were more or less similar in depth. This contrasting nest depth
condition caused different pattern of nest bottom temperature between natural and artificial ones. The nest bottom of artificial nest was slightly warmer than the
original conditions natural nests. 31
Median 25-75
Non-Outlier Range Outliers
natural depth artificial depth
40 45
50 55
60 65
70 75
80 85
D ep
th cm
Figure 14 Nest depth of green turtle C. mydas natural and artificial nest in cm. Mean = 65.7 ± 10.2 cm natural depth; 50.6 ± 4.3 cm artificial depth