2008

pp.39–44

Asiatic Herpetological Research, Vol. 11

Observations on the Influence of Seasonality, Lunar Cycles,
and Weather Condition on Freshwater Turtle Activity in Sarawak,
East Malaysia (Borneo)
KAREN A. JENSEN1,* AND INDRANEIL DAS1
1

Institute of Biodiversity and Environmental Conservation
Universiti Malaysia Sarawak,
94300, Kota Samarahan, Sarawak, Malaysia.
*
Corresponding author E-mail: kitti_jensen@yahoo.com

Abstract.- Freshwater turtles were surveyed at two sites in Sarawak: Loagan Bunut National Park and Balai Ringin.
Capture results were tested against environmental factors such as lunar phase, weather and seasonality to examine
differences in activity level. Proportionally, soft-shelled turtles were most active during the full moon (29.0%) andthe last quarter lunar phase (29.4%). Hard-shelled turtles were active during the full moon 50.0% of the time. Bothsoft-shelled and hard-shelled turtles were more active during overcast periods (53.0% and 66.0%, respectively).
Seasonality did not seem to affect soft-shelled turtle activity, while hard-shelled turtles were active 50.0% of the time
during the dry South-west Monsoon from June to September.
Keywords.- Testudines, Malaysia, Borneo, capture success, environmental factors.

a
ina

Se
50

100

Sulu Sea

Ch

Scale
0

uth

Southeast Asia has a highly diverse freshwater turtle
fauna due to a combination of factors, including thepresence of major mountain massifs, some of the largest
archipelago systems in the world, large tracts of lowland
forests, streams and rivers, high precipitation and tropical climate (Iverson, 1992; Lovich, 1994). Due to theircryptic nature and the presence of intense hunting in the
recent past, however, these enigmatic species have beendifficult to study. Consequently, there is a paucity of
published information regarding the current status andbasic ecology of the Southeast Asian fauna, including
those populations endemic to Borneo. As part of a larger
study on the ecology of Amyda cartilaginea (describedin Jensen, 2006), the activity of freshwater turtles in
Borneo in relation to environmental factors, such as
lunar phase, precipitation, and seasonality, wereassessed.

Loagan Bunut National Park contains the only
freshwater floodplain lake in Sarawak (Sayer, 1991),
encompassing 650 ha2 at its maximum diameter. The
lake is completely dry during prolonged droughts.
Annually, the lake completely dries between three andsix times, typically in February, May, and June.
A variety of techniques were attempted to assess themost effective method for capturing Amyda cartilaginea. One method employed was the use of hoop
traps according to techniques described by Frazer et al.
(1990), Legler (1960), and Vogt (1980). Native hoop
traps called 'bubu' were ineffective in trapping turtles.
Another local fishing device called a 'selambau' caught
a single turtle in Balai Ringin.

150 (km)So

Introduction

Indonesia

Australia

N

BruneiMaterials and Methods

Sabah

Miri
South China Sea

The primary study area was Loagan Bunut National
Park (03° 44'−03° 00' N, 114° 09'−114° 17' E) in northern Sarawak, which is within a three hour drive to thetown of Miri. Field work was concentrated at the Park,but two visits were also made to Balai Ringin (01° 03'
00'' N, 110° 45' 00" E), a fishing village about two hours
driving distance from Kuching. Both sites are locatedwithin peat swamp forests (Fig. 1).

© 2008 by Asiatic Herpetological Research

Celebes Sea

Sarawak
Kuching

Loagan Bunut
National Park

Kalimantan
Balai Ringin

Figure 1. Locations of Balai Ringin and Loagan Bunut
National Park in Sarawak, East Malaysia.

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Asiatic Herpetological Research, Vol. 11

Table 1. Total number of individuals of freshwater turtle
species caught during the present study. The asterisk
refers to an unsexed carcass. Sites include: 1 = Loagan
Bunut National Park; 2 = Balai Ringin; 3 = Matang
Wildlife Centre; and 4 = Vicinity of Mulu National Park.
Site 1 Site 2 Site 3 Site 4 Total
Amyda cartilaginea

14

5

0

1

20

Adult males

6

0

0

1

7

Adult females

6

4

0

0

10

Juveniles

2

1

0

0

3

Cuora amboinensis

3

0

0

0

3

Adult males

0

0

0

0

0

Adult females

0

0

0

0

0

Juveniles

3

0

0

0

3

Cyclemys dentata 6 (1)*

1

0

0

7

Adult males

0

0

0

0

0

Adult females

1

1

0

0

2

Juveniles

4

0

0

0

4

Heosemys spinosa

0

1

3

0

4

Adult males

0

0

1

0

1

Adult females

0

1

1

0

2

Juveniles

0

0

1

0

1

Manual capture, otherwise known as 'muddling'(Cagle, 1943), was an effective, albeit labor-intensive,
method of collecting turtles in the surrounding forestsand streams, although it was only effective during low
water periods. The technique consists of wading throughstreams and probing areas of sand or mud and amongroots with a stick, hands, or feet. Comparisons withother studies were not possible as there are no comparative studies of Amyda cartilaginea available.
Hard-shelled turtles were searched for in forested
areas by walking 100 m transects (2 m wide) through theforest, looking under leaves, tree roots, and debris. The
turtles were most frequently located as they crossed
trails or other open areas.
At Loagan Bunut National Park, 51 field days werespent during five sampling trips. Over the course of 33
evenings, two hoop nets and 60 baited hand lines wereset, totaling 2,046 trap nights. At Balai Ringin, 16 fielddays were spent during two sampling trips; in total, 45
baited hand lines were set over 16 evenings, totaling 720
trap nights. There were 2,766 trap nights in total.
With the exception of the Balai Ringin trips, traps
were set for a minimum of seven days. The baits used,chosen on the basis of availability, consisted of parts ofchicken, pork, or local fishes such as Ikan Kali (Clarius
nieuhofii), Ikan Toman (Channa micropeltes) or Ikan

2008

Haruan (Channa striatus). If habitat conditions changed
noticeably, the traps were re-located to a nearby site withat least one meter of water depth.
Lunar phase was recorded at the time of capture to
test for possible differences in turtle activity level during
the different phases of the lunar cycle. Turtles that were
captured while physically active, as opposed to resting,were used in the present study. “Active” animals werequalified as those specimens caught with traps or lines
because they must have swam or walked to the area of
capture. Three Amyda cartilaginea were found by muddling and one Cyclemys dentata was found buried near
the trunk of a tree. These animals were inactive at thetime of capture and were not included in subsequent
analyses. One A. cartilaginea was caught by baited line
on a trip near Gunung Mulu National Park, and wasincluded in subsequent analyses, as were any active
hard-shelled turtles found in localities other than the
study sites.
Lunar phase was divided into four categories; newmoon, first quarter, full moon, and last quarter. New
moon was defined as when the non-illuminated side isfacing the Earth; at this time, the moon is not visible,
except during a solar eclipse. First quarter moon was
defined as the phase when one half appears to be illuminated by direct sunlight; during this phase, the illuminated fraction of the moon's disk increases. Full moon was
the phase when the moon was completely illuminated bydirect sunlight. Last quarter moon was defined as thephase when one half of the moon appears to be illuminated by direct sunlight; during this phase, the illuminated fraction of the moon's disk decreases. Moon phases
were obtained from the U.S. Navy Astronomical
Applications Department website (U.S. Navy, 2003). In
the analyses, hard-shelled and soft-shelled species werepooled separately due to their presumed different behavior, capture method, and habitat use.
To determine if weather affected capture success,weather conditions at the time of collection was recorded, being divided into three categories: clear, overcast,and raining. Overcast was defined as times when the sky
was completely cloudy and grey, and clear weather was
defined as entirely clear to having some white cumulus
clouds.
Seasonality was divided into the North-east
Monsoon (wet season), the South-west Monsoon (dryseason) and non-monsoonal times, which occurred during April, May and October. The North-east Monsoon
prevails from November to March and the South-west
Monsoon occurs from June to September. The Northeast Monsoon brings the majority of precipitation toSarawak, while the South-west Monsoon season is typically characterized by dry weather.

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Figure 2. Percentage of Amyda cartilaginea collected
while physically active during various lunar phases.

Figure 3. Percentage of hard-shelled turtles collected
while physically active during various lunar phases.

Twenty-two days were spent searching for turtles
during the North-east Monsoon, 15 days were spentsearching during the South-west Monsoon and 30 days
were spent searching during non-monsoonal times.

one female, and one juvenile) were also found by various Universiti Malaysia Sarawak personnel while performing wildlife surveys at Matang Wildlife Centre (01º36' 398" N, 110º 11' 33" E).

Results

Effects of lunar phase on capture success.- During the
new moon phase, traps and lines were set for 8 days; two
adult Amyda cartilaginea (one male, one female) were
captured. During the first quarter moon phase, traps andlines were set for 18 days; five adult A. cartilaginea (onemale, four females) were captured.
During the full moon phase, traps and lines were set
for 14 days; five A. cartilaginea were captured (fourfemales, one juvenile). During the last quarter phase,traps and lines were set for nine days; five A. cartilaginea were captured (two males, one female, two juveniles). These data are shown in Figure 2. The active
hard-shelled turtle species captured were Heosemys
spinosa (four individuals), Cuora amboinensis (three
individuals) and Cyclemys dentata (five individuals, oneof which was inactive). During the new moon lunar
phase, one juvenile Cuora amboinensis and one juvenile
Cyclemys dentata were collected over a period of threedays. During the first quarter lunar phase, 10 days werespent searching for turtles with only one female
Heosemys spinosa (8.3% of the total) captured. During
the full moon lunar phase, collections over 11 days produced one female and one juvenile Heosemys spinosa,
one juvenile Cuora amboinensis, and one female andtwo juvenile Cyclemys dentata. During the last quarter
lunar phase, collections over five days yielded one male
Heosemys spinosa, one juvenile Cuora amboinensis andone juvenile Cyclemys dentata (Fig. 3).
Results for both soft-shelled and hard-shelled turtles indicate that lunar phase may not have an influenceon their activity patterns. A larger sample size with atleast one radio-tagged species would provide more significant results.

Species richness.- A total of 34 individual turtles fromfour species were found at the sites examined (Table 1).
Loagan Bunut National Park.- A total of five freshwater turtle species were recorded over a period of 51 fielddays and 2,046 trap nights. In all, 14 Amyda cartilaginea
were captured: six males, six females and two juveniles.
Six Cyclemys dentata were collected: one female, fourjuveniles and one unsexed carcass. Three juvenile Cuora
amboinensis were collected.
Of the 14 Amyda cartilaginea captured at Loagan
Bunut National Park, three individuals were found by
muddling, and 11 were caught during the 2,046 trap
nights. Of the 11 trapped animals, ten were caught on
handlines with Ikan Kali and one was caught on a handline baited with Ikan Haruan. No more than a single turtle was collected per night, representing a 0.54% trap
success, with only 11 out of 2,046 trap nights being successful.
Balai Ringin.- Three freshwater turtle species were collected over a period of 16 days and 720 trap nights: one
female Cyclemys dentata, one female Heosemys spinosaand five Amyda cartilaginea (four females and one juvenile).
Of the turtles captured at Balai Ringin, three werecaught using handlines baited with Ikan Kali, one wasfound in a selambau and one was caught in a bubu. The
trapping success rate was 0.69%.
Additional species.- An adult Amyda cartilaginea wascaught in the vicinity of Mulu National Park (4° 1' 15"
N, 114° 54' 2" E). Three Heosemys spinosa (one male,

Effects of weather on capture success.- During clear
weather, three Amyda cartilaginea (one male, two juve-

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2008

Figure 4. Percentages of Amyda cartilaginea collectedduring different weather conditions.

Figure 5. Percentages of hard-shelled turtles collectedduring different weather conditions.

Figure 6. Percentages of all Amyda cartilaginea collectedbased on seasonality.

Figure 7. Percentages of all hard-shelled turtles collectedbased on seasonality.

niles) were collected, nine individuals were captured
during overcast weather (three males, six females), andsix individuals were captured when it was raining (fourfemales and one juvenile) (Fig. 4).
For hard-shelled turtles, 12 individuals were foundon the forest floor or on forest trails when it was clear,
while only four were found when it was raining (onefemale, one male and one juvenile Heosemys spinosaand one female Cyclemys dentata). When it was overcast, eight turtles were found (one female Heosemys
spinosa, three juvenile Cuora amboinensis, and fourjuvenile Cyclemys dentata) (Fig. 5).

time of capture, was included in this component of theanalysis since we were looking at the overall effects ofcapture and seasonality. Six of these turtles were collected during the wet season (one female Heosemys spinosa,
two juvenile Cuora amboinensis, and three juvenile
Cyclemys dentata). Three of the turtles were found during the dry season (one juvenile Heosemys spinosa, one
juvenile Cuora amboinensis, and one juvenile Cyclemys
dentata). Four turtles were captured during non-monsoon times (one male and one female Heosemys spinosa,
and two female Cyclemys dentata) (Fig. 7).
All four turtles found buried in mud or hidden in atree hollow were collected in the dry season. During theNorth-east Monsoon, these localities would have been
covered by at least two meters of water.

Effects of seasonality on capture success.- Amyda cartilaginea capture success was examined between seasons. As might be expected, the water levels of both thelake and its tributaries at Loagan Bunut National Parkand the riparian habitats in Balai Ringin were lower inthe dry season. Consequently, three of the 20 individuals
captured were found buried in the mud. During the wet
season, six female Amyda cartilaginea were captured,
while in the dry season, only seven soft-shelled turtles(three males, two females, and two juveniles) were captured. During the non-monsoon seasons, seven softshelled turtles (four males, two females, one juvenile)
were captured, representing 41% of the total (Fig. 6).
Thirteen hard-shelled turtles were collected. One
female Cyclemys dentata was found buried under thehollowed trunk of a tree, and although inactive at theDiscussion
Capture rates for both Amyda cartilaginea and hardshelled turtles were low, (0.54% and 0.69%, respectively), indicating that the populations of these species may
be at critically low levels, although this is difficult to
substantiate considering the paucity of historical data forsoutheast Asia.
Turtle capture rates were tested against three environmental factors: lunar phase, weather, and season. In
the lunar phase analysis, it appeared that a new moon
may have some influence on the movements of Amyda
cartilaginea. At a capture rate of 11.8% (compared to2008

Asiatic Herpetological Research, Vol. 11

29.4% for all other phases), the darkness of the sky may
have an effect on the foraging capabilities of thisspecies. Other predatory species have also been noted ashaving increased foraging activity with increased moonlight (Brigham and Barclay, 1992). A capture rate of
50.0% during the full moon phase indicated that hardshelled turtles may need lunar illumination for foraging
activity.
The effects of lunar phase on changes in animal
behavior are well known. Tigar and Osborne (1999)
hypothesized that fewer predaceous arthropods wereactive during full moons than new moons, possibly
because of the increased risk of vertebrate predation.
Álvarez-Castañeda et al. (2004) concluded that fewer
rodent remains were present in barn owl (Tyto alba) pellets during full moons, indicating that rodent activity
may be decreased during this phase, which is supported
by other studies that have found rodent activity to belinked to lunar phase. O'Farrell (1974) found that themost important factors affecting rodent activity was theamount of time between sunset and sunrise, as well as
lunar phase. Price et al. (1984) reported that brightmoonlight reduces the overall activity of nocturnalrodents. Church (1960a), concluded that ovulation of thecommon Asian toad (Duttaphrynus melanostictus) was
correlated with the lunar cycle in Java. Church (1960b)
also found this to be the case with the crab-eating or
mangrove frog (Fejervarya cancrivora) in Java.
In the present study, 53.0% Amyda cartilaginea
collections occurred during overcast weather, 29.0%
ocurred during rain events, and 18% occurred when theskies were clear. A total of 66.0% of hard-shelled turtles
captured during overcast conditions, 34.0% were captured during rainy conditions and none were captured
during clear weather, indicating that turtles may favor
overcast weather for moving and foraging. Seasons did
not have a dramatic affect on the capture rate of turtles,
however, more information is necessary to make thisdetermination with any confidence. Clearly, a large
amount of effort is required to examine the behavior of
turtles, as well as other animals, especially when conducted across multiple seasons, lunar phases, weather
conditions, or even years. This paper thus presents preliminary information on the influences of environmental
factors on turtle behavior in Borneo.

Acknowledgments
This project was made possible through financial support from Chelonian Research Foundation's (CRF)
Linnaeus Fund, British Chelonian Group (BCG)
Conservation Grant, Idea Wild, Universiti Malaysia
Sarawak ('The herpetofauna of Loagan Bunut'; fundamental grant number: 1/94/441/2004 [179] and 'Studies

43

on the natural history and systematics of the herpetofauna of peat swamp forest of Sarawak, East Malaysia';
fundamental grant number: 1/26/303/2002[40], theUNDP−GEF ('Conservation and Sustainable Use of
Tropical Swamp Forests and Associated Wetland
Ecosystems',
UNDP−GEF
FundedProject
MAL/99/G31). Thanks are due to the Sarawak
Biodiversity Centre for providing a research permit(Research Agreement Number: SBC−RA−0073−KAJ
and Research Permit Number: SBC-RP-0085-KAJ). We
also thank the Sarawak Forestry Department for providing permission to survey freshwater turtles in Sarawak(Permit number: 03697). Special thanks are due to theSarawak Forestry Corporation and the staff at Loagan
Bunut National Park for permission and use of equipment.

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Submitted: 05 January 2007
Accepted: 22 September 20072008