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Facultative river dolphins : conservation and social ecology of freshwater and coastalIrrawaddy dolphins in Indonesia
Kreb, D.
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Citation for published version (APA):Kreb, D. (2004). Facultative river dolphins : conservation and social ecology of freshwater and coastal Irrawaddydolphins in Indonesia. Amsterdam: Universiteit van Amsterdam.
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Page 2
Conservation of riverine Irrawaddy dolphins in Borneo
81
CHAPTER 6
Conservation management of small core areas: key to survival
of a critically endangered population of riverine
Irrawaddy dolphins in Borneo
Daniëlle Kreb and Budiono
In press: Oryx, 2004
Dolphins preference for fish-rich but human-crowded areas makes them
vulnerable to many human-induced threats. Awareness campaigns therefore
form a critical factor in their survival. Photo: Daniëlle Kreb
Page 3
Chapter 6
82
ABSTRACT
In order to clarify the previous status of the facultative Irrawaddy River Dolphin,
Orcaella brevirostris, in the Mahakam River in East Kalimantan, which was
‘insufficiently known’ following IUCN criteria, we collected data from early 1999 until
mid 2002 on abundance, habitat use, population dynamics and threats relevant to the
conservation of Indonesia’s only freshwater dolphin population. Our best estimates of
total population size varied between 33 and 55 dolphins (95% confidence limits: 31-
76) based on direct counts, strip-transect analysis, and Petersen and Jolly-Seber mark-
recapture analyses of photo-identified dolphins. Mean minimum annual birth and
mortality rates were nearly similar, i.e. 13.6% and 11.4% and no changes in abundance
> 8% were detected over 2.5 years. Dolphins primarily died after gillnet entanglement
(73% of deaths). Dolphins’ main habitat includes confluence areas between the main
river and tributaries or lakes. Dolphins daily intensively use small areas mostly
including confluences, moving up and downstream over an average length of 10 km
of river and within a 1.1 km2 - area size. These areas are also primary fishing grounds
for fishermen and subject to intensive motorized vessel traffic. Sixty-four percent of
deaths (from 1995-2001) with known location (n=36) occurred in these areas. Formal
interviews with local residents revealed a generally positive attitude towards the
establishment of protected dolphin areas. Because of the dolphins’ dependence on
areas that are also used intensively by people, primary conservation strategies should
be to increase local awareness and introduce alternative fishing techniques.
RINGKASAN
Dalam usaha memperjelas kondisi lumba-lumba Irrawaddy (Orcaella brevirostris) di
Sungai Mahakam Kalimantan Timur, yang mana “belum banyak diketahui”
berdasarkan kriteria IUCN, kami mengumpulkan data-data sejak awal tahun 1999
hingga pertengahan 2002 tentang jumlah, penggunaan habitat, perubahan populasi,
dan ancaman yang berkaitan dengan upaya konservasi satu-satunya lumba-lumba air
tawar di Indonesia. Diperkirakan jumlah populasi Pesut Mahakam berkisar antara 33
hingga 55 ekor (tingkat kepercayaan 95%: 31-76) berdasarkan perhitungan langsung,
analisis strip-transek, dan analisis penandaan-ulang Peterson dan Jolly-Seber dari
identifikasi foto lumba-lumba. Rata-rata terendah tingkat kelahiran dan kematian
pertahun hampir sama yakni 13,6% dan 11,4% dan tidak ada perubahan jumlah lebih
dari 8% selama 2,5 tahun. Kematian utama lumba-lumba adalah terperangkap rengge
(73%). Habitat utama lumba-lumba termasuk pertemuan antara sungai utama dan
anak sungai atau danau. Sehari-hari lumba-lumba secara intensif menggunakan daerah
yang kecil kebanyakan merupakan daerah pertemuan sungai, bergerak ke hulu dan ke
hilir dengan jarak tempuh rata-rata 10 km dan dalam ukuran areal 1.1 km2. Tempat-
tempat ini juga daerah utama penangkapan ikan dan lalu lintas kapal bermotor. Enam
puluh empat persen (64%) kematian (dari 1995-2001) dengan lokasi yang diketahui
Page 4
Conservation of riverine Irrawaddy dolphins in Borneo
83
(n = 36) terjadi di daerah ini. Wawancara formal dengan penduduk lokal umumnya
menyatakan sikap positif terhadap pembentukan daerah perlindungan lumba-lumba.
Karena ketergantungan lumba-lumba pada tempat yang juga digunakan intensif oleh
masyarakat, strategi utama konservasi adalah meningkatkan keperdulian dan
memperkenalkan cara alternatif menangkap ikan kepada masyarakat lokal.
INTRODUCTION
River dolphins and porpoises are among the world’s most threatened mammal
species. The habitat of these animals has been highly modified and degraded by
human activities, often resulting in dramatic declines in their abundance and range
(Reeves et al., 2000). Protection of freshwater dolphins and their habitat is a major
challenge since river systems are the veins of human activities in terms of transport,
fishing, and industrial processes, and are also heavily affected by forest fires, which
were more likely to occur near rivers (Fuller & Fulk, 1998) and likely caused a large
increase in sedimentation rates together with large-scale illegal logging practices
(Anon, 2000) with disrupting consequences for the aquatic ecosystem (e.g. Mackinnon
et al., 1997). In Indonesia one representative freshwater dolphin population occurs in
the Mahakam River in East Kalimantan, i.e., the facultative river dolphin Orcaella
brevirostris, commonly and locally referred to as Irrawaddy dolphin and pesut,
respectively. The species is found in shallow, coastal waters of the tropical and
subtropical Indo-Pacific but also in three major river systems: the Mahakam in
Indonesia, the Ayeyarwady in Myanmar, and the Mekong crossing through Vietnam,
Cambodia and Laos (Stacey & Arnold, 1999). These river populations were all
identified to consist of less than 100 individuals based on preliminary studies and
faced ongoing and pervasive threats to their long-term persistence (Kreb, 2002; Smith
et al., 2003).
In order to identify and monitor the population status and threats more
thoroughly and set a rationale for conservation action, a 3.5-years study from February
1999 until August 2002 was initiated. This article presents the results of this study and
an in-depth analysis of habitat preferences, population dynamics, threats and
recommendations for future conservation activities of the Irrawaddy dolphin
population in the Mahakam River. Since 1990 the species has been fully protected by
law in Indonesia and is adopted as a symbol of East Kalimantan Province. Prior to the
present study, no systematic data had been collected before on the Mahakam
population. A two-month preliminary study in 1997 revealed that sighting rates (0.06
dolphins/ km) in the middle Mahakam river segment (with highest dolphin densities)
were very low (Kreb, 1999). Based on data we collected during 1999 and 2000, the
IUCN status of this freshwater population was raised from ‘Insufficiently Known’ to
‘Critically Endangered’ (IUCN, 2003)
Page 5
Chapter 6
84
Study area
The Mahakam River is one of the major river systems of Borneo and runs from 118º
east to 113º west and between 1
º north and 1
º south (Fig 1). Regional climate is
characterised by two seasons, i.e. dry (from July-October, southeast monsoon) and
wet (November-June, northwest monsoon) (MacKinnon et al., 1997). The river
measures about 800 km from its origin in the Müller Mountains to the river mouth.
Rapids start upstream of Long Bagun at c. 600 km from the mouth, which limit the
dolphins from ranging further upstream.
Three major lakes and nearly all major tributaries and many smaller swamp lakes
are connected to the main river system in the Middle Mahakam Area (MMA) between
180 km until 375 km from the mouth. These lakes are very important fish-spawning
grounds and replenish the main river seasonally. Therefore, the MMA is an area of
intensive fishing activity with an annual catch of 25.000 to 35.000 metric tons since
1970 (MacKinnon et al., 1997).
Coal mining and logging companies occur along the entire length of the Mahakam
River, especially in the tributaries. A large gold digging company is located in the
upper Mahakam River segment together with several small-scale, illegal gold mines.
Infrastructure is poorly developed in East Kalimantan and the Mahakam River is the
main transport system.
METHODS
Field methods
We searched the Mahakam River from the delta to upper rapid streams (600 km from
the mouth) by boat from February 1999 until August 2002 for a total of 8925 km (837
hours), and observed river dolphins for a total of 549 h. We conducted 12 involved
extensive monitoring surveys in 6 survey periods, which covered the entire
distribution range (average duration 10 days; SD ± 2 days) during all types of water
levels (high, low, medium, increasing, decreasing) to invest distribution patterns,
annual recruitment and estimate population abundance using strip-transects, direct
counts and mark-recapture techniques through photo-identification, which are more
described in detail in Kreb (2002 & in press a). The distribution range was divided in 15
strip- transects (main river and tributaries) and 2 line-transects (Melintang and
Semayang Lakes). Each transect could be finished in one day. Another six intensive
surveys (average duration 12 days; SD ± 3 days) were conducted in areas of high
dolphin density to investigate preferred habitat and to locate dolphin groups for
further focal group follows (see below) to assess daily home ranges (Figure 1).
To monitor abundance and locate groups, surveys were conducted with 12-16 m
long motorised vessels (12-21 hp), travelling at an average speed of 10 km/ h.
Page 6
Conservation of riverine Irraw
addy dolp
hins in B
orneo
85
F
ig
ure 1. Stud
y area w
ith
a) to
tal d
olp
hin
d
istrib
utio
n area, b
) areas o
f h
igh
d
olp
hin
d
en
sity an
d c) co
astal Irraw
ad
dy d
olp
hin
area.
Dat
ah
Bila
ng
Sem
ayan
g
Jem
pang
Mua
ra
Ben
anga
k M
uara
Kam
an
Dam
ai
Mua
ra
Pahu
Lon
g B
agun
Kot
a B
angu
n B
atuq
M
uara
Je
lau
Tep
ian
Ula
k
Ram
baya
n Boh
oq
Muy
ub U
lu
Ked
ang
Ran
tau
Ked
ang
Kep
ala
Ked
ang
Pah
u
Loa
Kul
u
Mel
inta
ng
Conservation of riverine Irrawaddy dolphins in Borneo
85
Page 7
Chapter 6
86
The photographic effort during the extensive monitoring surveys was one hour per
sighting with a total observation effort of 545 h. Durin observation team existed of
three active observers: two front observers and one rear observer. The average
observation time and g all surveys 2074 photographs were made of dorsal fins. For
each sighting, the duration, location, group behaviour, group size, group composition
and environmental data, i.e. depth, clarity, surface flow rate, temperature, pH and type
of river section (river bend, straight stretch or confluence area) were collected. On
average five times a day, similar random samples were collected as those obtained
during sightings, whereas type of river section was recorded every fifteen min.
In order to assess daily home ranges, 58 groups were followed for 321 h in total
and on average 5.5 h daily (range 1.5-13 h) using a motorized canoe of 5 hp outboard
engine maintaining an average distance of 50 m. In addition, land-based observations
were made in the confluence area of Muara Pahu, c. 300 km upstream, which was
frequented daily by different dolphin groups. On average, five sequential days (32 days
in total) of land-based observation have been completed by two observers, which
overlooked the area some 7 until 10 meter above the water surface (depending on
water levels) during six different survey periods for a total of 286 h. When a group of
dolphins was sighted, we recorded group size and composition (Kreb, in press a),
changes in group-composition, and time spent in the area.
Formal interviews were conducted using questionnaires with mainly open
questions with residents and fishermen (n = 258) in six important dolphin areas to
determine their knowledge and attitude with regards to the dolphins and their
conservation. Respondents were questioned separately to ensure independence of
data.
In order to assess the minimum annual birth rates between November 2000 and
November 2001, the total number of different newborns were counted during 5
different surveys (both extensive and intensive surveys), which were more or less
equally distributed over the year with an average 2.5-month gap in between the
surveys. Newborns encountered during each of these surveys were assumed different
than those encountered during an earlier survey. We defined newborns to be of less
than one month of age if they complied with all three categories: 1) exhibited an
awkward manner of swimming and surfacing, 2) spent all their time in close proximity
to an adult and 3) were of less than ½ the average length of an adult, following Bearzi
et al. (1997).
Mortality was estimated from own observations and semi-structured interviews
conducted during a preliminary survey in 1997 and during the surveys from February
1999 until August 2002. Mortality was traced back as far as 1995. Incomplete or
untrustworthy accounts with missing locality, date, and traceable eyewitnesses were
disregarded (14% of n = 44).
Dolphin reactions towards different types of boat traffic were tested by
comparing dolphin group surfacing frequencies in presence and absence of different
types of boats (see Kreb & Rahadi, in press b, for a more detailed method description)
Page 8
Conservation of riverine Irrawaddy dolphins in Borneo
87
Analysis
To assess the importance of different river areas in terms of dolphin densities, the
river was divided in seven areas where at least one dolphin sighting was made. Total
sightings made in each of these different areas during 10 extensive surveys were
compared using a chi-square test. Sightings in tributaries within 1 km of the
confluence area were considered main river sightings. Sighting rates, densities and
abundance estimates based on strip-transects and direct counts were calculated
according to the formula described in Kreb (2002). Since no sightings were made in
any of the lakes during these extensive surveys, no analysis of the conducted line-
transects was required. The mean abundance estimates and coefficient of variation
(CVs) of two replicated surveys within each survey period, were added for all survey
periods and averaged to obtain the total mean population size (and mean CV). In
addition, abundance estimates were calculated per water level condition (combining
different years) averaging the estimates of each replicated survey. This was done since
there was no trend in abundance (see Results, Trends in abundance), and there was no
difference between the variation in abundance estimates per replicated survey within
the same time period and the variation in abundance estimates of surveys conducted
in different periods but at similar water level conditions. Because all rear sightings
(n=9) were associated with the dolphins’ positions in river bends (which is an
unpredictable variable), no detection correction factor g(0) was used to calculate
abundance and associated CVs. Instead, rear sightings were directly included in the
abundance estimates. Also, no seasonal variation was found in sizes of groups (see
Results, Population composition) so this component was also not included in the
calculation of CVs.
Abundance was also estimated using both the Jolly-Seber and Petersen mark-
recapture methods based on 728 selected identifiable dorsal fin pictures (Kreb, in press
a). Mean population size was calculated as the average of the mean abundance
estimates from strip-transects, direct counts and mark-recapture analysis. Mean group
size in the Mahakam was based on all on-effort sightings made during nine extensive
abundance surveys covering the entire distribution range. Groups were considered
different if a group joined after 15 min of observation or groups split during
observation time. To detect any trend in abundance, regression analysis was applied to
the natural logarithm of 5 mean strip- and direct count abundance estimates over a 2.5
years period (early 1999 until mid 2001). Statistical power was calculated by means of a
linear regression program TRENDS (Gerrodette, 1993). The same analysis was
performed to detect if there was any trend in mortality using data from 1995 until
2001.
Random environmental samples i.e., depth, flow rates, pH, temperature and
clarity were compared with samples collected at dolphin locations per water level
using a two sample T-test, prior to which a two-tailed F-test was applied to test for
similar variances, which were equal for all sample comparisons. Dolphin-preferred
areas within the main river were investigated by comparing the percentage of dolphin
Page 9
Chapter 6
88
sightings made per water level in straight stretches, river bends and confluences during
ten strip-transects surveys that covered the same area using a chi-square test. The
relative random availability of straight stretches, river bends and confluences were
tested using a chi-square test. When df was 1, Yates correction factor was applied. To
identify the year-round significance of a confluence area, for which highest dolphin
densities were found, the numbers of identified dolphins per water level were
compared using a chi-square test. To prevent biases, the correlation between the
number of pictures obtained and number of identified dolphins was tested using the
Product Moment Correlation Coefficient.
Daily home ranges were estimated by measuring the distance between the two
most widely separated sighting locations of the focal group. Minimum annual birth
rate was estimated by dividing the total number of newborns encountered in one year
(see Methods) with the mean population size. Minimum annual mortality rate was
estimated by dividing the number of dead dolphins during the study period
(interviews + observations) by years and mean population size.
RESULTS
Abundance and distribution
During ten extensive surveys, we made 76 on effort sightings of Irrawaddy dolphins in
the Mahakam (Table 1). The actual dolphin sightings were confined to the area in the
main river between Muara Kaman (c. 180 km from the mouth) and Datah Bilang (c.
480 km from the mouth) and the tributaries Belayan, Kedang Rantau, Kedang Kepala,
Kedang Pahu, Ratah and Semayang Lake. The cross-shaded area (Figure 1) of 195 km
length in the main river from Muara Kaman until Muara Benangak (c. 375 km from
the mouth) represents an area of high dolphin densities. The total dolphin distribution
area in the Mahakam, based on sightings and interviews with fishermen, starts about
90 km upstream of the mouth at Loa Kulu and ends some 600 km upstream at the
rapids past Long Bagun, including several tributaries and two lakes (Figure 1, single-
shaded areas).
Significant differences were found in sighting density among eight survey areas
where we made sightings (X2 = 35.91, df = 7, P < 0.01) (Table 1). The three areas
where most sightings were made include several confluence areas with tributaries and
lakes.
Seasonal variation in distribution pattern is summarized in Table 2 and illustrated
in Figure 2. At medium water levels sighting rates in the main river and tributaries are
similar. At prolonged high-water levels dolphins were more often found in the main
river than in the tributaries, whereas at rising high water levels (data not tabulated
since incomplete total area coverage) a lowest mean sighting rate (0.03 dolphins/ km)
was recorded in the main river indicating that dolphins had moved upstream into the
tributaries. At low water levels no dolphins were sighted in the tributaries.
Page 10
Conservation of riverine Irrawaddy dolphins in Borneo
89
All but one sighting of Irrawaddy dolphins in and near the Mahakam delta were
offshore the delta at low tide (n = 4), whereas one sighting was made 10 km upstream
of the delta at high tide. A mean salinity of 21 ppt was measured at dolphin
Table 1 Priority areas for conservation based on the combination of dolphin densities,
presence of newborns, observed matings and mortality, with low numbers
indicating high priority.
* Actual proposed conservation areas (1–3) are confined to smaller areas based on frequent sighting
locations (see results); ** Dolphins that died between 1995 – 2001 in the survey area; 5 dolphins
died outside the survey areas and 2 dolphins died with unknown location.
������������������������������
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������������ ������
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0
5
10
15
20
25
30
35
Medium Medium-high* High Low
Water Level
Nu
mb
er o
f d
olp
hin
s
������
Main River
������
Tributaries
������
Lake
������
Rapid area
Figure 2. Seasonal habitat use of dolphins based on strip-transect analysis.
The main river includes confluence areas of up to 1 km upstream
tributaries. * At medium-high water levels, tributary data is lacking
and thus not presented in the graph.
River survey segments of 40 km
length
Priority area
*
Dolphins/
km
Newborns
< 2 months
Mating
events
Deaths
**
Muara Kaman – Kota Bangun 2 0.13 12
Kota Bangun – Batuq 3 0.16 1 1
Batuq – Tepian Ulak 5 0.1 1 1
Tepian Ulak – Rambayan – Muara Jelau 1 0.31 8 1 13
Rambayan – Bohoq 6 0.04 2
Bohoq – Muara Muyub Ulu 6 0.04
Ratah 4 0.12 1
Muara Jelau – Damai 6 0.04 1
Page 11
Chapter 6
90
Tab
le 2. N
um
ber o
f sigh
tin
gs, d
olp
hin
d
en
sities an
d ab
un
dan
ce p
er river sectio
n an
d w
ater level co
nd
itio
n
based
o
n strip
-tran
sects.
Survey area
Tran
sects
To
tal
len
gth
(km
)
Mean
strip
width
(m
)
No
.
sigh
tin
gs
Mean
gro
up
size
No
.
do
lp
hin
s/
km
No
. o
f
do
lp
hin
s/
km
2
Ab
un
dan
ce
(strip
–
tran
sects)
Co
efficien
t
o
f V
ariatio
n
Middle m
ain
river*
Med
ium
-w
ater levels
9
621
200
16
4.5
0.1
2
0.5
8
23
27%
High
-w
ater levels
6
414
200
12
4.6
0.1
3
0.6
7
28
24%
Lo
w-w
ater levels
12
828
200
28
4.3
0.1
5
0.7
3
30
9%
Middle trib
utary**
Med
ium
-w
ater levels
3
228
43
7
4.5
0.1
4
3.2
12
62%
High
-w
ater levels
2
152
43
2
4.6
0.0
6
1.4
5
0%
Lo
w-w
ater levels
4
304
43
0
4.3
0
0
0
0%
Up
per trib
utary
Med
ium
-w
ater levels
3
33**
75
3
4.5
-
-
5
0%
High
-w
ater levels
2
33**
75
2
4.6
-
-
5
0%
Lo
w-w
ater levels
4
33**
75
4
4.3
-
-
4
0%
** in
cro
ss-sh
aded river area o
f F
igure 1. ; ** distan
ce fro
m m
outh
o
f trib
utary un
til rap
ids, h
ow
ever th
e do
lp
hin
s sigh
ted
th
ere o
ccup
y a 'c
lo
sed
' area in
b
etw
een
tw
o rap
id
stream
s o
f o
nly 2 km
, so
n
o sigh
tin
g rates h
ave b
een
calculated
.
Chapter 6
90
Page 12
Conservation of riverine Irrawaddy dolphins in Borneo
91
positions in the delta and is associated with brackish waters. Their most inshore
occurrence is about 20km upstream of the mouth at high tide according to interviews
with fishermen. Since the coastal dolphins have not been sighted or reported to move
further upstream than 20 km from the mouth and only enter the delta at high tide, we
consider these to belong to a different, coastal stock than the Mahakam population,
which range starts 180 km upstream the mouth according to our sightings. The coastal
and freshwater populations thus seem isolated from each other.
Total mean abundance estimates for the entire dolphin population in the
Mahakam derived from strip-transect analysis (method 1) and direct counts (method
2) made during nine extensive monitoring surveys, arrive at 37 individuals (mean CV
= 13%; 95% CL = 33-41) and 33 individuals (CV = 8%; 95% CL = 31-35),
respectively (Table 3). Independent abundance analyses based on photo-identification
and mark-recapture techniques gave total estimates of 55 dolphins (CV = 6%; 95%
CL = 44-76) following Petersen’s method (3) and 48 dolphins (CV = 15%; 95% CL =
35-63) according to the Jolly-Seber method (4). The total number of identified
dolphins during the study period is 59 individuals.
Table 3 Total abundance of dolphins in the Mahakam based on strip-transect analysis an
direct counts.
Water
levels
conditions
No.
T
Total T
length
(km)*
No.
Si
Mean
G
No. Si/
surveys
**
N
strip-
transect CV
95%
CL
N
count CV
95%
CV
Medium 15 882 26 4.5 8.7 40 19% 21-58 33 8% 26-40
High 10 599 16 4.6 8 37 17% 1-94 36 12% 1-74
Low 20 1165 32 4.3 8 34 9% 30-39 32 2% 31-33
Combined 45 2646 74 4.4 8.2 37 15% 33-41 33 8%
31-35
* Only including transect length of those sections where dolphins were sighted, excluding search effort in
areas where no dolphins were sighted during these extensive monitoring surveys (e.g. lakes and upper and
lower river section); ** For medium, high and low water levels 3, 2, and 4 surveys were conducted
respectively; T = transects; Si = Sightings; G = group size; N = abundance; CV = Coefficient of Variation;
95% CL = 95% Confidence Limit
Regression analysis of the natural logarithm of five mean strip-transect
abundance estimates showed a non-significant 1% increase in abundance (b=0.01,
t=0.52, df=3, P>0.05) (Figure 3). Direct count abundance estimates for the same
study period revealed no changes in abundance (b=0.001, t=0.18, df=3, P>0.05).
Power analysis revealed that in order to detect a 5% change (either positive or
negative) with high statistical power (90%) and mean CV of 13% or 6% (mean of the
CVs of each replicated strip-transect or direct count estimates per survey period) 28
“strip”-samples or seven “count”-samples are needed. In our study period (with five
Page 13
Chapter 6
92
samples) only changes as large as 20% (strip-transect estimates) or 8% (direct counts)
would have been detected with 90% power.
Trend in dolphin abundance in the
Mahakam River
0
20
40
60
80
100
Time period
Ab
un
dan
ce estim
ates
Figue 3. Trend in abundance estimates based on strip-transects.
No significant population changes occurred during the
study period. The vertical bars represent 95% confidence
intervals of the estimates.
Population dynamics
The dolphin population consisted on average of 61% adults, 30% juveniles and 9%
calves and neonates (Table 4). The mean group size observed during the extensive
monitoring surveys was 4.4 (SD = 2.2; range = 1-10). Population composition and
group size did not fluctuate during different water levels (H = 0.17, df = 2).
Minimum annual number of newborns during the study period was six dolphins.
Newborns (< one month of age) were observed at all water levels and in all months of
the year. Birth rates between 11 - 18% may apply (of N = 55 and 33 dolphins,
respectively). With six newborns per year, the minimum numbers of breeding females
within this population are 12 or 18 individuals if a 2- or 3-year reproduction cycle
applies, respectively.
During the 3.5 year study period minimally 17 dolphins died an unnatural death
(interviews and own observations). Minimum average annual mortality during the
study period is five dolphins (SD = 2, range = 3-8), which is between 9 and 15 % of
maximum and minimum abundance estimates, respectively. True mortality rates,
including deaths from natural causes, are unknown.
Y = 34.4 + 0.6x
r2 = 0.070
Med 99 Low 99 Med 00 High 01 Low
Page 14
Conservation of riverine Irrawaddy dolphins in Borneo
93
Table 4. Group composition during three different surveys with
different water level conditions.
Number of dolphins per water level during one survey
Group composition Medium 2000 High 2001 Low 2001 Mean numbers
Adults 19 58 % 22 61 % 20 63 % 20 61 %
Juveniles 10 30 % 11 31 % 9 28 % 10 30 %
Calves & neonates 4 12 % 3 8 % 3 9 % 3 9 %
Habitat preferences and home ranges
Environmental characteristics for different river sections at medium water levels are
presented in Table 5. All freshwater fish trade production comes from the middle
river section (including tributaries and lakes), which has the highest dolphin densities.
No significant differences were found between random samples and samples collected
at dolphin locations for most parameters and water levels. Only for depth
measurements at low water levels in the tributaries of the middle river section did we
find a significant difference in mean depth of random samples 7.5 m and of samples at
dolphin locations 16.7 m (t = 2.85, df = 16, P < 0.05). This suggests that dolphins
prefer to remain in deep water pools, such as confluence areas, during the dry season.
Their dependence upon confluence areas in particular during the dry season is
indicated in Figure 4. At low water levels, significantly more sightings occurred in
these areas than in river bends (X2 = 8.5, df = 1, P < 0.01), in spite of the fact that
river bends are significantly more numerous (X2 = 24.3, df = 1, P <0.01). Also, more
than half (54%) of the 59 dolphins photo-identified in the Mahakam during the 3.5
years study period occurred in the confluence area of Muara Pahu at low water levels
(see Abundance) (Table 6). Although photographic effort was largest at low water, no
correlation was demonstrated between the number of pictures obtained and the
number of identified dolphins (r = 0.893, df = 2, P > 0.05). Also, during the other
water level conditions the number of dolphins identified in this area is still high and
no significant differences were found in seasonal presence (X2 = 5.1, df = 3, P >0.05).
Dolphins occurred in the confluence area of Muara Pahu on average 42% of
daytime during every observation day and at all water levels (Table 7). The highest
daily occupancy was found at high water levels (65%). Dolphins still remained nearby
(< 10 km) at medium and low water levels, but they spent less time milling in the
confluence area itself. On average three different groups (range 2–6 groups) consisting
of a combined mean number of 12 individuals (range 5–19 individuals), frequented
the confluence area daily. Moreover, 44 (75%) of the 59 photo- identified dolphins
were sighted at least once in the confluence area (mean = 6 days, max = 17 days of 49
photo/ observation days in that area).
Page 15
Chapter 6
94
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0
10
20
30
40
50
60
70
High Medium Low
Water levels
% o
f d
olp
hin
sig
htin
gs
����Straight stretch
���River bend
����Confluence
Figure 4. Dolphins preferred areas within the main river. NB random relative
Availability of straight stretches was significantly higher than that
of bends and confluences (X2
= 112.3, df =2, P<0.01). Also, bends
were significantly more numerous than confluences (X2
= 24.3, df = 1, P<0.01).
Eight individuals were sighted exclusively within a 20 km radius of the confluence area
(mean number of sightings per individual = 9; range = 2–13 sightings). The
confluence area of Muara Pahu and another confluence area about 10 km upstream of
there, in the Kedang Pahu tributary, accounted for 89% of the sightings of newborns
observed during boat surveys (n = 9) (Table 1). The majority of deaths (64%) with
known location (n = 36) also occurred in confluence areas. Mating was observed
within different groups in the confluence of Muara Pahu and at one location between
Batuq and Tepian Ulak (Figure 1).
The average daily home ranges of 27 groups, which were followed for more than
6 hours, were 10 km long (SD = 8.6 km, range = 1-45 km) and 1.1 km2 in area (SD =
1.8 km, range 0.1–9 km2). One group of six photo-identified dolphins are ‘trapped’
between rapid streams in the Ratah River; they have been living for 3.5 years in a river
segment 2 km long and 0.2 km2 in area.
Page 16
Conservation of riverine Irrawaddy dolphins in Borneo
95
Table 5. Environmental characteristics of the Mahakam River collected during medium
water levels
* Mean salinity only applies to the delta area; ** Data representing direct catch (excluding aqua-culture)
for market sale within dolphin habitat based on data from the Kutai Fisheries Department (Dinas
Perikanan Kabupaten Kutai Tenggarong, 2000). N.B. Fish production data strictly applicable to the river
sections, tributaries or large lakes alone are not available and are therefore combined within the middle
river section to which they are connected; *** Fish production data in the upper river section only
available until 425km upstream, whereas actual total dolphin distribution area stretches until 560km
upstream.
Table 6. Seasonal occurrence of photo-identified individuals in the
confluence area of Muara Pahu during 4 different seasons on
5 days in sequence.
Water levels High
2001
Low
2001
Medium/ low
2001
Medium
2000
Identified dolphins 19 32 25 22
Selected identifiable pictures 28 64 37 46
N.B. Two additional survey periods of 5 continuous days were conducted at
medium-high water levels, but these were not included as the number of selected
identifiable pictures were too low (≤ 16 pictures) due to camera failure.
Table 7. Daily occupancy of dolphins in the confluence area of Muara Pahu expressed in
hours and percentage of daytime.
Water levels
Time (hours)
Medium-
low 2000
Medium-high
2000 2001
High
2001
Low
2001
Low-low
2001
Total
Search effort (km) 46.2 48.2 35.9 51.2 45.9 58.7 286.1
Dolphins present (hrs) 18.0 23.7 15.4 33.4 17.3 11.8 119.6
% daytime dolphins
present
39 % 49 % 43 % 65 % 38 % 20 % 42 %
(mean)
Random samples values ± standard deviation
River section
Mean
depth
(m)
Mean
surface
flow (m/s)
Mean clarity
(cm)/ Mean
salinity (ppt)*
Mean width
(m)/ Mean
distance off/
inshore (km)*
Bottom
substrate
Total fish
production
(ton) 1999**
Lower River 15 ± 5 0.8 ± 0.4 30 ± 9 370 ± 65 Mud 0
Middle River 17 ± 6 0.8 ± 0.3 26 ± 9 200 ± 54 Mud 23201
Upper River 12 ± 7 1.1 ± 0.3 20 ± 10 161 ± 48 Sand, cobbles 0***
MR tributary 9 ± 4 0.7 ± 0.5 22 ± 15 41 ± 14 Mud -
UR tributary 12 ± 8 0.8 18 75 ± 12 Rocky -
Lakes 2 ± 0.3 0 56 ± 9 - Mud -
Delta 5 ± 4 - 22 ± 9* 3km off-
10km
inshore*
Mud, sand 6931
Page 17
Chapter 6
96
Threats
Between 1995 and 2001, 38 deaths, mostly of adults (86%) were recorded on the basis
of interviews and two of our own observations (Figure 5). Most dolphins (74%) died
as a result of gillnet entanglement in nets with larger mesh sizes (7.5–17.5 cm).
Dolphins are obviously attracted to the gill nets and as we often observed them
feeding near these nets. Dolphins are also said to aid fishermen by guiding fish into
their nets. Many fishermen use the dolphins’ feeding patterns as indicators of the
location and time to set up gillnets and in this way increase the danger of
entanglement. However, frequent reports exist also of dolphins that have been
successfully released by fishermen from gillnets. Second cause of death involved
deliberate kills (10%), which mostly happened in isolated areas where dolphins rarely
occur. Five dolphins that incidentally died in gillnets were eaten and the skin of two of
them was also used as medicine for skin allergy (allegedly, the patients’ allergy
disappeared). Vessel strikes caused 5% of deaths.
From 1974 until 1988, 28 dolphins were live-captured and taken to Jaya Ancol
oceanarium in Jakarta. Two detailed local accounts of illegal captures in 1997 and 1998
0
2
4
6
8
1995 1996 1997 1998 1999 2000 2001
Year
Nu
mb
ers d
ead
gillnet entanglement killed
trapped in shallow water boat collision
birth process unknown
Figure 5. Dolphin mortality during 7 years based on reliable reports
and interviews in combination with own observations.
Major cause of death was through gillnet entanglement
(74% of all deaths n = 38).
of 3 and 4 dolphins respectively, were reported. Their fate and destination remain
unknown. In 2002 a request for live captures was submitted at the General
Directorate of Protection and Conservation of Nature (PKA) by the Regent of
Central Kutai Province, East Kalimantan for a new oceanarium along the Mahakam
River (8-12 dolphins) and by Jaya Ancol Oceanarium in Jakarta (4-5 dolphins).
Following intensive lobby by local NGOs and the ban on live captures since 1990 by
the Ministry of Forestry, the request for the captures has not been granted.
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Conservation of riverine Irrawaddy dolphins in Borneo
97
A range decline occurred in 20 years time between the 1980s and 2000 in a river
stretch of 120 km, from 60 km until 120 km upstream of the mouth, which is 15% of
total dolphin historic range, i.e. 820 km including tributaries based on own
observations and semi-structured interviews with local residents. The range decline
coincides with increased industrial activities, boat traffic and decreases in fish
populations (based on fishing data from 1990-2000 of the Fisheries Department in
Tenggarong).
A recent habitat decline involves the elimination of the Mahakam lakes as primary
areas of occupancy according to Tas'an and Leatherwood (1984). We only found
dolphins in the confluence area connecting to one lake (Semayang) and in the
southern part of that lake. The disappearance of dolphins from Jempang Lake and
dolphins decreased occurrence in the other two lakes (confirmed by residents) is
probably due to 1) Reduced depth of the lakes in the middle Mahakam area through
sedimentation (data from Environmental Controlling Body, Tenggarong) caused by
deforestation of the surrounding shorelines (agriculture, illegal logging and forest
fires). 2) High density of gillnets in fish seasons (own observations), which obstruct
dolphin movements.
Furthermore, other factors, which degrade the main distribution area, include: 1)
Noise pollution by frequent passing of high-speed vessels (40-200 hp) (mean = 4.6
boats/ h). These boats cause the dolphins to dive significantly longer within a range of
300 m distance of the dolphins than in their absence (Kreb and Rahadi, in press b).
Container barges (in 2001 mean=8.4 boats per day) daily pass through a narrow
tributary, Kedang Pahu, which represents primary dolphin habitat and occupy over
two-thirds of the width of the river and over half the depth of the tributary during the
dry season. Dolphins always changed their direction (if swimming upstream) when
they encountered loaded container barges and moved downstream ahead of the boats
back to the confluence area. 2) Chemical pollution of mercury and cyanid from leaks
in dams that retain chemical wastes from gold mining industries, which occurred in
1997 (pers. comm. A. Faroek) and from many small-scale and illegal operating gold
miners (own observations). In addition, the observed amount of coal, which falls into
the river during the process of over-loading into containers and while being tugged
along a tributary that represents primary dolphin habitat is most likely not negligible.
Also, during one survey in 2000 in that area we observed some dolphins to be affected
by changes in skin pigment of some parts of their bodies. However, it is not clear
whether these represent a skin disease and what caused this. These pigment changes
have never been observed on dolphins in other areas. 3) Possible (future) prey
depletion due to intensive fishing with gillnets, electricity and poison. Interviews with
fishermen (n = 108) revealed that 48% were opposed to using electricity for fishing,
but 43% were in favour of using this method. Reasons for favouring electric fishing
are that fish can be caught faster and more easily. This group also believed that fish
abundance is still high and unlikely to decrease.
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Conservation
Based on interviews (n = 258) we found that the majority of residents along the
Mahakam River was positively inclined towards the dolphins, felt they needed to be
protected and agreed upon establishment of protected areas (Table 8). The following
incident is illustrative of the good will of local residents. In 2002 an entire village in
important dolphin habitat helped the provincial wildlife conservation department
(BKSDA) with over 50 men to capture and transport a dolphin that was trapped in a
shallow lake, which would soon fall dry, back to the main river. Afterwards villagers
joined a symbolic meal to mark their commitment to dolphin conservation, whereas
the same village helped during earlier live captures for oceanaria. The general positive
attitude towards the dolphins may be linked with the local belief that the dolphins
have a human origin.
An ongoing conservation program, was initiated in November 2000 by a local
NGO, Yayasan Konservasi RASI (Conservation Foundation for the protection of
Rare Aquatic Species of Indonesia) focuses on the protection of the freshwater
Irrawaddy dolphin population in the Mahakam, and its habitat. Main activities that
have been conducted since 2000 include a yearly conservation/ awareness campaign
aimed at different layers of society; yearly monitoring of the dolphin population;
socio-economic survey related to fisheries; attitude assessment surveys with local
communities; demarcation of an important dolphin site by placing a large billboard in
Muara Pahu (Plate 1); establishment of patrolling teams in several villages consisting
of local fishermen who patrol their areas and report illegal fishing activities since 2002.
Table 8. Attitude assessment interview with local residents along the Mahakam River(n=258).
Questions Answers of
respondents
(n = 258)
% of
respondents
Explanation
Has the pesut
brought any
advantages to you?
Yes
No
Don’t know
75%
4%
21%
Advantages: indicates good fishing areas (47%); indicates
right time and season for fishing (20%); indicates long term-
rising and decreasing water levels (9%); is enjoyable to
observe (24%)
Disadvantages: has no commercial value like fish (100%)
Does the pesut need
to be protected?
Yes
No
99%
1%
Reasons: rare mammals species (30%); indicator of good
fish seasons (14%); has a tourism value (13%); to prevent
them from extinction (12%); regret the rare sightings (6%);
symbol of East Kalimantan (2%); preserve for future
generations (2%); don’t know (21%)
Would you agree of
establishing
protected dolphin
areas?
Yes
No
Don’t know
74%
4%
22%
Agreeing under conditions (27%): no fishing ban (59%);
profitable to residents (4%); positive for development (7%)
and for tourisme (7%); restricted to tributaries (7%); with
approval of fishermen (4%)
Disagree: too much disturbance (100%)
Would you regret if
pesut became
extinct?
Yes
No
Unrealistic
64%
30%
6%
Reasons for regret: pride of East Kalimantan (44%); rare
mammal species (28%); indicator of good fish seasons
(28%)
Reasons for no regret: pesut has no value (100%)
Unrealistic: still many dolphins, extinction is not possible
Page 20
Conservation of riverine Irrawaddy dolphins in Borneo
99
Plate 1. Installment of a welcoming billboard to indicate the major dolphin habitat in the
confluence area of Muara Pahu creating a local awareness and sense of belonging
(photo Hari Mulyono).
DISCUSSION
The low abundance estimates, nearly similar minimum birth and mortality rates,
degradation of habitat, depletion of fish resources and dolphins dependency on fish-
rich but human-crowded confluence areas, underline the critical situation with which
this freshwater dolphin population is faced with. Dolphin’s preference and small daily
movement patterns in confluence areas may be explained in terms of their depth, high
fish abundance and counter-currents, which causes fish to be momentarily ‘trapped’ in
the confluence area. Irrawaddy dolphins in the Mekong River (Stacey, 1996; Baird &
Mounsouphom, 1997) and Ayeyarwady River (Smith et al., 1997), and other river
dolphin species, i.e. the Amazon dolphin, Inia geoffrensis (McGuire & Winemiller, 1998),
Indus and Ganges dolphins, Platanista gangetica gangetica and P. g. minor (Khan & Niazi,
1989; Smith, 1993) and Yangtze dolphin, Lipotes vexilifer (Hua et al., 1989) also
preferred confluence or deep areas with counter-current eddies. Based on interviews
with fishermen, we found that the dolphins’ seasonal migration pattern coincides with
the pattern of fish migration, during which fish migrates upstream tributaries to spawn
Page 21
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when water levels start rising after the dry season at medium water conditions. At
prolonged high water levels fish disperses over a larger water surface area and may
enter freshwater swamps, which are inaccessible for dolphins, and they may return to
the confluence area, where they spent 65% of day-time (see results). During the
medium and low water levels, the dolphins still remain close to the confluence area,
but spent less time milling in the confluence area itself.
No historic data exist for the Mahakam population on population abundance,
densities or on annual birth and mortality rates so we do not know surely whether and
how these rates have changed. However, information of local residents indicates a
definite decline in most sections, although in the middle Mahakam some residents
doubt if numbers decreased or that the dolphins became less visible and more shy,
due to the intensive boat traffic. Following the observations of residents, this would
mean that the 120 km-range decline of the lower river section did not result in higher
densities in other areas. In this way, when multiplying the length of decline with
current sightings rates, a population decline of 14 individuals in 20 years may have
occurred, i.e. 0.7 dolphins per year. This would mean a 30% and 20% population
decline in 20 years compared to the present minimum and maximum population size,
respectively. It seems reasonable to assume that the habitat degradation and
consequent habitat loss for dolphins in the more downstream areas near Samarinda
indeed caused a population decline by causing an increased competition in more
upstream areas, which were already occupied. Competition for fish resources may
have increased the dolphins’ attraction for gillnets with fatal consequences. Moreover,
the live captures between the 70s and 90s may have caused a significant sudden
decrease in breeding population and past birth rates may have been higher than
current rates. Mortality mostly affects adults and birth rates may decrease due to loss
of breeding animals. Present rates are nearly similar to those recorded for the less
threatened, but ‘vulnerable’ Amazonian ‘Boto’ river dolphin, Inia geoffrensis, i.e. with
annual pregnancy rates of c. 10 – 15% (Martin & Da Silva, 2000).
If genuine efforts are made to reduce mortality, stem habitat deterioration and
protect the dolphins’ food supply, survival and even recovery of this, Indonesia’s only
freshwater population of dolphins, might be feasible. How viable this future
population will be in genetic terms remains a question mark since we have no data on
the degree of inbreeding. The dolphins’ dependence on small and possibly manageable
sites and the generally positive attitude of local residents towards the conservation of
the pesut may further enhance prospects for success. Protected deep-water areas that
are important for dolphins in the Mekong have also benefited fish populations and
fishermen livelihood (Baird, 2001). The pesut fits the definition of a flagship species,
which not only internationally, but especially locally, has charisma and thus may
effectively facilitate protection of other species and ecosystems with which it is
associated (Bowen-Jones & Entwistle, 2002). Recommendations for conservation
should benefit the freshwater ecosystem including dolphins and humans (Table 9)
(also in Reeves et al., 2003). Without establishment of protected areas, the future of
Page 22
Conservation of riverine Irrawaddy dolphins in Borneo
101
Indonesia’s only freshwater dolphin and symbol of East Kalimantan Province will
become increasingly bleak.
Table 9. Recommendations for freshwater ecosystem protection including dolphins and
humans.
ACKNOWLEDGEMENTS
We thank the Indonesian Institute for Sciences (LIPI), the provincial wildlife
conservation department (BKSDA) and local governments of Central- (KUKER) and
West Kutai (KUBAR) for granting permission to conduct field research. All field
assistants, particularly Ahang, Arman, Karen Damayanti and Syahrani, boatsmen, and
respondents are thanked gratefully. Funding for fieldwork was provided by Ocean
Park Conservation Foundation, Hong Kong; Martina de Beukelaar Stichting; Stichting
J.C. van der Hucht Fonds; Gibbon Foundation; Netherlands Ministry of Agriculture,
Nature Management and Fisheries (PIN/ KNIP); Van Tienhoven Stichting; World
Wildlife Fund for Nature (Netherlands); Amsterdamse Universiteits Vereniging. The
University of Mulawarman in Samarinda (UNMUL), Achmat A. Bratawinata,
Frederick R. Schram, Peter J.H. van Bree, Thomas A. Jefferson and Vincent Nijman
are thanked for their support and Martjan Lammertink, Randall R. Reeves, Tony R.
Martin, Martin Fisher, Tamara L. Mcguire and Ian G. Baird for their comments on the
manuscript.
No. Major recommendations
1
Establish conservation areas in: 1) the confluence area of Muara Pahu and Kedang Pahu
tributary until Bolowan, 2) the confluence area of Muara Kaman and tributary Kedang
Rantau, 3) the Pela tributary and southern part of Lake Semayang (Fig 1).
2 In conservation areas: 1) Set a speed limit for boats and 2) exclude large coal-carrying
ships, employing smaller barges or transport over land (upgrading an old, existing road)
3 1) Exclude gillnets in these areas, or 2) set regulations on type of gillnets used and on the
location, season, and manner of setting, and 3) introduce alternative fishing techniques.
Offer alternative employment options for gillnet fishermen.
4 Strict law-enforcement by local government to attain sustainable use of available fish
resources and stop illegal fishing, logging, pollution and dolphin-capture.
5 Conduct environmental awareness campaigns to increase concern for the conservation
of natural resources at both the political and community level.
6 Continue to monitor the dolphin population and the threats to it.
Page 23
Chapter 6
102
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