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Facultative river dolphins : conservation and social ecology of freshwater and coastalIrrawaddy dolphins in Indonesia

Kreb, D.

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Download date: 27 Aug 2019

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

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

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)

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.

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

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)

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

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.

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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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

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

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

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

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).

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.

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

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.

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.

Chapter 6

98

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

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

Chapter 6

100

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

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.

Chapter 6

102

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