MARINE AND FISHERY SCIENCES 35 (3): 437-444 (2022)

https://doi.org/10.47193/mafis.3532022010905

ABSTRACT. Six new records of the bull shark Carcharhinus leucas from five different river

basins of Sumatra, Indonesia, were reported as a result of captures by artisanal and recreational fish-

ers, including records from rivers of northern and western Sumatra for the first time. These findings

may highlight the importance of Sumatran river basins for the reproduction of this threatened species

in Indonesian waters. Inland records of C. leucas in Southeast Asia and in particular Indonesia are

scarce but important for nature conservation purposes and sustainable future fishery management.

Key words: Biogeography, Carcharhinidae, elasmobranchs, freshwaters, conservation, data-poor

area.

Nuevos registros continentales del tiburón toro Carcharhinus leucas de Sumatra, Indonesia

RESUMEN. Se reportaron por primera vez seis nuevos registros del tiburón toro Carcharhinus

leucas en cinco cuencas fluviales diferentes de Sumatra, Indonesia, como resultado de las capturas

de pescadores artesanales y deportivos, incluidos registros de ríos del norte y oeste de Sumatra.

Estos hallazgos resaltan la importancia de las cuencas de los ríos de Sumatra para la reproducción

de esta especie amenazada en aguas de Indonesia. Los registros continentales de C. leucas en el Sud-

este Asiático y, en particular, en Indonesia, son escasos pero importantes para la conservación de la

naturaleza y la gestión pesquera sostenible en el futuro.

Palabras clave: Biogeografía, Carcharhinidae, elasmobranquios, agua dulce, conservación, área

con datos escasos.

The Indonesian Archipelago can be considered as a data-poor area, as there

is currently no systematic study on the status of its shark populations (Jaiteh

et al. 2017). Although the Malay Archipelago has been identified as a hotspot

of elasmobranch biodiversity, containing about 30% of the more than one

thousand shark and ray species in the world (Last and Stevens 2009), this

region remains poorly investigated and a major blind spot for conservation.

This lack of knowledge can be understood as a lack of concerted research

effort on both marine and non-marine elasmobranchs in Indonesia, due to

financial limited research support and logistical difficulties in conducting

research in remote, hard-to-access, and politically unstable areas rather than

a lack of interest on this topic.

437

*Correspondence:

peter.gausmann@rub.de

Received: 30 May 2022

Accepted: 7 July 2022

ISSN 2683-7595 (print)

ISSN 2683-7951 (online)

https://ojs.inidep.edu.ar

Journal of the Instituto Nacional de

Investigación y Desarrollo Pesquero

(INIDEP)

This work is licensed under a Creative

Commons Attribution-

NonCommercial-ShareAlike 4.0

International License

Marine and

Fishery Sciences

MAFIS

NOTE

New inland records of the bull shark Carcharhinus leucas from Sumatra,

Indonesia

PETER GAUSMANN1, * and VERYL HASAN2

1Working Group Biogeography and Landscape Ecology, Department of Geography, Faculty of Geosciences, Ruhr University Bochum,

Universitätsstraße 150, 44801 - Bochum, Germany. 2Fisheries and Marine Faculty, Aquaculture Department, Airlangga University, 60115 -

Surabaya, Indonesia. ORCID Peter Gausmann https://orcid.org/0000-0003-3577-7349, Veryl Hasan https://orcid.org/0000-0001-5457-9335

Several shark species utilize specific inshore

locations (coastal embayments, estuaries, river

mouths) as nursery areas, but only a few elasmo-

branchs are euryhaline, able to transition

between marine and freshwater environments for

prolonged periods (Thorson 1972; Pillans et al.

2009). Carcharhinus leucas (Valenciennes,

1839), the bull shark, is a circumglobal, euryha-

line apex predator widespread in the coastal

areas of the tropical, subtropical, and warm-tem-

perate regions of all ocean basins (Compagno

1984; Last and Stevens 2009; Ebert et al. 2021;

Gausmann 2021). This species relies on low

salinity habitats for reproduction and in the early

stages of its life cycle (Thorson 1976). Rivers

and river mouths can be considered as important

nursery grounds for neonate, young-of-the-year,

and juvenile bull sharks, as they provide low-

mortality habitats and large amounts of suitable

food items (Heupel and Simpfendorfer 2011;

Matich and Heithaus 2015; Pillans et al. 2020).

Carcharhinus leucas has been reported histori-

cally from major streams of the world thousands

of kilometers inland (Gausmann 2021). Thus, the

bull shark is currently known as one of the few

shark species that penetrates freshwater for

extended periods due to its osmoregulatory com-

petencies (Pillans et al. 2005). Grant et al. (2019)

reviewed the use of non-marine habitats by elas-

mobranchs and produced a classification of elas-

mobranchs using freshwater based on the impor-

tance of freshwater habitats on the life history of

each species. According to these authors, only 4

shark species, 3 Glyphis spp. and C. leucas, can

be considered truly euryhaline. In the Indo-Pacif-

ic region, bull sharks are born at 60 to 75 cm

total length (TL), both males and females reach-

ing maturity at ∼10-20 years and 180 to 230 cm

TL and reaching a maximum recorded size of

400 cm TL (Wintner et al. 2002; Last and

Stevens 2009; McCord and Lamberth 2009).

Carcharhinus leucas is assessed as Vulnerable

(VU) on a global scale in the IUCN Red List

(Rigby et al. 2021).

Carcharhinus leucas is currently recognized

from Sumatra in available distribution maps

(Ebert et al. 2021; Gausmann 2021; Rigby et al.

2021). Only few verified inland records of juve-

niles and subadults from Sumatran freshwater

environments had been previously reported

(Batang Hari River Basin: Tan and Lim 1998;

Musi River: Iqbal et al. 2019). Carcharhinus leu-

cas is know from both marine and freshwater

Indonesian habitats (Gausmann 2021), but there

are gaps in the distribution due to a lack of veri-

fied records for many parts of Indonesia. Some of

the freshwater records of C. leucas from Indone-

sia are quite old (Boeseman 1964) and require

verification. In summary, distributional informa-

tion on C. leucas in Indonesia and Southeast Asia

is scarce (Kottelat 2013; Hasan et al. 2021), and

better information is needed on specific localities

for better management and conservation planning

for this species. The present study aims to report

hints on new potential nursery areas of C. leucas

for conservation purposes, to fill in gaps in the

distribution of this species in Indonesia, and to

outline the benefits of both artisanal and recre-

ational fisheries data to scientific studies.

Herein, catch data on C. leucas from Sumatra

Island, Indonesia, a data-poor area of Southeast

Asia, are summarized (Table 1). Moreover, distri-

butional data of immature bull sharks from Suma-

tra are provided from alternative and inexpensive

existing sources (Figures 1 and 2). The second

author of the present work started a call targeting

Sumatran fishermen to report catches of C. leucas

from riverine habitats for scientific investigation

and to gain distributional data for this species

from a remote region of Indonesia. A systematic

survey of entire towns or regions was not con-

ducted. However, six juvenile to subadult speci-

mens of C. leucas were landed and photographed

by artisanal and recreational fishers in the period

between 2013 and 2019, from five river basins on

Sumatra Island. These sites were located between

∼4 and ∼195 km inland from the mouths of these

rivers. Distances of catch sites to the sea were

438 MARINE AND FISHERY SCIENCES 35 (3): 437-444 (2022)

439

GAUSMANN AND HASAN: NEW INLAND RECORDS OF THE BULL SHARK FROM SUMATRA

Table 1. Inland records of Carcharhinus leucas in Sumatran river basins in the period 2013-2019. Numbers refer to locations in Figure 1.

Date of

catch

08.03.2013

07.05.2016

21.06.2017

29.09.2017

26.08.2019

08.09.2019

River

Basin

Buluh

Asahan

Babalan

Musi

Asahan

Indragiri

Water

temperature

(°C)

29-32

29-31

29-30

30-32

28-31

30-32

Province

Sumatera

Barat

(West

Sumatra)

Sumatera

Utara

(North

Sumatra)

Sumatera

Utara

(North

Sumatra)

Sumatera

Selatan

(South

Sumatra)

Sumatera

Utara

(North

Sumatra)

Riau

(East

Sumatra)

Name of village

or town

Padang

Pulau Raja

Pangkalanbrandan

Teluk Kijing

Tanjung Balai

Tembilahan

Coordinates

0° 49'54.4"S,

100° 18'52.7"E

2° 42'20.3"N,

99° 37' 17.6"E

4° 01'47"N,

98° 15'14.0"E

2° 58'58.1"S,

104° 07'47.1"E

2° 58'14.7"N,

99° 47'33.9"E

0° 18'11.7"S,

103° 14'32.2" E

Distance

from

sea/river

mouth

(km)

∼4

∼80

∼11

∼195

∼16

∼44

Used

fishing

gear

Small

hook

(<7/0)

Casting

net

Medium

hook

(>7/0)

Small

hook

(<7/0)

Medium

hook

(>7/0)

Gill net

Estimated

size (cm

−total

length)

∼70

∼130

∼75

∼70

∼120

∼70

Life

history

phase and

sex

Juvenile,

female

Subadult,

female

Juvenile

Juvenile,

male

Subadult,

female

Juvenile

measured by using a Geographical Information

System (GIS), although a small inaccuracy

remains. Some of these catches were incidental,

as C. leucas is not a target species for local small-

scale fisheries. Photos of the sharks were volun-

tarily shared with the authors by the fishers and

villagers, who consented to their use in this pub-

lication. The sizes of the reported sharks were

estimated by the authors from the received photo-

graphic material.

While the Asahan, Babalan, Musi, and Indra-

giri rivers drain into the Strait of Malacca and the

South China Sea, the Buluh River drains into the

Indian Ocean (Figure 1). Due to the remote loca-

tion of the catch sites, the only measured water

parameter was temperature, which was obtained

from nearby measuring stations. The five rivers

can be characterized as typical, low- to medium-

impacted lowland rivers of the wet tropics, with

peak discharges during the rainy monsoon season

(November to March) and a period of low flow

when rainfall decreases. Due to larger settlements

along the larger Musi and Indragiri rivers, these

are more polluted than the more pristine Asahan,

Buluh, and Babalan rivers. Catch sites with short

distance to the sea (Table 1, records 1, 3, and 5)

are presumably tidal-influenced but nevertheless

low salinity habitats.

Specimens recovered by fishers were in

acceptable condition, allowing for their identifi-

cation using visible features (blunt snout, small

eyes, lack of an interdorsal ridge, and typical first

to second dorsal fin ratio) cross-referenced with

information in the literature (Garrick 1982; Com-

pagno 1984; Ebert et al. 2013). Similar looking

carcharhinids, such as members of the genus

Glyphis and Lamiopsis were excluded by their

relatively large size of the second dorsal fin in

440 MARINE AND FISHERY SCIENCES 35 (3): 437-444 (2022)

Figure 1. Known records of Carcharhinus leucas in river basins of Sumatra from 2013 to 2019. Numbers refer to Table 1.

200 km

1mi00

Strait of

Malacca

Gulf of

Thailand

South

China

Sea

Indian

Ocean

Musi

River

Basin

Indragiri River Basin

River Basin

Batang Hari

Lake

Toba

comparison to the first dorsal fin. The similar C.

amboinensis was also excluded by the ratio of the

first to the second dorsal fins that were used to

separate C. leucas (<3.1:1) from C. amboinensis

(>3.1:1). Estimated sizes suggest that specimens

recorded herein were juveniles (∼70-75 cm TL)

and subadults (∼120-130 cm TL). Sex was deter-

mined by the presence/absence of claspers. No

specimens were preserved. Some of the captured

specimens were later on sold on the local markets

and some were directly consumed, with no spec-

imens released again.

Sites recorded herein (Figure 1; Table 1)

include the Musi River Basin (n =1), from where

C. leucas had been previously reported by Iqbal

et al. (2019), whereas records from the Asahan

(n =2), Buluh (n =1), Babalang (n =1) and

Indragiri (n =1) rivers are putative new records.

441

GAUSMANN AND HASAN: NEW INLAND RECORDS OF THE BULL SHARK FROM SUMATRA

Figure 2. Selection of photographs of bull shark specimens caught by local fishers in Sumatra. A) Subadult female of Carcharhi-

nus from the Asahan River, North Sumatra (Table 1: record 2). B) Juvenile of C. leucas from the Babalan River, North

Sumatra (Table 1: record 3). C) Local fisher holding a subadult female C. leucas from the Asahan River, North Sumatra

(Table 1: record 5). D) Underside of C. leucas specimen in D. E) Juvenile male C. leucas from the Musi River, South

Sumatra (Table 1: record 4). F) Recreational fisherman holding juvenile C. leucas was captured in the Indragiri River,

Riau, East Sumatra (Table 1: record 6).

Moreover, the present records of C. leucas from

North Sumatra (Asahan River) and West Sumatra

(Buluh River) represent first records for these

regions. Reported specimens were representative

of different life history stages of C. leucas from

juveniles to subadults, with juveniles dominating

(Figure 2). The farthest freshwater penetration

was that in the Musi River, the largest of the five

rivers (~750 km length), at approximately 195

km from the sea (Figure 1; Table 1).

Reports by fishers to scientists can be a valu-

able toolkit for the identification of crucial habi-

tats for sharks in data-poor regions. The use for

scientific purposes of animals caught by artisanal

and commercial fishers can be an effective tool

for the analysis of fish distributions, including

those of elasmobranchs (Giareta et al. 2021). The

confirmed presence of C. leucas in the Musi

River indicates that juvenile and subadult bull

sharks utilize this river as a freshwater habitat,

presumably as a nursery area. This was already

suggested by previous records of C. leucas from

the Musi River, therefore fulfilling the repeated

use criterion for nursery areas as outlined by

Heupel et al. (2007). The present data suggests

that numerous river basins on Sumatra may be

utilized as nursery areas by immature bull sharks.

Present records from four rivers (Buluh, Asa-

han, Babalan, Indragiri), in addition to the Musi

and Batang Hari rivers, increase the number of

known Sumatran river basins with occurrences of

C. leucas to six. Moreover, our data show that the

rivers of Sumatra likely represent an important

habitat in the life-history of this species in the

area, and that they therefore require management

alongside the coastal areas of Indonesia. Catch

dates indicate that these Sumatran rivers are uti-

lized by immature C. leucas at least between

March and September (Table 1). Our results sug-

gest that additional river basins of Sumatra and

Indonesia may also function as nursery areas for

bull sharks, so future records of C. leucas from

Indonesian and adjacent river basins in Southeast

Asia can be expected.

ACKNOWLEDGEMENTS

We thank the reviewers and editors for their

worthful comments and are grateful to the follow-

ing Sumatran fishers for reporting their catches of

Carcharhinus leucas: R. Puspita, R. Cenyo, D.

Warsa Ndut, M. Nur, D. Putrra, and T. Rismadi.

Forthermore, we are grateful to D. Whitmore for

the language editing.

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