First inland record of bull shark Carcharhinus leucas (Carcharhiniformes: Carcharhinidae) in Indonesian Borneo

An individual of bull shark Carcharhinus leucas (Müller & Henle, 1839) with c. 600-700 mm of total length was caught and photographed on 2019 in Barito River, South Kalimantan province, Indonesia. This finding is considered as a first inland record of C. leucas in Indonesian Borneo (Kalimantan). Collecting data using citizen science is needed to asses the occurence of C. leucas and evaluate the importance of riparian system in Kalimantan waters as nursery area or ranging habitat for this species.


Introduction
The requiem sharks or family Carcharhinidae are the dominant sharks (often in biodiversity, abundance and biomass) in tropical waters on continental shelves and offshores, but they also found in subtropical and warm temperate seas (Compagno & Niem 1998;Ebert et al. 2013). Most species of requiem sharks inhabit tropical continental coastal and offshore marine waters, with a few occuring in freshwater rivers and lakes (Ebert et al. 2013). A few requiem species (the little-known river shark Glyphis spp and the bull shark Carcharhinus leucas) appear to be the only living sharks that can live in freshwater for extended periods (Compagno et al. 2005).
At least 15 Indo-West Pacific species (6% of the total inshore-freshwater fauna) are possibly marginal freshwater elasmobranchs, and may occur in fresh water but may not travel up rivers to any great extent (Compagno 2002). Carcharhinus leucas (Müller & Henle, 1839) is a cosmopolitan elasmobranch in most Indo-West Pacific waters (including freshwater and brackish rivers and lakes) that occur in Indonesian and Bornean waters (Kottelat et al. 1993;Last et al. 2010). Unfortunately, there is no information if C. leucas has been recorded inland in Indonesian Borneo or Kalimantan. In this paper, we summarize first inland record of C. leucas in Indonesian Borneo.

Results and Discussions
The C. leucas found in Barito River has features of requiem sharks family: eyes on side of head; mouth large, arched and elongated, and extending well behind eyes; two dorsal fins, the first dorsal fin moderately large, much shorter than the caudal fin, its base located over the interspace between pectoral and pelvic fin bases. This shark is identified as C. leucas by greyish back and white belly; snout short; small eyes; first dorsal fin high; pectoral fins broad, with narrow pointed; tip of second dorsal and caudal fins dark (indicate a young individual) (Fig. 2). The features above are fitted well to the characters of C. leucas (Compagno & Niem 1998;Compagno et al. 2005;Ebert et al. 2013). Based on freshwater habitat localities, this specimen could be a species of freshwater shark from genus Glyphis, which also occur in Indonesia waters (Last & Stevens 1994;Fahmi & Adrim 2009;Fahmi 2010). However, It was shortly recognized that these specimens differ from Glyphis by its small second dorsal fin, while Glyphis has large relative size of the second dorsalfin (Last & Stevens 1994;Fahmi & Adrim 2009). A specimen of C. leucas found in Barito River show specific features of early young individual. Another recent finding of early young juveniles of C. leucas in Sumatra  indicate freshwater habitat as a nursery area for this species in Western Indonesia. Young individuals of C. leucas readily tolerate low salinities, and some of them born in freshwater (Compagno & Niem 1998). Early young individual of C. leucas in Barito River meet to other records of the juveniles of this species from around the world, including presence of early young C. leucas in Brisbane River, Australia, and a number of 14 small specimens of C. leucas in brackish Indian River lagoon system on the central east coast of Florida, USA (Snelson et al. 1984;Pillans 2006). The early youngs of C. leucas have the osmoregulatory plasticity to acclimate to salt water; and their preference for the freshwater inland of rivers where salinity is low therefore likely to be for avoiding predator and increased of prey abundance rather than because of a physiological constraint (Pillans et al. 2004).

IQBAL ET AL.
Ecologica Montenegrina, 24, 2019, 52-57 55 Carcharhinus leucas is most wide ranging requiem shark inhabiting marine, shallow waters, estuarine and up to upstream of large river (Compagno & Niem, 1998;Compagno et al. 2005;Ebert et al. 2013). Inland record of C. leucas has been reported in Malaysian Borneo, when a species has been reported as a dried fin provided by a villager in Sukau (Sabah) in 1996 and a juvenile (identification was made based on photographs) was caught in 2010 in main Kinabatangan River close to the Malbumi estate (freshwater habitat approximately 40 km upriver from the estuary) (Manjaji 2002;Min 2013). Recent finding of C. leucas in Barito River could be represent a first known inland record for Indonesian Borneo. The record of C. leucas c. 70 km in Barito River also represent further inland of this species in Bornean waters. A worlwide of global freshwater records of the C. leucas was compiled by Gausmann (2018). Previous known incidences presence of the C. leucas in freshwater area from around the world are: a freshwater record of 120 km inland in Zambesi River, Zimbabwe; recorded up to 420 km inland in Karun River, Iran; recorded of up to the distance of 130 km far inland in Lake Jamur, West Papua, Indonesia; a confirmed as far as 115 km inland at Wyrallah, Richmond River, Australia; a female C. leucas was reported in the Mearim River, 80 km far from the river's mouth, Maranhão State, Brazil; 67 juveniles C. leucas were monitored in Caloosahatchee River between 2003 and 2006 using 25 acoustic receivers, ranged 0 to 14 km with most more 5 km from the river's mouth, southwest Gulf Coast of Florida, United States; and recently a record of up to 75 km inland in Musi River, South Sumatra, Indonesia (Martin 2005;Heupel et al. 2010;Feitosa et al. 2016;Gausmann 2018;. The adaptation to freshwater environments has occurred independently many times in elasmobranch evolution (Lucifora et al. 2015). However, the factors affecting the poor penetration of elasmobranchs into freshwater environments are currently unknown, however, an important consideration may be the high urea requirement of many proteins in marine elasmobranchs (Ballantyne & Robinson 2010). It is more likely that C. leucas had not been reported because elasmobranch of Indonesian and Bornean waters had not been explored enough than species recently colonized in this area. Recent works suggest that few species of elasmobranch had been known occur locally but lacking for publication, such as Carcharhinus melanopterus, C. leucas, Fluvitrygon oxyrhynchus and Urogymnus polylepis (Iqbal & Yustian 2016;Iqbal et al. 2017;Iqbal et al. 2019a, b).
An individual of C. leucas found in Barito River has black tip of fins and size around c. 600-700 mm of total length, show specific characters of young individual (Compagno & Niem 1998). The young individual of C. leucas in Barito River is meet to other records of the young individual of this species from Indonesia, including presence of two species of C. leucas in Musi River, South Sumatra province (Iqbal et al. 2019a). The young C. leucas readily tolerate low salinities, and some are born in freshwater (Compagno & Niem 1998). In the future, collecting data using citizen science is needed to assess asses the occurence of C. leucas and evaluate the importance of riparian systems in Kalimantan waters as nursery area or ranging habitat for this species.  (print)) is peer-reviewed journal in which scienti c articles and reports are quickly published. The papers are in the elds of taxonomy, biogeography and ecology (for example: new taxa for science, taxonomic revision, and/or fundamental ecology and biogeography papers). Open access publishing option is strongly encouraged for authors with research grants and other funds. For those without grants/funds, all accepted manuscripts will be published but access is secured for subscribers only.

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