Encounter Records and Possible Use of Human-Modified Aquatic Habitats by the False Gharial (Tomistoma schlegelii) in Musi Rawas Regency, South Sumatra

The accelerating rate of land-use change in tropical regions has resulted in significant landscape transformations, converting natural ecosystems into agricultural fields, human settlements, and artificial water infrastructure [1]. From a conservation perspective, these environmental modifications often lead to habitat loss and fragmentation, posing severe challenges for large, wide-ranging predators [2, 3].

Indonesia hosts four crocodilian species: Crocodylus siamensis, Crocodylus novaeguineae, Crocodylus porosus, and Tomistoma schlegelii [4, 5]. The latter, commonly known as the false gharial or buaya sinyulong, is a large crocodilian characterized by its distinctive elongated snout [4, 6]. Ecologically, T. schlegelii shows a strong preference for peat swamp forests and low-gradient river systems with dense riparian vegetation [7]. Due to its naturally cryptic behavior and the widespread degradation of peatland habitats, the species remains relatively understudied while facing severe extinction risks [8, 9]. Consequently, T. schlegelii is classified as Vulnerable (VU) on the IUCN Red List, listed under CITES Appendix I, and fully protected under Indonesian law [8].

Historically, in South Sumatra Province, official records of T. schlegelii were concentrated in the eastern lowlands, particularly within the peat swamp ecosystems of the Lalan River basin in Banyuasin Regency [10]. While some crocodilian species are known to occasionally utilize human-dominated landscapes [11], documented encounter records for peat-swamp specialists like T. schlegelii in non-peatland, highly modified environments remain extremely limited [5].

Musi Rawas Regency, located in the western region of South Sumatra, has experienced substantial agricultural development and the expansion of artificial irrigation networks [9, 12]. In recent years, local media and community reports have increasingly noted opportunistic sightings, net entanglements, and captures of T. schlegelii within these irrigation canals and nearby aquaculture ponds [1]. These reports suggest that artificial water bodies may serve as alternative or temporary aquatic habitats, potentially influenced by ongoing environmental pressures on natural water bodies [9].

However, data regarding the presence of T. schlegelii in western South Sumatra primarily consist of opportunistic community sightings and rescue reports rather than long-term population surveys [5]. To address this knowledge gap, this study compiles and verifies encounter records of T. schlegelii in Musi Rawas Regency across a ten-year timeframe (2016–2026) [1].

By synthesizing direct observations and verified digital media mining, this study aims to: (1) document the contemporary geographic presence of T. schlegelii in western South Sumatra; (2) categorize the aquatic habitat types where encounters occurred to evaluate the possible use of human-modified environments; and (3) examine the implications for human-crocodile interactions to inform practical local targeted local risk mitigation strategies.

3.1 Spatial-temporal dynamics and encounter frequencies of Tomistoma schlegelii

Based on investigations, digital data extraction, and morphological verification spanning the ten-year period (2016–2026), a total of 14 unique encounter records of Tomistoma schlegelii were confirmed within the administrative boundaries of Musi Rawas Regency. This dataset provides a temporal encounter inventory for the species in the region.

Chronologically, the highest frequency of recorded occurrences was documented in 2021 and 2024, with each year accounting for 4 independent encounter cases across different sub-districts. However, this temporal distribution must be interpreted with caution. Rather than reflecting a true biological population growth or conflict escalation, these record peaks likely stem from reporting bias, increased social-media visibility, higher smartphone penetration, and varying online news search availability during those specific periods. The detailed chronological encounter records, including administrative locations, habitat settings, and interaction classifications, are presented in Table 1.

These encounter records confirm that the spatial range of Tomistoma schlegelii in South Sumatra Province extends beyond its historically documented strongholds in the eastern lowland peat swamps (e.g., Banyuasin Regency; [7]) to include verified, repeated encounters in the western inland region of Musi Rawas Regency.

Table 1. Encounter records, habitat types, and classified interaction categories of Tomistoma schlegelii in Musi Rawas Regency (2016–2026)

The observed temporal pattern from 2016 to 2026 requires careful interpretation. Rather than representing a true biological population expansion or a sudden escalation in crocodile numbers, the peaks recorded in 2021 and 2024 are largely attributable to reporting and detection biases [14, 15]. Increased smartphone adoption, expanded cellular coverage in rural sub-districts, and higher engagement with local social media platforms during these years significantly heightened the likelihood of opportunistically capturing and sharing crocodile encounters [16, 17]. Consequently, these temporal peaks reflect variations in public reporting visibility and search engine data availability rather than underlying demographic shifts in local Tomistoma populations.

The ten-year dataset reveals a notable temporal shift in the nature of reported human-crocodile encounters. Earlier records (2016–2021) were predominantly characterized by passive sightings, accidental net entanglements, or entrapment in irrigation floodgates. In contrast, interactions documented between 2023 and 2026 included direct physical encounters resulting in human injuries along the Lesing and Suban rivers. This shift does not necessarily indicate increased aggressiveness in T. schlegelii, but rather highlights intensifying spatial overlap between human water-use activities (e.g., fishing, bathing, and riverbank agriculture) and crocodile movement corridors, thereby elevating the probability of accidental physical encounters [14, 18].

From a zoogeographical perspective, these verified encounter records extend the documented presence of T. schlegelii in South Sumatra Province beyond its historically recognized strongholds in eastern lowland peat swamps (such as Banyuasin Regency [7]) to include verified, repeated encounters in the western inland region of Musi Rawas Regency. However, in accordance with precautionary ecological principles, these 14 opportunistic encounter records confirm recent occurrence and repeated encounters [19, 20], but cannot be used to extrapolate population density, reproductive success, or long-term population stability in the regency.

3.2 Proportion of recorded encounters across aquatic habitat types

Historically, published records of Tomistoma schlegelii in South Sumatra have been centered on eastern peat swamp forest ecosystems, such as the Merang–Lalan hydrological system [8, 10]. The 14 verified encounter records in Musi Rawas Regency expand the known geographical occurrence of this threatened crocodilian in South Sumatra.

Among the total 14 opportunistic records collected, 57.1% (8 records) were documented within human-modified aquatic environments (primary/secondary irrigation canals and aquaculture ponds), while 42.9% (6 records) occurred in natural river systems. These percentages represent the proportions of recorded encounters within our opportunistic dataset and are not corrected for search or reporting effort. Therefore, they should not be interpreted as quantified habitat selection, preference, or true habitat-use rates, as total habitat availability and detection probabilities were not measured [21].

Similar utilization of human-modified waterways by T. schlegelii has been documented in degraded peat swamp landscapes in East Kalimantan and Sarawak, where artificial canals act as temporary corridors during seasonal water fluctuations [10]. high connectivity between natural tributaries (e.g., the Lesing River) and primary irrigation canals suggests that local water management infrastructure inadvertently facilitates crocodile movement, particularly during high-flow seasonal periods.

Rather than indicating permanent residency or true habitat preference, the presence of individuals within the Musi Rawas irrigation network likely reflects opportunistic dispersal between fragmented river segments. Open water-control infrastructure (such as unmonitored sluice gates) facilitates the ingress of crocodiles into agricultural waterways, effectively transforming drainage systems into functional dispersal pathways within highly modified anthropogenic landscapes [22, 23].

Furthermore, the ingress of crocodiles into artificial infrastructure is likely reinforced by localized resource attraction. Musi Rawas Regency features extensive freshwater aquaculture networks supporting high fish biomass, including cultivated species such as Oreochromis niloticus, Clarias sp., Channa sp., and Osteochilus vittatus. While artificial canals and aquaculture ponds lack the complex structural and hydrological features of natural peat swamps required for nesting and long-term reproduction, they provide temporary foraging refugia and movement corridors across agricultural landscapes.

3.3 Socio-ecological implications and human-wildlife interactions

To evaluate human-crocodilian interactions more precisely, verified encounters were classified into four distinct categories: passive sightings (n = 4), entanglements/captures (n = 5), aquaculture loss (n = 2), and human injury (n = 3) (Table 2). Notably, all physical injuries to humans (n = 3) occurred exclusively within natural river channels (the Lesing and Suban rivers) between 2023 and 2026 during direct water-use activities:

1. September 14, 2023 (Lesing River, Purwodadi District): A resident spearfisher in the late afternoon (16:00 WIB) sustained severe lacerations to the head and left hand. Species identity was confirmed as T. schlegelii based on the victim's detailed description of the characteristically narrow, elongated snout and corroborating local sighting reports.

2. August 3, 2025 (Suban River, Tuah Negeri District): A victim swimming across the river at 15:00 WIB suffered critical injuries resulting in the traumatic amputation of the left leg. The species was confirmed via the victim's description of the crocodile's slender, elongated snout.

3. January 13, 2026 (Lesing River, Megang Sakti District): A resident harvesting riverbank forage/grass at 09:00 WIB sustained bite wounds to the right thigh, witnessed and verified by nearby community members.

Table 2. Summary of Tomistoma schlegelii encounter categories by habitat type and timeframe (2016–2026)

Notably, all physical injuries to humans (n = 3) occurred within natural river channels (Lesing and Suban rivers) between 2023 and 2026 during direct water-use activities such as fishing or bathing. Between 2023 and 2026, a total of three attack incidents involving Tomistoma schlegelii were recorded in the study area. Each incident varied in terms of habitat context, victim activity, and injury severity (Table 1).

Conversely, interactions in human-modified landscapes consisted predominantly of non-fatal operational encounters, such as passive sightings, net entanglements/trapping in irrigation canals, and localized aquaculture predation. This distinction demonstrates that safety risks to human life are heavily concentrated along natural river stretches, whereas anthropogenic waterways primarily induce non-lethal infrastructure interactions and nuisance encounters [24].

The temporal sequence of these encounters suggests an evolving nature of human-crocodile interactions. Earlier records (2016–2021) involved passive sightings or accidental trapping in floodgates, whereas recent years (2023–2026) experienced direct physical attacks. The operational drivers underlying these conflicts vary by habitat type. Natural River Systems: Conflicts in natural rivers are driven by direct physical overlap during daily water utilization, such as fishing, bathing, sand mining, or riverbank vegetation collection. This shared spatial use significantly heightens the risk of accidental physical encounters [25, 26].

Modified Infrastructure (Canals and Ponds): Interactions in canals and private aquaculture ponds are impelled by animal movement corridors or localized resource attraction (e.g., opportunistic foraging on cultured fish). These intrusions frequently trigger local panic, leading to defensive trapping or retaliatory capture [27].

Shared spatial use of aquatic resources increases the risk of conflict for both local communities and crocodilian populations [28]. For communities, encounters cause severe safety hazards, physical trauma, and economic losses through aquaculture predation. For T. schlegelii, presence in anthropogenic spaces exposes individuals to risks of retaliatory killing, incidental net mortality, or permanent displacement [29].

Although several individuals captured by residents were successfully rescued and transferred to the South Sumatra Natural Resources Conservation Agency (BKSDA), reactive relocations alone are insufficient for long-term conservation. Sustainable management requires proactive landscape-level conflict mitigation, public risk awareness campaigns, and community-based monitoring networks [14, 15, 30].

3.4 Management considerations and practical recommendations

To manage human-wildlife interactions effectively and support the conservation of Tomistoma schlegelii in mixed-use agricultural landscapes, practical management strategies must combine spatial risk zoning, community involvement, physical infrastructure modifications, and rapid response mechanisms [31]. Based on the spatial distribution of encounter records and severe attack hotspots documented in this study, a tiered conservation and risk-mitigation priority matrix was developed for Musi Rawas Regency (Table 3).

Table 3. Proposed conservation and risk-mitigation priority matrix for Tomistoma schlegelii in Musi Rawas Regency based on recorded encounter and attack data

3.4.1 Spatial mapping and conflict risk zoning

Local conservation authorities (e.g., BKSDA South Sumatra) and municipal spatial planners can utilize Geographic Information System (GIS) mapping to delineate high-encounter hotspots along major river systems (e.g., the Lesing and Suban rivers) and interconnected primary irrigation canals [32]. Delineating conflict risk zones enables targeted resource allocation rather than broad, costly interventions. Installing clear, high-visibility warning signage in high-risk zones and constructing safe, barrier-protected community water access points (e.g., enclosed river-bathing enclosures) can effectively minimize direct physical overlap between residents and crocodilians during routine water-use activities [33].

3.4.2 Community education and public awareness

Although T. schlegelii has often been described as relatively less aggressive toward humans than Crocodylus porosus, the injury cases documented in this study demonstrate that serious attacks can occur when humans and crocodiles overlap at close range in riverine habitats [21]. Outreach should aim to prevent widespread panic and retaliatory killings while maintaining appropriate safety vigilance. Integrating local biodiversity conservation topics and river ecosystem awareness into regional school curricula can further enhance long-term conservation literacy among younger generations [34].

3.4.3 Localized response teams and co-management

Establishing localized conflict response units co-managed by BKSDA, local municipal authorities, village leaders, and community volunteers is essential for ensuring swift, coordinated responses to crocodile sightings or unexpected canal intrusions [35]. These community-based units should be equipped with standard reporting protocols, basic monitoring tools, and training in safe handling procedures. Implementing a rapid-response network mitigates public safety risks while reducing unnecessary mortality or permanent displacement of T. schlegelii individuals from regional aquatic networks [15].

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