Sambas watershed is located at three regencies which are Bengkayang, Sambas, and Pemangkat with total area of 245,700 Ha and consists of two main river, Sambas and Kumba Sajingan river. Major land use in Sambas upstream is palm oil plantation, which is owned by three corporation which are Wilmar International, Duta Palma and KPN corp with total estimated area 97,380.9 Ha( Milliedefensie et al., 2007; MCI, 2013; SGS Indonesia, 2015; EoF, 2018; Walhi, 2020; Supriadi, 2020). Other anthropogenic activities which affects water quality are settlements, sand mining, illegal logging, paddy farming and rubber plantation. Before 2000, community used river as main clean water resources, when palm oil plantation operated, they started to harvest rainwater and collected water from the springs.
Water quality monitoring (2019) at 57 sampling sites, 66.7% was above the national standard due to high free chlorine level (0.03 mg/L) where the highest concentration was 0.67 mg/L at palm oil irrigation canal and 0.27 mg at Sambas tributary. Application of potassium chloride (MOP-fertilizer) and paraquat dichloride (herbicide) were suspected to be the source of chlorine contamination. Other finding was that 28% of sampling sites which were palm oil impacted tributaries and irrigation canals had phosphate above standard (0.2 mg/L). Nutrient enrichment in tributaries was indicated with densely populated water hyacinth. Sambas river water quality has been decreasing for the last 3 years based on environmental protection agency (DinPerKimLH), from unpolluted to slightly polluted. This assessment was done with unrepresentative sampling sites (3 sites along the river) (DinPerKimLH, 2020). Chlorine concentration even at lowest one damages the water resources. Increasing chlorine concentration cause damage to gill structure and serious problem for long term and makes them prone to stress related disease (Bartel, 2020).
T.R. Robert in 1976 conducted fish inventory at Kapuas watershed and found 120 genera and 40 family. Meanwhile, no record was found on Sambas fish inventory. Research area spread in two regencies (Bengkayang and Sambas) at West Kalimantan. Fish inventory was done by collecting fish species from middleman who collected fish from fishermen and following fishermen activities.
There was 25 fish species from 7 order (Cypriniformes, Siluriformes, Synbranchiformes, Osteoglossiformes, Beloniformes, Gobiiformes, and Anabantiformes) recorded in July to August 2020. Trophic structure of the recorded fish species was dominated with omnivore -invertivore/herbivore, where diet combines plants and animal with main diet consists of insect, mollusk and crustacea (invertivore) or plants (herbivore) (63.6%) and piscivore – invertivore (37.4%). Omnivore dominance occurs because specific components of diet are inadequate, where opportunistic omnivorous foraging habits make them more successful than specialist one (such as piscivore). Inverse correlation between omnivore and specialist (such as: invertivore and insectivore). The presence of native carnivore is an indication of river health because these fish are depended on complex trophic structure. In a decreasing river system, native carnivore tend to decrease or completely disappear (Rumondang, 2013). In case of Sambas river, there was no species which is native carnivore or piscivore (diet contains only smaller fish), which indicated that the availability of smaller fish inadequate to support the population.
Pesticide active agent such as glyphosate and paraquat which was used by palm oil plantation was toxic to aquatic life with mild to moderate toxicity to different species (FAO, 2020; Monsanto, 2020), where for example paraquat is moderately toxic to aquatic invertebrate which main diets for Sambas river fish species. Research on the impact of paraquat to aquatic invertebrate found that 50% population died in a day to 14 days after exposed 0.00086 to 29 mg/L paraquat (Eisler, 1990). Glyphosate is known highly toxic to fish fry of walking catfish (Clarias gariepinus) and nile tilapia (Oreochromis niloticus), where lethal dose inhibited efficiency gas exchange in fish and the most damage organ were gill, liver and kidney. Stress behavior shown were continuously jumping into air and breathing air, restless, moving from surface to bottom repeatedly and staying at the bottom.
Sambas tributaries plays important role in managing fish diversity and population as fish reserve. Species such as wallago catfish (Wallago leeri) and giant snakehead (Channa micropeltes) migrates from main river to tributaries to spawn. For the last 2 years, flooding wasn’t occurred in the area. This raise concern as flooding is an important event to maintain fish population as flooded riparian area and inundated forest become the breeding and nursery ground for fishes like giant featherback (Chitala lopis), hampala barb (Hampala macrolepidota) and tinfoil barb (Barbonymus schwanenfeldii). Giant featherback is included in the list of rare and threatened species based on PERMENLHK no. P20/MENLHK/SETJEN/KUM.1/6/2018 and IUCN red list status of extinct
species (Ng, 2020).
Small fishermen household whose income solely came from fishing struggling to met their daily needs. Their production cost (buying/ maintaining fishing nets/traps and boats, gasoline) was higher than their income. Mr. Asmadi, a local fisherman (60 years old), said that since palm oil plantation expansion (25 years ago) his catch was dramatically decreased. The number of fishermen going down drastically, for example there used to be 25 lanting house (10 years ago) at Sentangau river, but now only eight (8) left. Before the expansion, fisherman who have 100 ilars (a fishing trap) got hundreds of kilos, while now they only able to get four to ten kilos. Massive fish kills which occurred July last year and suspected due to illegal palm oil mill wastewater discharge is another threat which concern fishermen every year. Conservation effort to rehabilitate Sambas river should be involve multi-stakeholder in particular palm oil plantation as main pollution resources to add water quality in their water management plan. Flowing irrigation canals into artificial wetland to improve water quality before it is discharge into tributaries should be done to protect tributaries which become fish reserve and prospective area for fish protection area. Working with university to map population, habitat characteristic, reproductive and feeding behavior of giant featherback is important to establish fish protection area to support sustainability of its and other species stock in Sambas river. While working simultaneously with fishermen to provide additional income.
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