FISHES

The Pelagus area is located in the middle stretches of Batang Rajang, in the central part of Sarawak, under the administrative division of Kapit. The area is well-known for its long and dangerous rapids that extend for a distance of 12.8 km. Over the years, these “rapids of death” have capsized many boats along its treacherous and unpredictable waterways. To determine the fish composition in the Pelagus area, three study sectors were sampled, namely, Nanga Benin, representing the downstream area; Nanga Peraran, the midstream area; and Punan Bah, which represents the upstream areas. At each sector, sampling stations were established along the Batang Rajang and its tributaries (Fig. 1; Table 1). Field sampling was conducted in April and August of 2014, as well as January and July of 2015. Fishing methods applied include gill nets of various mesh sizes (2.5 cm, 3.81 cm, 5.08 cm, 7.62 cm and 10.16 cm), 3-layered nets, cast nets (Fig. 2–3) and electro-shocking. Similar fishing efforts were employed at the different stations (Fig. 4) and at other study sectors. Fishes caught were mostly identified in the field (Fig. 5), but others were brought to the laboratory for further study

Changes in Water and Sediment Quality of a River Being Impounded and Differences Among Functional Zones of the New Large Tropical Hydroelectric Reservoir

Though more large tropical reservoirs are being constructed to meet the increasing energy demand, knowledge on the impact of damming a tropical river and the differences along the river after its impoundment is scarce. Thus, the present study aimed to increase our understanding of such differences both longitudinally and vertically. Water and sediment samples were collected at three different functional zones in the Murum River basin 10 months after impoundment began. Results show that the impoundment has an impact on both the water and sediment. Longitudinal variations of water and sediment characteristics were observed at different functional zones. The upstream riverine zone subjected to anthropogenic activities serves as the main input of suspended solids and nutrients to the reservoir. The nitrogen changed from a high nitrate and low ammonia condition prior to impoundment to a low nitrate and high ammonia condition due to the accumulation of organic matter and slow nitrification rate after impoundment. In the transitional and lacustrine zones, vertical stratifications of dissolved oxygen and temperature were observed. The thickness of a well-oxygenated column for sensitive aquatic organisms was only 2 m at some stations. Water quality in all zones showed impairment during the filling phase as compared to the good water quality index before impoundment. The reduction of suspended solids in the surface water column in the transitional and lacustrine zones is a positive change for aquatic organisms. Sediment characteristics were found to be distinct in the transitional zone, where it was lower in sand and higher in silt, clay, organic carbon and nutrients in contrast to the riverin

Macroinvertebrates

The drainage system of the Pelagus area comprises first to sixth order streams, with slow to fast flowing water and moderate gradient channels. The tributaries are important feeder streams in sustaining hydrological functions of the main Rajang River, especially as a result of the construction of two hydroelectric dams in the upper stream, the Bakun Dam and Murum Dam. Macroinvertebrates sampling was conducted twice at 27 tributaries between 2013 and 2016. Three replicates of kick-net sampler (30 × 32 cm, 400-micron mesh size) were made for each visit, yielding a total of 162 samples. Hand collecting at night along riverbanks and forest trails was carried out for semiterrestrial crabs. Specimens caught from local fishing tools, such as castnet (‘jala’) and traps (‘bubu’) were also recorded. The multiple sampling techniques used have produced a macroinvertebrate inventory for the Pelagus area, which shows over 79 species in 52 families and 12 orders, comprising aquatic insects, crustaceans, molluscans and aquatic worms. All crabs and some taxa of aquatic insects are endemic to Borneo. Macroinvertebrates were assigned to functional feeding groups, and field observations of species occurrence on major substrate types were recorded. Analysis of functional feeding groups shows that predators and gathering-collectors are common in all stream orders. Macroinvertebrates are well represented in third order streams, which imply that the stream order is the most productive. High beta diversity (dissimilarity) between lower order stream (1st order) and higher orders (> 3rd order) suggests that conservation management of river basin should be inclusive in all stream orders. Macroinvertebrates are good indicator for stream condition in the Pelagus area. Low taxa richness of sensitive orders such as Ephemeroptera, Plecoptera and Trichoptera (EPT) may indicate that effects of logging activities persist after 30 years. EPT-values also show low adaptation to new and unstable substrates originating from the logged catchment area.Some larger species, such as shrimps, prawns (e.g., Macrobrachium rosenbergii), snails and crabs are important sources of protein for the local people

MACROINVERTEBRATES

The drainage system of the Pelagus area comprises first to sixth order streams, with slow to fast flowing water and moderate gradient channels. The tributaries are important feeder streams in sustaining hydrological functions of the main Rajang River, especially as a result of the construction of two hydroelectric dams in the upper stream, the Bakun Dam and Murum Dam. Macroinvertebrates sampling was conducted twice at 27 tributaries between 2013 and 2016. Three replicates of kick-net sampler (30 × 32 cm, 400-micron mesh size) were made for each visit, yielding a total of 162 samples. Hand collecting at night along riverbanks and forest trails was carried out for semiterrestrial crabs. Specimens caught from local fishing tools, such as castnet (‘jala’) and traps (‘bubu’) were also recorded. The multiple sampling techniques used have produced a macroinvertebrate inventory for the Pelagus area, which shows over 79 species in 52 families and 12 orders, comprising aquatic insects, crustaceans, molluscans and aquatic worms. All crabs and some taxa of aquatic insects are endemic to Borneo. Macroinvertebrates were assigned to functional feeding groups, and field observations of species occurrence on major substrate types were recorded

Seasonal variations in water quality of a tropical reservoir: Considerations for cage aquaculture expansion

A study of water quality of the 30 year-old Batang Ai hydroelectric reservoir at different depths and locations was conducted to give a better understanding of the water quality status for aquaculture expansion. The study was conducted at four locations where two were identified as potential cage culture sites but nearby current operations. Temperature and dissolved oxygen (DO) profilings and 13 other parameters at 0.2, 10 and 20 meters depths were also studied. It was found that the difference in DO between seasons were significant. Pockets of high nutrients and hydrogen sulphide were observed at 10 and 20 m nearby the two cage culture sites in dry season. Additionally, regardless of season, those sites showed significantly higher 10 m and 20 m suspended solids. At one of the locations near cage culture, dry season total phosphorus and ammonia were the highest at all depths and chlorophyll-a was at eutrophic level at 10 m depth. All these are attributed to aquaculture waste, pre-marketing fish processing and the lack of mixing. Water Quality Index shows that the 0.2 m depth is suitable for sensitive aquatic organism. However, dry season 10 m water column of the two potential cage culture sites was polluted. Though the cages do not normally extend to 10 m deep, when overturn occurs, it could cause fish kills. Thus, in reservoir cage culture, elimination of reservoir pre-market processing is crucial and considerations have to be made on the proximity to the current operations and dry season water quality limitations. © 2018, BIOFLUX SRL. All Rights Reserved

Tolerance of Barbonymus schwanenfeldii under sulfide exposure

Hydrogen sulfide, a common occurrence in hydroelectric dam environment, is potentially toxic to living organisms in the environment. However, studies on the response of indigenous fish species when exposed to sulfide are still lacking in literature. Thus, behavioral responses and mortality of an indigenous fish species, Barbonymus schwanenfeldii, were determined in the laboratory where juveniles were exposed to different concentrations of sulfide. Three experiments were conducted during the exposure, namely, gradual sulfide exposure, sulfide exposure under lowering DO condition and gradual sulfide exposure under lowering pH condition. Methylene blue method was used to analyze the water for actual total sulfide concentrations. Behavioral responses, dissolved oxygen level and pH were taken and recorded. Four behavioral responses observed in sulfidic water were huddling, aquatic surface respiration, loss of equilibrium and mortality. However, in negative control no such responses were observed during the duration of the experiment. As the sulfide concentration increased, the time taken to the occurrence of behavioral responses decreased indicating increased toxicity. The LC50 at 6 h was estimated as 507.8 µg L -1 total sulfide (490 µg L -1 H2S) at 95% confidence level. Under sulfide exposure in lowering pH condition, mortality was significantly faster than the other two experimental conditions. This study shows that juveniles showed behavioral response to all sulfide concentrations tested and lowering both DO and pH levels increased the sulfidic toxicity as they led to faster mortality of juveniles. Key Words: huddling, aquatic surface respiration, loss of equilibrium, toxicity, mortality

Length-weight relationship of six loach species from tropical forest streams in Sarawak, Malaysia

Length weight relationships (LWRs) are presented for six loach species belonging to two families of Gastromyzontidae and Nemacheilidae captured in the Baleh River Basin, Sarawak, Malaysia. One time sampling was conducted at each station representing first- to fourth-order tributaries in the Baleh River Basin from April 2014 to November 2015. Loach samples were collected via electrofishing method and measured for total length to the nearest 0.1 cm and weighted to the nearest 0.1 g immediately after capture. The values of the equation parameter ‘b’ of the LWR falls within the range of 2.5 to 3.5 for six loach species in Sarawak, Malaysia

Assessment of water quality and pollutant loading of the Rajang River and its tributaries at Pelagus area subjected to seasonal variation and river regulation

Other than seasonal variation, river regulation due to hydropower generation can influence the water quality downstream. Therefore, the objectives of this study were to determine the water quality and estimate the pollutant loading of the Rajang River and its tributaries at the Pelagus area downstream of the Bakun hydroelectric Dam. The study was conducted at 11 stations three times, in July 2015 during dry season (spillway opened), in January (spillway closed) and March 2016 (spillway opened) during wet season. Results of the water quality classification show deterioration from 91% Class II in dry season to 64–82% Class III in rainy season mainly due to an increase in total suspended solids caused by soil erosion in the river basin. The pollutant loads were high particularly during wet season with TSS reaching 945,763 Mg/day, and hence, mitigation measures to reduce the pollutant loads in the river are essential. Nevertheless, two tributaries, Mela River and Kapit Hulu River where stations 4 and 5 are located, are recommended for the conservation of sensitive aquatic organisms as they are classified as Class II throughout the seasonal variation indicating good quality freshwater. The Bakun dam turbine discharge affected the downstream river water quality as shown by the low dissolved oxygen content of < 5 mg/L extending beyond 204 km downstream of the dam when the spillway was closed. Thus, raising the level of dissolved oxygen downstream of the dam during closed spillway and reducing suspended solids are recommended for the benefits of sensitive aquatic organisms