A survey on Marine Fish Species In River of Mahakam East Kalimantan, Indonesia

A first survey on a community marine species in river of Mahakam East Kalimantan was performed in December 2015 and May 2016. Fish samplings were carried out from two locations the lower and the middle part of Mahakam. Whilst hydrometric observation of current velocity, water depth and tide was measured not only at the locations but also along the river from 2013 to 2017, tide was only observed in the lower part of Mahakam. However, marine fish species were recognized to reach up the middle part of Mahakam, 230 km from coastline. To describe a community fish structure and its dissimilarity of the two surveyed locations, diversity and bray Curtis index were applied. Almost 15 marine fish species identified in river of Mahakam was demersal fish and index of the similarity of marine fish community between the locations only 0.106.


Introduction
Mahakam is the biggest river (more than 900 km in length) in East Kalimantan province. Its associated floodplain such as lake Semayang and Melintang in the middle part and the estuarine waters of the Mahakam Delta in the lower part have valuable natural resources for people who live along the river. According to Yang et al. (2005) that growth rate of intertidal wetlands at the delta front depends on the riverine sediment supply. These areas are used not only for fishing and aquaculture activities but also for other purposes like sand mining source and local traditional ferry (Suyatna, 2007). An annual sediment load of the Mahakam river ranges from 50 to 100 Mt/yr (Milliman and Farnsworth, 2011) while Krishna river in India 170.4 Mt/yr (Vaithiyanathan et al., 1988). Sediments are an essential component of rivers that functions as the input for the food chains and trophic webs and the migration trigger of fish (Eric and Eric, 2012). However, suspended sediments including turbidity may affect fish survival rates by altering their physiology, behaviour and habitat (Berman et al., 2001), and are significant contributors to decline in populations of aquatic organisms in lotic waters through local food chain beginning at the primary trophic level (Henley et al., 2000). A river with high sedimentation decreases light penetration into the water column and hence, reduces photosynthesis (Rosli and Yahya, 2012). Kalimantan already lost a large part of its original rain forest because of massive logging from the 1970s to the 1990s for reasons of timber production (Jorde, 2013) and other purpuses such as palm plantation, in December 2013 the province had granted location permits to a total of 344 companies, covering 3.9 million hectares; IUP permits to 215 companies, covering 3.1 million hectares; and HGU concessions to 127 plantation companies, covering 1.1 million hectares (Anerson et al., 2015). Research findings on impact of the oil palm plantations conducted in West Kalimantan and Papua as well as coal mining indicated soil erosion and water pollution (Obidzinski et al., 2012 andRashid et ai., 2014) i.e excessively high sediment loads as mentioned by Buschmans et al., (2011) andPorter-Bolland et al., (2011) and effluent from palm oil mills and chemical and fertilizer run-offs that enters rivers causing a high concentration of heavy metals, particularly lead, in the fish (Shell  et al., 2009), such economic development has not been only worried affecting to fish life of their migration but also to people health that consume as foods, and globally riverine fish face many anthropogenic threats including riparian and floodplain habitat degradation, altered hydrology, migration barriers, fisheries exploitation, environmental (climate) change, and introduction of invasive species (Cooke et al., 2012). Fish of Mahakam and from its floodplain have been poorly studied in the past, with very rarerly published fish information available. In relation to this, the study was not only focusing on fish community structure but also to identify marine and introduced species found in Mahakam environment, the hydrological aspect was also discussed.

Materials and Methods
Data of hydrometric measures such as current velocities, water (river) surfaces (tide) and river depths was gathered in different dates and various years, 2013 to 2017. The hydrometric surveys were realized in collaboration with coal mines and oil palm companies prior to constructed their loading ports. The surveys used tide staff for leveling surface water (every 30 minutes observation), Braystoke current flow meter made in UK for measuring current velocities (at surface, middle and bottom of river) and echosounder GPS map 2108 Garmin for measuring depth.
In December 2015, fish samplings were carried out in an area of floodplain of Semayang lake, Kotabangun located in the middle part of Mahakam (230 km from coastline) using trap net of Sawaran. Principally, sawaran (fish trap) consisted of main guiding barrier net 110m in length equipped with wing net 10m in length and its height of 1.0m on both sides, all fish from around swamp plants that move to the lake would follow the guiding barrier net into a chamber sizing 4.0m (l) x 2.0m (w) x 1.75m (h) where fish were collected after being left for 24 hours, from morning to the next morning. And In June 2016, fish samplings were done in river of Mahakam at Sungai Meriam located in the middle part of Mahakam (44 km from coastline) using minitrawl measuring 11m long and 13.5 m wide, main net mesh size 2.0 inches and cod end net 0.5 inches, motorized with a boat sizing 11m x 1.2m x 1.0m to tow the net from 5.0 to 10 minutes (hauling).
Fish identification was referred to the field manuals according to Kottelat (1992) Masuda et al., (1975); Seah et al. (2009);Iqbal (2011). Diversity index such as Shannon-Weaver, Sympson, Margalef species richness (using log) including Bray Curtis index of dissimilarity between two locations were made by statistical program of the PAST version 3.13 (Palaeontological Statistics) while mapping was realized with Map INFO v. 8.5.

Hydrography
It is important that all measured sampling points of hydrometric survey is shown to indicate their distributions along river especially at sampling location of fish ( Figure. 1). On the basis of survey downtown of Samarinda which belongs to the lower part of Mahakam was significantly influenced by tide of Makassar strait but not for the middle part of Mahakam and its associated floodplains such Semayang lake ( Table 1).
The Table 1 showed the various water level by date. Lower part of Mahakam indicated daily regular fluctuation of water level of two high and low a day, the highest level recorded 1.45m. The river that experienced two nearly equal high and low water level each day is classified as the type of tide mixed semidiurnal (Hicks, 2006). While the middle part of Mahakam did not show such fluctuation that means there was no effect from the sea, the level just descended or ascended depending on the season (wet and dry season). In the wet season 2017 (measured by tide staff, a vertical graduated rod) recorded water level from February to May increased 4.11m (from 2.77m to 6.88m see the Table 2. Mislan (2015) monitored water level in the middle part of Mahakam within 21 years from between 1989 and 2010 reached up to 11.28m (observation starting from 3.06m to 14.34m), the lowest level was occured in the year of 1997 and almost lakes being dried out completely (Sarwono, 1989).
This phenomenon may positively correlate between water depth and current velocity and fish diversity (Lakra et al., 2010) even with fish habitat suitability as well (Macura, 2016).
The results of measurement of water depths and velocities along the Mahakam and its associated floodplains Semayang and Melintang lake during the study are presented in the table below.    According to the table 2, between depth of Mahakam and associated floodplains was differed, depth of Mahakam, tributary that flowed into Semayang, floodplains of Semayang and Melintang were measured 34.2 m, 4.6 m, 6.6 m and 1.9 m and respectively (Table 2), while depths of two sampling fish locations (lower and middle part of Mahakam) are presented in the Figure 2.
Current velocities varied from 0.19 to 1.22 m/sec. Velocities flowing from the middle to the lower part of Mahakam being progressively decreased (1.27 to 0.22m/sec), velocities in floodplains (Semayang and Melintang) were not detected. Hooper and Kohler (2000) reported the main factors that affect the velocity are such as slope gradient (gradient is the drop of the elevation of a river), the roughness of the channel and size of river and tide, and according to Syvitski et al. (2012) the bottom river of Mahakam from 0 m downstream to 591 km upstream has slope gradient 100 m above sea level and therefore tide was only observed to affect within the lower part of Mahakam.

Fish structure community
Number of fish identified from two sampling locations were 45 species which consisted of 20 species from the lower part of Mahakam, Sungai Meriam Anggana representing 14 families, seven orders, one class (Actinopterygii) and 29 species in the middle part of Mahakam Kotabangun (floodplain or lake Semayang) representing 20 families, seven orders and two classes (Actinopterygii 27 species and Osteichthyes 2 species). Lengthweight size distribution of all fish species of the two locations was presented as shown in the Table 3.  Of 20 fish species observed in the lower part of Mahakam, 13 fish were marine species including brackishwater fish (Figure 3). While from 29 fish species observed in the middle part of Mahakam, only one species was commonly living in marine area, Lampa-lampa or Bilis (Bareback anchovy, Papuaengraulis micropinna).  All marine fish species found both in the lower and middle part of Mahakam was known to distribute along coastal and sea waters of Makassar strait from southern to northern of Panajam Paser Utara district (Bappeda and Fpik Unmul, 2017), Kutai Kartanegara district (Suyatna et al., 2010), Bontang city (Suyatna et al., 2016) and Sangatta Utara district (Juliani and Suyatna, 2014). Both marine and freshwater fish species in the lower part of Mahakam was also reported in the result of a biophysical observation of Mahakam river .

Suyatna et al., 2017, A survey on Marine Fish Species In River of Mahakam
Based on the Table 4, number of fish species of both locations belonged to moderate. However, higher value of shannon and evenness index observed in the middle part of Mahakam (floodplain of Semayang) explained the population size of fish was more homogenous and no species dominance. Species richness was also higher at the same sampling location. While the value of the bray curtis index showed the similarity of fish species number between the lower part and the middle part of Mahakam was only 0,106 meaning significant different.

Conclusion
This study succeeded observing a marine fish species community in river of Mahakam. Thirteen species was identified in the lower part of Mahakam, 44km from coastline and only one species was found in the middle part of Mahakam, 230km from coastline. On the basis of a community of fish, the two sampling locations showed almost completely different. Unexpected fish the introduced fish of Carp (Cyprinus carpio) and Nile Tilapia (Oreochromis niloticus) were also observed in the middle part of Mahakam.