Importance of Unregulated Rivers As Last Refuges of Native Fishes

International Journal of Fisheries and Aquatic Studies 2019; 7(1): 180-189 E-ISSN: 2347-5129 P-ISSN: 2394-0506 (ICV-Poland) Impact Value: 5.62 Importance of unregulated rivers as last refuges of (GIF) Impact Factor: 0.549 IJFAS 2019; 7(1): 180-189 native fishes; implications of habitat alteration and © 2019 IJFAS www.fisheriesjournal.com exotic species introduction in Sri Lanka Received: 14-11-2018 Accepted: 18-12-2018 SL Rajakaruna, KB Ranawana, AMTA Gunarathne and HMSP SL Rajakaruna Postgraduate Institute of Madawala Science, University of Peradeniya, Sri Lanka Abstract River Mahaweli in Sri Lanka was greatly altered by dams under the Mahaweli diversion Scheme. Fish KB Ranawana assemblages in segments of five tributaries of Mahaweli; Badulu Oya, upstream of Ulhitiya Oya and Department of Zoology, Faculty Loggal Oya (unregulated streams) and, Minipe and downstream of Ulhitiya Oya (regulated streams) were of Science, University of compared. Sampling was carried out in three selected 100 m segments from each study stream using Peradeniya, Sri Lanka hand nets, drag nets and cast nets. 40 fish species in 10 families were recorded. Ulihitiya downstream AMTA Gunarathne recorded the lowest abundance and species richness. Unregulated streams demonstrated a higher Department of Botany, Faculty proportion of endemics (Dry: 41 – 54% and Wet: 50 – 60%) while regulated streams had highest of Science, University of proportions of exotics in both seasons (Dry; 26 and 72 %; Wet: 34 and 66 % in Minipe and Ulhitiya Peradeniya, Sri Lanka downstream, respectively). The results suggest that native and endemic fishes are more sensitive to altered habitat conditions highlighting the importance of protecting the remaining natural habitats. HMSP Madawala Department of Botany, Faculty Keywords: river regulation, endemic fish, aquatic habitat conservation, dams, reservoirs of Science, University of Peradeniya, Sri Lanka 1. Introduction The fluctuations of river flow by river regulation can affect fish assemblages in rivers through [21, 1] physical displacement, behavioral changes and loss of habitats . By the time the world reached the twentieth century, most of the major rivers have been fragmented by dams or reservoirs to generate hydropower [14]. Several studies in different parts of the world have been conducted to see the impacts of river regulation on fish populations and have identified [11] reductions in diversity of native fish populations . A study showed that the abundance of native fish was higher in the catchments of unregulated river, Paroo while the alien fish species were dominating in the catchments of highly regulated Murray and Murrumbidgee rivers in Australia [11]. A study that compared the fish diversity between a regulated river (The Deerfield river in Western Massachusetts) and an unregulated river (West river in southern Vermont) in the USA has reported that the small, shallow and slow water fishes are adversely affected by [3] river flow regulation . Another study carried out in the USA comparing two segments (regulated and un-regulated) of the River Tallapoosa revealed that during the peak of the hydropower generation, the temporal habitat stability reduces, and as a result small-bodied fish including juveniles of some species and spring spawning fish, those adapted to shallow waters, [10] were reduced . Damming in the Mekong River in China has disturbed the upstream spawning of some biologically and economically important fish species, as the juvenile life stages of some species were trapped in impoundments of the river [7]. The plan to construct a dam across the River Frazer in British Colombia in Canada was halted as a result of the interventions by the fisheries associations and the scientists after evaluating the impacts on the [9] migration of anadromous Pacific Salmon by the construction of a dam across Frazer . A study in India demonstrated a decline of native fish diversity from upstream to downstream in a study conducted in the regulated river, Betwa and suggested that these decreases are due to loss of habitats following the river regulation [17]. In India, the construction of Farakka Correspondence barrage across the river Ganga has adversely affected some native fish species such as SL Rajakaruna Postgraduate Institute of Tenualosa ilisha (F. Hamilton, 1822), Catla catla (F. Hamilton, 1822) and Cirrhinus mrigala Science, University of (F. Hamilton, 1822) as the construction of the dam has caused considerable changes in the Peradeniya, Sri Lanka physical habitats of the river. As well as dam construction, introduction of exotic fish also has ~ 180 ~ International Journal of Fisheries and Aquatic Studies been identified as a major cause for reduction in fish diversity like River Mahaweli. A comparative study has been in India [17]. conducted by selecting free-flowing (un-regulated) and The Accelerated Mahaweli Developmental Project (AMDP) is regulated streams in the Mahaweli downstream, as the prior the largest river diversion program undertaken by the information on fish assemblages lacks. Government of Sri Lanka to date constructing five major dams and number of reservoirs across the longest river in Sri 2. Methodology Lanka. In Sri Lanka, Southwestern and Mahaweli 2.1 Description of the study sites ichthyological zones show the highest freshwater fish Five study sites (river segments) were selected in the diversity in the island [12]. At the time of inception of the immediate downstream of the Randenigala and Rantambe AMDP, it was predicted that the reduction of flow velocity twin reservoirs (with storage capacities of 861 and 21 million and increase in sediment loads could affect fish species, m3, respectively). All study sites are located in the especially the threatened endemic species including Green Intermediate Zone of the country with an annual rainfall of Labeo (Labeo fisheri D.S. Jordan and Stark, 1917), Blotched 1,500 to 1,700 mm. The terrain is more or less flat with a Filamented Barb (Puntius srilankensis Senanayake, 1985) and maximum elevation reaching up to 874 m asl and the area is Martenstyn Barb (Puntius martenstyni Kottelat and characterized by relatively undisturbed natural vegetation of Pethiyagoda, 1991) [13]. Some indigenous fish species, those dry-mixed evergreen forests [22]. The study streams included need to move upstream to reproduce, also were predicted to three un-regulated (UR) streams namely Badulu Oya (BAD- be affected by river regulation [30]. UR), upstream of Ulhitiya Oya (ULH-UR) and Loggal Oya However, no comprehensive study has been carried out so far (LOG-UR) and two regulated (R) streams, Minipe (MIN-R) to evaluate the present status of fish population in the and downstream of Ulhitiya Oya (ULH-R) (Figure1). Badulu Mahaweli river basin since the initiation of the project in late Oya (Oya = stream), Loggal Oya and Ulhitiya Oya are three 1970s. Not only in River Mahaweli, despite experiencing major tributaries of the River Mahaweli. The area receives major consequences of dam construction and river regulation rainfall mainly from the north-east monsoon (from October to in the region, comparatively few studies have been January) followed by a long dry spell from February to undertaken so far in tropical streams [27]. Therefore, this study August with a minor rainy season in April and May. Mean was designed to investigate the implications of dam annual temperature in the region is 31.5 °C (Hasalaka construction and fish species introduction in a tropical river Weather Station of Irrigation Department, Sri Lanka). Fig 1: Locations of the three un-regulated ((BAD-UR, ULH-UR and LOG-UR) and two regulated river segments (MIN-R and ULH-R) in the immediate downstream of the Randenigala-Rantambe reservoirs in Sri Lanka. ~ 181 ~ International Journal of Fisheries and Aquatic Studies 2.2 Sampling protocol depth) was analyzed in R 3.4.1.using non parametric Kruskal Fish sampling was carried out in three selected 100 m Wallis (KW) test and then post-hoc analysis for pair wise segments from each study stream. Sampling was carried out comparison done with dunn’s test whenever KW was six times per season (dry season from March to August 2014 significant. Shannon Diversity Index was calculated to and wet season from September 2014 to February 2015). determine the species diversity using the following formula. Three types of nets were used to sample fish; hand nets for smaller fish in pools, drag nets for smaller fish in runs and riffles and cast nets (mesh size 1.5 cm × 1.5 cm) for bigger fish in pools, runs and riffles. At each sampling event, the sampling was carried out for one hour (an effort). At each sampling, live fish samples were taken for identification Where R= Number of species; purposes. Number of individuals belonging to each species th Pi= Proportion of individuals or the abundance of i species was counted and they were photographed before releasing to Ln= Log base n the same habitat. The catch per unit effort (number of fish caught per net) and the number of species collected were 4. Results recorded. Riffles and runs were sampled in the opposite 4.1 Physical features of study streams direction to the water flow whereas pools were sampled The velocity of the water flow recorded randomly in different [31] towards the water flow . Few specimens from each species stream habitats (runs, riffles, and pools) showed differences were preserved in 70% ethanol for the confirmation of between streams and seasons (Figure 2.a). During both identity. Preserved specimens were transferred to a laboratory seasons, the mean flow velocity was significantly higher in in the Department of Zoology, University of Peradeniya and MIN-R compared to other study streams (Dry season: P= [25] identified using available guides . The velocity and the 1.01e-07, Wet season: P=1.55e-12) (Figure 2a). Of all study depth of each sampling site were randomly measured using streams, ULH-R showed the slowest flow velocities in both the flow velocity meter (Valeport, Electromagnetic Flow seasons.

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