Abstract
Present study was carried out to assess the abundance and diversity of fin-fish and prawn species in the selected five reservoirs in the Northern Province, Sri Lanka. Fin-fish and prawns caught by multi-mesh gillnets, and rod and hooks, were sampled from January to December 2017. Relative abundance and diversity indices were calculated and, differences and similarities among reservoirs in different months were assessed. The hierarchical clustering was used in constructing dendrogram. Of the 27 finfish species and two freshwater prawn species identified in total, the highest number of species were observed in Muthayankattu reservoir (26 species) while Puthumurippu reservoir had the lowest (14 species). Oreochromis niloticus was the dominant species in all the reservoirs. Small reservoirs (Puthumurippu, Kalmadu and Muhathankulam) showed high Shannon-Weiner diversity index and evenness, though low in dominance index, compared to large reservoirs (Vavunikulam and Muthayankattu). Selective harvest methods, number of fishers and seasonal variation of hydro-climatic factors such as rainfall, strong wind and water level significantly influenced the diversity of fish species. Increasing fishing pressure and use of destructive fishing methods during low water level were the main contributors for diversity loss in the five perennial reservoirs studied.
Highlights
Reservoirs in tropics are primarily used for irrigation and/or hydroelectricity, and can cause high water level depletion since fisheries is a secondary activity (De Silva, 1996)
The study was conducted in five perennial reservoirs (Figure 1) in Northern Province of Sri Lanka, viz., Vavunikulam, Muthayankattu, Puthumurippu, Kalmadu and Muhathankulam with areas of 1275 ha, 1255 ha, 151 ha, 74 ha and 211 ha, respectively at Full Supply Level (FSL)
High species numbers were observed in large reservoirs; Muthayankattu (26) and Vavunikulam (23), followed by small reservoirs; Muhathankulam (22), Kalmadu (21) and Puthumurippu (14)
Summary
Reservoirs in tropics are primarily used for irrigation and/or hydroelectricity, and can cause high water level depletion since fisheries is a secondary activity (De Silva, 1996). Majority of reservoir fisheries are artisanal and highly seasonal in many parts of the world (Welcomme, 2001). Sri Lanka does not possess any natural lakes whereas its fish population is dominated by traditionally unexploited fish species (De Silva, 1988; Pet et al, 1999). These endemic and indigenous fish species are not completely adapted to lacustrine conditions. Exotic species play a major role in reservoir fisheries (De Silva, 1996)
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