Fish Assemblage Structure of Two Contrasting Stream Catchments of the Mahaweli River Basin in Sri Lanka: Hallmarks of Human Exploitation and Implications for Conservation

Abstract

Patterns of fish community composition in the Mahaweli ichthyological region of Sri Lanka were examined in agricultural tributaries of the Uma-oya catchment of the upper Mahaweli River in comparison to more pristine streams in a nature reserve in the Amban-ganga catchment. The Uma-oya catchment shows characteristics commonly observed in extensive agricultural exploitation such as impaired water quality and altered riparian vegetation. The most abundant fish species in the two regions were Garra ceylonensis, Devario malabaricus, and Rasbora daniconius, although their relative abundance differed between sites. G. ceylonensis and Neomacheilus notostigma were the only endemic fish species in common but the latter has been extremely depauperate. Endemism is higher in the reference sites (62.5%) than agricultural sites (ca. 25%); some of the reference streams showed greater diversity with unique fish species and a few species that have not been recorded previously in the catchment. The ichthyofaunal similarity between two catchments was 39% and fish species diversity was negatively correlated with stream gradients (Pearson correlation (-0.630); r 2 = 39.6% p = 0.028). Species density and biomass of G. ceylonensis and D. malabaricus were positively associated with some water quality parameters. The presence of exotic fish species were amongst the primary discriminants between human exploited and least-exploited (reference) streams. The possible negative impact of exotic Oreochromis niloticus (Nile tilapia) on indigenous G. ceylonensis is highlighted. This paper provides impetus for making several hypotheses for sustainability of stream fish assemblages in highly exploited agricultural catchments in Sri Lanka.

Species Diversity, Distribution and Abundance of Fishes of Seti Gandaki River Basin, Pokhara, Nepal

“…Generally, higher values of the Simpson Index or concentration of dominance (C) were observed in the present study indicating more effect of dominant groups upon others. Similar values were reported by Sumith et al (2011), andShukla andSingh (2013) in the Mahaweli River basin, Sri Lanka, and in the Aami river, India. To conclude, cyprinids had higher density than balitorids, channids, mastacembelids, sisorids, amblycipitids, belonids, cobitids and bagrids at all sites in the present water-bodies.…”

“…Likewise, lower values of equitability (J') of fish were observed in the present study, which could be related to human perturbations in the water-bodies. Similar values were mentioned by Brownlow and Bolen (1994), Lasso (2001) and Sumith et al (2011) in alluvial streams, North Carolina, USA; in the Upper Rio Negro, Bolivian Amazon; and in the Mahaweli river basin, Sri Lanka, respectively. Generally, higher values of the Simpson Index or concentration of dominance (C) were observed in the present study indicating more effect of dominant groups upon others.…”

Fish fauna of Doon Valley, District Dehradun, Uttarakhand, India

“…The overall assessment regarding the family-wise representation all over Doon Valley in general and Eastern and Western drainages in particular, has revealed the domination of the members of family Cyprinidae (Hora and Mukherjii, 1936;Uniyal and Mehta, 2007) as has also been reflected in earlier observations from Himalayas and Doon Valley (Grover et al, 1994;Uniyal, 2002;Johal, 2002;Nautiyal, 2005;Pathani and Upadhyay, 2006;Negi and Negi, 2010b) or other parts of the country (Bhat, 2003(Bhat, , 2004Lakra et al, 2010;Shahnawaz et al, 2010) and abroad (Jayaratne and Surasinghe, 2010;Sumith et al, 2011). This fact lends support to the widely acclaimed fact that Cyprinidae tops the list of 9 largest (most species -rich) families viz., Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae and Scorpianidae (Nelson, 2006).…”