| dc.description.abstract | A study of the diversity and ecology of the freshwater fishes of four river systems of Uttara Kannada District, Karnataka, India
The Uttara Kannada district (74°9’ to 75°10’ E longitude and 13°55’ to 15°31’ N latitude), which lies along the central part of the hill ranges called the Western Ghats, has a number of perennial as well as temporary water bodies such as tanks, pools, lakes, streams, and rivers. There are both smaller east flowing rivers (Dharma, Varada) as well as larger west flowing rivers (Kali, Aghanashini, Bedti, Sharavati, Venkatapura, etc.). Very little work has been done on the fish communities of this region, except for taxonomic accounts of fishes in some areas. Four of the west flowing rivers were chosen to study the diversity, distribution, and ecology of freshwater fish communities.
These rivers experience varying levels of human disturbances. Among the four rivers studied, Kali has four major dams along its stretch: Supa, Bommanahalli, Kodsalli, and Kadra. Sharavati has two major dams-Linganamakki and Gersoppa. At Dandeli, effluents from paper mills along Kali have affected water quality. Bedti is polluted to some extent by sewage discharge from Hubli and surrounding areas, while Aghanashini has minimal effluents, mostly limited to agricultural runoff and pesticides. Local fish kills caused by poisoning and dynamiting further reduce species richness and abundance. Therefore, a detailed study on fish species diversity, composition, distribution patterns, and the effects of disturbances is needed to highlight the need for protection and conservation of these natural riverine habitats.
Objectives of the Study
The main objectives of this thesis were:
To study the diversity and composition of fish species found in the four rivers.
To study the distribution patterns of these species across different scales-diurnal, site wise, habitat wise, regional, and across rivers-and their status in terms of rarity, endemicity, and endangerment.
To examine variation in species composition with habitat types, and variation along the stream gradient (from headwaters to downstream regions).
To correlate fish community structure with environmental gradients (changes in physical stream parameters).
To understand correlations between morphological features, habitat preferences, and feeding ecology of selected species.
To study the kinds of human disturbances affecting fish communities and the changes in species composition caused by these disturbances.
Methods
Data were collected on fish species, physical characteristics of study sites, chemical characteristics of water, riparian vegetation, etc. Fish sampling was carried out over two years (December 1996 – April 1999) at 24 pre selected sites representing natural and disturbed conditions. Six sites were selected on each river-three in the up ghat region (>300 m elevation) and three in mid and down ghat regions. Thus, eight “environmental regimes” were recognised (up ghat and down ghat in each river). Only perennial streams were sampled.
Habitats were sampled using gill nets, cast nets, drag nets, and hooks for rare or elusive species. Morphological measurements of 18 abundant, widely distributed species were taken to analyse ecomorphological relationships.
Main Results
A total of 10,771 individuals belonging to 92 species were identified.
25 species (27.2%) were endemic to the Western Ghats.
Cyprinidae was the most dominant family (45 species).
Rarefaction comparisons (per 1000 individuals) showed:
Sharavati had the highest species richness.
Aghanashini had the lowest.
Bedti had the highest abundance per sample.
Frequency distribution patterns showed:
32 species occurred at only one site.
At a regional scale, 58 species occurred in 1–3 environmental regimes; 34 occurred in 4 or more.
28 species occurred across all four rivers; 18 of these occurred in 6 or more environmental regimes.
Bedti and Aghanashini were most similar in species composition; Sharavati was least similar.
Regional comparisons showed that similar regions on different rivers were more alike than different regions on the same river.
Species richness across habitats:
Pools had the highest species richness.
Riffles had the lowest and most species in riffles were also common in pools and runs.
Upstream–downstream gradient:
Downstream regions had higher richness due to changes in habitat structure and physical characteristics.
Ecomorphology:
Body size/shape, head dimensions, mouth position, barbel presence, eye position, etc. correlated strongly with habitat and feeding preferences.
Index of Biotic Integrity (IBI) rankings for 9 sites showed:
Kali sites (Dandeli, Bommanahalli) were most disturbed.
Aghanashini and Bedti sites were least disturbed.
Fish communities can serve as effective indicators of disturbance for conservation planning. | |
