FISH DIVERSITY IN SELECTED ESTUARIES OF SOUTHERN TAMIL NADU
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Date
2014
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Fisheries College and Research Institute, Thoothukudi, Tamil Nadu Fisheries University
Abstract
This study was taken up to document the rich fish diversity of estuaries of southern Tamil Nadu to understand their current status. The study on the species diversity and abundance was conducted between September 2013 and June 2014 at three selected estuaries in southern TN namely Korampallam-Thermal estuary (N 8.76 609 4, E 78.16 519 4), Punnakayal estuary (N 8.64 703 6, E 78.12 354 4) and Manakudy estuary (N 8.08 952 8, E 77. 48 461 5).
Fish specimens for the present investigation were collected by using cast net (18 mm size) from the above estuaries. The fish samples were sorted up to species level. A total of 5216 samples were encountered during study period and the number of species identified was 80 belonging to 11 orders, 41 families and 61 genera from three estuaries of southern Tamil Nadu, India. Among the 41 families represented during the study period, the family Mugilidae was found to be dominant with 818 numbers of samples, which consisted of 4 genus and 5 species. On an average 36±6.3 numbers of fishes were caught from Thermal estuary. At Punnakayal estuary it was observed as 57.25±16 and in Manakudy estuary it was 57±16. Punnakayal estuary was represented with 76 species, the highest species richness, of which 41 species were found to be commonly represented in all the three stations and 5 species were restricted to Punnakayal estuary alone. The study on species abundance revealed to be dominated by Mugil cephalus, Liza parsia, Etroplus suratensis, Nematalosa nasas, Arius subrostratus, Siganus lineatus, Oreochromis mossambicus, Chanda nama, Terrapon jarbua and Sillago sihama. The total length of individual fishes from cast net catches were recorded and biological characters like length frequency, length at first maturity and fecundity were studied for five species namely E. suratensis, M. cephalus, N. nasas, S. lineatus and . subrostratus. Length frequencies graph was generated using the FiSAT computer software for E. suratensis (3-25.5cm), M. cephalus (3.5-38cm), N. nasas (3.8-24cm), S. lineatus (7-32cm) and A. subrostratus (7-34cm). The length at maturity varied between species and it was estimated for N. nasas (13.5 cm TL), A. subrostratus (14.8 cm), E. suratensis (17.4 cm), S. lineatus (22.5 cm) and M. cephalus (23.2 cm). The fecundity length relationship revealed a high correlation in E. suratensis and S. lineatus while it was poorly correlated for M. cephalus and A. subrostratus. The average absolute fecundity of A. subrostratus was fewer with 28 while it was observed as higher in S. lineatus (2.5 lakh). Environmental data collected at each site included water depth from 0.8m to 3m range. Salinity was recorded higher 32.5(±13.3) at Thermal bridge estuary while the lowest 17.5(±18.7) was realized at Manakudy estuary. Temperature fluctuated between 24.8 to 31˚C and pH ranged from 7.0 to 7.3. Zooplankton samples were collected by bolting silk (no 10, mesh size-158 μm) plankton net at surface water and analyzed. The species composition and abundance data were recorded during the four seasons namely, Summer (Apr-May), Pre-monsoon (Aug-Sep), Monsoon (Oct-Dec) and Post-monsoon (Jan-Mar) and biodiversity indices were calculated for various seasons for all the three stations using PRIMER v6 statistical package developed by Plymouth Marine Laboratory, UK. The highest Shannon – Wiener diversity (H’) value was observed at Punnakayal estuary (4.161) followed by Manakudy estuary (4.15) and lowest at Thermal Bridge estuary (3.65). The highest Margalef’s species richness (‘d’) value was observed higher at Punnakayal estuary (12.91) followed by Manakudy estuary (12.77) and the lowest at Thermal Bridge estuary (7.93). The Pielou’s evenness (J’) was estimated for the different seasons falls in the range of 0.96501-0.9795, 0.95929-0.97391 and 0.96084-0.9730 for Thermal Bridge estuary, Punnakayal estuary and Manakudy estuary respectively. The highest taxonomic diversity value was observed at Punnakayal estuary (85.04) during summer and the lowest at Thermal Bridge estuary (78.06). Among the three estuaries studied, the taxonomic distinctness (Δ*) was found to be lowest at Thermal bridge estuary during monsoon and the highest was observed in Punnakayal estuary during summer season. Other taxonomic diversity indices also indicated significant temporal and spatial differences. The total phylogenetic diversity (sPhi+) value for Thermal estuary was 2333.333 whereas the value was relatively higher at Manakudy estuary (4166.667) and Punnakayal estuary (4233.333). Analyses on seasonal variability in Bray Curtis similarity index for individual estuary revealed Korampallam-Thermal estuary, Punnakayal estuary and Manakudy estuary had 84.706%, 82.181% and 83.09% of similarity respectively between summer and pre-monsoon seasons. Bray Curtis similarity measures among the fish communities separated the stations into several clusters based on seasons. Thermal bridge estuary sampling data form a separate cluster while Manakudy and Punnakayal form another cluster. The result indicated that the similarity between Punnakayal estuary and Manakudy estuaries are higher up to 98.557%. In present study, the range of ANOSIM value is 0.1 which indicates the goodness of the fit. The analysis on diversity indicated a stable and rich fish community at Punnakayal and Manakudy estuary.