International Research Journal of Biological Sciences ___________________________________ ISSN 2278-3202Vol. 1(4), 17-21, August (2012) I. Res. J. Biological Sci. International Science Congress Association 17 Decline of fish diversity in the anthropogenically polluted Thane creek along the Central West Coast of India Quadros Goldin1,2 and Athalye R.P.B.N. Bandodkar College of Science, Chendani, Thane 400601, Maharashtra, INDIA Sálim Ali Centre for Ornithology and Natural History (SACON), Anaikatti Post, Coimbatore 641108, Tamil Nadu, INDIAAvailable online at: www.isca.in Received 15th June 2012, revised 19th June 2012, accepted 26th June 2012Abstract The fish diversity and associated environment of 12 strategically selected intertidal stations along the extremely polluted Thane creek on the west coast of India were studied for a year and compared with past available data to investigate changes in the creek ecology due to various anthropogenic activities like industrial, domestic, and solid waste disposal along with land reclamation. Hydro-sedimentological investigations revealed enhancement of total nitrogen (TN) and organic carbon (Corg) load and hypoxic levels of dissolved oxygen (DO) over the years. Silt component of sediment was increasing, with proportionate decrease in clay due to various anthropogenic disturbances. 12 species of fish were recorded along the entire length of the creek with dominance of only 5 species that occurred throughout the year, namely Mugil cephalus, Mystus gulio, Mystus shingala, Tilapia mossambica and Scylla serrata where as the other fishes were rare in their occurrence. A comparison with the past literature for the study area revealed decline in the fish diversity. As per the energy transfer theory, it was observed that the benthos in the study area can support an average fishery yield of at least 256937.2 kg/year (i.e. 21411.433 kg/month). This however is not fully utilized because the fishes were found to feed mostly on phytoplankton and the locals also reported very poor fishery catch in the creek. Keywords: Hydro-sedimentology, benthos, energy transfer, fish, coastal pollution. IntroductionThe coastal waters within the 30 meters of the continental shelf offer good feeding ground for many crustaceans and fishes, many of which spend a part of their life cycle in the creeks or in estuaries. It is generally thought that the mangrove habitats surrounding these ecosystems are widely utilized by these marine fauna. Studies in various parts of the world have recognized the importance of mangroves and sea grass beds as nurseries for fishes. Several hypotheses have been proposed to explain the high abundance of juvenile fishes in mangroves and sea grass beds. The hypothesis, are based on avoidance of predators, the abundance of food and interception of fish larvae, viz., (a) the structural complexity of these biotopes provide excellent shelter against predators, (b) these biotopes are often located at a distance from the off shore waters and are therefore less frequented by predators, (c) the relatively turbid waters of the bays and estuaries decrease the foraging efficiency of the predators and (d) these biotopes provide a great abundance of food for fishes8,9. But, the use of these biotopes as nurseries is not much apparent in the Indo-Pacific region. The distribution and abundance of fish in estuarine and coastal environments is dependent on physical, chemical and biotic factors10. Increasing awareness of possible effects of man on the marine environment has led to a search for early warning indicators of any induced changes11. The near shore waters of industrialized cities are prone to different types of pollution, which get build up from various sources12. Further, with increasing development of shorelines and draining of mangrove swamps, it is vital that the importance of mangroves as fishery habitats be accurately defined13, to provide useful advice for coastal management and alternative land use decisions. Study area: Thane creek (Long. 72.55’ to 73.02’ E and Lat. 19.00’ to 19.15’ N) is a mangrove fringed tropical coastal ecosystem along the central west coast of India. The creek is 26 km long which extends northwards from the Bombay harbour bay and joins the Ulhas River by a minor connection near Thane city. The creek is narrow and shallow in the north where Ulhas river flows into it through a minor connection and is broader and deeper towards the sea. Due to geomorphic head near Thane city, the creek receives negligible fresh water flow from the Ulhas River. Hence, except during monsoon, it is tidally influenced with dominance of neritic waters. In all, 12 stations were selected with the following criteria: i. Maximum stretch (26 km) of the creek gets represented; ii. Uniform distribution of stations along both the banks; and iii. Sites of known polluting sources and human interference get represented; figure-1. Station 1 was the first station from the Ulhas river side and station 12 was nearest to the sea. Trombay (station 12) had significant fishing activity while other stations received a variety of effluents, sewage discharges, or solid wastes. International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202Vol. 1(4), 17-21, August (2012) I. Res. J. Biological Sci. International Science Congress Association 18 Material and MethodsThe study stations were sampled monthly from May 1999 to April 2000 during neap high tide for analyzing parameters like dissolved oxygen (DO), dissolved inorganic phosphate (PO43-P), and nitrate-nitrogen (NO3--N) using standard methods14. Salinity was estimated using the Mohr’s argentometry method. Sediment samples for benthic fauna study were collected during low tide from low water level mark (LWLM), mid-water level mark (MWLM) and high water level mark (HWLM). At least five samples were collected from each water level. Each sample was collected up to a depth of 10 cm using quadrants of 0.01 msize and 10% MgCl was added to sedate the organisms. Sediment was sieved through a 0.5 mm mesh sieve and animals retained were preserved in 5% buffered formaldehyde. The preserved fauna were sorted into macro benthos and meiobenthos before weighing to finally calculate their density (ind. m-2) and biomass (g m-2; wet wt). The density and biomass values are used to estimate the annual production using the formula suggested by Elmgren15, and there by evaluate the demersal fishery potential of the creek. Sediment samples, collected separately from the intertidal area, were dried to analyze organic carbon (Corg16, sediment texture17, total nitrogen (TN)14, and total phosphorus (TP)14. The fish specimens were collected during the entire study period from the fishermen across the creek during their fishing activity and identified for the species18. Results and Discussion Characteristics of water bodies influence the quality of water individually and in combination with various pollutants, thereby, influencing the biota therein19. Station-wise average hydro-sedimentological values are given in table 1. The salinity in the creek increased seawards. Though the overall average DO was 2.35 ± 0.79 mg l-1, markedly low values were recorded at stations 2, 3, and 4 with DO falling close to zero in some instances under the influence of sewage point sources in the upstream zone. The average PO-P values were noticeably high at upstream stations 1–4, as this region was narrow and shallow and received heavy sewage load. For the same reason, higher levels of NO-N were found at stations 1 and 2. Gross pollution of water has its origin mainly in urbanization, industrialization, agriculture and increase in human population observed in past one and a half century20. Sediment texture analysis revealed that silt component was more dominant (average 66.74 ± 6.20%) than the clay (average 28.65 ± 3.5%) and sand (2.2 ± 1.21%) fractions. Corg and TN in the sediments declined seawards. Thane creek has apart from mangroves, industries, urban settlements and villages along both its banks. The inhabitants of these villages are mostly fishermen who depend upon the creek. However the heavy industrialization and urbanization along the creek has resulted in release of effluents in quantities far exceeding the assimilating capacity of the creek. Environmental pollution from human activities is a major challenge of civilization21 high input of waste results in fluctuating trend in catch rate along with low species diversity. Fishes constitute economically very important group of animals22 which is directly or indirectly related with human health23industrial activities which lead the acidification of water bodies, fish communities have suffered significant changes in the community composition during the present study although the fish catch was not estimated, the different species of fish occurring in the creek were collected seasonally from several fishermen in the creek while fishing. It was observed that the fishing activity was mainly restricted to the lower stretches (marine end) of the creek, while at the riverine end fishing was an activity of the monsoon season only when the commercially important fishery would occur. Surface water bodies get polluted due to urban sewage discharge24. In the tropical country like India, highly seasonal rainfall and heavy discharge of water during monsoons results in high flushing rate25. During the investigation a total of 12 species of fish were recorded, consisting of 11 species of fin fish and 1 crustacean. The 11 fin fishes include Mugil cephalus, Mystus gulio, Mystus shingala, Tilapia mossambica, Lates calcarifera, Elops saurs, Coilia dussimieri, Trichirus savala, Cleupia toli and Johnius spp., while the only crustacean was Scylla serrata. Among the above fishes only 5 species were dominant and occurred throughout the year, namely Mugil cephalus, Mystus gulio, Mystus shingala, Tilapia mossambica and Scylla serrata where as the other fishes were rare in their occurrence. All these 5 species occurred throughout the length of the creek, while the other species were restricted to the marine end of the creek. During the monsoon Mugil cephalus, Mystus gulio andMystus shingala were reported in fairly large numbers from the upper stretches of the creek, later in the year their catch reduced significantly with occurrence of only Tilapia mossambica and Scylla serrata. However, greater abundance and fish species diversity throughout the year in the shallow region of the creek was observed during the monsoon during the 1981-82 and 1991-94 study, attributing the shallow region of the creek as a fairly sustainable nursing ground during the monsoon26. Although the present observation corroborates their view, a significant reduction in the diversity is also noted, with the conspicuous absence of prawns from the entire stretch of the creek. The presence of Metapenaeus monoceros, Macrobrachium rosenbergii and Penaeus indicus from the shallow region of the creek was reported earlier26, while during the study in 1983, the presence of Parapenaeopsis hardwickii, Macrobrachium rude, Metapenaeus brevicornis, Exopalaemon stylifera and Penaeus indicus from the lower stretches of the creek was observed27. The absence of these species during the present study can be attributed to the increased pollutant load in the creek, which repelled most of the commercially important fish and crustacean species. From the benthic faunal biomass, the average annual total production of 988.22 g/m/yr was calculated15 and is presented in table 2. The values generated are used to estimate the International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202Vol. 1(4), 17-21, August (2012) I. Res. J. Biological Sci. International Science Congress Association 19 demersal fishery potential of the creek. Assuming that the average width of the mudflats of the creek was 100 m. (including both the banks) and the length as approximately 26 km, the total mudflat area is approximately 2600,000 m using this approximation the total production of the study area amounts to 2569372000 gm/yr i.e. 2569372 kg/yr. The energy transfer from one trophic level to the next is of the order of 10 % (ecological efficiency)28. Using this generalization it can be concluded that the benthos in the study area can support an average fishery yield of at least 256937.2 kg/year i.e. 21411.433 kg/month. This however is not fully utilized because the fishes were found to feed mostly on phytoplankton and the locals also reported very poor fishery catch in the creek. Table-1 Average and standard deviation values of water and sediment parameters at the intertidal stations during 1999-2000 Table-2 Station wise annual production estimates (gm/m2 wet wt.) and percentage contribution of macrofauna and meiofauna Station Macrofauna Meiofauna Total Annual Production Macro +Meio (gm/m) % Contribution Actual Density no/mActual Biomass gm/mAnnual Production = biomass x 2.5 (gm/m) Actual Density no/m Actual Biomass gm/mAnnual Production = biomass x 8 (gm/m) Macro-fauna Meiofauna Stn 1 8757 70.900 177.25 598626 25.076 200.608 377.86 46.91 53.09 Stn 2 9655 67.989 169.97 609358 18.144 145.154 315.13 53.94 46.06 Stn 3 7940 126.322 315.80 601894 22.806 182.449 498.25 63.38 36.62 Stn4 33230 252.108 630.27 847240 30.819 246.551 876.82 71.88 28.12 Stn5 2860 17.268 43.17 657988 31.255 250.041 293.21 14.72 85.28 Stn6 60717 576.156 1440.39 967387 47.143 377.145 1817.53 79.25 20.75 Stn7 64455 369.107 922.77 817797 41.208 329.661 1252.43 73.68 26.32 Stn8 39363 319.675 799.19 662971 35.683 285.467 1084.65 73.68 26.32 Stn9 56345 579.408 1448.52 1034740 43.583 348.663 1797.18 80.60 19.40 Stn10 35227 388.225 970.56 701273 45.773 366.181 1336.74 72.61 27.39 Stn11 34485 640.492 1601.23 877944 33.921 271.365 1872.59 85.51 14.49 Stn12 1968 27.597 68.99 752430 33.389 267.111 336.10 20.53 79.47 Average 29584 286.274 715.68 760804 34.067 272.533 988.22 72.42 27.58 Station Salinity (ppt) DO (mg l-1) PO-P (mg l-1) NO-N ( mg l-1) Sand (%) Silt (%) Clay (%) Corg (%) TN (%) TP (%) 1 10.98 ± 9.6 2.73 ± 1.5 0.180± 0.092 0.987 ± 0.582 2.67± 2.42 68.33 ± 12.67 30.00 ± 11.28 2.61 ± 0.44 0.176 ± 0.054 0.6 44± 0.275 2 12.35 ± 10.5 1.13 ± 1.0 0.450 ±0.168 0.893 ± 0.640 3.97 ± 3.11 70.83 ± 12.40 21.67 ± 10.30 3.90 ± 0.38 0.281 ± 0.064 0.656 ± 0.300 3 19.29 ± 13.0 1.47 ± 1.5 0.354 ±0.114 0.945 ± 0.370 9.57 ± 3.42 64.17 ± 16.21 26.67 ± 11.55 2.76 ± 0.53 0.206 ± 0.040 0.770 ± 0.392 4 16.21 ± 12.6 2.00 ± 1.0 0.400 ±0.120 0.970 ± 0.581 1.51 ± 2.12 72.50 ± 9.65 25.00 ± 10.00 2.83 ± 0.44 0.205 ± 0.035 0.819 ± 0.374 5 15.83 ± 10.6 2.16 ± 1.0 0.398 ±0.069 0.976 ± 0.790 1.07 ± 1.23 71.67 ± 11.15 24.17 ± 12.40 3.46 ± 0.52 0.257 ± 0.060 0.772 ± 0.377 6 19.35 ± 11.5 2.98 ± 1.0 0.340 ±0.098 1.073 ± 0.491 1.12 ± 1.53 63.33 ± 20.15 33.33 ± 13.71 2.38 ± 0.26 0.164 ± 0.046 0.736± 0.276 7 21.70 ± 12.5 2.52 ± 1.4 0.255 ±0.124 1.029 ± 0.506 0.63 ± 0.80 70.83 ± 15.64 28.33 ± 9.37 2.73 ± 0.30 0.194 ± 0.042 0.708 ± 0.319 8 23.25 ± 12.5 2.21 ± 1.6 0.213 ±0.092 0.863 ± 0.426 0.76 ± 0.66 64.17 ± 14.43 33.33 ± 11.55 2.10 ± 0.38 0.149 ± 0.043 0.675 ± 0.330 9 23.40± 12.1 2.90± 1.7 0.204 ±0.087 0.939 ± 0.397 1.33 ± 2.09 62.50 ± 18.15 33.33 ± 13.03 2.41 ± 0.33 0.164 ± 0.039 0.586 ± 0.298 10 23.38 ± 12.3 2.29 ± 1.3 0.172 ±0.100 1.022 ± 0.337 2.07 ± 3.50 59.17 ± 13.11 36.67 ± 16.14 2.00 ± 0.23 0.141 ± 0.049 0.587 ± 0.280 11 23.83 ± 11.6 2.75 ± 1.4 0.210 ±0.112 1.108 ± 0.643 0.82 ± 1.52 62.50 ± 18.15 29.17 ± 15.64 2.23 ± 0.25 0.162 ± 0.035 0.591 ± 0.326 12 28.60± 11.6 3.11 ± 1.1 0.100 ±0.035 0.836 ± 0.279 0.88 ± 1.12 70.83 ± 15.05 22.08 ± 10.76 2.14 ± 0.39 0.134 ± 0.033 0.619± 0.327 International Research Journal of Biological Sciences ________________________________________________ ISSN 2278-3202Vol. 1(4), 17-21, August (2012) I. Res. J. Biological Sci. International Science Congress Association 20 ConclusionDuring the 1991-93study, 22 species of fish and 68% reduction in the fishery of the shallow region of Thane creek in comparison to the data of 1981 – 82 was recorded26. Although a quantitative data was not collected during the present study a comparison of the number of fish species indicated a substantial decline in the fishery of Thane creek. Further the local fishermen communicated an almost 75 % decline in the fishery in comparison to the fish catch obtained in the 1990’s. The locals also informed about the gradual changes in occupation of the fishermen due to unsustaining yields, which have resulted with the rising effluent and sewage load. Moreover they complained that fish kill due to sudden release of harmful and toxic chemicals, were now a regular feature in the creek. Urbanization and industrial activities have done much harm to the natural and aquatic environment29. Loss of wetland has disastrous effects on wildlife and biodiversity30. In addition the perils of non-biodegradable matter loomed large in the creek it had even succeeded in forcing the fishermen to change their fishing gears from the traditional dol nets to gill nets, with infrequent use of wall nets. This is because the dol nets would invariably get clogged with the non-biodegradable waste like thermocol, plastic bags etc., instead of the actual fish catch. With the fishery becoming obscure in Thane creek, commercial fishing in the creek was observed to be a dying occupation. AcknowledgementsThe authors thank the Principal, B.N.Bandodkar College of science and its Head of Zoology department for providing the logistic support. We are also grateful to Mr. Prakash Patil and Mr. Pravin Koli who diligently helped in the field and made this study possible. 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