Ichthyofaunal diversity of the Adyar Wetland complex, Chennai, Tamil Nadu, southern India
M. Eric Ramanujam 1, K. Rema Devi 2 & T.J. Indra 3
1 Principal Investigator (Faunistics), Pitchandikulam Forest Consultants, Auroville, Tamil Nadu 605101, India
2 Scientist E, 3 Assistant Zoologist, Zoological Survey of India (Southern Regional Station), 130, Santhome High Road, Chennai, Tamil Nadu 600028, India
1 email@example.com (corresponding author), 2 firstname.lastname@example.org, 3 email@example.com
Abstract: Most parts of the Adyar wetland complex—Chembarampakkam Tank, Adyar River, Adyar Estuary and Adyar backwater (including a wetland rehabilitation site)-—were sampled for ichthyofaunal diversity from March 2007 to June 2011. A total of 3,732 specimens were collected and 98 taxa were identified. Twenty-two new records are reported from the estuarine reach. Forty-nine species were recorded at Chembarampakkam Tank. In the upriver stretch 42 species were recorded. In the middle stretch 25 species were encountered. In the lower stretch only five species were recorded. This lack of diversity in the lower stretch of the river can be directly linked to pollution, especially the lower reaches from Nandambakkam Bridge to Kotturpuram which exhibit anoxic conditions for most of the year. In brackish, saline and marginal waters of the estuarine reach 66 species were recorded, of which 47 occurred in the estuary proper, 34 at the point of confluence with the Bay of Bengal and 20 in the backwater which forms the creek. At the rehabilitation site, popularly referred to as the Adyar Eco Park, which is the westernmost region of the backwater, 28 species were recorded in 2011 which is a sharp increase from just four in 2007 when the area was an environmental disaster. A significant finding was Mystus cf. gulio which showed a marked morphometric difference concerning its maxillary barbels and efforts are on to discern its taxonomic status.
Keywords: Adyar Eco Park, Adyar Poonga, alien species, homogenisation, rehabilitation, translocated species, water quality, wetland complex.
Ichthyofaunal constituents of two areas of the Adyar wetland complex have been documented: the Adyar Estuary (Raj 1916; Panikkar & Aiyar 1937; Anon 1950; Evangeline 1967b; Nammalwar 1982) and one source of the river at Chembarampakkam (Ragunathan 1978; Daniels & Rajagopal 2004). These benchmarks have proved invaluable to the present analysis because it is now possible to correlate historical data to present findings.
In addition, an ‘Adyar Poonga Ecological Restoration Plan’, popularly referred to as the ‘Master Plan’, for the rehabilitation of a part of the Adyar Creek was submitted which contained information of species encountered on the proposed site (Anonymous 2007) and this was followed by a survey of parts of the Adyar Wetland complex (Ramanujam et. al. 2008, 2010). This allows for further comparative analysis and it is now possible to report on colonisation processes at the rehabilitation site.
This is a consolidated report representing data generated from 2007–2011. It aims to present findings of ichthyofaunal diversity of the Adyar Estuary, Adyar Creek, Adyar River and Chembarampakkam Tank. It also correlates historical data to present surveys of the estuarine reach. Such a comparative analysis has not been attempted for Chembarampakkam as results and analysis of a more intensive survey have already been published (Knight 2010b). Nevertheless, the results of our sampling are included in Table 1 as there are a few records that are unique to this survey.
Study Areas (Image 1)
Chembarampakkam Tank (1300’N & 80003’E): This is a large reservoir with a catchment of approximately 357km2 with bunds running for at least 9km around it. It offers a number of seasonal microhabitats - first there is extensive open water that is deep. Along the margins, where earth has been quarried, there are smaller temporary pools supporting dense growth of Hydrilla and Urticularia. Elsewhere, the water flows as small streams towards the sluice gates and beyond creating smaller ponds with water lilies and emergent vegetation including Cyperus and Ipomea carnea (Daniels & Rajagopal 2004). The man-made Bangaru Canal constructed in 2004–2005 connects it via the Kortaliyar River to the Poondi Reservoir and there forth to the Krishna River. The outfall of the canal occurs at Settipalayam.
Adyar River: The river flows for about 42km before joining the Bay of Bengal in Adyar. It varies in depth from approximately 0.75 m in its upper reaches to 0.5 m in its lower reaches. It discharges upto 940 million cu m of water to the sea annually. From its origins to Tiruneermalai the water is unpolluted. A little after Tiruneermalai, the Pammal drain joins the river bringing tannery effluents and sewage. In spite of this, fishing activities are common during the rainy seasons up to Nandambakkam [the stretch of river from sources to Nandambakkam has been referred to as upriver in this manuscript]. The river receives a sizeable quantity of sewage and other pollutants from Chennai after reaching Nandambakkam Bridge and the water quality from here to M.R.T.S. Bridge at Kotturpuram is poor [this stretch has been referred to as downriver]. Just below the Adyar Boat Club the Buckingham Canal joins the Adyar River. This canal, built between 1806 and 1878 is a 420km channel running parallel to the coast from Vijayawada on the banks of the Krishna River in Andhra Pradesh to Alamparai, near Marakkanam, in Tamil Nadu. The canal connects most of the waterways along the coast, including the Adyar.
Adyar Estuary (1300’N & 80016’E): Historically, it was a typical bar-mouth estuary, i.e., the mouth remained closed for most of the year (about 9–10 months) during the dry period due to the formation of a sand bar and during the north-east monsoon (October to December) heavy freshwater flow from upriver opened the barrier to the sea. This condition was temporary and existed only during the monsoonal period. The reason for this is that the southeastern seaboard of India, also known as the Coromandel Coast, has a dissymmetric climatic regime - i.e., though the average rainfall in a year is about 1,200mm, the bulk of it (approximately 800mm) falls during the north-east monsoon due to depressions formed in the Bay of Bengal (Blasco & Legris 1972; Meher-Homji, 1974–1975). Due to the shallowness of the estuary, as one approaches the point of confluence with the Bay of Bengal, a few island formations can be seen east of the Tiruvika and Elphinstone bridges. As with all estuaries worldwide, this was an ‘oscillating ecosystem’ and the temporal occurrence of free swimming faunal elements was at one time dictated by the opening and closing of the sand bar (Panikkar & Aiyar 1937). There are strong indications that the entire area was well vegetated with mangroves and mangrove associates, not only on the bank of the Theosophical Society campus, but also on the islands and mudflats and records indicate that they occupied an area of about 48ha (Selvam et al. 1994).
Estuaries, the world over, are indicators of environmental health, not only because of anthropogenic activities affecting them directly, but also because all the accumulated upriver abuse is discernable here. This is especially pertinent to estuaries within metros - many of the world’s great cities (like London, New York and Tokyo), and Indian ones too (Calcutta, Mumbai and Chennai), developed around them because they were natural harbours. As a result, they are centres for accumulated pollution and have been dredged or filled and transformed into seaports, parks, cities and garbage dumps. Many have been obliterated and most surviving ones are endangered (Castro & Huber 1997). The Adyar estuary is no exception. It is heavily polluted by a variety of industries, commercial establishments and direct and indirect discharge of sewage resulting in physical, chemical and biological changes. The discharge of sewage and industrial effluents is indicated by the high quantities of dissolved solids, total suspended solids, total dissolved solids, HOD, COD, ammonia and sulphates, and the concentration of heavy metals like cadmium and lead is higher than safe levels (Sivakumari et. al. 2005). The morphology of the estuary too has been tampered with. During the survey the mouth was kept open in the hope that pollutants would wash away into the sea. The vegetation is a faint shadow of its former self - only a few Avicennia marina exist on the banks of the Theosophical Society campus. The islands have been completely overrun by Prosopis juliflora and are hotbeds of antisocial activities.
Adyar Creek: The overwhelming factor here is encroachment. Encroachments from all quarters, viz.: government agencies (e.g., Ambedkar Mani Mandapapam), builders (e.g., Belisha Towers, Raja Muthia Chettiar Residential Apartments, Leela Hotel, Rani Meyyamai Apartments, Jain Sagarika) and slums at Srinavasapuram. As a result, the morphology of the wetland has been irrevocably altered and the water spread has shrunk drastically.
It is ironic that the first anthropogenic activity that intruded into the wetland concerned fish. Under the ‘Second Five Year Plan’ (1956–1961) the Brackish Water Fish Farm was established which was the first of its kind in Tamil Nadu (then the Madras State). The farm was 55.4 acres in extent of which 36 acres comprised of a reservoir formed by the construction of a regulator across the narrowest portion of the creek. The operation of this regulator (which consisted of three pairs of screw gearing shutters) during tidal ingress and egress facilitated the entrapping of fish, mostly during the juvenile stages. A series of nurseries, rearing ponds, stock ponds and marketing ponds covering an area of 19.4 acres was situated on the southern bank of the reservoir (Evangeline 1967a).
Since then, development based on reclamation took precedence because of the burgeoning human population associated with urbanization. The area between the seafront and creek was converted into a housing colony to accommodate displaced slum dwellers. This place of relocation, called Srinivasapuram, was begun in 1976–1977. Originally the housing colony consisted of LIG (Low Income Group) flats, but almost immediately hutments and small brick structures sprang up around them. Encroachments into the wetland were inevitable and a post tsunami count disclosed 647 huts in Srinivasapuram, of which 54 occupied the creek itself.
Development, construction and encroachment are ongoing processes and construction debris and other wastes continue to be dumped into the creek extending its banks up to 20m and obliterating all mudflats. Due to this the creek has shrunk in width to only a narrow channel which hardly allows any tidal influence to the upper parts on a daily basis. In addition, a bus terminus and a memorial to Dr. Ambedkar were constructed on prime wetland habitat and more development activities based on reclamation were planned. A group of concerned citizens, members of EXNORA and Citizen Consumer and Civic Action Group (CAG), moved the court and a stay order prevented further development. In February 2008 the Government of Tamil Nadu’s proposal to develop an eco-park and rehabilitate the wetland was accorded permission by the Madras High Court and the ‘Adyar Poonga Ecological Restoration Plan’ was put into operation. This included clearing of thousands of tonnes of rubble, stopping pollution entering the site, elimination of alien invasive Prosopis juliflora and Eichhoria crassipes, planting of mangroves and other suitable coastal vegetation, etc. Since bio-inventorisation processes were fundamental to evolve conservation strategies, faunal surveys were undertaken and this report is an outcome of such an exercise.
Period: The survey went through three phases:
1. The institutional ‘Master Plan’ stage was the preliminary phase that documented vertebrate diversity from March–June 2007.
2. A vertebrate diversity inventorisation process of the Adyar Wetland complex was jointly undertaken from July 2007 to October 2008 by the Zoological Survey of India (Southern Regional Station), Pitchandikulam Forest Consultants and Trust for Environment Monitoring and Action Initiating. Sampling occurred in Chembarampakkam, Adyar River, Adyar Estuary and the creek - including the rehabilitation site.
3. Updating is a continuing process. Sampling at Chembarampakkam had to be discontinued as the governmental TOR was confined to the creek and estuary alone.
This is a consolidated report of all three phases—i.e., from March 2007 to June 2011, a period of four years and three months.
Fish were collected with the help of local fishermen who used hand-operated dragnets, seine nets, cast nets, and the hook and line. In addition, small fish that commercialists ignore were collected by the survey team using dip nets. Identification was according to established literature (Daniels 2002; Jayaram, 1981, 2006, 2010; Talwar & Kacker 1984; Talwar & Jhingran 1991).
Results and Discussion
A total of 101 species were encountered during the survey. Forty-nine species occurred in Chembarampakkam Tank, 22 in the upriver stretch from Chembarampakkam to Nandambakkam and four in the downriver stretch from Nandambakkam to Kotturpuram [the four species were Puntius chola, Mystus cf. gulio, Oreochromis mossambica and Anabas testudineus]. The lack of fish fauna can be linked to poor water quality because in summer, even when the sandbar is opened, this stretch is reduced to a languid line of sewage and sullage. It is unreasonable to suppose that fishes do not occur in polluted water stretches—Narayanan (1980) reported seven species from polluted waters of the Cooum [for the record: Megalops cyprinoides, Muraena sp., Leiognathus sp., Terapon jarbua, Oreochromis mossambica, Liza microlepis and Mugil cephalus] and subsequently two other species were recorded in it as recently as 2007 [Oreochromis mossambica and Mystus gulio (Bai et al. 2007)]. Fifty-seven species were recorded in the estuarine reach of the Adyar, of which 49 were encountered in the estuary, 35 at the point of confluence with the Bay of Bengal and 20 in Srinivasapuram Creek. At the rehabilitation site (Adyar Poonga) 28 species have been recorded so far of which 13 species were encountered in brackish water east of the spillway and 21 in fresh water west of the spillway. For more details refer Table 1 and Fig. 1.
Prior to this survey five studies were conducted in the estuary from 1916–1982: in order of reporting, Raj (1916), Panikkar & Aiyar (1937), Anon (1950), Evangeline (1967b), Nammalwar (1982). Including this survey 144 species have been known to occur in the estuarine reach. From a casual perusal of Fig. 2 one would be inclined to conclude that the species inventory during this survey is higher than those of 1916 (which recorded 33 species), 1937 (50 species), 1967 (41 species) and 1982 (45 species). This may not be an accurate estimate as the ambiguity concerning the area, period and intensity of surveys may have created a bias. Another bias could have arisen from fundamental sampling procedures - for example, fisheries oriented samplings may have focussed principally on commercially viable species. The present survey was the most comprehensive, intensive and longest running one—for a period of four years and three months—and hence may have recorded more diversity. Another eye opener is the Fishery Report from April 1949 to March 1950 (Anonymous 1950) which documented 73 species. What is pertinent is that 87 species recorded during earlier surveys were not encountered during this survey. For further details refer Table 2 and Fig. 2.
Twenty-three new records have been established for the estuarine reach. Among the findings was Caranx tille. Talwar & Kacker (1984) mentioned that “there is no positive record of C. tille in our region (though mentioned in the literature)”. Another notable finding was Mystus cf. gulio. The specimens encountered in the wetland showed a marked aberrant feature—viz., the maxillary barbels were very short. This is in stark contrast to the description by Jayaram (2003, 2006) who mentioned that the maxillary pair reached the middle or sometimes almost end of pelvic fins. This is ironic because the common name for Mystus gulio is the “Long Whiskered Catfish”. Efforts are on to determine the taxonomic validity of the specimens. Nevertheless, morphometric values of the specimens have been presented here (Table 4). This is pertinent because Linder (2000) states “Mystus gulio: as presently understood, is a collection of brackish Mystus that likely represent many valid species” and the presence of a new taxon at the restoration site could have immeasurable conservation value.
The heartening factor is the colonization processes underway at the rehabilitation site. In 2007 only four species were recorded (Anonymous 2007) when the site was an environmental disaster. After the removal of debris, prevention of pollution entering the site, removal of invasive Water Hyacinth Eichhornia crassipes, expanding the water spread and linking the water bodies, 13 species were recorded during the follow up survey from July 2007 to October 2008 (Ramanujam et al. 2008). Presently the count stands at 28. For further details refer Table 3 and Fig. 3.
The striking feature of the survey was the number of alien species encountered in the wetland. Two fish species listed as some of the “100 of the world’s worst invasive alien species” (Lowe et al. 2000) occur in the wetland (and even the rehabilitation site)—viz., Mosquito Fish Gambusia affinis and Egyptian Mouthbreeder or Tilapia Oreochromis mossambica. Though it is unknown when the first was introduced [Ragunathan (1978) is the first record for the wetland], the introduction of O. mossambica and the aftereffects are well documented. Devadoss & Chacko (1953) suggested the introduction of O. mossambica for fisheries purposes and 15,000 specimens were introduced below Saidapet Road Bridge in December 1957 (Evangeline 1967b). As early as 1958 it was reported from fishermen’s catches in the estuary (Chacko & Venketaswami 1958) and in 1964–1965 it had overtaken the mullet fishery - the mullet catch accounted for 19.02%, whereas the tilapia catch was 25.17%, an increase of over 5% (Evangeline 1967b). During the present survey the related Etroplus suratensis was not encountered and neither was it mentioned in an earlier report (Nammalwar 1982). Yet records state that it “was one of the most economically important fish of the Adyar river” (Anonymous 1950). The situation is alarming because two closely related alien species have been reported, viz.: Oreochromus aureus from Pallikaranai marsh in Chennai (Knight & Devi 2009) and O. niloticus in Chembarampakkam (Knight 2010b). In addition, the highly aggressive hybrid ‘Flowerhorn’ Cichlasomax Amphilophus has been encountered in Chennai waterways (Knight 2010a), and if it gets established, is sure to spread to other wetlands, not only within Chennai, but even the Godavary and Krishna rivers due to linkages. Other exotics encountered were the suckermouth armoured catfishes Pterygoplichthys sp. and Pseudacanthicus sp., Guppy Poecilia reticulata, Threespot Gouramy Trichogaster trichopterus and Giant Gouramy Osphronemus goramy. Poecilia reticulata was recorded during the survey period July 2007–October 2008 at the rehabilitation site but not after that. It is interesting that Gambusia affinis was not recorded during that time and it is possible that it displaced P. reticulata at a later date.
While the problem of exotics is addressed from time to time in literature, little is said of fish from other parts of India, especially the large number of north Indian carps (introduced to boost inland fisheries) that have invaded areas where they do not occur naturally (Daniels 2006) and Gibelion catla is a typical example of such a translocated species. The linking of rivers has led to some species like Lepidocephalus guntea colonizing new areas. This species, a native of the Godavary and Krishna rivers (David 1963; Jayaram 1995), was encountered in sizable quantities during the July 2007–October 2008 survey phase at Chembarampakkam. At one time it was believed that L. guntea had replaced the native L. thermalis (Ramanujam et al. 2008) since the latter were not encountered at that time and even earlier (Daniels & Rajagopal 2004), but subsequently many specimens of L. thermalis were found during the later phase of surveys. Though pollution is presently touted to be the greatest threat to the wetland, it might be that homogenisation and colonization by alien species can be the greater threat to biodiversity. The fact is that invasive alien species are the second major cause of extinction of native and endemic species (Wilcove et al. 1998) and in the long run, if the wetland is restored to a semblance of its former self (and there are instances of the Thames, Sienne and other polluted waterways being restored since the technology and precedents exist), it will be the hardy aliens that will colonise and dominate newly restored habitats. Since there have been too few successful precedents of removal of alien fish, their removal may not only be expensive but unsuccessful since methodologies to cope with the phenomenon are still in their infancy on a global scale.
The occurrence of the Dwarf Gouramy Colisa lalia is controversial with some authorities claiming that it is not native to this part of India [Raghunathan (1978) had recorded Colisa fasciata at Chembarampakkam] and others favouring the opinion that it is indigenous to the region and populations boosted by the aquarium trade releases (R.J.R. Daniels pers. comm. 2010). The Dwarf Panchax Aplocheilus parvus, a native of the fresh waters of the east coast, was introduced as a larvicidal species into an artificial pond in June 2009 and has since spread into the wetland.
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