Clam resources in all the eight estuaries of Dakshina Kannada, viz., the Nethravathi, Gurpur, Mulky,

Udyavara, Swirna, SIti, Coondapoor and Uppunda were assessed during 1984. The total clam

resources 'standing stock) of these estuaries are estimated at 4900 t. About 92% of this resource was

found in the Mulky estuary. The clam resources were negligible and formed less than 1% in the

Udyavara, Swarna, Siti, Coondapoor and Uppunda. Meratrix casta js the chief species followed by

Paphia malabarica and Villorita cyprinoides. Species-wise distribution of clams in different

estuaries along with the environmental parameters and biological characteristics of different clam

species are presented. Information on the utilisation and marketing is also given

Meiyappan, M M

Rao, G Syda

CMFRI Digital Repository

ASSESSMENT OF CLAM RESOURCES IN THE ESTUARIES OF DAKSHINA KANNADA G. Syda Rao and M. M. Meiyappan Central Marin* Fisheries Researcii Institute Cochin-682031. ABSTRACT Clam resources In all the eight estuaries of Dakshlna Kannada, viz., the Nethravsthi, Gurpur, IVIuiky, Udyavara, Swirna, SIti, Coondapoor and Uppunda were assessed during 1984. The total clam resources 'standing stock) of these estuaries are estimated at 4900 t. About 92% of this resource was found in the Mulky estuary. The clam resources were negligible and formed less than 1% in the Udyavara, Swarna, Site. Coondapoor and Uppunda. Meratrix casta js the chief species followed by Paphia malabarica and Villorita cyprinoides. Species-wise distribution of clams in different estuaries along with the environmental parameters and biological characteristics of different clam species are presented. Information on the utilisation and marketing is also given. INTRODUCTION Rao and Rao (1985) and Narasimham et al (>1986). Gopal et al (1975) and Rao (1983) Clams are the chief molluscan resources of jeait on shell deposits while Rao (1984) made the estuaries and back waters along the Kama- abservations on the clam fishery, take coast. They are gaining importance In the economy and in recent times an export trade MATERIAL AND METHODS for frozen clam meat is being developed. Earlier works on the clam resources of this area The clam survey of the Nethravathi, Gurpur, are by Alagarswami and Narasimham (1973), Mulky, Udyavara, Swarna, Sita, Coondapoor 20 CMFRI and Uppunda estuaries was conducted during April-May 1984, Salinity, oxygen, temperature, pH and sediment data were collected and analysed from each bed. Depending upon the extent of clam bed, the number of samples varied. If the area is under 5 ha, 5 samples were collected, and 10 sampIes/5-20 ha, 20 samples/20-50 ha, 30 samples/50-100 ha and 50 samples if the area is more than 100 ha. One square matre of the bed was sampled with the help of a galvanised iron frame, the sedi-ment was passed through a 2 mm mesh to retrieve the clams. A portion of the sample was examined for biological analysis, like length frequency, condition index, and stage of maturity. The average weight of clam species in each bed was taken into consider-ation to quantify the clam resources in each bed. The extent of the clam beds was cal-culated based on length and average width of the bed. All the estuaries and clam landing centres of Dakshina Kannada were visited once in a month during 1983 to collect data on the quantity landed, species composition, number of persons involved and method of collection. These observations were supplemented with the the enquiries from the fishermen and merchants-RESULTS Nethravathi estuary: There were three beds covering 48 ha. Villorita cyprinoides was found in all the three beds (Table 1). The total stand-ing stock was estimated at 75 t. Most of the clams were small sized. The substratum was sandy and salinity ranged from nil to 17ppt. The dissolved oxygen ranged from 5 to 5.7 ml/I and pH varied between 7.5-8.0. In this estuary clams are exploited by hand picking. During 1983, 149 t of V. cyprinoides and 233 t of A/7. casta were exploited. During the current survey M. casta were observed only in stray numbers. In 1979 (Rao and Rao 1985), M. casta \Nas observed in good concentrations. Gurpur estuary: The total standing stock of clams during April 1984 was estimated at 3451 (Table 1) in 72 ha. P. malabarica was the dominant species, followed by V. cyprinoides and M. casta. The substratum is sandy; salinity ranged from 26.16 to 35.5 ppt, dissloved oxygen from 4.1 to 5.1 ml/I and pH 7 5 to 8.0. The exploit-ation of clams was by hand picking, clam nets and shell-dredge. Shell-dredge was mostly used to collect P. malabarica as it was found in slightly deeper waters, near the mouth of the estuary. In 1979 (Rao and Rao 1985), P. malabarica was not observed. The estimated clam landings during 1983 (Table 2) from this estuary were about 1281 t, out of which about 50% were P. malabarica. Mulky estuary: This is a small but very important estuary for clam resources with maximum stand-TABLE 1. Clam resources of Karnataka south zone (Dakshina Kannada). (in tonnes). ApriUMay 1984 Estuary Nethravathi Gurpur Mulky Udyat/ara Swarna Site Coondapoor Uppunda (Baindoor) Total M. cas\a @ 84.2 3663.00 33.8 @ 3.42 18.8 @ 3803.22 P. malabarica — 164.82 744.00 @ — — @ @ 908.82 I/, cyprinoides 75.426 94.800 @ @ @ @ — — 170.226 Total 75.426 343.82 4407.00 33.80 @ 3.42 18.8 @ 4822.266 @ indicates stray occurrence of the species. BULLETIN 42 21 TABLE 2. Species wise dam landings of the estuaries of Daicsfiina Kannada during 1983 (in tonnes). Estuary M. casta M. meretrix P. malabarica v. cyprinoides K. opima Total' Nethravathi Gurpur Mullcy Udyavara Swarna Sita Coondapoor Uppunda 233 307 1814 216 — 362 53 11 — — — — — 8 43 ... — 600 578 6 — — 528 80 149 374 — — 15 2 8 — — — — — — 5 8 69 382 1281 2392 222 15 377 640 160 Total 2,996 51 1,792 548 82 5,469 /o 54.8 0.9 32.8 10.0 1.5 ing stock when compared to other estuaries. The total standing stock during May 1934 was 4407 t, spread over an area of 232 ha, occupy-ing almost one third of water spread of the estuary. M. casta was dominant followed by P, malabarica. Clams from this estuary are marketed in most parts of Dakshina Kannada. Here clams are collected by hand-picking and clam nets. The magnitude of clam landings from this estuary varied from 40 t to 951 t during 1978-82 (Rao 1934). However the land-ings have showed considerable improvement during 1932-84 and amounted to 1659 t and 31091 respectively. In general M. casta was the dominant species. The substratum is sandy; salinity ranged between 35.1 to 35.65 ppt, dis-solved oxygen from 39 to 4.7 mi/1 and pH from 6.5 to 7.5. Udyavara estuary: A 10 ha clam bed was located, with a standing stock of 34 t of M. casta (Table 1). In 1980 good stocks of M. casta and P. malabarica were observed (Rao and Rao 1285), During 1983 the clam landings were estimated at 222 t (Table 2) compared to 250 t during 1980. The substratum is sandy. The salinity ranged from 29.83 to 35.16 ppt, oxygen from 4.1 to 5.1 mI/1 and pH from 6.5 to 7.5. Swarna estuary: This estuary joins the sea, after confiuencing with the Sita estuary. No recognisable clam beds were observed in this estuary. V. Cyprinoides and M. casta were available in negligible numbers. The estimated clam landings during 1983 were about 15tof V. cyprinoides. In 1979 also (Rao and Rao 1985) very poor clam resources were observed The sediment is sandy, salinity varied from 28.2 to 35.65 ppt; dissolved oxygen from 4.1 to 4.6 ml/1 and pH from 6.5 to 7 5. Sub-soil shell-deposits are exploited from this estuary on a large scale. Sita estuary: In this estuary also, the clam re-sources were negligible. M. casta ware found in very low densities in an area of 9 ha. In 1979, Rao and Rao (1985) reported on good clam resources. The estimated annual landings of clams during 1983 were 377 t. The sediment is sandy; salinity ranged from 28.2 to 35.6 ppm, dissolved oxygen from 4.1 to 4.6 ml/I and pH from 6.5 to 7.5. Coondapoor estuary: This is one of the biggest estuaries in Karnataka. However, very limited clam resources were observed. In 1979, moder-ate clam resources were observed (Rao and 22 CMFRI Rao 1985). During 1983 the estimated dam landings (table 2) from this estuary were 6401, mostly comprising P. malabarica. Other clam species observed are M. meretrix, M, casta V. cyprinoides and K. opima. There is heavy sub-soil shell deposit exploitation in this estuary (Rao 1983). The substratum is sandy, salinity ranged from 30.4 to 35.15 ppt; dissolved oxygen from 4.2 to 4.6 ml/I and pH value of 7 was recorded. Uppunda estuary: This is the smallest estuary in Dakshina Kannada. No recognisable clam bed was observed. Few specimens of P. Mala-barica. K. opima, M. casta and /W. meretrix were collected. A total of 160 t of clams were landed during 1983 (Table 2). During 1980, Rao and Rao (1985) also observed very poor clam resources. The sediment is sandy; salinity ranged from 33.49 to 35.65 ppt, dissolved oxygen 4.0 to 4.1 ml/I and a pH value of 7 was obtained. Conditior) index: The condition index based on pooled samples from all the estuaries of Dak-shina Kannada are 9.35 for M. casta 14.45 for P. malabarica and 10.09 fori/, cyprinoides. It shows that P. malabarica has more flesh, when compared to the other two species, particularly after 30 mm length. There were some variations in the condition index from estuary to estuary. Maturity stages: Most of the clam species ob-served in these estuaries were in indeterminate condition. However few M. casta in the Mulky estuary wera in mature and spent condition. Similarly in the Nethravathi estuary about 29% of V. cyprinoides were in mature and spent condition. Utilization and marketing: Flesh of P. malabarica and V. cyprinoides is used for gastronomic purpose. M. casta, when available in plenty, particularly between September-January period are exploited for their shells. The clams are marketed in fresh condition in diiferent villages of Dakshina Kannada. REMARKS The total estimated standing stock of clams in the estuaries of Dakshina Kannada was about 4800 t. M. casta is dominant (79%) followed by P. malabarica (19%) and V. cypri-noides (2%). K. opima and M. meretrix were observed in stray numbers. Rao and Rao (1985) estimated the standing stock of clams from these estuaries at 53000 t during 1979-80. The present estimate of standing stock is slightly lower when compared to the previoas assess-ment. This is mainly due to the poor clam resources in most of the estuaries; other than Mulky and Gurpur estuaries. Appearence of considerable stocks of P. malabarica in the Gurpur estuary indicates that the proportion of different species in a given estuary can undergo fluctuations over a period of time. When compared to the earlier study (Rao and Rao 1985) the variation in the individual estua-ries of Dakshina Kannada, as a whole, is small, although fluctuations in the individual estuaries are wide. In general, compared to earlier study there is a significant increase in the proportion of P. malabarica. The near absence of M. meretrix and other species of clams in the Coondapoor estuary, where extensive sub-soil shell deposit exploitation is practised, is note-worthy (Rao 1983). ACKNOWLEDGEMENTS We are grateful to Dr. K. Alagarswami, formed Head of Molluscan Fisheries Division for encouragement. Dr. K. A. Narasimham, Officer-in-Charge, Kakinada Research Centre of CMFRI, for cirtically going through the manu-script and Shri D. Nagaraja for his Technical assistance. REFERENCES ALAGARSWAMI, K, AND K. A. NARASIM-HAM. 1973. Clam, cockle and oyster resources of the Indian coasts. Proc. Symp. Living resources of seas around India, 648-658. GOPAL, B., M. MUNISWAMAIAH AND B. M. KRISHNAREDDY. 1976. Lime shell deposits of Mangalore taluk, south Kanara District. Geological Studies No. 11 4., Govt, of Karnataka. Dept. of Mines and Geology, Bangalore. RAO, G. SYDA. 1983. Exploitation of clam shell deposits in the Kundapur estuary. Mar. Fish. Infor. Serv. TSESer.. 49; 20-22. RAO, G. SYDA. 1984. Clam Fishery of Mulky estuary during 1978-82. Indian J. Fish., 31 (2) 228-232. RAO, G. SYDA AND K. SATYANARAYANA RAO. 1985 Survey of clam and oyster resources of soma Karnataka estuaries Indian. J. Fish., 32 (1) : 74-89. NARASIMHAM, K. A., G. SYDA RAO AND G. P. K. ACHARI. 1986. The clam resources. R&D Series for Marine Fishery Re. sources Managements, CMFRI, Cochin. BULLETIN 42 23 

Assessment of clam resources in the estuaries of Dakshina Kannada

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Assessment of clam resources in the estuaries of Dakshina Kannada

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