SURVEY OF LAKE TAMBLEOAM. 41 



SURVEY OF LAKE TAMBLEGAM, SEPTEMBER, 1911.* 



By Joseph Pearson. 

 (With seven Charts. ) 



T AKE TAMBLEGAM covers an area of about seven square 

 -L-^ miles, and is connected with the large outer bay of Trincomalee 

 by a narrow channel some hundreds of yards across. The specific 

 gravity of the water varies considerably with the season of the year, 

 owing to the number of rivers flowing into the lake. In September, 

 after months of dry weather, the specific gravity is about the same 

 as in the open sea. The floor of the lake consists of a level stretch 

 of soft gray mud brought down by the rivers, and over the greater 

 part of the lake the depth does not exceed one fathom. It is upon 

 these mud beds that the windowpane oyster (Placuna 'placenta) finds 

 its natural habitat. 



The main conditions under which this mollusc lives may be 

 summarized as follows : (1) High temperature of the water owing 

 to the shallowness. This high temperature is varied by inrushes 

 of cold river water during the wet season. (2) Soft, slimy mud, 

 upon which the oyster rests by means of its lower convex valve. 

 According to Hornell, the shell sometimes is implanted in the mud 

 in a vertical position, like a Pinna. The divers say that the young 

 oysters rest on tlie top of the mud, while the adult oj'sters become 

 almost imbedded in the mud. (3) Tlie water is never clear, and 

 always contains a lot of mud in suspension. This is particularly 

 the case from May to Januar}', when the rough sea churns up the 

 soft mud. From October to December this is aggravated by an 

 inrush of fresh water carrying a large amount of mud in suspension. 

 This latter period is probably the most critical time of the year. 



I 



* The chief literature dealing with Lake Tamblegam is as follows : — 

 1857. — Kelaart. Report on the Tamblegam Pearl Oysters, 8vo., (i pp. 



Trincomalee. 

 1906. Hornell. Report on the Placuna placenta Pearl Fishery of Lake 



Tampalakamara. • ' Ceylon Marine Biological Reports," 



Part II., No. 2. Colombo. 

 1907. Willey. Report on the Windowpane Oysters in the Backwaters of 



the Eastern Province. Spolia Zeylanica, Vol. V., Part 



XVII. 

 1908. Placuna Fishery. Inspection of March, 1908. Spolia 



Zeylanica, Vol. V., Part XIX. 



1908. Ceylon Administration Reports (Marine Biology). 



1909. Ceylon Administration Reports (Marine Biology). 



G ' 0(19)11 



