112 



CEYLON PEARL OYSTER REPORT. 



fisheries, and the area covered by these fragments and so made available for the 

 attachment of pearl oysters, might be largely extended by artificial " cultching." 

 Laivp' areas of the important Cheval Paar, for example, would be improved by 

 further cultching. 



Fig. 3. Nullipore ball (Lithothamnion fruticulosum) with tags of byssus where pearl oysters have 

 been attached (to the right), and a. similar ball still covered with young pearl oysters (to the left) ; 

 natural size. 



The temperature of the sea-water in which the pearl oysters live in the Gulf 

 of Manaar is high. In our experience in 1902 it ranged from about 77 F. in 

 January to close on 90 F. in April. In February, 1904, the range was from 80 to 

 84, in March from 81 to 86, and in April from 84 to 88 F. In all cases the 

 temperature was taken at a depth of 2 feet below the surface of the sea, at 7.30 A.M., 

 noon, and 5.30 P.M. each day. Probably the normal range during the greater part 

 of the year is from 82 F. to 86 F. 



The specific gravity we found to be fairly constant at 1*023 on the pearl banks; 

 at Galle it was slightly lower, averaging 1*022 ; at Trincomalee in the inner bay, and 

 especially in Tampalakam, it was distinctly lower (1*015 to 1*019). At exceptional 

 spots and seasons in the Gulf of Manaar we have found the specific gravity lower 

 than the normal. Off Chilaw, in November, 1902, it was slightly above 1*019, and 

 on the Muttuvaratu Paar in the same month it averaged about 1 *020. No doubt on 

 occasions of great floods on the land it may be lower still on those paars that are 

 near the mouths of the rivers. There is no reason to think (as has sometimes been 

 stated) that some admixture of fresh water is necessary for the prosperity of the 

 oyster or for pearl-formation. On the contrary, exceptional floods are probably harm- 

 ful to any paars they may reach. On the other hand, it is possible that the outflow 

 from the great land-locked lagoons (e.g., Portugai Bay and Dutch Bay) influence the 

 sweep of the coastal currents and help to determine spat-falls on the neighbouring 

 banks. The great tidal outflow from Dutch Bay probably influences deposition OR 



