WINDOW -PAKE OYSTER. 237 



(»f all the boats coming ashore would be necessary, and in the event 

 of young oysters occurring in the "catch," the boatmen concerned 

 would be required to return the oysters to the water. 



Establishment of a Close 8eason. 



On further consideration of the question of a close season I feel 

 obliged to modify the opinion I expressed in Spolia Zeylanica 

 Volume VIII., Part XXIX. I then agreed with Mr. Hornell that 

 without knowing the spawning period of the oyster the local condi- 

 tions at Tamblegam rendered it easy to establish an effective close 

 season from May to January, since during these months the water 

 is too rough for successful diving. Weather conditions render diving 

 possible only from January to May, but if January or February' 

 prove to be the spawning months, as I believe likely, it will be 

 unwise to allow fishing until spawning has actually taken place. I, 

 therefore , think that the window-pane oyster fishery should only be 

 prosecuted from March 1 to the end of May in any one year. This 

 period of 3 months gives ample time to complete the fishery. 



Eefect of Excessive Rainfall. 



As Dr. Willey has pointed out, the rainfall plays a very imi:»ortant 

 part in the bionomics of the window-pane oysters. I have expressed 

 the view elsewhere in this report, that though too much fresh water 

 is harmful a certam proportion mixed with the sea water is necessary. 

 The rain has a further use in carrying down the mud, which when 

 deposited in Lake Tamblegam forms a suitable habitat for the 

 window-pane oyster. The continuity of my observations on the 

 window-pane oyster were rather abruptly interrupted at the end of 

 1911, when, as the result of the abnormal rains, the greater portion 

 of a yomig bed of o3^sters was wiped out. Chart 3 shows the 

 comparison between this bed before and after the rains, and in 

 Appendix 2, thi-ough the kindness of Mr. A. J. Bamford of the 

 Colombo Observatory, I am able to give the rainfall in various parts 

 of the Tamblegam district for the months of October, November, 

 and December. 



Pearl Production. 



During the last two years the oysters present on the beds have 

 been too young for pearl production. In consequence little progress 

 has been made with the question of the best age for fishing the 

 oysters for pearls. This branch of the work Avill be steadily pro- 

 secuted as the oysters get older. At present it may be said that 

 oysters in the first and second years do not bear pearls of any size 

 and in any quantity. From the results of previous work it would 

 seem that oysters of less than three years do not contain many 

 pearls. The fourth year appears to be the critical time. 



