WINDOW-PANE OY3TER. 



223 



REPORT ON THE WINDOW-PANE OYSTER 

 INVESTIGATIONS, 1912. 



By Joseph Pearson, 



Government Marine Biologist. 

 (With nine Plates.) 



1. Introduction 



2. Division into Areas, and 



Results of the Year's 

 Work . . 



3. Kate of Growth 



231 I 8. Pearl Production 



4. Transplanting 



. . 234 ' Appendices 



237 



238 



Introduction. 



THE progress of my preliminary investigations at Tamblegam 

 during 1911 was published in Spolia Zeylanica, Volume 

 VIII., Part XXIX. Two inspections were made last year — a short 

 visit in January, which revealed the presence of a few 2- or 3-year 

 old oysters ; and one in the following September, when a bed of 

 young oysters was discovered. This bed was not sufficiently large 

 to hold out any hopes of a fishery, and my design was to keep these 

 oysters as a breeding reserve for future fisheries . In my report on the 

 survey, I expressed the behef that these oysters had been deposited 

 subsequent to the January inspection, since no small oysters had 

 been found early in the year. 



In January, 1912, Mr. G. M. Henry, who has assisted me thi'ough- 

 out the course of these investigations, visited Tamblegam in order 

 to make an inspection and to erect an oj'ster enclosure in Nachchik- 

 kuda. He discovered that most of the oysters which were present 

 in the previous September had died . This may be directly attributed 

 to the excessive rainfall which took place in the concluding months 

 of 1911. On Plate 3 a comparison is given of the distribution of the 

 oysters before and after the rains of 1911, which will convey some 

 idea of the havoc which was wrought. A sufficient number of 

 oysters, however, were left to enable measurements to be taken in 

 order to follow up the work on the growth-rate of Placuna, which 

 was commenced in the previous September. In May, 1912, 1 made 

 a further inspection, and then discovered a large bed of young 

 oysters extending over an area of nearly three square miles and 

 consisting of over fifty million individuals. A spatfall had evidently 

 taken place since the January inspection, and this occurrence agreed 



