PLACUNA FISHERY. 137 



IV. — Pearl- YIELD, 



During the course of the 1908 fishery it became clear that the crop 

 of pearls was a great deal better than that of last year, and the 

 actual figures sliow a disproportionate increase. For, whereas in 

 1908 the lessees' half share of oysters numbered only 130,568, or a 

 little more than one-fifth of their share (627,672) in 1907, the weight 

 of pearls secured in 1908 is returned at 92 rupees, double the 

 quantity recorded in the preceding year.* This result is somewhat 

 surprising, and can only be attributed to the continued growth of the 

 pearls. After a pearl has reached a certain size , its further growth by 

 the apposition of fresh layers of nacre must add greatly to its volume 

 and value as compared with the earlier stages in its formation. 



As this is the first occasion on which a comparison of the pearl- 

 yield in successive years has been possible, it may be tabulated 



as under : — Lessees' Share Rupee Weight 



Date. of Oysters. of Pearls. 



1907 .. 627,672 .. 46 



1908 .. 130,568 .. 92 



The practical conclusion to be drawn is that in the case olPlacuna 

 the maximum pearl-yield coincides with the period of sexual 

 maturity. If subsequent observations should confirm this conclu- 

 sion, it will become an economic fact of controlling importance. 



From what has been said it will be clear that a short lease is a 

 pitfall » fatal to the spawning oysters. It is not to the interest of 

 contractors holding a lease of only five years' duration to spare the 

 spawners, but, on the contrary, it is their business to take as many 

 as they can get, to which in fact they are legally entitled. 



Moreover, seeing that superficial dimensions give no safe index 

 to the state of maturity of the oysters, it follows that the provision 

 as to size hmit can only be a very crude approximation, especially 

 when it is considered that size depends upon a dozen environmental 

 conditions. The three-year theory of the longevity of Placuna seems 

 to be based at least, in part, upon the length of Hfe permitted by 

 boring whelks, sponges, and human enterprise. When dead shells 

 are brought to the surface with the two valves still adhering together, 

 it is generally found that one of the valves, usually the convex valve 

 near to the cardinal teeth, has been perforated by some enemy ; and 

 I attribute the mortality on the Nachchikkuda bed chiefly to 

 the whelks, whose erect, subcyhndrical egg-capsules are attached in 

 dense clusters to dead valves of Placuna lying upon the bottom of 

 the lake ; each capsule contains a multitude of embryos, and ovi- 

 position appears to be clironic. 



V. — Rainfall. 

 In my former report I urged the desirability of noting the rainfall 

 in connection with the annual condition of the Placuna beds. In 



* Cf. my June report, op. cit., 1907, p. 40, 



7(8)08 



