window-pane oyster. 231 



Rate of Growth. 



The investigations of the last 12 months have enabled us to 

 ascertain the rate of growth in the earher stages of the oyster. 

 Measurements of large series of oysters have been made at every 

 inspection, and by taking the average of a sufficiently large series 

 the approximate rate of growth has been determined. 



This investigation has demonstrated the extraordinarily rapid 

 superficial gi'owth of the oj^ster m the first year. In the September 

 inspection many oysters were fomid having a measm^ement of over 

 5 inches in the short diameter, although the average for the whole 

 lake was shghtly less than 4 inches. 



Hornell's recommendation of a size hmit of 5| inches in short 

 diameter for fishable oysters is shown to be misound, as they attain 

 this size at the age of 2 years, and so far as my experience goes no 

 2-year old oysters are pearl-bearers. In fact, it will be impossible 

 to impose a size limit, as superficial growth is no criterion of pearl 

 production. For the first 18 months the increase in size is 

 mainly superficial. After that the inci;ease is mainly in thickness. 

 The only rehable method is to know the age of the oysters on the bed 

 by havuig determined the date of the spatfall. After that it will be 

 merely a matter of calculation to determine, when they will be ready 

 for fishing. 



In Appendix 3 a table is given showing the measm-ements from 

 which I have determined the growth -rate, and on Plate 5 a cm've of 

 the growth-rate is given. In compiling the table and curve I was 

 not able to use measurements from the same series of oysters. The 

 first three sets of measurements are taken from the same batches 

 of oysters — those which were deposited this year. The fourth, fifth, 

 and sixth sets of measurements belong to the series of oysters which 

 appeared in 1911. The measurements were taken this year. The 

 last three measurements are compiled from Dr. Willey's report of 

 the 1908 inspection. 



Appendix 3 and Plate 5 show quite clearly what we should have 

 expected, namely, that the rate of increase of growth is highest in 

 the yoimger stages, and that it gradually becomes less as the oyster 

 grows older. 



In Appendix 4 and Plate 4 I have tried to show the rate of 

 growth of first-year oysters for each area of the bed during 1912. 

 Unfortunately these figures do not help us much in determining 

 which are the best parts of the bed, but so far as they go they lend 

 support to Dr. Willey's statement that the oysters on the Kakkai- 

 munai bed (area K) are dwarfed. At any rate, their rate of 

 increase was less than one-third of that in area C. 



It is interesting to compare the relative abundance of the oysters 

 with the growth-rate. This is shown in Appendix 4, and it is seen 

 that with the exception of areas J, S, and M, and to a smaller extent 

 area G, a large growth ratio is found where the oysters are scarce, and 



