Pig. 89. Temperature and Growth. The broken line represents the 

 curve of the average monthly temperature of the water during the year 1906 at 

 the Powder Hole, Monomoy Point, and the numbers on the sides indicate the 

 degrees. The other curve represents the growth of the 1905 scallop set during 

 the year 1906, and the same figures which corresponded to the degrees in tempera- 

 ture now stand for the size of the scallop in millimeters (25.4 millimeters equal 

 1 inch). Tracing the growth of the scallop, size 34 millimeters, January 1, no 

 growth is noticed until May 1, when the water assumes a temperature of about 

 49 F. During the month of May there is a rapid growth, which slackens during 

 June and July, the spawning months, as is shown by the drop in the curve, and 

 is again resumed during August, September and October. The growth perceptibly 

 slackens during November, and probably ceases altogether after the middle of 

 the month, when the water is about 43 F. To all practical purposes the growth 

 ceases November 1, at a temperature of 49 F., which is directly comparable to 

 temperature of the water when growth began, May 1. Therefore, it is apparent 

 that the growth of the scallop, as typified by shell formation, depends upon the 

 temperature of the water, at least 45 F. being necessary for growth. The ces- 

 sation of growth is not due to any decided fall in the food supply but rather to the 

 inactivity of the scallop, which becomes sluggish in cold water. 



Growth {Millimeters). 



May 1, 

 June 1, 

 July 1, 

 August 1, 



34.00 

 39.71 

 42.12 

 45.10 



September 1, 

 October 1, 

 November 1, 

 December 1, 



. 51.00 

 . 56.80 



. 62.90 



Fig. 90. The plotting shows the comparative growth of large and small 

 scallops of the same age during their second summer. Division B (38.50 milli- 

 meters) by the end of the season has gained the greater part of the difference at 

 the start between it and Division A (49.50 millimeters), reducing the margin from 

 11 to 3.27 millimeters. These scallops were confined in the same pen, and num- 

 bered Division A 125, Division B 200. This tendency perhaps accounts for the 

 uniformity in size of scallops in any particular locality at the end of the second 

 summer's growth, when the scallop is ready for market. 



Growth (Millimeters) . 



