24 THE SCALLOP FISHERY 



(3) Very little variation was found in the sets of 1906 and 1907 

 on the raft spat collectors, but the 1908 and 1909 sets were slightly 

 earlier, though fewer in number. The temperature of the water at the 

 time of set was about 70° F. In 1906 the set began July 26 and reached 

 its height August 4; in 1907, July 24 and August 2; in 1908, July 18 

 and July 26; in 1909, July 22 and July 29, respectively. 



In the above cases, more especially the first, temperature seems to be 

 the controlling factor. The warmth of the water determines an early 

 or late spawning season, as is shown by the difference in the start of the 

 seasons of 1906 and 1907, the latter being nine days behind the former. 

 In each case spawning did not start until the water had assumed a tem- 

 perature of 61.5°. and had been over 60° for a few days. Spawning 

 does not take place until the temperature of the water is sufficiently high 

 to enable the young larvse to live. Thus, in comparing the two years 

 we find that the variation in the spawning compares in every detail 

 with the variations in temperature, and, when other factors are elimi- 

 nated, depends directly upon it. The average summer temperature 

 controls the length and completeness of the spawning season, as is 

 directly manifested by the time and amount of set. 



(6) Conditions influencing the Spawning Season. — In any given 

 area the spawning depends on the latitude and on the climate, tempera- 

 ture again being an important factor. In Ehode Island, in the warmer 

 waters of Narragansett Bay, the season lasts from June 1 to July 1, 

 reaching its height about June 15, Risser (2), as compared with 

 June 15 to August 15 in Massachusetts waters. Naturally the farther 

 south the earlier the season, as the warmer waters hasten the spawning. 



While the temperature is the main factor in determining the spawn- 

 ing, it is by no means the only one. The natural conditions of any local- 

 ity, such as its suitability for growth, for food, depth of water, kind of 

 bottom, enemies, exposure, and other factors which make up the environ- 

 ment of the scallop, play their part in determining the spawning 

 season. Scallops in shallow water spawn slightly earlier than those in 

 the deep, probably due to difference in temperature, while those under 

 favorable growing conditions probably spawn in advance of scallops 

 less favorably situated. 



(c) Length of Season in Massachusetts Waters. — The different local- 

 ities present considerable variation not only within their borders but 

 with each other. The four sections of the scalloping territory given in 

 chapter VI. are useful for a comparison of the spawning season, owing 

 to their divergent conditions. The work of determining the spawning 

 season, as described in chapter VII., was conducted during 1905 and 

 1906 by (a) general observations of the ovary; (6) color chart records; 

 (c) appearance of set. 



(1) On the north side of Cape Cod conditions are not favorable for 

 scallops and there is but a small industry. In Cape Cod Bay the water 



