12 



Spawning Grounds. — In Massachusetts the fresh-water ponds 

 which form the headwaters of the coastal streams furnish the 

 spawning grounds. Two classes are found: (1) the ordinary 

 tributary tidal stream, with one or more fresh-water ponds 

 at its source at a variable distance from the ocean, and (2) 

 the fresh or brackish shore pond (Fig. 1) separated from 

 the salt water by a narrow sand beach through which there 

 is a shifting natural opening or an artificial channel. The 

 ponds of Martha's Vineyard belong to the latter type, and the 

 alewives enter directly from the salt water through temporary 

 openings. 



Spawning Season. — The spawning season varies slightly 

 from year to year, the approach of the alewives to the shores 

 being regulated chiefly by temperature. According to the 

 United States Bureau of Fisheries records the alewife is seen in 

 the Potomac River by March 4, but in New Brunswick does 

 not enter the St. John River until May 10, although present 

 in the Bay of Fundy in April. The first fish appear earlier in 

 certain streams. In Massachusetts the greater part of the run 

 occurs between the middle of April and the first of June. In 

 some streams the first fish come as early as the last week in 

 March, and in others are still running by the last of June. In 

 1920 the run started as follows: March 20, Mattapoisett River; 

 April 1, Agawam River, Herring River, Wellfleet, Bass River; 

 April 10, Herring River, Harwich; April 15, Mashpee River; 

 j\Iay 1, Monument River and Stony Brook, Brewster. 



Temperature and Spawning. — Temperature is the most im- 

 portant factor in regulating the spawning season from the ap- 

 pearance of the adult alewives off the coast to the development 

 of the young. A certain minimum is necessary to permit the 

 spawning to take place, and above 55° F. the development of 

 the egg becomes more rapid in direct proportion with the in- 

 crease in temperature, until the maximum is attained — about 

 70° F. The 1920 temperature of Nye's Pond, a spring-fed 

 body of water where alewives naturally spawn, is given in the 

 following table. The first alewives came May 10, and were 

 descending as late as August 20. 



