BIOLOGY OF THE ATLANTIC MACKEREL 151 



of the course of events from the time the eggs are spawned until the young mackerel 

 attain the juvenile phase and closely resemble the adults in form and habits. Other 

 papers in this series, now in course of preparation, deal with (1) habits and migrations, 

 (2) age and rate of growth, and (3) fluctuations in abundance of the commercial stock. 



Acknowledgments. — The entire portion of the mackerel's life considered in this 

 paper is passed suspended in the waters of the sea, hence as a member of the plankton 

 community. Accordingly, the data were secured by towing fine-meshed plankton 

 nets through the waters of the spawning grounds. A preliminary cruise in Massa- 

 chusetts Bay was taken in 1926 on the U. S. Fisheries steamer Gannet, Captain Green- 

 leaf, commanding. Cruises in succeeding seasons 1927 to 1932 were on the U. S. 

 Fisheries research steamer Albatross II, Captain Carlson, commanding. In June 

 1932 the Albatross 77 was taken out of service and completion of that season's program 

 was made possible by the kindness of the Woods Hole Oceanographic Institution in 

 putting at our disposal for two cruises during June and July the ketch Atlantis, Captain 

 MacMurray, commanding. 



Numerous persons assisted in the scientific work aboard ship. Of these, E. W. 

 Bailey, Wm. C. Neville, and Herbert Ingersoll took part in many cruises. Wm. C. 

 Herrington's suggestions contributed greatly to the development of the use of current 

 meters to measure flow through the plankton nets. 



In the separation of eggs and larvae from the other planktonts, numerous persons 

 assisted, but the major portion of the responsibility rested on Mildred Moses, whose 

 vigilance insured a constant level of accuracy in removal of the desired material. Her 

 performance of subsequent numerical computations was also an important contribu- 

 tion to the present results. 



To C. P. Winsor I am indebted for suggestions relating to the statistical treat- 

 ment of the mortality curves. 



Certain tabulations and the graphs used herein were products of W. P. A. official 

 project No. 165-14-6999. 



Throughout the investigation, and in all of its many phases, the constantly avail- 

 able encouragement and advice of Henry B. Bigelow has been invaluable. To the 

 extent that this account proves readable, the reader may thank Lionel A. Walford 

 whose editorial suggestions have been freely followed. 



ACCOUNT OF FIELD WORK 



As before mentioned, when work began in 1925 it was strongly suspected that the 

 fluctuations were due mainly to annual variations in the comparative success of sur- 

 vival through the larval stages (Bigelow and Welsh, 1925, pp. 198-199). Accord- 

 ingly, work on the early life history was begun at the outset of the investigation in 

 1926. At that time, it was not known where most of the spawning took place or 

 where the nursery grounds for larvae were located. The literature recorded the 

 occasional finding of eggs in the sea south of the Gulf of St. Lawrence, but no larvae; 

 yet the spawning population apparently favored the southerly waters off the United 

 States coast as much as the northerly waters off the Canadian coast. Massachusetts 

 Bay was a spring mackerel fishing ground well known to be visited at this season by 

 numerous ripe adult individuals, so the first search took place there. Towing in 

 various parts of the bay yielded large numbers of eggs, especially in that portion of the 

 waters partially enclosed by Cape Cod. Not only were the eggs abundant, but num- 

 bers of larvae in various stages of development were found. 



