152 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Encouraged by this success in waters south of the previously known distribution 

 of larvae, search was in 1927 extended south of Cape Cod. Here eggs were found in 

 abundance from the offing of Cape Cod nearly to the mouth of Chesapeake Bay. As 

 in Massachusetts Bay, larvae were present in abundance also. 



To determine whether this was the usual condition, the survey was repeated in a 

 single cruise during May of 1928, when approximately the same conditions were 

 found. 



These three seasons of prospecting for mackerel eggs and larvae completely al- 

 tered the previous notion that spawning was more successful in the northwest portions 

 of the range of the species. Not only were specimens regularly obtained from Massa- 

 chusetts Bay to Chesapeake Bay, but the numbers of individuals per tow were greatly 

 in excess of those taken by similar methods in the Gulf of St. Lawrence during the 

 Canadian Fisheries expedition of 1914-15. Evidently this southerly region was far 

 more important than previously supposed, and hence a suitable one in which to study 

 variations in the survival rate during early stages. 



However, it was still necessary to determine the length of the spawning season 

 and the duration of the period of larval development. For this purpose, successive 

 cruises were made during the spring and early summer months of 1929. These proved 

 that in the area between Cape Cod and Cape Hatteras spawning began in early April, 

 and larval development had nearly run its course by the end of July. 



In 1930 and 1931, such successive cruises during the spawning season were re- 

 peated and every opportunity was taken to devise methods of estimating the abund- 

 ance of the various young stages. 



This development of quantitative technique required the determination of verti- 

 cal distribution so that the proper levels would be fished; determination of the incu- 

 bation and growth rates so that cruises might be planned at proper intervals to include 

 all the important events; and finally, it required devising a reliable method of meas- 

 uring the amount of water strained by the tow nets so that hauls would be com- 

 parable from time to time and place to place. By 1932 knowledge and techniques 

 were advanced sufficiently for the survey of that season to provide adequately quan- 

 titative data for the more important sections of this report dealing with growth, 

 drift, and mortality. Toward the close of this season, the Albatross II was withdrawn 

 from service as a Government economy measure. This prevented continuing the 

 research into its next phase, that is, the measurement of mortality and its accompany- 

 ing hydrobiological conditions through a series of seasons, to see how mortality is 

 affected by particular conditions in seasons of good survival contrasted with other 

 conditions in seasons of poor survival. Since the hoped-for resumption of surveys 

 has not yet been possible, the present available results are now reported. 



SYNOPSIS OF RESULTS 



Most mackerel reach reproductive maturity when 2 years old. Some precocious 

 individuals, usually males, first spawn a season earlier and others of both sexes a year 

 later. The percentage of the latter is higher among the females than the males. 



Mackerel are said to spawn 360,000 to 450,000 eggs in a season, but this is a point 

 needing further study. Doubtless smaller individuals spawn fewer and larger indi- 

 viduals more eggs than this. The eggs are ripened in successive batches; it is not 

 known how many batches or what interval of time intervenes between their discharge. 



Spawning takes place over nearly the entire spring and summer range of the species , 

 from off Chesapeake Bay to Newfoundland. By far the most important ground is 



