156 FISHEKY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



was applied during the season of 1932. With similar observations in enough additional 

 seasons, it should be possible to determine what recruitment can be expected from 

 given sizes of spawning stocks for particular infant mortality rates. Thus there will 

 be determined an adequate spawning reserve, for it will be one that produces the 

 needed average recruitment over the observed range of infant mortality rates. 



LIFE HISTORY 



REPRODUCTIVE AGE 



According to information formerly available (Bigelow and Welsh, 1925, p. 205), 

 "Some few females ripen when still not more than 11 inches long; most of them, and 

 all males, at 12 to 13 inches." Present observations indicate first attainment of 

 maturity at somewhat larger sizes, the difference possibly being due to the manner 

 of measurement. The lengths given below were from snout to tip of the middle rays 

 of the caudal fin, whereas the earlier measurements may have excluded the caudal fin. 



Of 1,116 mackerel sampled from catches of traps in the vicinity of Woods Hole, 

 Mass., and at three localities on the shores of Massachusetts Bay between June 24 

 and July 21, 1925, the smallest male with mature gonads was 26 cm. (10M inches) 

 long and the smallest female 29.5 cm. (UK inches). At 30.5 cm. (12 inches) 30 per- 

 cent of the males and a negligible percentage of females were mature. At 34 cm. 

 (13H inches) about two-thirds of the males and one-half of the females were mature; 

 and at 37 cm. (14% inches) nine-tenths of both sexes were mature. (See fig. 2.) 



It is possible that our data may not be typical because they were taken somewhat 

 after the peak of spawning, which usually falls in May and June, and some individuals 

 which hadjspawned early, and whose gonads had somewhat recovered, might have been 

 mistaken for immature individuals. The number so mistaken cannot have been large 

 for there was little difficulty in recognizing the two categories, "ripe" and "spent," 

 which make up our class of "mature." The mistakes, if any, because the spawning of 

 some individuals was too long past, should have been mostly among the larger sizes, 

 because they are usually first to appear along the coast and presumably the earliest 

 to spawn. But among these (52 specimens over 38 cm. hi length were examined) only 

 1 individual appeared immature, hence the error, if any, must have been small. 



By means of size and age relations to be published in another paper of this series, 

 it may be concluded that only a few males, and even fewer females, spawn as yearlings. 

 Four-fifths of the males and two-thirds of the females spawn when 2 years old, and 

 virtually all of both sexes when 3 years old. 



FECUNDITY 



Various statements have appeared in the literature purporting to give the numbers 

 of eggs spawned by individual mackerel. Brice (1898, p. 212) in "The Manual of Fish 

 Culture" states that the average number of eggs at one stripping is about 40,000, that 

 a 1% pound fish gave 546,000, and that the largest fish yielded probably a full 1 ,000,000 

 eggs. Bigelow and Welsh (1925, p. 208) say, "Mackerel is a moderately prolific fish, 

 females of medium size producing 360,000 to 450,000 eggs, but only a small part of 

 these (40,000 to 50,000 on the average) are spawned at any one time." But Moore, 

 whose report appears to be based on more intensive study than others, more cautiously 

 states (J. P. Moore, 1899, p. 5) "seldom 50,000 and frequently a much lesser number of 

 ova are produced at one time, but the aggregate number matured (in a spawning season) 

 in one female of average size is several hundred thousand." This is probably as precise 

 a statement as is warranted at the present time. 



