DISTRIBtTTION OF EGGS AND LARVAE OF JACK MACKEREL 



265 



Table 18. — Annual mean, median, and modal temperatures 



at which spawning occurred, 1951-54 



[At 10 meters; In °C.] 



Table 19. — Summary: Distribulion of temperatures at 10 

 meters, at all stations occupied, February through July, 



1951-54 



[In O.S'C. intervals] 



Turner (1948: p. 351) says, "The reproductive 

 rhythms of the female, as in the male, are influ- 

 enced by numerous factors in the external environ- 

 ment as well as by physiologic factors conditioning 

 the internal enwonment." Since httle is known 

 about the internal factors governing the spawning 

 of fishes, no comprehensive explanation for the 

 variation in the distribution of spawning jack 

 mackerel can be given at this time. It is con- 

 cluded that temperature is important, but not the 

 controlling factor in spatial-temporal distribution 

 of spawning jack mackerel. 



SURVIVAL OF THE LARVAE 



The method used by Ahlstrom (1954b) to de- 

 termine the survival of larvae has been retained 



so that interspecific comparisons might more easily 

 be made for fish occupjing the area surveyed by 

 the Cahfornia Cooperative Oceanic Fisheries In- 

 vestigations. All larvae of a species were with- 

 drawn from a station sample and measured. The 

 measurements are grouped into size classes and 

 adjusted by the standard haul factor (p. 250). 

 These standardized counts are integrated over time 

 and space (p. 251) and adjusted for growth. The 

 products are summed for the year to give an 

 estimate of abundance of the size class. The 

 decline in abundance of successively larger size 

 classes provides an estimate of survival. 



REGIONAL ESTIMATES OF ABUNDANCE 

 OF LARVAE 



The regional estimates of abundance by size 

 class for jack mackerel larvae are given in table 

 20 for 1952, table 21 for 1953', and table 22 for 

 1954. These tables are summarized in tables 23 

 and 24, and the annual estimates of abundance 

 and survival are given in table 25. It wall be noted 

 that the curves shown in figure 11 derived from 

 this table are very similar, suggesting that the 

 number of larvae surviving a 30-day period has 



1,000 



100 



10 



01 



.01 



001 



10 



20 30 40 50 60 



DAYS OF DEVELOPMENT 



Figure U. — Abundance curves of jack mackerel larvae 

 to age 57 days, 1952-54. 



