ABSTRACT 



Distribution and abundance of eggs and larvae of the jack mackerel, 

 Trachurus symmetricus (Ayres), and survival of the larvae are described, 

 utilizing quantitative data collected on monthly cruises of the California 

 Cooperative Oceanic Fisheries Investigations during 1951-54. 



Spawning in the period 1951-1954 occurred from Washington to 

 Magdalena Bay, Baja California. In each of the 4 years it began in 

 February and ceased by October. The peak month of spawning was 

 March in 1951 and May in 1952, 1953, and 1954. About 30 percent 

 of the spawning occurred during the peak month. Estimates of egg 

 abundance varied by less than a factor of 2 during the 4 years studied. 



The effect of temperature on the rate of development of eggs was 

 investigated. Regression statistics are given \ for the developmental 

 rate. Reliability of the regression was checked by direct observation 

 of developing eggs at controlled temperatures. 



The annual estimates of survival for 1952, 1953, and 1954 indicate a 

 reasonably constant survival of month-old jack mackerel larvae in 

 these years. 



The growth rate of jack mackerel larvae was approximated from 

 data derived by direct observation of developing jack mackerel larvae 

 under laboratory conditions and was described by two successive 

 logarithmic growth curves. The second curve originates at yolk sac 

 absorption and has the lesser slope. 



Survival data may be broken into two periods: the first period, 

 concurrent with the fast growth period, is characterized by poor sur- 

 vival and may be the critical period; in the second, survival is much 

 better and growth much slower. 



