DISTRIBUTION OF EGGS AND LARVAE OF JACK MACKEREL 



263 



Table 16. — Average temperalures at 10 meters during jack 

 mackerel spawning, by season and size of sample, 1951- 

 54 



Figure 9. — -Monthly median temperatures at 10 meters, 

 at which jack mackerel eggs were spawned. 



monthly intervals and the median temperatures 

 at 10 meters computed for each month. The 

 monthly median temperatures are shown in 

 figure 9 and indicate that spawning generally 

 occurs at lower temperatures in spring than in 

 late summer. The within-year median temper- 

 ature shift is greater than the between-year 

 temperature variation (see below). 



The data from table 13 are summarized in 

 tables 15 and 16. A difference in optimum 

 spawning temperature between small hauls (1-100 

 eggs) and large hauls (101 eggs and more) is 

 noted (fig. 10). The reason for the difference is 

 that a large proportion of the large hauls were 



T.^BLE 15. — Summary: Distribution of temperatures at 10 

 meters of stations having jack mackerel eggs, by size of 

 sample, 1951-64 



[In 0.5° C. Intervals] 



taken during the peak of the season (April and 

 May), and have therefore a more restricted 

 temperature distribution. 



The early, late, and annual distributions of 

 temperature at a depth of 10 meters, by 0.5° C. 

 increments, for all stations occupied in 1951-54 are 

 given in table 17. These differ from the distribu- 

 tion of temperatures at which jack mackerel 

 were taken in two ways: their temperature range 

 is greater, and they show less tendency to cluster 

 about a central value. 



