DISTRIBUTION OF EGGS AND LARVAE OF JACK MACKEREL 



257 



Table 10. — Comparison of estimates of regional distribution 

 using selected stations on selected lines and all data, 1951-54 



1 Hundredths of a percent are used so trace amounts of spawning may be 

 indicated (see p. 252). 

 ' Region not occupied. 



the north in region 2 and were farther offshore in 

 the intermediate area. 



Spawning in 1953 began in February and rose 

 to a peak of nearly 30 percent of tlie total in May, 

 and then declined. Only small nxmibers of eggs 

 were taken in October. Early spawning was 

 centered in region 3, with a fair amount in region 2. 

 The center of spawning was about 240 miles 

 farther south than the early spa^vning of 1951, 

 and most of the spawning was inshore. From 

 this center, spawning moved both north and south 

 and somewhat offshore to the intermediate area. 

 During the final 2 months, the center of spawning 

 was again in region 3 and inshore. 



The monthly distribution of spawning for 1954 

 is very similar to that for 1953. Spawning ex- 

 tended from January to October and reached a 

 peak of nearly 30 percent of the total in May. 

 Early spawning was centered in region 3 about 

 150 miles offshore (intermediate area) and no 



eggs were taken off California. In the next 2 

 months the heavier concentrations extended north 

 to region 2 and south to the northern edge of 

 region 4, with some inshore movement. During 

 tlie final 2 months the center shifted northward 

 to region 2 and inshore. The distribution and 

 relative abundance of jack mackerel eggs for 

 1951-54 are illustrated in Farris (1958: figs. 3-6). 

 Tlie remarkable similarity of monthly distri- 

 bution of spawning in 1952 through 1954 (peak 

 month. May) is illustrated in figure 4. The year 



g .10 



FEB MflR APR MAY JUNE JULY AUG SEPT OCT 



Figure 4. — Proportion of annual spawning of jack 

 mackerel, by months, 1951-54. 



1951 appears to have been an anomalous year 

 with an early peak of spawning in March. The 

 proportion of spawning that occurred during the 

 peak month of each year, including 1951, was 

 approximately three-tenths of the total for the 

 year. Furthermore, over seven-tenths of the 

 spawning for any year occurred during the first 5 

 months. 



Of the 4 years studied, 1951 had the highest 

 proportion of the annual total number of eggs 

 in region 1. High proportions of the annual total 

 eggs were found in regions 3 and 4 during 1953, 

 with a small proportion being taken in regions 1 

 and 2. 



BOUNDARIES OF THE SPAWNING AREA 



The northern and western boundaries of jack 

 mackerel spa\vning during August and September 

 were established by expedition Norpac, an exten- 

 sive study of the north Pacific in 1955 conducted 

 by the California Cooperative Oceanic Fisheries 

 Investigations and other agencies (Ahlstrom, 

 1956: p. 39; Ahlstrom and Kramer, 1957: p. 55). 

 These boundaries may be less certain than the 

 others because the study of the area was more 

 limited in time. The eastern and southern 



