HUNTER and KIMBRELL: EARLY LIFE HISTORY OF PACIFIC MACKEREL 



If larvae were not fed, most died between ages 4 

 and 7 d and none survived longer than 7 d (Figure 

 2C). Highest survival (on the eighth day after 

 hatching) occurred when food was added for the 

 first time at age 2.5 d; survival was somewhat 

 lower if food was added at 3.5 d and negligible if 

 added at 4.5 d (Figure 2F). Thus at 19' C starva- 

 tion appeared irreversible if food was not provided 

 before 4.5 d. 



Pacific mackerel larvae, unlike herring or an- 

 chovy (Blaxter and Hempel 1963; Lasker et al. 

 1970), did not cease swimming or feeding at the 

 time of irreversible starvation. At age 5 d, the 

 incidence of larvae with rotifers in their stomachs 

 was relatively high (80%) (Figure 2D), but the 

 average number of rotifers per positive stomach 

 was much less than in larvae fed first at age 2 or 3 d 

 (Figure 2E). Thus at age 5 d, most larvae were still 

 able to feed, but owing to their weakened condi- 

 tion, none were able to capture enough prey to 

 survive. 



Vulnerability of larvae to starvation persisted 

 through metamorphosis. All juvenile Pacific 

 mackerel appeared emaciated and swam slowly by 

 the fourth day of starvation. Mortality of 10% oc- 

 curred in the group starved 4 d; 50% mortality 

 occurred in those fish starved 5 d. All juveniles 

 surviving 4 and 5 d of starvation recovered when 

 food was added; no mortality occurred in the con- 

 trols. Thus, newly metamorphosed Pacific mack- 

 erel were able to withstand 1 or 2 d more of starva- 



tion than first-feeding larvae, but they were better 

 able to recover from food deprivation. 



Growth 



Growth in length of Pacific mackerel larvae was 

 slow and almost linear over the first 10-15 d until 

 larvae reached about 6-7 mm SL; there followed a 

 rapid acceleration through metamorphosis. We 

 did not fit equations to these data because none of 

 the standard growth equations gave a good fit to 

 the entire growth curve. The effect of temperature 

 on growth was not distinguishable over the initial 

 growth period, but became obvious during the 

 period of rapid growth (Figure 3, Table 1). To pro- 

 vide an index of the effect of temperature on 

 growth, we expressed the duration of the larvae 

 period (hatching to metamorphosis, 15 mm) as a 

 function of temperature (inset in Figure 3). The 

 Qio was 3.0 when calculated from the equation in 

 Figure 3 for the temperature range of our observa- 

 tions ( 16. 8'-22.1° C). 



The length-weight relation for Pacific mackerel 

 larvae and juveniles is shown in Figure 4. The 

 form of this equation was developed by James 

 Zweifel and used by Hunter ( 1976) to express the 

 length-weight relation for northern anchovy lar- 

 vae. The curvilinear nature of the length-weight 

 relation, still evident in the log-log plot ( Figure 4), 

 indicates that if a linear regression of logj^ weight 



Table l. — Growth data (millimeters SL) for seven groups of Scomber japonicus larvae reared at different mean temperatures from 



hatching through metamorphosis. 



'Juvenile growth (age. n.x, and (SD)): 26 d. 13,34.4 mm (4.37); 29 d, 9, 43.9 mm (3.60); 39 d. 5, 55.0 mm (8.74); and 47 d. 9. 67.3 mm (10.30). 



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