METHOT and KRAMER GROWTH OF NORTHERN ANCHOVY LARVAE 



33°N 



Figure l. — Sampling sites for north- 

 ern anchovy larvae off southern 

 California. Box indicates the region 

 shown in detail in Figure 4. 



34''N 



32°N 



I19°W 



tured primarily during the last 1 or 2 min of an 

 oblique tow, and some large larvae were still alive 

 at the time of preservation. 



Brothers et al. (1976) found a 5-day difference 

 between posthatch age and number of increments 

 for anchovy larvae reared in the laboratory at 16' 

 C. At 19' C the lag is 3 days and at 12.5= C it is 

 about 9 days ( Methot unpubl . data ). These lags are 

 very close to the age at completion of yolk absorp- 

 tion (19° C, 2.9 days; 16° C, 4.7 days; 12.5= C, 8 

 days — Zweifel and Hunter (see footnote 2)); the 

 larvae are about 4.2 mm at this age. Since de- 

 velopmental events, such as a functional jaw, 

 occur at a constant size at all temperatures in this 

 range (Zweifel and Lasker 1976), we assume that 



increment formation also begins at a constant size 

 of 4.2 mm at all temperatures. The number of 

 increments represents the age in days after yolk 

 absorption. 



RESULTS 



Standard length of each larvae in a sample was 

 plotted against the mean number of increments 

 (Figure 2). Each data point represents the integral 

 of the growth rate of an individual larva over its 

 lifetime, and a trend line through these points 

 estimates the average growth history of larvae in 

 the region sampled. Possible biases in this esti- 

 mate of growth rate are discussed below. 



415 



