FISHERY BULLETIN: VOL. 74, NO. 4 



egg production were followed by proportionately 

 high peaks in larvae, relative to 1955 and early 

 1956 (January-April) (Figure 4c). Both the one 

 peak in eggs in 1954 (June) and the highest peak in 

 1956 (June) led to particularly heavy recruitment. 

 Incipient spawners and larvae were both un- 

 evenly distributed in the study area, the larvae 

 usually more patchy than the spawners (Brinton 

 and Wyllie in press). A possible effect of relative 

 aggregation of spawners on recruitment was 

 considered. A monthly index of survival of newly 

 hatched larvae was determined as the ratio of the 

 mean density of larvae observed on a given cruise 

 to the density of ripe eggs calculated for the 

 previous month— usually one cruise earlier. (As 

 noted above, this ratio is >1.0 in about one-third of 

 the instances, indicating that spawning is under- 

 estimated. The indices are, therefore, regarded 

 only as relative to each other.) Cruise-to-cruise 

 differences in patchiness of spawners were es- 

 timated by comparing, among cruises, variances 

 of number of ripe eggs carried by incipient 

 spawners. Each variance was derived by use of 

 numbers from all stations of a cruise. The regres- 

 sion of patchiness in relation to survival of calyp- 

 topis larvae showed a slope not significantly 

 different from zero (Figure 7). Evidently, 

 differences in the degree of aggregation of 

 spawners on the scale observed (32-64 km between 

 stations) did not affect sun-ival of newly hatched 

 larvae. 



S £ 



w 

 to 



< 

 a. 



RELATIVE RECRUITMENT 



^0. LARVAE, l-4mm, PER CRUISE, PER lOOOm^ 

 NO EGGS PER PREVIOUS CRUISE. PER lOOOm' 



Figure 7.— Index of patchiness of ripe unspawned eggs of 

 Euphausia pacifica in relation to index of recruitment during 

 succeeding month. Slope of regression not significantly different 

 from (P>0.05, <-test). Standard deviation is used as a measure of 

 dispersion and in no way assumes normality of the data. 



Temperature Relationships of 

 Spawners and Larvae 



Abundances of spawners and recently hatched 

 larvae (calyptopes of <2.5 mm) were plotted in 

 relation to ambient temperature at 10 m depth 

 (Figure 8). A relationship of spring-summer up- 

 welling to maxima in reproduction, however indi- 

 rect, was evident in foregoing observations. There- 

 fore, data for the months of strong upwelling 

 (April-July) are separated from those of the other 

 months. 



Both spawners and larvae occurred across a 

 range 10°-21.6°C, virtually the available range. 

 When lumped by 0.5°C increments, close to 40% of 

 the stations yielded some calyptopis larvae and 

 40% yielded incipient spawners. During August- 

 March (Figure 10a) larvae were most concentrated 

 within the range of 12°-16.5°C, the same as the 

 spawners. There, mean densities of larvae were 

 50-200/1,000 m\ During April-July (Figure 8b), 

 maximum densities of larvae, 200-7,000/1,000 m'^. 



TEMPERATURE RELATIONSHIPS (1953-56 DATA) OF 

 Jl^^ SMALL (<2 5mr,i) E poatKa LARVAE 

 fi'*\ RIPE (SPERMATAPHORE-BEARING) FEMALES 

 e'o MAXIMUM NUMBER 



WEAK-UPWELLING MONTHS (AUGUST -MARCH) 



8 



S: 7000^ 



loo- 

 se- 



12" 14" 16" 



STRONG- UPWELLING MONTHS (APRIL -JULY) 



5" §• 



i I 



\l 



k 



^j 





^l 



I 



12" 14" 16" 18" 20" 



TEVf=ERATURE ("C AT Om DEPTH) 



Figure 8.— Densities of Euphausia pacifica larvae <2.5 mm 

 length and ripe females in relation to water temperature at 10 m 

 depth, a, August-March; b, April-July. 



744 



