FISHERY BULLETIN: VOL. 69, NO. 1 



361 |0e| 1 10 1 |I2| b2| M |06| |08| 1 10 1 ||2| |02| |04| |06| 



1963 ' 1964 ' 1965 



1966 



Toil lo4l bel 

 1967 



Figure 4. — Size frequency histograms for all stations, 1963-67. Dashed lines are an estimate of average 

 growth of individual year classes. "0" indicates no samples for that month. 



22 

 20 



^'^ 

 § 12 



-J 8 

 6 



2 

 



S 



OUR 

 RESULTS 



OUR 

 RESULTS 



>'l I I I I I.I I I I I I M I I I I I I I I I I 



6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 



I MONTHS I 



Figure 5. — Comparison of generalized growth curves 

 of E. pacifica. 



in the summer and fall. Nemoto (1957 and per- 

 sonal communication) believes that E. pacifica 

 grows rapidly, reaching a length of 17-18 mm 

 after 1 year. Many individuals spawn after 1 

 year and then may continue to live for another 

 year, reaching a maximum of 22 mm after 2 

 years. We find no convincing evidence, how- 



ever, for continuation of large adults through a 

 second year. Large euphausiids disappeared 

 from our samples by the winter (Fig. 4). 



Thus our results indicate a faster growth rate 

 and shorter life cycle than those of Ponomareva 

 and Nemoto for the northwestern Pacific but a 

 similar maximum size. Our growth rates off 

 Oregon averaged 0.065 mm/day for the entire 

 life span, about twice those for the other field 

 studies of E. pacifica. Maximum rates for rap- 

 idly growing juveniles were 0.095 mm /day. 

 These rates are higher than Lasker's (1966) 

 maximum rates for juvenile E. pacifica reared 

 in the laboratory, suggesting that growth in 

 nature may exceed "optimal" conditions in the 

 laboratory. 



Although our estimates of the growth of E. 

 pacifica are higher than previousl.v reported, 

 they approximate the estimates for .sevei'a! other 

 species of euphausiids. A length of about 22 mm 

 after 1 year was also found by Mauchline ( 1966) 

 for Thysanoessa raschii; by Ruud (1936), 

 Mauchline (1960), and Einarsson (1945) for 

 Meganyctiphanes norvegica; by Einarsson 

 (1945) for Thysanopoda aciitifrons; by Ruud 



84 



