ROTHLISBERG and MILLER: LARVAL I'ASDAU N JORDASl OFF OREGON 



MARCH 



luiiJ 



APRIL 



1 10 20 30 



VI 



VII 



T 10 3 

 -10 2 

 ■10 



I I I — I— \* 



VII 



-ilO- 



- 10 : 



10 



1 10 20 30 



1 10 20 30 



STATION 



FIGURE 10.— Stage-specific larval distribution in March and April 1972. Larval abundance summed by stage 



over all transects. 



creased to HI by 4 May. There was rapid increase in 

 median stage between 22 April and 1 June 1971, 

 coinciding with rapid increase in surface tempera- 

 ture through May. In early cruises of 1972, larvae 

 were confined to stations inshore of 20 nmi. Tem- 

 peratures at those stations were about 2°C warmer 

 than in 1971, and development was greater through 

 22 April, when median stage was V. Individuals up to 

 Zoea XI were already present, which did not occur in 

 1971 until after the May spurt in development. Fast- 

 er development in 1972 corresponded to water tem- 

 peratures consistently higher than in 1971 from 

 mid-March until June. By May of both years larvae 

 were mostly dispersed between 10 and 50 nmi. Over 

 that range temperatures were about the same and in- 

 creasing from early May through June. Despite this, 

 the increase in median stage slowed through June in 

 both years. The median stage on 29 June was nearly 

 XH in 1971 and XIII in 1972. The difference is not 

 significant, and Zoea X through juvenile stages were 

 present on that date in both years. 



Larval Survival — Estimates from 

 Field Sampling, 1971 and 1972 



To assess larval survival in the field, total abun- 

 dance was calculated for each larval stage over all 

 cruises and stations (no./l,000 m 3 X sampled depth 

 = no./ 1,000 m 2 ). In each year the total number of 

 Zoea I was taken to be 100% of the larval hatch, and 

 the number of each successive stage was expressed 

 as a percent of that hatch (Fig. 12). Sampling effort 

 was very similar between the two years in respect to 

 timing and total number of cubic meters of water 

 filtered (72,246 m 3 in 1971; 67,979 m 3 in 1972), so 

 that the difference in survival probably was not an 

 artifact. 



We caught 1,653 Zoea I in 1971 and 530 in 1972. 

 There is a reversal in this estimate from the order of 

 the years in respect to hatch as estimated from egg 

 counts in the commercial catch. Table 2 shows that 

 the latter estimate was quite close in the two years: 

 1.75 X 10 12 and2.20 X 10 12 in 1971 and 1972,respec- 



465 



