O'Farrell and Larson: Year-class formation in Clupea palllasi 



135 



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Figure 3 



Juvenile herring {Clupea pallasi) CPUE distribution by station and month for 1999 

 and 2000. April 1999 (A) dark bubbles represent the 21 April survey leg and light 

 bubbles represent the 28-28 April survey leg. May 1999 (B) dark bubbles represent 

 the 18-19 May survey leg and light bubbles represent the 24-27 May survey leg. 

 June 1999 (C) dark bubbles represent the 9-10 June survey leg and light bubbles 

 represent the 15 June survey leg. March 2000 (D) dark bubbles represent the 8-9 

 March survey leg and light bubbles represent the 13-14 March survey leg. April 2000 

 (E) dark bubbles represent the 4-5 April survey leg and light bubbles represent the 

 10-11 April survey leg. May 2000 (F) dark bubbles represent the 22-24 May survey 

 leg and light bubbles represent the 10 May survey leg. June 2000 (G) dark bubbles 

 represent the 6-7 June survey leg and light bubbles represent 13 June survey leg. 



the spawning-date distribution because some samples 

 were discarded and otoliths were unavailable. Because 

 of evidence for intrayear growth-rate variation, other 

 age-at-length data were not used to infer spawning 

 dates for these fish. The standard length data for the 

 fish not included in this analysis were used for all other 

 analyses in our study. 



Precision of multiple otolith readings was calcu- 

 lated for all otoliths examined. Average percent error 

 (Beamish and Fournier, 1981) was 3.60% in 1999 and 

 1.64% in 2000, indicating that aging precision was less 

 than 4 days for 100-day old herring in both years. 



Growth 



Different patterns of age at length (40-50 mm) were 

 observed in 1999 and 2000. In 1999, specimens between 



40 mm and 50 mm were captured in three survey legs. 

 A significant decrease in the number of otolith incre- 

 ments for juveniles 40 mm-50 mm standard length 

 was detected in 1999 (Fig. 5A; Kruskal-Wallis test; 

 r7=27.93, P<0.0001). Nonparametric multiple compari- 

 sons indicated that there was a nonsignificant difference 

 in otolith increment counts for herring caught in the 

 April 1999 and the May 1999 surveys, but herring from 

 these surveys had significantly higher median otolith 

 increment counts than those from the June 1999 survey. 

 In this later survey, juvenile herring were caught that 

 were a product of spawning events occurring late in 

 the spawning season. Figure 5C displays the median 

 and range of spawning dates of the specimens aged 

 for Figure 5A. Juvenile herring that were a product of 

 spawning between 27 February 1999 and 7 March 1999 

 reached a 40-50 mm size range significantly faster than 



