FISHERY BULLETIN: VOL. 86, NO. 1 



Table 11. — Within- and between-hydrographic period ichthyoplankton composition 

 comparisons presented as range, mean, and standard errors of percent similarity index 

 (PSI) values and numbers (N) out of total comparisons hiaving moderate to high (e.g., 

 -65) values. A. Total larvae. B. OL (other larval taxa) fraction. 



The OL percentage composition similarly does 

 not demonstrate clear hydrographically related 

 patterns (Table IIB). As with the total larvae, 

 comparisons of cold vs. other years yield most of 

 the moderate to high PSI values. Highest values 

 (88.1 and 85.2) come from comparisons of cold vs. 

 El Nino (1965 vs. 1967) and cold vs. warm (1964 

 vs. 1969) years. Comparisons within and between 

 transition, warm and El Nino years give primar- 

 ily low values. Recalculation of PSIs to accommo- 

 date for Triphoturus mexicanus lowers mean val- 

 ues for comparisons with 1973 and 1983 by only 

 0.4-2.3 and does not affect the overall results. 



Chronological Considerations of 

 Species Composition 



When the total larval and OL PSI data are con- 

 sidered in terms of chronological rather than hy- 



drographic periods, various patterns become ap- 

 parent (Table 12). For the total ichthyoplankton, 

 comparisons within the 1964-69 data set and be- 

 tween this and the 1970-73 data set give similar 

 means, ranges, and proportions of moderate to 

 high values. In contrast, comparisons within the 

 1970-73 data set provide more similar values and 

 a significantly higher mean value than results 

 from comparisons within the 1964-69 set (Z test, 

 P < 0.01). This suggests that, despite the varied 

 hydrographic conditions represented during the 

 1970-73 period, conditions were favorable for a 

 repeated fairly similar anchoveta-dominated 

 ichthyoplankton assemblage during July- 

 September months. 



Chronologically grouped comparisons of the OL 

 fraction provide somewhat different patterns 

 from those of the total ichthyoplankton (Table 

 12B) and indicate a marked change in species 



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