LOEB and ROJAS: ICHTHYOPLANKTON COMPOSITION AND ABUNDANCE 



proportions between 1964-69 and later years. 

 Comparisons within the 1964-69 OL data set 

 yield all of the high and most of the moderate PSI 

 values. The mean PSI value from these compari- 

 sons is significantly higher (P < 0.05) than that 

 from 1964-69 vs. 1970-73 comparisons. As with 

 the total larvae, the 1970-73 PSI values are sim- 

 ilar and moderately high and the 1983 compari- 

 son values are relatively low compared with other 



Table 12. — Within- and between-time period ichthyoplank- 

 ton composition comparisons presented as ranges, 

 means, and standard errors of percent similarity index 

 (PSI) values and numbers (A/) out of total comparisons 

 having moderate to high (e.g.. -65) values. A. Total larvae. 

 B. OL {other larval taxa) fraction. 



years. Accommodation for T. mexicanus abun- 

 dance reduces slightly (1.1-3.1) the mean values 

 from comparisons with 1970-73 and 1983 data 

 sets and strengthens the significance of difference 

 (P<0.01) between 1964-69 and 1964-69 vs. 

 1970-73 mean values. 



The difference in OL PSI values between 1964- 

 69 and 1970-83 is, to a great extent, due to abun- 

 dance shifts of Group II and Pair II species. The 

 abundance ranks of all three Group II species 

 (Table 7) indicate significantly higher abun- 

 dances during 1970-83 than in earlier years 

 (Man Whitney U tests, all P's < 0.05). Addition- 

 ally, the averaged abundance estimates from 

 these four years are significantly higher than 

 from earlier years (Z tests; P < 0.01 for Bathyla- 

 gus nigrigenys and Vinciguerria lucetia,P < 0.05 

 for Diogenichthys spp.). Together B. nigrigenys , 

 V. lucetia, and Diogenichthys spp. (primarily D. 

 laternatus ) contributed 46.5-72.8^7^ of the OL col- 

 lected during 1970-83 compared with 5.8-37.1% 

 during 1964-69 (Table 13). 



In contrast. Pair II species Lampanyctus parvi- 

 cauda and Triphoturus mexicanus were rela- 

 tively less abundant during 1970-83 than in pre- 

 vious years. These two species contributed 

 21-66% of the OL during 1964-69 compared with 

 <22% during 1970-83 (Table 13). With adjust- 

 ments to T. mexicanus abundance these species 

 proportions in 1973 and 1983 decrease to 11.8% 

 and 13.2%, and those of the Group II species in- 

 crease to 49.9% and 71.4%, respectively. The rela- 

 tive abundance decrease of Pair II was primarily 



Table 13.— Percentage contribution by dominant OL (other larval taxa) species collected 

 sampling penods, 1 964-83. Species arranged according to group affiliations based on across 

 patterns. 



during July-September 

 ■year ranked abundance 



17 



