ZOOPLANKTON OF CENTRAL PACIFIC 



379 



July. With further sampHng the results showed 

 a rather uniform level of abundance for the 9- 

 month period April through December (King, 

 1954) with a reduction from January to March. 

 Figure 13 shows the results of our sampling to date 

 for the Countercurrent and for the equatorial 

 region of the South Equatorial Current with the 

 volumes combined, irrespective of longitude, into 

 four quarterly periods of 3 months each. In the 

 Countercurrent the highest average volume was 

 obtained for the second quarter, April, May, and 

 June, which occurs during the period when north- 

 east trade winds are predominant at those lati- 

 tudes. Along the Equator the last six months of 

 the year, the period of strong southeast trade 

 winds (Crowe, 1952) averaged higher than for the 

 first two quarters. From an analysis of variance, 

 however, we conclude that the differences among 

 seasons are not statistically significant (F=1.87, 

 P>0.05), but again differences between subdi- 

 visions of the current system are highly significant 

 (F = 8.38, P<0.01). 



If we segregate the data geographically ac- 

 cording to divisions of the current system and 

 seasonally into two 6-month periods, i. e., (1) 

 January to June, which includes roughly the time 

 of lightest winds along the Equator in the central 

 Pacific, and (2) July to December, the period of 



JAN-FEB-MAR APR-MAY-JUN 



JUL-AUG-SEP OCT- NOV- DEC 



Figure IS. — Seasonal variations in zooplankton volumes 

 (adjusted) for the Countercurrent with boundaries at 

 about 5° N. and 10° N. latitude, and for the South 

 Equatorial Current from about 5° N. to 5° S. latitude; 

 longitudes 120° \V. to 180° combined; the limits of the 

 0.95 fiducial interval are shown for each mean. [The 

 number of samples for each season and each subdivision 

 of the current system is indicated in parentheses.] 



• — — o JANUARY - JUNE 



■-o JULY - DECEMBER 



O 



O 30 

 O 



<J 20 - 



10 - 



' ' ' ' I 



(A) ZOOPLANKTON VOLUMES | 



SEC 



r 



J I L 



o 

 o 



I ' 

 (B) YELLOWFIN CATCH 



J I 1__L 



SEC , DIV 



• /I 



I 



/ \i 



CONvl CC 

 I 



■f--2^ 



I II I 



I 

 I 

 I 



1/ 

 / 



.*'!' 



I 



I 



J LJ_ 



/»-.>^ 



"1 — 1 — r 



NEC 



-LU I I I \ \ L 



TT 



"1 — I — I — r 



I 



\\ 



_1_L 



'-1-0-; 



14. 12= 10= 8° 6° 4° 2° 0° 2° 4° 6° 8° 10° 12° 14° 16° 18° 

 S — LATITUDE— N 



Figure 14. — Variation with the current system in (A) 

 zooplankton volumes (adjusted) and (B) yellowfin long- 

 line catch for the two 6-month periods, January-June, 

 a period with northeast or light and variable winds, 

 and July-December, a period of prevailing southeast 

 trade winds (in the central equatorial Pacific). 



strong southeast trades, we find an interesting 

 difference (fig. 14A). In both groups, the peak 

 abundance in zooplankton occurred at the Equa- 

 tor, but during the latter half of the year under 

 the influence of the southeast trades the abun- 

 dance continued high into the convergent zone. 

 When the data from this zone are examined by 

 means of the "t" test we find, however, that the 

 mean for January-June is not significantly differ- 

 ent (P>0.05) from the mean for July-December. 

 Our data indicate that along the Equator 

 there was considerable difference in zooplankton 

 abundance among years. Figure 15 presents aver- 

 age zooplankton volumes for the Countercurrent 

 and the equatorial region of the South Equatorial 

 Current which were visited repeatedly from 1950 

 to 1954. From an analysis of variance we may 

 conclude that differences between the two sub- 

 divisions of the current systems are highly signifi- 

 cant (F=27.60, P<0.01), differences among years 

 are also highly significant (F=7.33, P<0.01), but 



