FISHERY BULLETIN; VOL. 73, NO. 2 



125° * 



120** 



io"v» 



I20»W 



II5-W 



IS-N. 



KTH 



5'N 



O*. 



ys 



ZOOPLANKTON 

 ( ml/ 1000 m^ ) 



<50 

 50-100 

 100-200 

 >200 



.KTH 



• JOROtN 



o cnouwCLi. 



aru 



S*N 



.9*S 



Hsrw 



Figure 19.-Day standing stock of zooplankton by 0.5-m net 

 (ml/1,000 m'), cruises Jordan bl -Cromwell 51, November- 

 December 1970. 



April cruise large catches of skipjack forage were 

 obtained by midwater trawl as well as by 

 micronekton net in the area of the maximum 

 between lat. 0° and 5°N, and one was obtained also 

 at about lat. 10°N where the micronekton net in- 

 dicated a rather low concentration. This result 

 from a single trawl haul thus indicates an area of 

 rich forage of unknown extent at about lat. 10°N, 

 which the sparse data from the micronekton net 

 hauls do not show. The forage may have been 

 patchy in this area. 



The expected resemblance between the spatial 

 distributions of forage and skipjack is not strongly 



lO'N 



5*N- 



5'S 



ZOOPLANKTON 

 ( ml/ 1000 m3 ) 



<50 



50-100 



100-200 



200-400 



>400 



I6'N 



9*N 



5*S 



II5*W 



Figure 20.— Day standing stock of zooplankton by 0.5-m net 

 (ml/ 1,000 m'), cruise J&rdan 60, March-April 1971. 



evident when Figures 23 to 26 are compared with 

 charts of skipjack availability on the same cruises 

 (Figures 5 to 8). However, Table 3 shows that 

 mean catch per line-hour and mean number of 

 schools per hour for all fishing days in a zone of 

 latitude was highest in November-December from 

 lat. 1° to 5°N, where the principal forage 

 maximum was located (Figures 23 and 24). Table 4 

 shows that the same indices were highest in 

 March- April from lat. 9° to 11°N, where Figures 25 

 and 26 show no forage maximum, although one 

 may have existed there as explained above. A 

 secondary skipjack maximum occurred in March- 

 April in the equatorial region, south of lat. 3°N, 

 where a forage maximum was present. 

 Attempts were made to correlate forage con- 



398 



