TRAWLING FOR FORAGE ORGANISMS IN CENTRAL PACIFIC 



291 



"20' 25* JO* 35* «• «• 50 



NOBTH L4T1TUDE 



Figure 19. — Variation in trawl catch (volume in milliliters 

 per hour of hauling) with latitude of the 6-foot Isaaes- 

 Kidd trawl, John R. Manning cruise 22, September- 

 October 1954, and Hugh M. Smith cruise 27, January- 

 February 1955. 



are plotted in figure 19. If the volumes north of 

 40° N., exclusively Manning cruise 22, and south of 

 25° N., exclusively Smith cruise 27, are omitted 

 from the analysis, we find no significant difference 

 (^ = 0.614:, P>0.b) between cruises. 



Employing the 10-foot trawl on Smith cruise 

 31 (September-December, 1955) and on STnith 

 cruise 35 (August-October, 1956) to the equatorial 

 Pacfic, we obtained catches with mean volumes 

 not significantly different (2^=0.657, P>0.4). De- 

 spite a wide variance in the data, there was a close 

 similarity in the catch means when summarized 

 by latitudinal zone (fig. 20). 



On the basis of these simple "t" tests of the 

 difference between means, we found in two in- 

 stances no significant differences between cruises 

 to the same general area at about the same time 

 of year but in different years, and in a third in- 

 stance no significant difference between two 

 cruises to the same area but at different seasons 

 (late summer and winter). These findings, to- 

 gether with those of the previous sections of this 

 report, seem to indicate that the tropical marine 

 fauna sampled by our midwater trawls is highly 

 uniform in abundance both in space and time. 



637256 0—62 1 



Variations in Composition of the Catch 



It is evident from appendix tables 7 and 8 

 that there are north-south differences in the kinds 

 and numbers of organisms captured bj* the Isaacs- 

 Kidd trawls. These are summarized in a general 

 manner in tables 14 and 15. "We conclude that the 

 largest number of categories of organisms was 

 captured in the South Equatorial Current and in 

 the Countercurrent (table 14) ; Hawaii and the 

 North Pacific Current were next in rank ; the poor- 

 est zones with respect to kinds of organisms were 



• HUGH M SMITH CRUISE 31 

 o HUGH M SMITH CRUISE 35 



ig. 5- 5' 10- !«• 28- 55* 50" 



S- LATrTUOC-N 



Figure 20. — Variation in trawl catch (volume in milli- 

 liters and nmnber of orRanisnis i)er hour of hauling) 

 with latitude of the lO-foot Isiiacs-Kidd trawl, Hugh 

 M. Smith cruise lU, Sei)teuil)er-I)eceniber, 1055, and 

 Hugh M. Smith cruise .35, Atigust-Octobcr, 1956. (Lim- 

 its of the 0.95 fiducial interval are indicated for each 

 mean. Number of hauls in each area is shown in 

 parentheses.) 



