TRAWLING FOR FORAGE ORGANISMS IN CENTRAL PACIFIC 



289 



and 50° N., averaged higher than those to the 

 south. In this summer season it appears that the 

 nortliern boundary of the transition zone occurred 

 at about hititude -iO" N., longitude 157° W., and 

 then sloped to the south in a westerly direction. 



Sampling with the 10-foot Isaacs-Kidd trawl 

 was conducted on two cruises to the equatorial 

 Pacific during which hauls were made along north- 

 south sections. On Smith cruise 31, in October 

 and November 1955, six or seven hauls were made 

 at night on each of three longitudes, 140° W., 120° 

 W., and 112° "W., within the latitudinal range of 

 8° S. to 7° N. (fig. 16). In this case, as evaluated 

 by a two-way analysis of variance, the differences 

 among longitudes were significant (F=6.81; 

 d.f. = 2 and 10; P <0.05). Catches were generally 

 higher in volume north of the Equator than south. 



NORTH ,.ATITJ0C 



- LATITUDE - M 



riGURE 15. — Variation in trawl cuUh (volume in milli- 

 liter.s per hour of hauling) of the 10-foot Isaats-Kitld 

 trawl on four north-south .sections, Hiiffh M. Smith 

 cruise 30, July-August 1955. 



Figure 16. — Variation in trawl catch (volume in milliliters 

 per hour of hauling) of the 10-foot Isaacs-Kidd triiwl 

 on three north-south sections, Hugh M. Smith cruise 31, 

 October-November 1955. 



During one part of cruise 31, hauls were made 

 each night while the Stnith was running general- 

 ly to the east on a meandering course along the 

 northern boundary of the Countercurrent. Vol- 

 imies of the catches obtained on these hauls are 

 plotted in figure 17 in relation to longitude and 

 the position of the current boundary. There ap- 

 pears to be a doming or peaking in the volumes in 

 the neighborhood of longitude l-tO° W. and again 

 at 115° W. with a single high catch at 125° W. 

 There is no apparent relation between volume of 

 catch and distance north or south of the current 

 boundary. 



On Smith cruise 35, in August to October, 1956, 

 8 to 11 hauls were made on each of 4 longitudes, 

 160° W., 151° AV., 143° AV., and 135° W., within 

 the latitudinal range of 20° S. to 11° N. (fig. 18). 

 On three of the four sections, the peak volume 

 occurred within 2° of the Etpiator. Although dif- 

 ferences among longitudes were not significant 

 (F=0.37; d.f. = 3 and 32; /^>0.05), there is in- 

 dication of a trend in the region of tlie Equator 



