160° 



155° 



The areas to be scouted with the vessel were selected to include and extend beyond those 

 fished by the local fleet, but they were, of course, severely limited by the distance that a single 

 vessel could travel. A series of courses in the form of crosses was decided upon, as shown in 

 figure 1. These tracks were followed carefully on GILBERT cruises 11 and 13, which contributed 



the bulk of our observations for an 

 evaluation of scouting techniques in 

 the subsequent sections. The other 

 GILBERT cruise that provided some 

 data was cruise 7, which followed 

 the track indicated in figure 2. The 

 cross patterns have the advantage of 

 providing replicate coverage of the 

 s ame area on successive days. They 

 also serve to standardize the heading 

 of the vessel in relation to the sun 

 and to the prevailing seas, which the 

 trade winds usually push from the 

 northeast quadrant. Also, early in 

 the investigation it was expected that 

 the schools of skipjack nnight be mi- 

 grating through the areas and that 



20° 



AREA! 



AREAD 



AREAEZ 



20' 



160° 



155° 



Figure 1. --Scouting plan for GILBERT cruise 11, April 

 11 to 28, Areas I and II, and for GILBERT 

 cruise 13, June 13, to July 11, all areas. 



such a pattern of s/iouting might show 

 a "Doppler effect"— , which would 

 indicate the direction and speed of 

 the schools. However, no Doppler 

 effect was found, and the cross pat- 

 tern wasted the time of the vessel 

 during the night because it was not 

 possible to use that period to nnove 

 the vessel to another scouting loca- 

 tion for the following day. 



During the autumn of 1953, 

 a different scouting plan was devel- 

 oped in which a particular area was 

 scouted during a day and then the 

 night was used to nnove on to another 

 area. This plan consisted of S- 

 shaped courses, as shown in figure 

 3, which provided an estimate of the 



number of schools to be sighted within an area in which the schools could be assumed to be ran- 

 domly distributed. Such an assumption avoided the troublesonne problem of deciding whether a 

 concentration of schools sighted during a particular part of a day on a straight run arose from 

 chance variation or for some special reason. It also avoided the troublesonne west to east run 

 on which the prevailing northeasterly tradewinds frequently caused the vessel to take spray 

 over the bridge, resulting in poor scouting conditions. The length of this S-shaped section was 

 95 miles or about 10 hours' running time. With about 12 hours of daylight this left 2 hours for 

 fishing schools and experimenting with them. Night was then almost fully utilized in the run to 

 the next station. This plan resulted in covering areas out to 230 miles northeast and 350 nniles 

 south and west of Oahu. 



4/ 



— The name is given to the physical effect of an apparent change in the frequency of sound 



or light where observer and source are approaching or separating. A similar difference might 



be expected if a given number of fish schools were meeting or traveling with the vessel. 



