Scouting conditions were classified as follows: 



Good- good visibility in all directions, vessel not taking any spray on bridge and sailing 

 snnoothly, binoculars usable regularly. 



Fair- good visibility in all directions but occasional spray, usually from one side of 



the vessel, hampering regular use of binoculars on that side; one door on bridge 

 usually closed because of spray, vessel with moderate pitch or roll. 



Poor- 



fairly continuous spray over bow to bridge deck, impossible to use binoculars, 

 heavy pitching and rolling o£ vessel. 



The relation of scouting conditions to direction of travel of vessel is shown in table 7, 

 which shows the scouting performed on GILBERT cruises 11 and 13 along the courses shown in 

 figure 1. In executing these patterns the day's run was always toward one of the cardinal points 

 of the compass. The east to west runs were almost zilways performed under good conditions 

 whereas the west to east runs encountered almost all of the poor conditions. Both northward and 

 southward runs were performed under about equal amounts of good and fair conditions. 



Table 7. --Summary of hours scouted and flocks seen under good, fair, and 

 poor conditions on GILBERT cruises 11 and 13 



The scouting conditions have surprisingly little effect on the relative efficiency with which 

 schools are sighted at varying distances. Table 8 shows the number seen under each condition of 

 scouting at various distances and the estimated percentages. The estimated percentages seen 

 under good and fair conditions are not significantly different at any distance. However, no schools 

 were seen under poor conditions beyond 2 miles, and the nunnbers seen at the shorter distances 

 are small enough to introduce a large variability due to ciiance. 



A further comparison of the average number seen per day (table 7) indicates that 38 per- 

 cent fewer schools were seen under poor conditions than under good conditions, and the fair con- 

 ditions were but little better than the poor. These differences are large enough to be expected by 

 chance (as indicated by a chi-square test) only about once in 50 times; hence they are statistically 

 significant. Since the variation in conditions arose alnnost wholly from the heading of the vessel 

 relative to the northeasterly trade winds, differences in the number seen nnust either have been 

 due to visibility or to a Doppler effect resulting from a migratory movement of the fish in one 

 generally consistent direction. It will be shown in a later section that the latter was probably not 

 responsible. 



