schools seen when the vessel was at various distances from the unit area (fig. 5), A simple 

 accumulation of these may be transformed to a percentage of the total number seen in that area. 

 Thus only 0.2 percent were seen in the most distant zone, including 3-3/4 and 4 miles, 5.9 per- 

 cent had been seen when the vessel had approached within 2-1/4 miles, and only 42.4 percent of 

 the total number seen had been seen when the vessel approached to less than 1-1/4 miles. 



Table 3. --Relation of distance from vessel and number of flocks seen on GILBERT 



cruises 11 and 13— 



1? 



— Three flocks omitted because of incomplete data. 



— Three seen in 2ifter-quadrant8. The entries in this column are the sunns of 

 the schools sighted at quarter -mile intervals listed in the stub. 



— In two forward quadrants only. 



NUMBER SEEN 

 PER SQUARE MILE 



NUMBER OF 

 FLOCKS SEEN 



CUMULATED 

 PERCENT SEEN 



Figure 5. --Flocks seen in concentric segments of the scanning area on GILBERT 

 cruises 1 1 and 13. 



If we consider these percentages to be estimates of efficiency, several assumptions must 

 be made. First, movement of schools in and out of the scanning area before detection must have 

 been equal. Second, it is necessary to assume that the speed and course of the fish schools and 

 accompanying bird flocks were unrelated to the speed and course of the vessel. Since the skipjack 



