BIRD FLOCKS 



SKIPJACK SCHOOLS 



TOTAL FISH SCHOOLS 



Figure 5. -Seasonal variation in rate of sighting for three major island groups 



schools, and the remainder were mostly schools 

 whose species composition could not be identi- 

 fied. As can be seen in table 2 about three- 

 fourths of the schools were sighted in the North- 

 ern Hemisphere and one-fourth In the Southern 

 Hemisphere. 



Within the summary area the amount of ef- 

 fort reported for any 5°-quarterly unit ranged 

 from 1 to 2,160 hours with a mode, based on 

 10-hour groupings, of 10-19 hours. Three areas 

 received the major portion of the effort, the 

 Hawaiian and Line Islands areas in the North 

 Pacific and the Marquesan-Tuamotu Islands area 

 in the South Pacific. Effort was distributed about 

 evenly among the four quarters of the year in the 

 northern sector of the summary area, but in the 

 southern sector effort during June-August was 

 only about half that of any other quarter. 



About 95 percent of the floclcs, 99 percent 

 of the total schools, and 99 percent of the skip- 

 jack schools were sighted within the summary 



area (fig. 1). Approximately one-third of the 

 sightings but only one-fifth of the effort were in 

 the South Pacific, with the result that the rates 

 of sighting of flocks and schools in that area 

 were much higher than in the North Pacific. 

 Taken by 5°-quarterly units, the modal rate of 

 sighting was zero. However, this was due largely 

 to the high incidence of zero sightings for areas 

 in which less than 30 hours of effort had been 

 expended (fig. 6). Because of this, squares with 

 less than 30 hours of effort appear unshaded in 

 the charts as an indication that the amount of 

 effort was insufficient to accurately assess the 

 abundance of flocks and schools. 



Only 214 schools of yellowfin tuna were 

 sighted during the 12-year period, about 5 per- 

 cent of the total schools. As shown in table 2, 

 they were seen at all seasons of the year in 

 about equal numbers, and in both the North and 

 the South Pacific. Because of the low numbers 

 sighted, charts were not prepared for this 

 species. 



