Table 10. --Comparison of plane and vessel scouting 



— Incidental scouting while vessel was enroute to hydrographic section in Kaiwi Channel--some 

 flocks seen at station. 



Another factor which may lessen the efficiency of the plane is the tendency of the bird 

 flocks to assemble and disperse while following a school. Hence, more schools will be seen if 

 an area is watched for a longer tinne. If we t2ike 1/3 mile as the effective scanning radius of the 

 plane, as suggested by the observations in the preceding paragraph, it will be possible to observe 

 a particular spot of ocean not more than the time required to fly 2/3 of a mile, or 24 seconds in 

 a plane flying at 100 knots. On the other hand, a similarly effective scanning radius for the 

 vessel may be 2 miles, which would permit watching a spot up to 24 minutes from a vessel mov- 

 ing at 10 knots. 



Despite the small number of flocks and schools sighted on most flights, it is significant 

 that four of the eight fish schools seen on Flight No. 2 were not accompanied by birds. Such a 

 discovery of an unaccompanied fish school was never made fronn the vessels during the following 

 year. This suggests that when conditions are right for fish schools to be spotted directly (as 

 they were on Flight No. 2), the airplane is effective in locating them, as has been reported by 

 Harrison (1931) and Gushing et al. (1952). However, when the sea has white caps, as it usually 

 does around Hawaii, and the fish schools must be located by the accompanying birds, the airplane 

 is not as effective as a vessel. 



MOVEMENT OF SKIPJACK SCHOOLS 



The seasonal appearance and disappearance of the skipjack schools as well as the sea- 

 sonal change in the average size suggest that the species is migratory, coming and going with 

 the seasons, and that there may be different populations moving through the area at different 

 tinnes. Our data offer little conclusive evidence of any migrations of the skipjack but do provide 

 some information regarding the seasonal distribution of schools and the movements of schools 

 during limited periods of observations. 



Perhaps nnost conclusive is the seasonal shift in abundance between the northeast and 

 southwest sectors off Oahu. The results of the standardized scouting from February to November 

 (table 11) indicate that in the northeast sector the skipjack were less abundant in February and 

 during the fall months of September through November than in April and June. This is the kind of 

 change in distribution that might be expected if the fish move south in the winter, and the absence 

 of schools in the northeast sector during the 4 days of scouting in November suggests that Hawaii 

 nnay be near the northern limit of the skipjack in the winter months. 



There also are shifts of schools from one locality to another around the islands during the 

 fishing season. This is well known to the fishermen and is evident in the statistics of fluctuating 

 catch by area. It is also indicated in our scouting data by the very low number of schools per 

 day seen in Area III during June, when they were abundant in other localities. Our data are too 



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