Iyellowfin schools Sskipjack schools ^total fish schools Dbird flocks 



LINE ISLANDS 



u. 





PHOENIX ISLANDS 



%% 



111 



i 



I mdmn I -_^l I 



HAWAIIAN ISLANDS 



ILL 



MAR- MAY JUN-AUG 



SEP -NOV DEC-FEB 



Figure 4. --Seasonal distribution of tuna school 

 sightings In the Line, Phoenix, and Hawaiian 

 islands. (Total fish schools per day includes 

 unidentified schools as well as yellowfin and 

 skipjack, table 1. The figures on the graph, 

 such as 0/32, indicate a niJinber of days of 

 scouting, in this case 32, during which no 

 schools were seen.) 



not true of the deep- swimming yellowfin (Murphy and 



Semloceanic Observations 



The semloceanic sight- 

 ings, made between 60 and 180 

 miles from land, are treated 

 somewhat differently from the 

 island observations in that 

 the numbers of birds sighted 

 are listed in addition to the 

 numbers of flocks. This was 

 possible because the esti- 

 mates of the size of the 

 smaller flocks In the areas 

 farther from land were rea- 

 sonably accurate. 



Comparison of the seml- 

 oceanic fish sightings (table 

 8) and the Island sightings 

 (table 1) shows that yellow- 

 fin schools are more abundant 

 close to land. In the Line 

 and Phoenix islands yellowfin 

 predominated near land and 

 skipjack dominated the semi- 

 oceEtnlc zone. In the Hawai- 

 ian area all yellowfin noted 

 were close to the islands, 

 although skipjack predominated 

 there as well as offshore. 

 Thus it appears that in the 

 central Pacific surface 

 schools of yellowfin are 

 rather closely associated 

 with land; however, this is 

 Shomura 1953a) . 



Although the composition of the fish schools is different farther from land, 

 the abundance, disregarding kind, appears to be nearly as great in the semloceanic 

 as in the island areas (1.3 versus 1.8 per day, tables 1 and 2). If the number of 

 schools sighted is taken as an index, it can be concluded that the area Immediately 

 surrounding these small Islands (0 to 60 miles from land) has about the same pro- 

 ductivity as the outlying zone (60 to 180 miles from land), but the ecology of the 

 waters immediately around the Islands favors surface schools of yellowfin tvina and 

 that of more distant waters favors schools of skipjack. 



Oceemic Observations 



Oceanic observations are considered to be those made farther than 180 miles 

 from land. Rather than associate them with any particular island group they were 

 tabulated by areas of the oceein 10 degrees of latitude high and 10 degrees of longi- 

 tude wide (table 3). The bird sightings were tabulated by number only, because the 

 occurrence of flocked birds is a rarity at these distances from emergent land. 



It has already been inferred that there are fewer birds in the open ocean than 

 in the Island and semloceanic areas. This is very pointedly shown In table 3, for 

 the mean number of birds sighted per day for all oceanic observations is only 37.2, 

 whereas 135.6 were seen per day in the semloceanic areas (table 2). Fish schools 

 were sighted at the rate of only 0.5 per day in the oceanic area as against 2.3 per 

 day in the semloceanic areas. Thus It appears that the reduction in the fish 

 schools sighted is almost exactly proportional to the reduction in numbers of birds. 

 This, coupled with the acknowledged difficulty of locating schools of fish unless 

 they are accompanied by birds, leads us to question whether the actual abundance 

 of fish is any less in the open ocean than it is nearer to land. 



