The height of the waves also had little effect 

 on fishing. Our data showed that most fishing 

 occurred in waters with moderate wave height; 

 only nine schools were chummed in waters 

 considered very rough (table 17). Testing the 

 ratios of the number of schools with catches to 

 those without, relative to the height of the 

 waves at the time of fishing, we found that they 

 were reasonably constant, with the exception of 

 those schools chummed in very rough waters 

 ( X^= 0.42; d.f. = 2; p > 0.75). 



Predominant birds and size of bird flocks. -- 

 While pursuing a school, skipjack tuna fisher- 

 men rely heavily on the behavior, species, and 

 number of birds in the flocks to give them in- 

 formation about the species, size, and move- 

 ment of the fish. For example, Japanese tuna 

 fishermen know from the birds' wild horizontal 

 flights that a school is near the surface, and 

 from the birds' slow flight, high above the 

 water, that the school is swimming deep (Ima- 

 mura, 1949). 



In examining the relationships of catches 

 with predominant birds and with bird flock size 

 at the time of fishing, we found that petrels and 

 shearwaters were most frequently associated 

 with skipjack tuna schools. Of 1,235 flocks 

 identified to predominant species, petrels and 

 shearwaters predominated in 963 flocks or 78 

 percent, whereas terns predominated in only 

 235 flocks or 19 percent. Small flocks of 

 boobies or frigate birds predominated infre- 

 quently. Using only data for schools chummed 

 (table 18), we found that the predominant spe- 

 cies associated with the school at the time of 

 fishing was not a good indicator of success in 

 fishing ( X^= 2.25; d.f. = 3; p >0.50), 



Rather than predominant species, the size of 

 the bird flock associated with the school ap- 

 peared to be a good indicator of fishing success. 

 Bird flocks accompanying fish schools varied 

 in size from fewer than 10 to several hundred 

 birds, so to simplify estimation we used only 

 three categories: 10 or fewer, 11 to 50, and 

 50 or more birds. Size estimates of 1,249 



Table 17. — Number and percentage of 620 schools with catches and 442 schools without 

 catches, fished by seven Hawaiian skipjack tuna fishing vessels and tabulated by 

 the height of the wave at the time of fishing, June-August 1967 



Wave height 



Schools 



With 



catches 



Without 



catches 



Total 





Number 



Percent 



Number 



Percent 



Number 



Percent 



1 



Calm (<0.3 m.) 

 Moderate (0.3-1.5 m. ) 

 Rough (1.5-3.7 m.) 

 Very rough (>3.7 m. ) 



34 

 471 

 107 

 8 



5.5 

 75.9 

 17.3 



1.3 



32 

 331 

 78 



1 



7.2 

 74.9 

 17.7 



0.2 



66 

 802 

 185 

 9 



6.2 

 75.5 

 17.4 



0.9 



Table 18. — Number and percentage of 613 schools with catches and 437 schools without 

 catches, fished by seven Hawaiian skipjack tuna fishing vessels and tabulated by 

 types of predominant birds in the flock associated with the schools at the time of 

 fishing, June-August 1957 



Predominant birds 



Schools 



With catches 



Without catches 



Total 



Number Percent Number Percent Number Percent 



Tern 



120 



19.6 



78 



17.8 



198 



18.8 



Petrel-shearwater 



470 



76.7 



349 



79.9 



819 



78.0 



Booby 



17 



2.8 



7 



1.6 



24 



2.3 



Bo 'sun bird 



2 



0.3 



3 



0.7 



5 



0.5 



Frigate bird 



1 



0.2 







1 



0.1 



Other birds 



3 



0.4 







3 



0.3 



21 



