SCOTT and FLITTNER: BEHAVIOR OF BLUEFIN TUNA SCHOOLS 



Table 6. — Comparison of eflfectiveness of aircraft assist- 

 ance by school type for purse-seine sets on bluefin tuna, 

 1960-67. 



Table 7.— Comparison of average catch per successful 

 set and percentage success for assisted and unassisted 

 sets on the four most common daytime bluefin tuna 

 school types. 



craft and, therefore, the greater area and depth 

 of visibility to an airborne spotter would increase 

 the possibility of spotting the subsurface schools 

 which otherwise might not be visible to observers 

 aboard a vessel (Green, 1966). 



However, there are differences in both catch 

 per successful set and percentage success be- 

 tween assisted and unassisted sets in the same 

 school type (Table 7). All of the schools show 

 increased percentage success with aircraft as- 

 sistance, and all but black spots exhibit larger 

 school size with aircraft assistance. This indi- 

 cates that the larger size and greater vulnera- 

 bility of schools set on with aircraft assistance 

 is the result not only of the unequal distribution 

 of the various school types between assisted and 

 unassisted sets but also due to the skill of the 

 airborne spotter in locating larger schools, and 

 by his ability to increase the ship's chances of 

 capturing the school. 



ioral types made up a very small percentage of 

 the total sets made. Whether this is indicative 

 of the actual occurrence of these types or the 

 propensity of the fishermen to record them and 

 the log abstractor to copy them is unknow^n. The 

 problem of multiple schooling types has been dis- 

 cussed elsewhere (Scott, 1969). 



Bluefin were captured in sets with yellowfin, 

 skipjack, and albacore. Bluefin were also ob- 

 served schooling with whales (Table 1). In 

 spite of large amounts of flotsam and jetsam oc- 

 curring in the fishing area, only two reports of 

 this school type were logged. No porpoise-asso- 

 ciated schools were reported. This is probably 

 due to the absence of porpoise in the areas in 

 which bluefin are generally found. Further data 

 are needed before meaningful conclusions can be 

 drawn with respect to the occurrence or lack of 

 porpoise-associated schools in the bluefin fishery. 



DISCUSSION 



Striking differences in catchability, size, and 

 geographical distribution have been demonstrat- 

 ed for the various types of bluefin schools. Sug- 

 gestions as to possible reasons for these differ- 

 ences are offered but in most instances additional 

 behavioral information is needed. We hope that 

 definitive field and laboratory behavioral studies 

 will be made in order to further strengthen or 

 disprove interpretations which we have drawn 

 from the logbook data. Studies on other scom- 

 broids would also be valuable for comparative 

 purposes. The possibility that there are two or 

 more types of breezing schools should be studied 

 in detail, and the percentage success of sets on 

 breezing schools known to be feeding compared 

 with nonfeeding schools should also be inves- 

 tigated. 



ACKNOWLEDGMENTS 



MULTIPLE SCHOOLING 

 CHARACTERISTICS 



Almost every possible combination of the 13 

 different school types occurred. However, 

 schools recorded as showing two or more behav- 



The logbook records of California tuna purse 

 seiners were made available through the courtesy 

 of the Inter-American Tropical Tuna Commis- 

 sion under Dr. J. L. Kask, Director, and Dr. 

 James Joseph, who succeeded him. Craig J. 

 Orange, of the Commission, provided assistance 



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