498 



Fishery Bulletin 93(3). 1995 



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Individuals counted in school (>) 



Figure 2 



Frequency distribution of counts of giant and 

 large-medium bluefin tuna, Thunnus thynnus, 

 schools photographed by spotter pilots in New 

 England waters, July-September 1993. 



be within one hour of nearest coastal reference) often 

 provides good conditions for locating fish. There was 

 no discernible relation between lunar cycle or estimated 

 slack tide and timing of greatest survey effort. 



Surface schooling configurations of bluefin tuna, 

 documented during the survey, included "soldiers" 

 (small school of giants, fish swimming abreast in a 

 parabola or straightline formation, Fig. 3A), "cart- 

 wheels" (spinning wheel-like formations, Fig. 3B), 

 surface sheets (Fig. 3C), and densely packed domes 

 (Fig. 3D). Basking sharks and, less frequently, hump- 

 back, fin, and other whales, were also photographed 

 in association with bluefin tuna schools. 



Discussion 



Spotting and survey effort 



Most of the bluefin tuna were photographed over a 

 four-day period in August by only a few of the par- 

 ticipating pilots, indicating that survey effort was 

 strongly affected by environmental conditions and 

 pilot effort. Fish spotters flew on less than half the 

 survey period, grounded largely by inclement 

 weather. They photographed all sizes of bluefin tuna 

 schools, but small to medium-sized schools (>5 counts 

 <200) were located and photographed most fre- 

 quently. Although initially instructed to document 

 schools of any size, some pilots reported not bother- 



ing to photograph very small schools, particularly 

 on "good" fishing days. 



Search and photographic efforts of participating 

 fish spotters varied widely, reflecting differences in 

 commercial involvement in the fishery and in moti- 

 vation. For example, one pilot photographed a mini- 

 mum of 6,767 giant and large-medium bluefin tuna 

 over five days under excellent survey conditions. 

 However, his survey effort in hours represented <10% 

 of the estimated 400 total flight hours he expended 

 in the 1993 season. This result suggests that aerial 

 photography of giant bluefin tuna can be accom- 

 plished with a small team of motivated pilots. In con- 

 trast, a fish spotter in partnership with seining op- 

 erations photographed far fewer fish (467) because 

 his total survey effort was limited to the few days 

 permitted for his boat to achieve its seasonal quota. 

 If all nine participating pilots had undertaken simul- 

 taneous surveys throughout the season, more com- 

 plete documentation might have been achieved. 



Throughout the survey we maintained frequent 

 phone contact with the pilots in an effort to improve 

 the quality of aerial and position photographs. Al- 

 though we were able to count tuna in the majority of 

 submitted frames, there was clearly a learning curve 

 in the spotters' attempts to take high-resolution pic- 

 tures. Blurring from aircraft vibration and underex- 

 posure were the most frequent problems with tuna 

 school photographs. Unreadable Loran frames more 

 often than not resulted from excessive glare on the digi- 

 tal readout, from improper film advance, or because 

 the pilot had shifted position and had subsequently 

 blocked the camera's view of the Loran. This problem 

 could be eliminated if position were electronically logged 

 each time the spotter photographed bluefin schools. 



Enumeration analysis 



In general, we assumed that environmental condi- 

 tions were fairly uniform (low wind and sea states, 



