Lutcavage and Kraus: Feasibility of photographic assessment of Thunnus thynnus 



497 



to be separated by at least one nautical mile (nmi) in 

 order to be tallied independently. Spotters and fish- 

 ermen reported maximum travel rates of 4-10 knots 

 for bluefin tuna in the study area. With the assump- 

 tion that swimming speeds were 10 knots, similarly 

 sized schools photographed by different pilots on the 

 same day had to be far enough apart so that it was 

 unlikely that schools could have travelled from one 

 location to the other in a given time period. 



Results 



The bluefin tuna survey area, fish spotter land bases, 

 and locations of photographed schools are depicted 

 in Figure 1. A total of 126 bluefin tuna schools, rep- 

 resenting a cumulative count of 13,973 fish, were 

 successfully photographed by spotter pilots on 17 

 days out of a 50-day survey period, for a total of 35 



pilot-days. Pilots reported that, to the best of their 

 knowledge, they photographed only giant or large- 

 medium bluefin tuna size categories (>70 inches 

 SFLl, those targeted by the New England fishery. 

 The position of surveyed schools, indicated by TD 

 values or lat./long. on the pilot's navigational sys- 

 tem, was established for 56 schools. Numbers offish 

 counted in schools ranged from 5 to 1,294 individu- 

 als (Fig. 2). Total giant and large-medium tuna counts 

 were >1,000 fish on four survey days, with a maxi- 

 mum count of 4,894 tuna on 8 August (Table 1). A 

 data summary of schools for three high count survey 

 days (8-10 Aug) is given in Table 2. 



From one to four spotters participated on high- 

 count days, but no more than four pilots photographed 

 fish on any given survey day. Spotters photographed 

 schools from 0900 to 1803 h, but the greatest effort 

 occurred during midday between 1200 and 1600 h 

 (Table 3). Spotters report that slack tide (estimated to 



Figure 1 



Aerial survey area for giant bluefin tuna, Thunnus thynnus, in New England 

 waters, July-September 1993. Land bases of participating spotter pilots are 

 indicated by stars. Filled circles indicate positions of photographed tuna 

 schools. 



