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Fishery Bulletin 93(3), 1995 



the Great Australian Bight (Morgan, 1992; Chen and 

 Polacheck 2 ). Aerial surface-detection radar surveys 

 targeting bluefin tuna and other tunas have been 

 explored by the French in the Mediterranean and 

 tropical South Pacific areas (Petit et al., 1992). 



Recently, members of the New England commer- 

 cial giant bluefin tuna industry suggested that spot- 

 ter pilots might provide a platform to examine the 

 potential applications and limitations of direct visual 

 assessment of giant and large-medium bluefin tuna. 

 In coastal waters off New England, spotter pilots 

 have located surface schools of giant bluefin tuna that 

 are then targeted for capture by harpoon, hook and 

 line, and purse-seine operations. In 1993, the New 

 England Aquarium (NEA) and East Coast Tuna As- 

 sociation (ECTA) initiated a collaborative project in- 

 volving fish spotter pilots locating and photograph- 

 ing surface schools of bluefin tuna normally targeted 

 by the fishery. Our objective was to determine 

 whether aerial photography could be used to provide 

 information on the relative abundance, schooling char- 

 acteristics, and spatial distribution of bluefin tuna. 



Methods 



The present study relied on a simple technical frame- 

 work involving only voluntary participation by com- 

 mercial spotters and the use of two cameras, one to 

 photograph tuna schools (for enumeration) and an- 

 other to document school location. Nine commercial 

 spotter pilots participated in this survey while en- 

 gaged in the 1993 seasonal fishery. All fish spotters 

 flew single engine aircraft (models Cessna 172 and 

 182, Citabria, SuperCub) and were based on Cape 

 Cod or in lower Maine. Four pilots spotted for sein- 

 ing operations, five were associated with harpoon or 

 general category fishing (hook and line), and at least 

 two participated in all three categories. Bluefin tuna 

 were photographed from 23 July to 13 September, 

 when participating pilots ceased activities because 

 fishing quotas were filled. 



Each pilot was provided with a hand-held 35-mm 

 camera (Nikon N8008s) and an autofocus zoom lens 

 (70-210 mm, F3.5/4.5, SIGMA Corp.) to photograph 

 tuna schools. Synchronized databacks on cameras 

 (Nikon, MF-21) imprinted date and time directly on 

 exposed film. A second viewfinder camera (Shot- 

 master Ultra Zoom, 38-60 mm, f6.9 lens, Ricoh Corp. ) 



2 Chen, S. X., and T. Polacheck. Data analysis of the aerial sur- 

 veys ( 1991-1994) for juvenile southern bluefin tuna in the Great 

 Austrialian Bight. 1994 SBT Recruitment Monitoring Work- 

 shop, Hobart, Tasmania. Available from T. Polacheck, CSIRO, 

 Div. Fisheries, GPO Box 1538, Hobart, Tasmania 7001. 



was mounted overhead in the aircraft cabin to docu- 

 ment positions from onboard global positioning sys- 

 tem (GPS) or LORAN units located in or below the 

 dashboard. Both cameras had auto advance features 

 and were linked via cable so that they were simulta- 

 neously triggered when pilots depressed a remote shut- 

 ter control. A photographic record of position (in TD 

 Loran lines or lat./long. ) could then be provided for each 

 photographically documented tuna school. A digital 

 clock synchronized with the 35-mm camera databack 

 was mounted near the LORAN/GPS within range of 

 the viewfinder camera. We could then verify sequence 

 linkage between frames of tuna schools and locations 

 if film advance speeds were not perfectly matched. 



Tuna schools were photographed with color slide 

 film (Ektachrome 400 ASA, Kodak), selected for 

 depth of penetration and contrast characteristics 

 (NMFS, 1975; Lockwood et al. 3 ). Lenses were fitted 

 with a circular polarizing filter or haze filter for glare 

 reduction. Aircraft positions recorded by the 

 viewfinder camera were read directly from developed 

 black and white film (Tri-X 400 ASA, Kodak). 



Pilots were supplied with labelled film canisters 

 and with stamped and coded direct mailers for color 

 processing, and were instructed to mail the film im- 

 mediately when it was finished. Black and white film 

 was returned directly to us and processed locally. 



Analysis 



Processed film was logged with an identification code, 

 and a cursory examination was made on a light table 

 with a film eye loupe. Tuna counts were made by 

 projecting selected slides of schools and by visually 

 counting individual fish. Images were enlarged by 

 projection to a standard size (78 x 52 cm) onto a sheet 

 of drafting-quality tracing paper marked with 10 x 

 10 cm square gridlines. Positions of clearly identifi- 

 able fish were marked and the total tallied per grid 

 square and per slide frame. Upon completion of the 

 tally, each sheet was labelled with the film identifi- 

 cation code, frame number, time, and total fish count. 

 No attempt was made to estimate the total number 

 offish in the school. 



Since bluefin tuna are fast-swimming, mobile fish, 

 it was possible for pilots to photograph the same 

 school at slightly different locations on a single day. 

 A school might be difficult to distinguish from adja- 

 cent, similarly sized schools. When photographed by 

 a spotter in close succession, these schools had to 

 have distinctly different spatial configurations or had 



3 Lockwood, H. E. Technicolor Graphics Services, Inc., Houston, 

 TX 77058. 



