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Fishery Bulletin 95(2), 1 997 
in previous aerial surveys conducted by the National 
Marine Fisheries Service. 
Methods 
Bluefin tuna were sighted and counted by two tuna 
spotter pilots each having over 20 years of experi- 
ence in the commercial bluefin tuna, yellowfin, and 
tropical tunas purse-seine fisheries. It is standard 
practice for spotters to identify species and to esti- 
mate average size, weight, and total tonnage before 
a set is made. The two spotter pilots, having partici- 
pated in the 1994 New England bluefin tuna aerial 
survey (Lutcavage and Kraus, 1995), flew a single- 
engine aircraft (Supercub, tailnumber 344Z, and 
Cessna 172, tailnumber 270Q) that had viewing ac- 
cess from both sides. Flights originated from Execu- 
tive Airport, Fort Lauderdale, FL, and required ap- 
proximately a 40-55 min transit to reach the Great 
Bahama Bank area near Bimini. The two pilots be- 
gan spotting fish when they reached the Florida 
Straits. The survey was targeted to occur between 
11:00-13:00 h, similar to the time of day covered by 
the 1974-76 surveys. The data acquisition system 
(Tunalog, Cascadia Research, Inc.) consisted of a glo- 
bal positioning system (GPS), a laptop computer with 
mouse (for event marking), and a 35-mm camera, 
identical to that used in the New England bluefin 
tuna spotter survey (Lutcavage and Kraus, 1995), to 
photograph schools. Position was automatically 
logged every 15 seconds, and daily flight tracts were 
reconstructed and bluefin tuna positions plotted with 
OPCPLOT, version 7.0. 
Each day the transect aircraft (Supercub 344Z, 
except on 28 May) surveyed a zigzag transect line of 
approximately 70 nmi in length along Tuna Alley, 
beginning at a southernmost point near 24°45'N and 
following a zigzag pattern north to approximately 
25°48’N. The starting point was set far enough south 
to incorporate the southernmost limit of the pre- 
sumed migration route on the Great Bahama Bank 
where bluefin tuna are visible from the air (Rivas, 
1954; Mather et al., 1995). On the first survey day 
(19 May) the transect aircraft 344Z carried an ob- 
server (Hoggard) to establish and verify survey pro- 
tocol. The starting point of the transect was stag- 
gered slightly so that daily transects were not iden- 
tical. Surveys were conducted at an altitude of 750- 
1,000 feet and at a true airspeed of 80 knots. The 
transect legs forming the zigzag were flown to points 
approximately 3 nmi west of Tuna Alley and were 
bounded on the east by the shallows of the Great 
Bahama Bank. The transect was repeated unless rain 
squalls and strong winds greatly reduced visibility. 
The spotter conducting the transect noted any blue- 
fin tuna encountered during transit to the starting 
point. 
The “discovery” aircraft Cessna 270Q did not fly 
dedicated transects, (except on 28 May). Its mission 
was to search Tuna Alley and adjacent areas between 
N. Bimini and Orange Cay in order to identify the 
general limits of bluefin tuna travel patterns, and to 
locate, photograph, and observe the behavior of any 
bluefin tuna encountered. The spotter was free to 
determine his own search patterns and carried an 
observer on six survey days. There were two aircraft 
present in the study area on 14 out of 17 survey days. 
Pilots remained in radio contact with one another, 
except for the period of time when the Supercub 344Z 
was conducting the transect. At the beginning of each 
survey and at the end of each transect leg pilots re- 
corded their estimation of wind strength and direc- 
tion, visibility, cloud cover, and water color. During 
surveys they were instructed to mark the location of 
all sighted bluefin tuna with the mouse event marker 
and to document them with photographs when pos- 
sible. Radio contact with local sport fishing boats 
targeting bluefin tuna allowed the spotters and ob- 
server to collect general information on sea surface tem- 
perature, sizes of landed fish, and additional sightings. 
Results 
Spotters flew a total of 11,910 nmi ( 158 hr, including 
time in transit), encountering bluefin tuna on 10 
out of 17 survey days. Approximately 7,126 nmi (115 
h) were flown over the Great Bahama Bank. Of these, 
1,502 nmi were trackline distance (usually 2 
transects/day). Spotters documented 53 bluefin tuna 
schools overall and estimated a total count of 839 
fish (Table 1). No bluefin tuna were sighted on any 
transits over the Florida Straits; turtles, sharks, 
delphinids, and flying fish, however, were sighted on 
numerous occasions. Most bluefin tuna sightings oc- 
curred north of 24°30'N, and within the presumed 
migratory route identified by Rivas (1954) and 
Mather et al. (1995). Other sightings on or adjacent 
to the Great Bahama Bank near Tuna Alley included 
loggerhead sea turtles ( Caretta caretta ), unidentified 
dolphins, tiger ( Galeocerdo cuvier) and other sharks, 
a single sperm whale ( Physeter macrocephalus), 
schools of skipjack tuna ( Katsuwonus pelamis ), Ber- 
muda chub ( Kyphosus sectatrix ), permit ( Trachinotus 
falcatus), and other unidentified fish. 
Sightings ranged from individual bluefin tuna to 
loosely aggregated schools from 20 to 100 individu- 
als, all judged by spotters to be large giants (> 226 
kg, or about 196 cm), similar in size to giants landed 
