300 
Aerial survey of giant bluefin tuna, 
Thunnus thynnus, in the Great 
Bahama Bank, Straits of Florida, 1 995 
Molly Lutcavage* 
Scott Kraus 
Edgerton Research Laboratory 
New England Aquarium, Central Wharf, Boston, Massachusetts 02110 
*E-mail address: mlutcavg@neaq.org. 
Wayne Hoggard 
Southeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
3209 Frederic Street, Pascagoula, Mississippi 39568 
Abstract .—Aerial surveys were con- 
ducted daily from 19 May to 9 June 
1995 to document the apparent abun- 
dance and migration behavior of giant 
bluefin tuna, Thunnus thynnus , over 
the Great Bahama Bank region of the 
Straits of Florida. Our objectives were 
to conduct an aerial assessment of gi- 
ant bluefin tuna in this region and to 
compare our results with previous 
aerial surveys conducted in the 1950’s 
and 1970’s. Two professional bluefin 
spotter pilots flew 70-nmi transect sur- 
veys along “Tuna Alley” as well as sur- 
veys into adjacent areas in search of 
bluefin tuna. The present study area 
was broader than that surveyed in the 
1970’s, which consisted of repeated 
flight tracks, each 1 nmi, across Tuna 
Alley at a point just south of South Cat 
Cay. Spotter aircraft carried a data ac- 
quisition system consisting of a global 
positioning system (GPS), a laptop com- 
puter, and a 35-mm camera to photo- 
graph schools. A total of 839 giant blue- 
fin tuna were documented, within 
range of totals counted in the 1974-76 
surveys (368-3,125 bluefin tuna). 
Single fish and loosely aggregated 
schools of up to 100 fish were seen trav- 
elling steadily north along the western 
flank of the Great Bahama Bank. They 
did not engage in feeding, smashing, or 
cartwheeling behaviors that are exhib- 
ited in New England waters. All blue- 
fin tuna appeared to be “large giants,” 
weighing an estimated 227 kg and over. 
There is little information document- 
ing the origins and previous locations 
of giant bluefin tuna travelling along the 
Great Bahama Bank; therefore the use 
of direct counts of bluefin tuna in this 
region as an index of spawning biomass 
would require further documentation. 
Manuscript accepted 27 September 1996. 
Fishery Bulletin 95:300-310 ( 1997). 
In the 1950’s, and later in 1974-76, 
the U.S. National Marine Fisheries 
Service conducted aerial surveys for 
bluefin tuna, Thunnus thynnus, mi- 
grating along the Great Bahama 
Bank region (Rivas, 1954, 1978). It 
is generally believed that large blue- 
fin tuna travel along the Straits of 
Florida from late April through mid- 
June on their way to feeding grounds 
at higher latitudes where they are 
usually resident from June through 
October. The bluefin tuna found on 
the Great Bahama Bank are giants 
(over 185 cm/107 kg) and are be- 
lieved to have recently spawned in 
the Gulf of Mexico or in the Straits 
of Florida (Rivas, 1978; Mather et 
al., 1995). Sport fishermen since the 
1930’s and researchers alike believe 
that these fish are members of the 
seasonal assemblage occurring off 
New England and maritime Canada 
(Farrington, 1939; Rivas, 1954; 
Mather et al., 1995). Fish tagged 
and released on the Great Bahama 
Bank have been recovered prima- 
rily in the northeastern U.S., Cana- 
dian, and Norwegian waters. 
Recreational fishermen and re- 
searchers have identified a narrow 
region of the Great Bahama Bank 
off South Cat Cay as Tuna Alley 
(Fig. 1) because travelling schools 
seem to concentrate in this region 
and are easily visible by air (Rivas, 
1954, 1978; Anonymous 1 ). In three 
surveys conducted from May through 
June 1974—76, survey aircraft flew a 
1-mi long transect across Tuna Al- 
ley, at 25°31'N and 79°18'W, for 
about 60 minutes (Rivas, 1978). 
Flights were conducted on days 
when weather was suitable for fly- 
ing for a total transect effort rang- 
ing from 38 to 52 hours per survey 
period (Rivas, 1978). The number of 
bluefin tuna encountered was mul- 
tiplied by the number of minutes in 
a day to derive a daily abundance 
estimate. This estimate was then 
multiplied by the assumed 50-d 
migration interval to derive an es- 
timate of spawning population size. 
Over the three-year survey period 
this estimate ranged from 9,630 to 
99,360 fish. Rivas ( 1978) linked the 
presence and apparent abundance 
of bluefin tuna in the area with envi- 
ronmental factors, such as increased 
wind speed and (less strongly) with 
1 Anonymous. 1975. A study of the appli- 
cation of remote sensing techniques for 
detection and enumeration of giant blue- 
fin tuna. Southeast Fish. Sci. Center, 
Natl. Mar. Fish. Serv., NOAA, Miami FL. 
Contribution rep. 437, 48 p. 
