Lutcavage et a I.: Aerial survey of Thunnus thynnus in the Straits of Florida 
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Table 1 
Giant bluefin tuna aerial survey, 19 May-9 June 1995, over the Great Bahama Bank. Sea water temperatures provided by 
charter boats. Wind speed and direction estimated by pilots based on sea state. 
Sea water 
temp (°C ) 
Date 
Total no. 
of bluefin 
Total no. of 
sightings 
Winds (knots) 
North end 
South end 
19 May 
0 
0 
S 15-20 
21 May 
0 
0 
SSW 10-15 
22 May 
0 
0 
WNW <10 
WNW 10-15 
23 May 
0 
0 
WNW 8 
26.4 
25 May 
0 
0 
ENE 10-15 
26 May 
0 
0 
CALM 
26.7 
28 May 
8 
1 
ENE 8 
SSE 10-12 
28.6 
29 May 
8 
2 
E 15 
E 12-15 
29.2 
30 May 
45 
4 
CALM 
ESE 8-10 
28.9 
31 May 
75 
9 
CALM 
SE <10 
28.9 
1 June 
181 
3 
E 10-12 
ESE 15-20 
2 June 
125 
9 
ESE 20 
SE 20-30 
29 
3 June 
149 
10 
SSE 20 
ESE 25-30 (squalls) 
27.9 
4 June 
186 
8 
ESE 12-15 
S/E 25+ (squalls) 
28.5 
7 June 
59 
5 
WSW 15 
W 5-8 
29 
8 June 
1 
1 
NNW 8-10 
WSW 8 (squalls) 
9 June 
1 
1 
CALM 
Totals 
839 
53 
by anglers (Beare 2 ). Bluefin tuna were first observed 
in Tuna Alley on 24 May from a sport fishing boat but 
were not observed from the air until 28 May. Sightings 
peaked in the first week of June (Table 1) and declined 
gradually to the last survey day (9 June) when only 
one giant was seen. According to interviews conducted 
with charter boat captains, aerial sightings were con- 
sistent with the timing and general location of bluefin 
tuna sightings by recreational vessels. However, aerial 
sightings were more extensive and covered a much 
broader area than that covered by charter boats, which 
tended to limit their fishing on Tuna Alley to a strip of 
approximately 12 nmi between Bimini and Victory Cay. 
The last bluefin tuna was sighted in Tuna Alley on 11 
June, and all fishing ended by 12 June. Surface seawa- 
ter temperatures taken by charter boats during the 
survey ranged from 26 to 29°C, and the prevailing winds 
were primarily from the E/SE sectors (Table 1). 
A general account of sightings per unit of effort 
(SPUE) and search mileage is given in Table 2. Daily 
transects were conducted by the Supercub 344Z on 
all but one survey day (28 May), and the 4 June 
transect was abandoned because of squalls at the 
starting point (Table 3). Three out of 53 sightings 
(with counts of 100, 6, and 1 bluefin tuna, respec- 
tively) occurred on transect. 
2 Beare, Captain D. 1995. 2462 Lighthouse Point, FL 33064. 
Personal, commun. 
Although our analyses of environmental conditions 
occurring during the survey are limited, some gen- 
eral conclusions can be drawn. Tropical storm Allison 
in the Gulf of Mexico generated strong winds and 
squalls that affected the survey region beginning on 
1 June. General SPUE was highest from 1 to 4 June, 
associated with strongest winds, although fish were 
also seen on completely calm days with light and 
variable winds. Peak sightings occurred in the six 
days following the new moon on May 29. Although 
the majority of search effort occurred between 11:00 
and 13:00 h, the largest school of an estimated 100 
bluefin tuna was sighted on 1 June at 09:53 h. On 
this day pilots had an early start because wind con- 
ditions (ESE 15-20 kn) were expected to be espe- 
cially suitable for the appearance of bluefin tuna. 
According to interviews with charterboat captains, 
a total of no more than 10-20 bluefin tuna were 
sighted over the survey period on Tuna Alley by rec- 
reational vessels before survey aircraft had arrived 
in the morning at the study site. 
Discussion 
The total number of bluefin tuna seen in the 1995 
survey (839) was generally within the range of blue- 
fin tuna counted in the 1974-76 surveys (368-3,125). 
Upon examination of school positions for possible re- 
