352 
Fishery Bulletin 109(4) 
0 
14 May 6 Jun 
1 7 Jul 
6 Aug 28 Aug 
16 Oct 
Temperature (°C) 
7 Nov 5 10 15 20 25 30 
100 - 
200 - 
300 
400 - 
-p 500 - 
£ ° 
cL 
<D 
Q 100 
Hourly depth, 27 Apr- 1 7 Dec 2002 
I I 
I I 
, Bigeye thresher shark ( I D 2948 1 ) 
1 7 July 2002 Hourly depth ( 120 hrs) 
v v yt u 
I July 2002 
Bigeye thresher 
Alopias superciliosus 
(77=3) 
E 200 
CD 
Q 300 
I 
25 
20 
15 
10 
5 
100 
. 200 
300 
400 
500 
O 
Day 
Sftl, 
Night 
— r 
D 
20% 10% 0 10% 20% 
Day 
Night 
9 
F 
— A 
-h 
15:00 19:00 23:00 03:00 07:00 11:00 
Time of day (HST) 
20 % 10 % 0 10 % 20 % 
Percent of time (%) 
Figure 4 
Bigeye thresher (Alopias superciliosus ) depth and thermal ranges as identified by pop-up satellite archival tags 
(PSATs). (A) Representative vertical movements. Dashed lines indicate expanded area shown in C. (B) Tempera- 
ture-depth profiles obtained from the aggregated data from all sharks. (C) Expanded section from panel A with 
horizontal black bars representing nighttime. (D) Percentage of time spent in individual temperature strata 
(±standard deviation, SD) for daytime and nighttime diving activities (all tags). (E) Average hourly depth (±SD) 
readings calculated for all samples, illustrating variability at crepuscular times (all tags). (F) Percentage of time 
spent individual depth strata (±SD) for daytime and nighttime diving activities (all tags). 
3 ) mesopelagic-II species that included bigeye threshers 
plus outgroups bigeye tuna and swordfish. The epipe- 
lagic group could be further broken down by body size 
and latitude because juvenile silky sharks south of 10°N 
formed the most distinctive cluster (i.e., exhibited the 
longest branch lengths). Moreover, another distinctive 
epipelagic cluster was composed entirely of presumably 
mature silky and oceanic whitetip sharks >200 cm TL 
whose PSATs separated from the sharks at latitudes 
above 18°N. The cophenetic correlation (0.86) indicated 
“good” fit between the data matrix and resultant den- 
drogram. A similar clustering pattern was obtained 
with daytime depth data (cophenetic correlation^ 0.88) 
but it included five mismatches to the pattern observed 
with daytime temperature (i.e., black marlin ID 13208, 
silky shark IDs 38573, 38581, 38601 were placed in 
mesopelagic-I and blue shark ID 13095 was placed in 
the epipelagic group). The mismatches, however, may 
have been attributable to the relatively poor resolution 
of PSAT depth data in comparison with the temperature 
data. There was, however, no discernible pattern with 
nighttime depth (cophenetic correlation=0.77) and tem- 
perature data (cophenetic correlation=0.88) because all 
species generally remained near the surface. 
Discussion 
Rates of at-vessel and postrelease mortality 
Mortality for blue sharks at the time of gear retrieval 
in commercial longline fisheries operating in the 
