348 
Fishery Bulletin 109(4) 
Table 2 
Number of pelagic sharks caught and those retrieved dead from shallow-set longline gear targeting swordfish (Xiphias gladius). 
Mortality estimates from the Hawaii-based commercial longline fishery are provided for comparison (na=not available). 
Species 
No. 
caught 
Samples 2 
taken 
No. 
dead 
% 
dead 
% dead 
commercial fishery 2 
Shallow 
Deep 
Blue shark ( Prionace glauca ) 
203 
37 
12 
5.9 
5.7 
4.0 
Crocodile shark ( Pseudocarcharias kamoharai) 
3 
2 
2 
66.7 
na 
13.6 
Oceanic whitetip shark ( Carcharhinus longimanus ) 
19 
6 
1 
5.3 
7.4 
20.7 
Shortfin mako ( Isurus oxyrinchus) 
8 
4 
0 
0 
20.5 
7.5 
Silky shark (Carcharhinus falciformis) 
35 
3 
4 
11.4 
na 
21.8 
Bigeye thresher (Alopias superciliosus) 
12 
1 
3 
25.0 
22.6 
16.5 
Pelagic thresher shark (Alopias pelagicus ) 
28 
0 
10 
35.7 
na 
na 
Total 
308 
53 
32 
10.4 
na 
na 
1 Sampled for biochemical correlates of morbidity and mortality (Moyes et al., 2006). 
2 At -vessel mortality estimates of pelagic sharks from the shallow-set longline gear targeting swordfish (Xiphias gladius) and deep-set longline 
gear targeting bigeye tuna ( Thunnus obesus ) in the Hawaii-based longline fishery, 2004-06 (Walsh et al., 2009). 
Table 3 
Meta-analysis of postrelease mortality of blue sharks ( Prionace glauca) as determined from pop-up satellite archival tags 
(PSATs). The postrelease mortality rate estimate was determined with a random-effects model, where each study was assumed 
to have its own postrelease mortality rate and variance. Details of the analysis can be found in the text and in Borenstein et al. 
(2009). Nonreporting PSATs were not used in the analysis. 
Study 
Samples 2 
Postrelease mortality rate 
95% confidence interval 
Weng et at. (2005) 
2/17 
0.118 
0.030-0.368 
Campana et al. (2009b) 
7/37 
0.189 
0.093-0.347 
Stevens et al. (2010) 
1/8 
0.125 
0.017-0.537 
Musyl et al. (present study) 
1/16 
0.063 
0.009-0.335 
Summary effect 
11/78 
0.150 
0.085-0.251 
1 Postrelease mortality in blue sharks (Prionace glauca) determined with PSATs over (!) the total number of reporting PSATs for each study 
tests were significantly different among daytime and 
nighttime comparisons (Figs. 3 and 4; Appendices 2 and 
3). The dichotomy between coefficients of variability in- 
dicates that bigeye threshers are significantly more ac- 
tive at nighttime than during daytime. The aggregated 
temperature-depth profile (Fig. 4B) and vertical move- 
ments indicate that bigeye threshers spend most of their 
time beneath the uniformed temperature surface layer, 
and that increased variability in vertical movement pat- 
terns occurs during crepuscular transitions (Fig. 4E). 
Oceanic whitetip sharks and silky sharks showed 
similar vertical movement patterns (Figs. 5 and 6, re- 
spectively), and the depth and temperature data indi- 
cated that both species were largely confined to the 
uniform temperature surface layer (Figs. 3, 5, and 6; 
Appendices 2 and 3). Although oceanic whitetip sharks 
and silky sharks exhibited plasticity in their daytime 
and nighttime vertical movements, both species spent 
>95% of their time at temperatures that were within 
2°C of the uniform temperature surface layer (Table 4). 
Oceanic whitetip sharks (Fig. 5E) and silky sharks (Fig. 
6E) exhibited pronounced movements at crepuscular 
periods and both species showed significant correlations 
between average nighttime depths and lunar illumina- 
tion (Appendix 2). 
Further analysis of silky shark data indicated dis- 
tinct depths and temperatures occupied north and south 
of 10°N, delimited by the NEC (Fig. 1C). Comparisons 
of pooled day and night data showed that silky sharks 
north of 10°N remained significantly deeper (medi- 
an=54 m, mean=57 m ±0.4 SE, interquartile range 
[IQR] =22-86 m) than immature silky sharks south of 
10°N (median=32 m, mean=32 m ±0.3 SE, IQR=11— 48 
m) (MWBC, 2 = -108.9, Monte Carlo PcO.OOOl). Likewise 
silky sharks north of 10°N experienced significantly 
cooler temperatures (median=25.5°C, mean = 25.4°C 
±0.01 SE, IQR=24.7-25.9°C) than silky sharks south 
of 10°N (median = 28.4°C, mean = 28.3°C ±0.007 SE, 
