354 
Fishery Bulletin 109(4) 
Temperature (°C) 
16 Dec 6 Jan 5 10 15 20 25 30 
Silky shark 
Carcharhinus falciform is 
(n=\Q) 
o 
20 
•g 40 
£ 60 
Q 80 
100 
120 
All tags 
[ 
F 
15:00 19:00 23:00 03:00 07:00 11:00 
Time of day (HST) 
60% 40% 20% 0% 20% 40% 60% 
Percent of time (%) 
Figure 6 
Silky shark (Carcharhinus falciformis ) depth and thermal habitat as identified by pop-up satellite archival tags 
(PSATs). (A) Representative vertical movements. Dashed lines indicate expanded area shown in C. (B) Temperature- 
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 for daytime and 
nighttime diving activities (all tags). (E) Average hourly depth (± standard deviation, SD) readings calculated for 
all samples illustrating variability at crepuscular times (all tags). (F) Percentage of time spent in individual depth 
strata for daytime and nighttime diving activities (all tags). (Note: To prevent excessive clutter, SDs were not shown 
in some panel figures). 
Campana et al. (2009a), using PSATs, determined 
that 19% (CI*=8-32%) of blue sharks tagged in the 
North Atlantic longline fishery targeting sword- 
fish and released alive subsequently died. We could 
find only two other published studies where PSATs 
had been used with blue sharks and that provided 
postrelease mortality estimates. Weng et al. (2005) 
and Stevens et al. (2010) reported 11.8% (CI*=0-29%) 
and 14.3% (CI*=0-42%) postrelease mortality, re- 
spectively. As determined by meta-analysis with all 
available data from 78 reporting PSATs, the summary 
effect of postrelease mortality of blue sharks was 15% 
(95% Cl, 8.5-25.1%). However, because only two of 
four studies were specifically designed to estimate 
mortality, experimental bias could be a confounding 
factor, as well as small and unrepresentative sample 
sizes (Campana et al., 2009b; Musyl et al., 2009). 
We could find no equivalent postrelease mortality 
estimates for bigeye thresher, shortfin mako, silky 
sharks, or oceanic whitetip sharks. Heberer et al. 
(2010), using PSATs, reported a 26% postrelease 
mortality rate of common thresher sharks released 
from recreational gear where fight-times >85 minutes 
identified survivors from moribund individuals. Our 
postrelease mortality rates for pelagic sharks were 
similar to PSAT tagged istiophorid billfish released 
from commercial pelagic longline gear in the Atlantic 
(average postrelease mortality rate was 9%, CI*=2- 
18%) (Kerstetter et al., 2003; Kerstetter and Graves, 
2005, 2008). 
