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Fishery Bulletin 109(4) 
son et al., 2009). Knowledge of these vertical move- 
ment patterns may allow fishing crews to target the 
opportunity of mismatch between hook depth and the 
sharks’ vertical distributions and thus possibly mini- 
mize bycatch (Beverly et al., 2009). For effective man- 
agement measures to be implemented, it is also benefi- 
cial to have accurate estimates of both at-vessel and 
postrelease mortality rates (Carruthers et al., 2009). 
These data are necessary for estimating total fishery- 
induced mortality and for improving stock assessments 
(Kitchell et al., 2004). Mitigation strategies could then 
be given special consideration for species with high 
rates of postrelease mortality (Carruthers et al., 2009). 
Information on postrelease mortality in blue sharks 
(Carey and Scharold, 1990; Weng et al., 2005; Moyes 
et al., 2006; Campana et al., 2009a; Queiroz et al., 
2010; Stevens et al., 2010), bigeye threshers ( Alopias 
superciliosus ) (Nakano et al., 2003; Weng and Block, 
2004), shortfin makos ( Isurus oxyrinchus ) (Holts and 
Bedford, 1993; Klimley et al., 2002; Sepulveda et al., 
2004; Loefer et al., 2005), and common thresher sharks 
(A. vulpinus) (Heberer et al., 2010) is available from 
studies with acoustic tracking and pop-up satellite ar- 
chival tags (PSATs). In two studies (Moyes et al., 2006; 
Campana et al., 2009a), the investigation of postrelease 
mortality of blue sharks released from longline fishing 
gear was the primary goal, but mortality rates may 
have been confounded by specific aspects of fishing 
practices (Musyl et al., 2009). Hook type, time spent 
hooked on the line, fight time, leader material, fish 
size, and handling and discard practices can influence 
the at-vessel and postrelease mortality of pelagic shark 
species (e.g., Diaz and Serafy, 2005; Moyes et al., 2006; 
Campana et al. 2009a; Carruthers et al., 2009; Heberer 
et al. 2010; Hoey and Moore 1 ). 
Our goals were to measure postrelease mortality 
rates and vertical movement patterns in the five most 
commonly captured pelagic shark species in the Hawaii- 
based commercial longline fishery: blue sharks, big- 
eye threshers, oceanic whitetip sharks ( Carcharhinus 
longimanus ), shortfin makos, and silky sharks (C. fal- 
ciformis)( Walsh et al., 2009). All five species represent 
a significant portion of the shark bycatch in global fish- 
eries and their life history characteristics make popu- 
lations vulnerable to fishing pressure (Cortes, 2000; 
Camhi, 2008; Dulvy et al., 2008; Stevens, 2008; Chang 
and Liu, 2009). Moreover, there is little or no informa- 
tion about their postrelease survival, population ecology, 
and movement patterns in the central Pacific Ocean. As 
far as we know, there are no published reports on the 
movements and postrelease mortality of silky sharks 
and oceanic whitetip sharks, and several authors have 
commented on the paucity of information on the biol- 
1 Hoey, J. J., and N. Moore. 1999. Captain’s report: multi- 
species catch characteristics for the U.S. Atlantic pelagic 
longline fishery. National Fisheries Inst, report to NOAA, 
National Marine Fisheries Service, Silver Spring, MD, 78 p. 
[Available from http://www.sefsc.noaa.gov/seaturtlecontrac- 
treports.jsp, accessed May 2011.] 
ogy and ecology of these apex predators (Bonfil, 2008; 
Bonfil, et al., 2008; Dulvy et al., 2008). Results from 
this study extend the work presented in Moyes et al. 
(2006) and are expected to be useful in the mitigation 
of shark bycatch and mortality. 
Materials and methods 
Sharks were caught by pelagic longline fishing gear 
(from March 2001 through November 2006) deployed 
from the NOAA research vessels Townsend Cromwell 
and Oscar Elton Sette and by using methods described 
in Moyes et al. (2006). In brief, longline gear (-400-800 
hooks per set) was deployed at night (usually immedi- 
ately after dusk) and retrieved in the morning. Because 
we used four to six hooks between floats; hook depths 
were generally <100 m as determined by attached time- 
temperature-depth recorders (Wildlife Computers, Red- 
mond, WA). 
Soak times ranged from 10 to 24 hours with an aver- 
age of 15 hours, and before 2004, we employed 15/0 size 
circle hooks, squid (Illex spp.) bait, and green chemical 
light sticks attached to the monofilament nylon leader 
-90 cm above each hook. However, because of regula- 
tions introduced in 2004 to reduce sea turtle bycatch 
in the Hawaii-based shallow-set (nighttime) commer- 
cial longline fishery targeting swordfish (Gilman et al., 
2007; Walsh et al., 2009), we began using 16/0 and 18/0 
circle hooks (no offset), and Pacific saury (sanma, Colo- 
labis saira) as bait. In addition, to improve shark catch 
rates by reducing bite-offs from monofilament leaders, 
we added -25 cm of seven-strand braided stainless steel 
cable immediately above the hook. 
Sharks were hoisted aboard by a sling and restrained 
by the crew as described in Moyes et al. (2006). Sharks 
showing an absence of movements or reaction of the 
nictitating membrane to light touching of the eye were 
deemed dead and were not tagged (i.e., these samples 
would bias the postrelease mortality estimate). Tagged 
sharks were measured to the nearest centimeter for 
total length (TL), and hooks were removed by cutting 
them in half with bolt cutters unless they were too 
deeply ingested, in which case, the leader line was cut 
as close to the mouth of a shark as possible. PSATs 
(model PTT-100, Microwave Telemetry, Columbia, MD) 
were affixed to the dorsal fin by drilling a 10-15 mm di- 
ameter hole near the base of the fin and threading sev- 
en-strand braided stainless steel cable encased in soft 
plastic tubing (which acted as the harness) through the 
wound. Next, a second tether (made of -123-kg break- 
ing strength fluorocarbon leader material) was used to 
attach (with stainless steel crimps and thimbles) the 
PSAT to the dorsal fin harness. The only exception was 
applied to bigeye threshers, which were tagged in the 
water by using a harpoon, and for these sharks the tag 
head was affixed to the end of the tethers on the PSAT. 
For these sharks, total lengths were visually estimated. 
PSATs were programmed to acquire temperature and 
pressure (depth) readings every 15-60 minutes and 
