438 
Fishery Bulletin 108(4) 
be swallowed and hence for the hook to lodge in an 
undesirable location (Prince et al., 2007). 
In previous studies, internal or deep hooking loca- 
tions have been associated with an increased incidence 
of trauma in istiophorids and other large pelagic fishes 
(Domeier et al. 2003; Horodysky and Graves, 2005; 
Prince et al., 2007; Skomal, 2007). In the present study, 
trauma, as evidenced by bleeding, was significantly 
lower for blue marlin, white marlin, and sailfish caught 
on circle hooks than for those caught on J hooks. The 
low incidence of bleeding associated with natural baits 
rigged with circle hooks for white marlin that we ob- 
served (1.0%) concurs with the value of 1.7% reported 
for white marlin by Graves and Horodysky (2008) and 
the range reported for the congeneric striped marlin 
caught on live baits with circle hooks (3-4%, Domeier et 
al., 2003). The frequency of bleeding with circle hooks 
observed for sailfish (2.5%) in this study is slightly low- 
er than the values reported for Pacific sailfish caught 
on natural baits (6%) and for Atlantic sailfish caught on 
live baits with circle hooks (5-13%; Prince et al., 2002, 
2007). We noted bleeding in 33% of the white marlin 
and 33% of the sailfish caught on natural baits with J 
hooks. This value is somewhat lower than those report- 
ed for white marlin (45%) and Pacific sailfish (56.8%) 
caught on trolled natural baits, and higher than those 
reported for striped marlin (21%) and Atlantic sailfish 
(21-25%) caught on live baits (Prince et al., 2002, 2007; 
Domeier et al., 2003; Horodysky and Graves, 2005). 
The incidence of bleeding in white marlin and sailfish 
caught on J hooks was significantly higher than that 
for blue marlin caught on the same terminal tackle and 
is consistent with an increased incidence of internal 
hooking rates in the former species observed in this and 
previous studies (Prince et al., 2002; 2007; Domeier et 
al., 2003; Horodysky and Graves, 2005). 
To directly follow the fate of blue marlin caught on 
trolled natural baits or on bait and lure combinations 
rigged with either circle or J hooks and released, we 
deployed 61 PSATs, of which 59 remained attached for 
the ten-day tracking period. All 29 blue marlin caught 
on circle hooks rigged with natural baits or bait and 
lure combinations survived for ten days after release. 
In a study of 59 white marlin caught on natural baits 
rigged with circle hooks, Graves and Horodysky (2008) 
reported a single mortality. Together, these studies 
reveal a very low level of postrelease mortality for bill- 
fishes caught on circle hooks in natural bait trolling 
fisheries. In contrast, Domeier et al. (2003) reported 
an adjusted rate of postrelease mortality of 17.4% for 
striped marlin caught from stationary vessels on live 
baits rigged with circle hooks. These results support the 
contention of Cooke and Suski (2004) that the magni- 
tude of the conservation benefits of circle hooks varies 
among species, gear types, and fisheries. 
PSAT depth records indicated that two of 30 blue 
marlin caught on artificial lure and natural combina- 
tions rigged with J hooks died after release, resulting in 
an estimated postrelease mortality of 6.7%. This value 
is approximately one-fifth of the postrelease mortality 
reported by Horodysky and Graves (2005) for 20 white 
marlin caught on natural baits rigged with J hooks 
(35%) and less than one-fourth of the value of 29.4% 
reported by Domeier et al. (2003) for 24 striped marlin 
caught on live baits rigged with J hooks. The reduction 
in postrelease mortality of blue marlin caught on natu- 
ral baits with J hooks relative to postrelease mortality 
of white marlin caught on the same terminal tackle 
parallels the reductions observed in the frequency of 
internal hooking locations and bleeding between these 
species. 
In this study, the use of circle hooks in natural baits 
resulted in significantly reduced internal hooking and 
bleeding for blue marlin, white marlin, and sailfish. 
Because blue marlin caught on J hooks experienced 
significantly lower incidences of internal hooking loca- 
tions and trauma than white marlin and sailfish caught 
on the same terminal tackle, the conservation benefit 
resulting from the use of circle hooks for blue marlin 
is less than that experienced by the other two species. 
This asymmetry was also evident in the analysis of 
postrelease survival. There was a trend for decreased 
postrelease mortality of blue marlin caught on natu- 
ral baits with circle hooks (0%) than for blue marlin 
caught on artificial lures and natural baits with J hooks 
(6.7%), but the difference was much smaller than that 
previously reported for white marlin caught on natural 
baits rigged with the two hook types (0% and 35%, 
respectively; Horodysky and Graves, 2005). Although 
these results provide support for recent management 
measures implemented by NMFS that require the use of 
non-offset circle hooks in natural baits for all Atlantic 
billfish tournaments, it is important to realize that the 
conservation benefits of this measure vary asymmetri- 
cally among the different billfish species. 
Acknowledgments 
We thank Captains J. Grant, R. Cox and J. Ross for 
compiling information on hook location and fish condi- 
tion. B. DeGabrielle, J. Tierney, J. Thiel, K. Neill, D. 
Dutton, J. Schratweiser, and many others provided assis- 
tance in catching and tagging blue marlin. M. Domeier 
and the International Game Fish Association provided 
logistical support. Funding for this study was provided 
by the Gulf States Marine Fisheries Commission (Bill- 
fish-2005-11), the National Marine Fisheries Service 
(NA07NMF4720295), and the Offield Family Foundation. 
This article is VIMS contribution number 3107. 
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Arocha, F., and M. Ortiz. 
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