Graves and Horodysky: Conservation benefits of circle hooks in multispecies recreational billfish fisheries 
435 
animal to ingest the bait before feeling tension on the 
line (see Jolley, 1974; Mather et al., 1975; Prince et al., 
2007, for a description of this fishing method), although, 
in some instances the fish attacked trolled baits before 
an angler could reach the rod and drop back. The loca- 
tion of the hook and the presence or absence of bleeding 
(visible blood) was noted at the time of capture. Hooking 
locations were classified as external when all or part of 
the hook was visible outside of the fish’s mouth, includ- 
ing fish that were foul hooked (hooked in areas away 
from the fish’s mouth), and internal if no part of the 
hook was visible when the fish’s mouth was closed. 
Postrelease survival 
PSATs were attached to 61 blue marlin caught in rec- 
reational fisheries in the western Atlantic Ocean. Fish 
were caught by using J hooks and circle hooks that were 
rigged with natural baits consisting of ballyhoo or Span- 
ish mackerel (Scomberomorous maculatus ) . Baits were 
rigged in a manner typical for the fishery. J hooks were 
inserted inside the baits, which were fished in combina- 
tion with a skirted artificial lure (e.g., Ilander [L & S 
Bait Company, Largo, FL], chugger [Mold Craft Lures, 
Pompano Beach, FL], or Seawitch [C & H Lures, Jack- 
sonville, FL]) attached directly ahead of the bait (Fig. 
1, C and D). Circle hooks were rigged externally on the 
baits, either on top of the head or directly in front of the 
bait. In some cases, a small artificial lure (chugger) was 
placed between the circle hook and the bait. 
Blue marlin were caught on 30-130 lb (13.6-59.1 kg) 
class sportfishing tackle in waters off the United States 
mid-Atlantic coast; St. Thomas, U.S. Virgin Islands; 
Punta Cana, Dominican Republic; La Guaira, Venezuela; 
and Porto Seguro, Brazil, between September 2007 and 
October 2009 (Appendix 1). As is typical for the fishery, 
the vessel was maneuvered by the captain to assist the 
angler in the capture of the fish. Blue marlin were not 
brought alongside the vessel until they were considered 
to be sufficiently calm to allow accurate tag placement. 
The first 61 fish available to us were tagged with a 
Microwave Telemetry PTT 100 HR tag (Microwave Te- 
lemetry, Inc., Columbia, MD), programmed for release 
after 10 days. This tag model records temperature, 
pressure (depth), and light levels approximately every 
90-120 s. The tags were rigged as described in Graves 
et al. (2002), and deployed as described in Horodysky 
and Graves (2005). The location of the hook and pres- 
ence or absence of bleeding was noted for each fish at 
the time of tagging. If practical, the hook was removed 
from the fish before its release. As is customary in this 
fishery, blue marlin that were unable to maintain their 
position upright in the water column were resuscitated 
by using the forward motion of the vessel to facilitate 
movement of water over the fish’s gills before release 
(Appendix 1). 
Survival of released blue marlin was inferred from 
temperature and depth profiles following the protocols 
of Horodysky and Graves (2005). Net displacement of 
each fish was calculated as the minimum straight line 
distance from the point of release to the point of tag 
pop-up. Cochran-Mantel-Haenszel (CMH) or Fisher’s 
exact tests were used to address the effect of the J 
hooks and circle hooks on hooking location, hook-in- 
duced trauma, and survival. A Yates correction for 
small sample size was applied in conducting CMH tests 
when expected cell values were less than 5 (Agresti, 
1990). All statistical analyses were conducted in the 
Statistical Analysis System, vers. 9.1 (SAS Institute, 
Cary, NC). Bootstrapping simulations were performed 
to determine the 95% confidence intervals of the esti- 
mates of mortality after release by using the software 
developed by Goodyear (2002). 
Results 
Hooking location 
Hooking location and the presence or absence of bleeding 
were noted for 123 blue marlin, 272 white marlin, and 
132 sailfish caught on natural baits rigged with either J 
hooks or circle hooks (Table 1). The incidence of internal 
hooking with J hooks ranged from 19.1% (blue marlin) 
to 44.4% (white marlin), and the frequency of internal 
hooking locations for fish caught on circle hooks was 
considerably lower, ranging from 1.8% (blue marlin) 
to 6.2% (sailfish). For blue marlin, white marlin, and 
sailfish, J hooks had a significantly higher probability 
of internal hooking locations than circle hooks (P<0.007, 
P<0.0001, P<0.001, respectively). The frequency of inter- 
nal hooking locations for J hooks in blue marlin (19.1%) 
was less than half the value observed for white marlin 
and sailfish (44.4% and 41.2%, respectively), and the 
difference between blue marlin versus white marlin and 
sailfish combined was significant (P<0.0014). 
The occurrence of trauma (bleeding) mirrored the pat- 
tern observed for internal hooking locations between the 
two hook types for each of the three billfishes. Across 
the three species, over 81% of the instances of bleeding 
(44/54) were associated with internal hooking loca- 
tions (7/9 blue marlin, 20/24 white marlin, and 16/17 
sailfish). Bleeding of fish caught on circle hooks ranged 
from 0% in blue marlin to 2.5% in sailfish (Table 1). For 
blue marlin, white marlin, and sailfish, J hooks had a 
significantly higher probability of inducing bleeding 
than circle hooks (P<0.0141, P<0.001, P<0.0001, re- 
spectively). As with the occurrence of internal hooking 
locations with J hooks among the three species, the 
frequency of bleeding observed in blue marlin (13.2%) 
was less than half that observed in white marlin and 
sailfish (both 33.3%); blue marlin had significantly 
lower rates of bleeding resulting from the use of J hooks 
than white marlin and sailfish combined (P<0.027). 
Postrelease survival 
Sixty-one blue marlin were caught on natural baits 
rigged with circle hooks (30) or on a combination of 
artificial lure and natural bait rigged with J hooks (31), 
