436 
Fishery Bulletin 108(4) 
Table 1 
Hooking location (frequency; 95% confidence interval) and presence or absence of trauma (bleeding, not bleeding) for observed 
recreational catches of blue marlin (Makaira nigricans, zi = 123), white marlin (Kajikia albida, n-212), and sailfish (Istiophorus 
platypterus, n = 132), caught on natural baits rigged with either J hooks or circle hooks in the western North Atlantic Ocean. 
Hook location 
Trauma 
Species 
Hook type 
Internal 
Externa] 
Bleeding 
Not bleeding 
Blue marlin 
Circle 
1 (1.8%; 0-5.4%) 
54 (98.2%; 90.0-99.9%) 
0 (0%; 0-2.0%) 
55 (100%; 93.5-100%) 
“J” 
13(19.1%; 10.6-28.5%) 
55 (80.9%; 69.5-89.4%) 
9 (13.2%; 6.2-23.6%) 
59 (86.8%; 78.7-94.8%) 
White marlin 
Circle 
4 (2.0%; 0. 6-5.0%) 
196 (98.0%; 94.5-99.5%) 
2 (1.0%; 0-2.4%) 
198 (99.0%; 96.4-99.9%) 
“J” 
32 (44.4%; 32.7-56.6 %) 
40 (55.6%; 43.4-67.3%) 
24 (33.3% ; 22.4-44.2%) 
48 (66.7%; 54.6-77.3%) 
Sailfish 
Circle 
5 (6.2%; 2.0-13.8%) 
76 (93.8%; 86.0-97.8%) 
2 (2.5%; 0.3-8. 6%) 
79 (97.5%; 91.4-99.7%) 
“J” 
21 (41.2%; 27.6-55.8%) 
30 (58.8%; 44.3-72.4%) 
17 (33.3%; 20.7-47.9%) 
34(66.7%; 52.1-79.2%) 
tagged with Microwave Telemetry PSATs, and released. 
Three blue marlin were released off the U.S. mid-Atlan- 
tic coast; 26 off St. Thomas, U.S. Virgin Islands; 2 off 
Punta Cana, Dominican Republic; 21 off La Guaira, 
Venezuela, and 9 off Porto Seguro, Brazil (Appendix 1). 
Estimated fish weights ranged from 70 lb (31.8 kg) to 
500 lb (227.3 kg) (mean=216.4 lb [98.2 kg]). Fight times 
(including tag attachment) ranged from 4 to 85 minutes 
(mean=19.4 minutes). After tag placement, eight fish 
exhibited difficulty maintaining an upright orientation 
alongside the boat and were resuscitated for periods 
ranging from one to ten minutes before their release 
(Appendix 1). 
All 61 PSATs reported after detachment from the 
fish. Two tags detached prematurely — both on the first 
day of deployment — and were excluded from survival 
analyses. The 59 tags that remained attached for the 
ten-day deployment period successfully transmitted 
between 18% and 96% (mean = 81%) of the archived 
data. Most of these PSATs remained at sea during the 
data transmission period which typically lasts about 
30 days before the battery power is exhausted. How- 
ever, six tags washed ashore during the period of data 
transmission, resulting in reduced data reception from 
these tags. Two tags were recovered by beachcombers 
and returned to us, allowing recovery of 100% of the 
archived data. 
We inferred the survival of 57 of 59 fish (96.6%) 
that carried the tags for the 10-day deployment from 
analyses of pressure (depth) and temperature profiles 
over the 10-day tagging period (Appendix 1). Surviv- 
ing blue marlin exhibited multiple daily vertical move- 
ments as evidenced by the temperature and pressure 
(depth) profiles throughout the course of the ten-day 
tagging period. Many animals demonstrated a distinct 
diurnal patterning to their dives, remaining near the 
surface at night and making deep dives during the day 
(Fig. 2A). Net displacement ranged from 10 to 943 km 
(mean=226.9 km). 
The two mortalities inferred from the PSAT data 
occurred among the 30 blue marlin caught on artifi- 
cial lure and natural bait combinations rigged with 
J-hooks. Both individuals were hooked internally 
and bled profusely from the gill area at the time of 
capture. The archived data indicated that these in- 
dividuals sank to the bottom shortly after release 
and remained there for 48-96 hr, after which time 
a release mechanism was activated by the constant 
depth data in each PSAT and initiated tag release 
and data transmission (Fig. 2B). The two mortalities 
of blue marlin caught on artificial lure and natural 
bait combinations with J hooks resulted in an esti- 
mated postrelease mortality rate of 6.7%. The results 
of 10,000 bootstrap simulations at an underlying true 
mortality of 6.7% indicated that the approximate 95% 
confidence intervals (Cl) for the mortality estimates 
of blue marlin caught on J hooks for an experiment 
with 30 tags would range from 0% to 22% (with the 
methods of Goodyear, 2002). None of the 29 blue mar- 
lin caught on natural baits with circle hooks died 
during the ten day period, resulting in a postrelease 
mortality estimate of 0%, with corresponding 95% 
Cl ranges from 0% to 12.5%. The difference between 
the estimates of postrelease mortality for blue mar- 
lin caught on J-hooks and circle hooks was not sta- 
tistically significant (Fisher’s exact test: P=0.26). 
Discussion 
The goal of this study was to determine whether blue 
marlin derive similar conservation benefits from the 
use of circle hooks in the recreational fishery as has 
been previously reported for other istiophorid billfishes. 
A direct comparison of hooking locations with the use 
of J hooks and circle hooks in natural baits rigged as 
they are typically fished in the recreational fishery 
indicates that the use of circle hooks results in sig- 
