22 
Fishery Bulletin 11 7(1-2) 
tuna available to retain live fish or to account for any 
dead captures. This management measure is accompa¬ 
nied by a closure of 2 areas in the spring to minimize 
encounters with bluefin tuna and by the use of weak 
hooks that facilitate escape. 
Mitigation of bycatch of bluefin tuna in PLL fish¬ 
eries has been a high priority for the NMFS. The re¬ 
sults of this study generally indicate that management 
measures taken by that agency to minimize bycatch 
of bluefin tuna are effective, measures that reduce the 
probability of capture of bluefin tuna on a longline and, 
then, once captured, provide opportunities to vessels to 
retain dead fish or to release live fish. The currently 
mandated weak hooks do appear to have some conser¬ 
vation benefits. In our analysis, we observed that at- 
vessel mortality was 11% lower for weak hooks than 
for traditionally used circle hooks, and Foster and 
Bergmann 1 estimated that weak hooks also could re¬ 
duce the bycatch of bluefin tuna by 56.5%. Gallagher 
et al. (2017) found a strong correlation of plasma lac¬ 
tate with maximum acceleration of hooked sharks, a 
correlation indicating that the behavioral response of 
the fish could influence the probability of mortality. De¬ 
spite the high probability that we would observe an at- 
vessel mortality, our hook timer data revealed that it is 
possible for bluefin tuna to survive after >14 h on the 
line and that the behavioral response of an individual 
fish might contribute to the probability of its mortality. 
These findings might explain why we see a reduction 
in at-vessel mortality associated with the weak hook, 
with the more vigorous fighters that would likely die 
on the line able to straighten a weak hook and escape 
capture. Nevertheless, it is important to note that the 
at-vessel catch estimate is based on observed reduction 
in bycatch of bluefin tuna and that the actual fate of 
escapees from weak hooks remains unknown (Serafy 
et al., 2012b). 
Because the degree of injury sustained by fish that 
straighten their hooks and elude observation has yet 
to be quantified, the total mortality estimate in our 
study may be considered conservative. On the other 
hand, it is possible that survival was enhanced for fish 
that would have otherwise died on the standard circle 
hooks because they were spared the prolonged stress 
and injury of being firmly hooked until gear retrieval. 
Further research is warranted on this topic; however, 
determining precisely how to track the survival of fish 
that have effectively escaped capture by straightening 
weak hooks is a serious, perhaps insurmountable, re¬ 
search challenge. In any case, on the basis of observed 
interactions in the POP database, the results of our 
study indicate that weak hooks provide the additional 
benefit of increasing at-vessel survival in comparison 
with standard circle hooks. Further mitigation efforts 
could be directed to evaluation of factors that might 
promote an even greater at-vessel survival rate; how¬ 
ever, changes in factors, such as gear configuration, 
set duration, set location, or bait, may negatively af¬ 
fect catches of yellowfin tuna and swordfish, the target 
species of PLL fisheries in the GOM. 
Acknowledgments 
We would like to thank J. Sheldon, J. Rollo, and R. 
Jones for all their hard work and dedication as observ¬ 
ers and for deploying many of the tags used in this 
project. We would also like to thank the captains and 
crews of the vessels from which we were allowed to 
tag fish. We thank C. Porch, E. Prince, and J. Hoo- 
lihan for their assistance in the design of this study. 
Lastly, we would like to thank S. Cushner, K. Keene, 
L. Beerkircher, and D. Foster for assisting in vessel 
coordination. 
Literature cited 
Block, B. A., S. L. H. Teo, A. Walli, A. Boustany, M. J. W. 
Stokesbury, C. J. Farwell, K. C. Weng, H. Dewar, and T. D. 
Williams. 
2005. Electronic tagging and population structure of At¬ 
lantic bluefin tuna. Nature 434:1121-1127. 
Burns, K. M., and J. T. Froeschke. 
2012. Survival of red grouper (Epinephalus morio) and 
red snapper ( Lutjanus campechanus) caught on J-hooks 
and circle hooks in the Florida recreational and recre- 
ational-for-hire-fisheries. Bull. Mar. Sci. 88:633-646. 
Carey, F. G., and K. D. Lawson. 
1973. Temperature regulation in free-swimming bluefin 
tuna Comp. Biochem. Physiol. A. 44:375-392. 
Coggins, L. G., Jr., M. J. Catalano, M. S. Allen, W. E. Pine III, 
and C. J. Walters. 
2007. Effects of cryptic mortality and the hidden costs of 
using length limits in fishery management. Fish Fish. 
8:196-210. 
Federal Register. 
1981. Atlantic bluefin tuna. Fed. Reg. 46:8012-8015. 
1992. Atlantic bluefin tuna fishery. Fed. Reg. 57:365-380. 
2011. Atlantic highly migratory species; bluefin tuna by- 
catch reduction in the Gulf of Mexico pelagic longline 
fishery. Fed Reg. 76:18653-18661. 
2014. Atlantic highly migratory species; 2006 consoli¬ 
dated Atlantic highly migratory species (HMS) fishery 
management plan; amendment 7; final rule. Fed. Reg. 
79:71510-71608. 
Fromentin, J.-M., and J. E. Powers. 
2005. Atlantic bluefin tuna: population dynamics, ecology, 
fisheries and management. Fish Fish. 6:281-306. 
Gallagher, A. J., E. R. Staaterman, S. J. Cooke, and N. 
Hammerschlag. 
2017. Behavioural responses to fisheries capture among 
sharks caught using experimental fishery gear. Can. J. 
Fish. Aquat. Sci. 74:1-7. 
Galuardi, B., F. Royer, W. Golet, J. Logan, J. Neilson, and M. 
Lutcavage. 
2010. Complex migration routes of Atlantic bluefin tuna 
(Tliunnus tliynnus) question current population struc¬ 
ture paradigm. Can. J. Fish. Aquat. Sci. 67:966-976. 
Graves, J. E., B. E. Luckhurst, and E. D. Prince. 
2002. An evaluation of pop-up satellite tags for estimating 
postrelease survival of blue marlin (Makaira nigricans) 
from a recreational fishery. Fish. Bull. 100:134-142. 
Goldsmith, W. M., A. M. Scheld, and J. E. Graves. 
2017. Performance of a low-cost, solar-powered pop-up 
