Whitney et a!.: Mortality of Carcharhinus limbatus caught in the Florida recreational fishery 
533 
capture stress and few studies have directly measured 
postrelease mortality because electronic tags can be 
cost prohibitive (Skomal and Bernal, 2010; Whitney 
et al., 2016). Studies that have assessed postrelease 
mortality in elasmobranch fisheries have found that 
postrelease mortality is variable between species and 
fisheries but can be quite high in certain circumstances 
(>60%, Sepulveda et al., 2015; for a review of elasmo¬ 
branch postrelease mortality, see Ellis et al., 2017). 
Efforts have been made to link perturbations in 
blood biochemistry to animal stress and mortality re¬ 
sulting from capture (Wells et al., 1986; Skomal, 2006; 
Hyatt et al., 2012). Exhaustive exercise such as fight¬ 
ing on a line, typically causes a marked decrease in 
blood pH (acidemia) resulting from metabolic (increas¬ 
ing H + as indicated by rising blood lactate and decreas¬ 
ing blood bicarbonate) and respiratory (increasing par¬ 
tial pressure of carbon dioxide [pC0 2 ]) acidoses (Wood, 
1991; Milligan, 1996; Kieffer, 2000; Skomal, 2007; 
Skomal and Bernal, 2010; Skomal and Mandelman, 
2012). These physiological indicators, if coupled with 
quantitative data on postrelease behavior or mortality, 
can provide insights into causative factors of physiolog¬ 
ical stress and mortality, as well as potential mitiga¬ 
tion measures (Skomal, 2007). 
One of the most commonly advocated fishing meth¬ 
ods to minimize physical trauma (e.g., gut hooking) and 
reduce postrelease mortality is the use of circle-hooks 
(Cooke and Suski, 2004). Over the past decade, studies 
on the relative impact of circle-hooks vs. traditional J- 
hooks on pelagic teleosts have indicated that the for¬ 
mer reduce the likelihood of injury to the fish by lodg¬ 
ing in the mouth or jaw as opposed to the esophagus or 
stomach, thereby increasing postrelease survivorship 
with little impact on catch per unit of effort (Skomal 
et al., 2002; Kerstetter and Graves, 2006; Serafy et al., 
2009; Serafy et al., 2012). Empirical data on these vari¬ 
ables are lacking in recreational shark fisheries, but 
there is some evidence that sharks are less likely to 
be foul-hooked with the use of circle-hooks than with 
J-hooks (French et al., 2015; Sepulveda et al., 2015; 
Willey et al., 2016). 
A main target species in the southeastern U.S. 
shark fisheries, both recreational and commercial, is 
the blacktip shark (Carcharhinus limbatus) (NMFS 1 ). 
Although management measures beginning in 1993 
have enabled blacktip sharks to rebound from a sharp 
decline (NMFS 1 ), current fishing pressure on the black¬ 
tip shark may be increasing as an alternative to pres¬ 
sure on the sympatric sandbar shark (C. plumbeus), 
which is prohibited to be captured in federal waters 
(NMFS 2 ). The NOAA Marine Recreational Information 
1 NMFS (National Marine Fisheries Service). 2006. Final 
consolidated Atlantic highly migratory species fishery man¬ 
agement plan, 1600 p. Highly Migratory Species Manage. 
Div., Off. Sustainable Fish., Natl. Mar. Fish. Serv., Silver 
Spring, MD. [Available from website.] 
2 NMFS (National Marine Fisheries Service). 2008. Final 
ammendment 2 to the consolidated Atlantic highly migrato¬ 
ry species fishery management plan, 705 p. Highly Migra- 
Program estimates that blacktip sharks are the most 
commonly captured shark species in the Florida recre¬ 
ational fishery, with 89% of individuals released alive 
after capture (National Marine Fisheries Service Marine 
Recreational Information Program, Recreational Fisher¬ 
ies Statistics, available from website). 
The impact of capture on blacktip sharks is un¬ 
known, but the blood biochemistry of blacktip sharks 
caught on longlines and drum lines indicates that the 
magnitude of the stress response in this species is 
greater than that measured in other carcharhinid spe¬ 
cies, such as sandbar sharks (Mandelman and Skomal, 
2009; Marshall et al., 2012; Gallagher et al., 2014). 
Furthermore, the observed at-vessel mortality rate for 
this species (88%) was much higher than that of the 
sandbar shark (43%) in one study of the North Atlantic 
Ocean longline fishery (Morgan and Burgess, 2007) and 
therefore raises further concerns about the response of 
blacktip sharks to capture. However, correlations be¬ 
tween blood stress indicators and postrelease mortality 
have yet to be determined for this species. 
In this study, we compared the effects of capture 
and hook type on blacktip sharks caught in the Florida 
recreational shark fishery. We compared sharks caught 
on circle and J-hooks to determine whether blood phys¬ 
iology, or visual at-vessel capture metrics, differed be¬ 
tween hook types. We then used multidimensional ac¬ 
celeration data loggers (ADLs) to measure postrelease 
mortality to determine whether hook type or at-vessel 
metrics could accurately predict postrelease survival in 
blacktip sharks. ADLs record the frequency and force 
of swimming movements, as well as the animal’s body 
orientation at subsecond intervals (e.g., Kawabe et al., 
2003; Shepard et al., 2008; Whitney et al., 2012). These 
high-resolution data can be used to identify and quan¬ 
tify specific behaviors according to tailbeat frequency 
and amplitude, including active swimming, stalling, 
gliding, rolling, etc. Recently this technology has been 
shown to provide definitive measures of mortality and 
postrelease recovery period in coastal sharks (Whitney 
et al., 2016). 
Materials and methods 
Blacktip sharks were handled in this study in accor¬ 
dance with guidelines of the National Research Coun¬ 
cil (2011). Work was completed under Florida Fish and 
Wildlife Conservation Commission permit #SAL-11- 
0041-SRP and approved under Mote Marine Laboratory 
Institutional Animal Care and Use Committee (IACUC) 
#13-11-NW2, as well as the Florida Aquarium ACUC. 
Field sites and sampling methods 
We selected 2 study sites off the coast of Florida 
with a known seasonal prevalence of blacktip sharks: 
tory Species Manage. Div., Off. Sustainable Fish., Natl. Mar. 
Fish. Serv., Silver Spring, MD. [Available from website.] 
