Aucoin et al.: An underwater tool to catch and release Ginglymostoma tirratum 
491 
of blood at most) that quickly coagulated. Although the 
elasticity in shark skin is connected to internal propul¬ 
sion muscles (Wainwright et ah, 1978; Naresh et al., 
1997), swimming and other movements never appeared 
compromised during regular observations of sharks in 
the holding tank, nor during our intermittent observa¬ 
tions of individuals in the canal. 
Values of hook wound parameters that were exam¬ 
ined, such as wound area, were small and remained 
small regardless of shark size (up to 80 kg). Medical 
studies have shown wound area and circumference to 
correlate with wound volume (Melhuish et al., 1994; 
Flanagan, 2003), which was not the case with regard 
to recorded hook depth in our study. Although we rec¬ 
ognize our measurements of hook depth were a crude 
estimate and not necessarily indicative of potential 
wound sinus formation, the fact that hook penetration 
was mostly superficial, with the hook often falling out 
by itself when the shark was hauled onboard, suggests 
internal injury was minimal. When the hook did pen¬ 
etrate deeper, hook penetration remained parallel to 
the skin on account of the bend in the J-hook, thus 
limiting perpendicular penetration. Reducing the hook 
gap (the space between the hook point and the hook 
shank) should further reduce perpendicular penetra¬ 
tion, but could be more prone to tearing the skin (mea¬ 
sured by circularity). Our results indicated that the 
type and size of hook we used was less prone to tearing 
the skin of larger individuals than the skin of smaller 
ones; therefore, it would be useful to experiment with a 
range of smaller hooks for smaller individuals in future 
studies. 
The poker-and-hook capture method is also well 
suited for nurse sharks because of their feeding behav¬ 
ior. Nurse sharks are obligate suction feeders capable 
of generating suction forces that are among the highest 
recorded for any aquatic vertebrate to date (Tanaka, 
1973; Motta et al., 2008). The poker-and-hook capture 
method prevents many sublethal effects or the delayed 
mortality that can be caused by traditional baited 
hook-and-line gear (or prevents both). This is especial¬ 
ly the case for more internally hooked fish as has been 
reported for blue sharks (Prionace glauca; Borucinska 
et al., 2001; Borucinska et al., 2002) and lemon sharks 
(Danylchuk et al., 2014). Nurse sharks further exhibit 
a suck-and-spit behavior or shake their head violently 
(or exhibit a combination of both) to reduce the size 
of food items (Motta et al., 2002; Motta, 2004), which 
could further increase the risk of hooking to sensory 
and vital organs concentrated anteriorly. 
The behavioral response of nurse sharks is also ap¬ 
propriate for the poker-and-hook capture method be¬ 
cause nurse sharks in our study always retreated upon 
being hooked underwater. Nonetheless, as inoffensive 
as nurse sharks may appear, they are still ranked 
fourth in documented shark bites on humans (Ricci 
et al., 2016). Nurse sharks are known to attack when 
approached too closely, especially in a confined space 
or if their retreat is prevented (Limbaugh, 1963; Nel¬ 
son et al., 1986). Our divers using this method were 
highly experienced in handling underwater wildlife. It 
is possible that the poker-and-hook method could trig¬ 
ger more erratic or aggressive responses in other shark 
species, and therefore shark safety and cautious plan¬ 
ning are advised with this technique for other species. 
Nurse sharks also exhibit relatively subdued fight¬ 
ing during capture compared with that of other sharks 
(Gallagher, 2015). Fighting intensity and hooking se¬ 
verity could be more pronounced with larger, more ag¬ 
gressive species. The tiger shark (Galeocerdo cuvier) 
has been captured on the water surface by a similar 
technique in order to attach satellite transmitters to 
their dorsal fin (Fitzpatrick et al., 2012). In the lat¬ 
ter tiger shark study, a detachable clamp and buoy 
system was closed around the base of the shark’s tail 
as it swam at the water surface near their boat. Re¬ 
markably, video footage of this technique indicates ti¬ 
ger sharks also become quickly subdued after momen¬ 
tarily dragging the attached buoy through the water. 
Whereas nurse sharks and tiger sharks are known to 
display more subdued behavior when hooked anteriorly 
or captured by their tails, blacktip sharks (Carcharhi- 
nus limbatus ) have shown bouts of intense fighting at 
the onset of being hooked anteriorly (Gallagher et al., 
2017). We speculate that blacktip sharks, as well as 
other shark species that exhibit intense fighting behav¬ 
ior when hooked anteriorly, would also fight intensely 
if captured by the tail. 
Shark breathing is another important consideration 
when using the poker-and-hook method to capture dif¬ 
ferent shark species. Although most sharks are facul¬ 
tative ram ventilators some are obligate ram ventila¬ 
tors that need to swim continuously to breathe (Milsom 
and Taylor, 2015). The common thresher shark ( Alo- 
pias vulpinus) is an example of an obligate ram venti¬ 
lator, and therefore pulling this species backwards or 
adding drag would affect their breathing and survival 
(Heberer et al., 2010; Sepulveda et al., 2015). Interest¬ 
ingly, common thresher sharks are usually pulled in 
backwards when fished because their caudal fin gets 
hooked when trying to immobilize bait perceived as 
prey (Aalbers et al., 2010). Large common thresher 
sharks do not survive capture times >85 min, unlike 
smaller common thresher sharks or individuals landed 
with much shorter capture times (Cartamil et al., 2010; 
Heberer et al., 2010). 
Capture time has been identified as a critical fac¬ 
tor in postrelease survival (Cooke and Suski, 2005). 
Nurse sharks in the canal were landed within a few 
minutes with the poker-and-hook capture method and 
with less effort than when similar-size individuals 
were landed by baited hook-and-line gear. It is likely 
that sharks were simply less agitated and traumatized 
when hooked posteriorly than when hooked anteriorly. 
However, pulling the shark backwards (with the buoy 
line attached to the shark tail) may have affected the 
functional mobility of the caudal fin or general swim¬ 
ming behavior, thus impairing thrust or swimming 
speed (see Wilga and Lauder, 2002). It is also possible 
that the backward motion or inverted position of the 
