Driggers et al.: Influence of bait type on catch rates of predatory fish on longline gear 
55 
A B 
Total number of individuals captures (all species) 
Figure 3 
Comparison of relationships between index of bait preference and total capture number of all species on individual long- 
line sets deployed in the northern Gulf of Mexico during March and April 2015 for (A) Atlantic sharpnose sharks {Rhi- 
zoprionodon terraenovae), (B) blacknose sharks {Carcharhinus acronotus), (C) sandbar sharks (C. plumbeus), and (D) 
red snapper (Lutjanus campechanus). The black lines represent locally weighted regression lines (determined through 
application of locally weighted scatterplot smoothing). 
duce bycatch rates of sharks. Watson et al. (2005) and 
Gilman et al. (2007) examined bycatch of blue sharks 
in pelagic longline fisheries and found that catch rates 
of this species declined when mackerel were used as 
bait. Similarly, Foster et al. (2012) found the use of 
Atlantic mackerel as bait to decrease bycatch of blue 
sharks; however, they also indicated that hooks baited 
with Atlantic mackerel were more efficient at capturing 
porbeagles (Lamna nasus) and shortfin makos (Isurus 
oxyrinchus). 
Cortes (1999) presented an exhaustive literature re- 
view of the diets of 149 shark species and found that 
the diet of blue sharks was dominated by cephalopods 
(49.4%). By comparison, teleost fish species composed 
55-98.2% of the diets of Atlantic sharpnose sharks, 
blacknose sharks, porbeagles, sandbar sharks, scalloped 
hammerheads, and shortfin makos (Cortes, 1999). The 
2 shark species that we examined and that do not have 
a primarily piscivorous diet, according to Cortes (1999), 
were the tiger shark and the smooth dogfish. The diet 
of tiger sharks was primarily composed of teleost fish 
species (35.4%), and sea turtles (23.8%), whereas crus- 
taceans (64.3%) and teleost fish species (16.6%) domi- 
nated the diet of smooth dogfish. Cephalopods were re- 
ported by Cortes (1999) to constitute 0.0-15.5% of the 
diets of the shark species we captured. The results of 
our study, combined with those of Watson et al. (2005), 
Gilman et al. (2007), and Foster et al. (2012), indicate 
that, despite being frequently characterized as opportu- 
nistic (e.g., Strasburg, 1958; Lowe et al., 1996), sharks, 
when presented with a choice between a bait that is 
a common prey item and one that is not a significant 
dietary component, will actively select the former. 
Although not statistically significant, the catch rate 
of clearnose skates was 2.7 times higher on hooks 
with northern shortfin squid than on hooks with At- 
lantic mackerel, indicating a strong preference for the 
former. This result was similar to the findings of Ariz 
et al. (2006) and Coelho et al. (2012), who found that 
batoids, more specifically ray species, captured on long- 
