54 
Fishery Bulletin 1 15(1) 
Figure 2 
Comparison by bait type of the number of hooks retrieved with 
whole bait present over the range of hook soak times used in 
this study for which predatory fish species were caught on bot- 
tom longline gear in the northern Gulf of Mexico during March 
and April 2015. Gray bars represent the bait that was Atlantic 
mackerel (Scomber scombrus) and white bars represent the bait 
that was northern shortfin squid (Illex illecebrosus). 
for a single bait type was observed were cap- 
tured more frequently with Atlantic mackerel 
than with northern shortfin squid. For exam- 
ple, sandbar sharks (Carcharhinus plumbeus) 
were caught 6.4 times more frequently with 
Atlantic mackerel than with northern shortfin 
squid. Furthermore, for those shark species 
that showed no statistically significant prefer- 
ence for a specific bait type, all were captured 
more frequently on hooks baited with Atlantic 
mackerel, and chi-square test P-values were 
<0.10, with the exception of the value for the 
scalloped hammerhead (F-0.66). 
Unlike other elasmobranchs, clearnose 
skates (Baja eglanteria) were caught more fre- 
quently on hooks baited with northern short- 
fin squid; however, there was no statistically 
significant difference in the observed and ex- 
pected catch of this species between the 2 bait 
types (x^=2.78, P=0.09). Among teleosts, red 
drum was the only species for which a signifi- 
cant bait preference (x^=8.65, P<0.01) was ob- 
served, and this species was caught 4.2 times 
more frequently with northern shortfin squid 
than with Atlantic mackerel. Other commer- 
cially and recreationally important teleosts 
that were captured include red snapper (Lut- 
janus campechanus) (x^=0.99, P=0.32) and tile- 
fish (Lopholatilus chamaeleonticeps) (x^ =0.04, 
P=0.85), neither of which had an observed significant 
bait preference. Although a significant bait preference 
was not found for yellowedge grouper (Hyporthodus 
flavolimbatus) (x^=2.45, P=0.12), 70% of all individu- 
als of this species were captured on hooks baited with 
Atlantic mackerel. 
The relationship between IBP and total catch was 
examined for Atlantic sharpnose shark, blacknose 
shark, sandbar shark, and red snapper. For all 3 shark 
species, a preference for hooks baited with Atlantic 
mackerel was observed at low rates of total catch; 
however, as catch rates increased, IBP values trended 
toward 0 (Fig. 3). This trend was most evident for sand- 
bar sharks, which were captured exclusively on hooks 
baited with Atlantic mackerel when the total catch con- 
sisted of 12 of fewer fish (Fig. 3). A preference for hooks 
baited with Atlantic mackerel also was observed for 
red snapper at low rates of total catch; however, unlike 
what was observed for sharks, red snapper were cap- 
tured regularly on hooks baited with northern shortfin 
squid regardless of total catch size (Fig. 3). Further- 
more, when more than 20 individuals were captured on 
a longline set, red snapper were captured exclusively 
on hooks baited with northern shortfin squid (Fig. 3). 
Discussion 
The results of our study indicate that when given the 
choice between hooks baited with northern shortfin 
squid or with Atlantic mackerel, the degree of bait pref- 
erence varies among fish species and that, when pres- 
ent, bait preference generally declines with increasing 
rates of total catch on longline gear. Specifically, shark 
species commonly captured as bycatch on longline gear 
in the northern Gulf of Mexico preferentially selected 
Atlantic mackerel over northern shortfin squid, par- 
ticularly when total catch rates were low. Although 
a statistically significant preference for hooks baited 
with Atlantic mackerel was documented only for the 
Atlantic sharpnose shark, blacknose shark, sandbar 
shark, smooth dogfish (Mustelus canis), and little gulp- 
er shark (Centrophorous uyato), the same trend was 
evident for all elasmobranch species captured, with the 
exceptions of the scalloped hammerhead and clearnose 
skate. There was no difference between the 2 bait types 
in catch rates, and therefore no difference in bait pref- 
erence, for economically important teleosts, with the 
exception of the red drum. Together, these results pro- 
vide support for an easily applied measure to reduce 
rates of shark bycatch and cause no effect on catch 
rates of target species or need for gear modifications. 
Several previous studies reported declines in catch 
rates of blue sharks that were associated with specific 
bait types (Watson et ah, 2005; Gilman et ah, 2007; 
Foster et ah, 2012) and found that bycatch of blue 
sharks was reduced when fish rather than squid were 
used as bait. Although our findings superficially seem 
in opposition to those of Watson et al. (2005) and Gil- 
man et al. (2007), differences among the studies can 
be explained by the diets of the species examined and, 
therefore, support the use of specific bait types to re- 
