Driggers et al.; Influence of bait type on catch rates of predatory fish on longline gear 
53 
Figure 1 
Map of sites where sampling was conducted with bottom longline gear in the northern 
Gulf of Mexico in March and April 2015. Black circles represent each sampling site. The 
grey lines indicate the isobaths at 10, 50, 100, 200, 500, and 1000 m. 
smoothing (LOWESS) with a 75% smoothing factor was 
applied to scatterplots to determine whether a trend 
was present in the relationship. All statistical tests 
were considered significant at an a level of 0.05. 
Results 
During March and April 2015, 131 longline sets were 
completed (Fig. 1) for this study, resulting in deploy- 
ments of 13,100 hooks and the capture of 1196 indi- 
vidual fish. Hook soak times ranged from 77 to 257 min 
(mean of 118.6 min, standard deviation [SD] 39.4), and 
hook-specific bait status was recorded for 12,888 gan- 
gions. Bait status of 212 hooks was not recorded due to 
technical difficulties; however, these hooks represented 
less than 2% of the gangions deployed. Of the moni- 
tored hooks, 8 were retrieved with the hook missing as 
a result of crimp failure (e.g. splitting or slipping). Of 
the 1944 gangions that were retrieved with whole bait 
present, there was no significant difference in the num- 
ber of Atlantic mackerel (n=956) and northern shortfin 
squid (/z=988) retained on hooks (x2=:0.49, P=0.48). This 
result indicates that both bait types were equally re- 
tained on hooks during deployment, soak, and retrieval 
in the absence of interactions with feeding organisms. 
Interactions between bait and feeding organisms were 
evident on 9742 gangions that were retrieved with 
partial or no bait remaining on hooks. In these cases, 
bait damage or loss was more common with northern 
shortfin squid (/i=5033) than with Atlantic mackerel 
(«=4709) (x^=10.71, P<0.01). There was no significant 
difference in the distributions of hook soak times when 
hooks were retrieved with whole bait present (Kol- 
mogorov-Smirnov statistic=0.97, P=0.31) (Fig. 2). 
All captured organisms were fish species with the 
exception of 1 loggerhead sea turtle {Caretta caretta), 
captured with bait of northern shortfin squid, and 1 
giant isopod, Bathynomus giganteus, captured with At- 
lantic mackerel. The total catch and size range of each 
species analyzed are presented in Table 1. There were 
no significant differences in species-specific length dis- 
tributions for individuals caught by bait type (P-values 
for all species were >0.05) (Table 1), and length distri- 
bution data were non-normal or heteroscedastic, with 
the exception of data for the red drum. The mean size 
of red drum captured on hooks baited with Atlantic 
mackerel (mean: 859.0 mm TL [SD 32.1]) was signifi- 
cantly smaller than the mean size of individuals cap- 
tured with northern shortfin squid (mean: 903.7 mm 
TL [SD 40.0]) it= -2.31, P=0.03). 
There was a significant difference in the median 
length of tiger sharks {Galeocerdo cuvier) captured on 
each bait type, with the median length of tiger sharks 
being smaller on hooks baited with northern shortfin 
squid (1337 mm FL) than on hooks baited with Atlantic 
mackerel (1922 mm FL) (W=52.5, P=0.05). There were 
no statistically significant species-specific differences in 
the median length of any other species between the 2 
bait types at a=0.05 (Table 1). However, at an a level of 
0.10, there were significant differences in the median 
length of blacknose sharks (1^=238.0, P=0.06) and scal- 
loped hammerheads {Sphyrna lewini) (W=78.0, P=0.09) 
captured on the 2 bait types. For blacknose sharks, me- 
dian length at capture was smaller when these sharks 
were caught with northern shortfin squid (1073 mm FL 
versus 1120 mm FL), whereas for scalloped hammer- 
heads the median length at capture was smaller when 
these sharks were caught with Atlantic mackerel (1443 
mm FL versus 1812 mm FL). 
The results of chi-square tests indicate significant 
differences in the expected and observed catches for 5 
shark and 1 teleost species (Table 1). All of the shark 
species for which a statistically significant preference 
