56 
Fishery Bulletin 115(1) 
line gear are caught at a higher rate on hooks baited 
with northern shortfin squid than on hooks baited with 
Atlantic mackerel. Ebert and Bizzarre (2007) showed 
that the clearnose skate has a diverse diet, with ap- 
proximately 21% fish and less than 1% squid species 
as prey items reported in stomach contents. However, 
Schwartz (1996) found that the fish component of the 
diet of clearnose skates was composed of small-bodied 
fish species, such as the striped anchovy (Anchoa hep- 
setus), Atlantic croaker (Micropogonias undulatus), 
spot {Leiostomus xanthurus), and blackcheek tongue- 
fish {Symphurus plagiusa). This finding indicates that 
a limited gape size resulted in more clearnose skates 
being captured on hooks with northern shortfin squid 
because that bait type is more malleable and, there- 
fore, more easily manipulated than Atlantic mackerel. 
Among teleosts, no consistent trend in preference for 
one bait type over another was found. For example, red 
snapper and tilefish showed no significant preference 
for either bait type; however, red drum had a signifi- 
cant preference for northern shortfin squid. Conversely, 
although not statistically significant, there was an ob- 
vious trend with yellowedge grouper toward a prefer- 
ence for Atlantic mackerel. The lack of bait preference 
shown by red snapper and tilefish was expected because 
both species are widely reported to be omnivorous and 
opportunistic (e.g., Steimle et al., 1999; Callaway et 
al., 2009; Moser et al.^). Yellowedge grouper have been 
reported to feed primarily on brachyuran crab and te- 
leost fish species (Heemstra and Randall, 1993); there- 
fore, the trend toward a preference for hooks baited 
with Atlantic mackerel was not unexpected. 
In contrast, the preference for bait of northern 
shortfin squid exhibited by red drum was not clearly 
related to the known diet of this species. The results of 
a number of studies indicate that red drum forage on 
a diverse group of prey, including invertebrate and fish 
species and that their prey varies depending on life 
stage, habitat, and season (e.g., Overstreet and Heard, 
1978; Scharf and Schlicht, 2000). For example, Booth- 
bly and Avualt (1971) examined the stomach contents 
of red drum sampled within a coastal marsh system 
along the coast of Louisiana and determined that crus- 
taceans dominated the diet from late spring through 
fall but fish species became more important during 
colder months. As pointed out by Overstreet and Heard 
(1971) and Scharf and Schlicht (2000), dietary shifts 
likely were related to seasonally mediated changes in 
abundance of prey species. However, Matlock (1987) re- 
ported that, in general, adult red drum consume more 
individuals that are fish species than individuals that 
are invertebrate species. Therefore, the preference that 
red drum showed for the northern shortfin squid in 
2 Moser, J. G., Jr., A. G. Pollack, G. W. Ingram Jr., C. T. Gled- 
hill, T. A. Henwood, and W. B. Ilriggers III. 2012. Develop- 
ing a survey methodology for sampling red snapper, Lutja- 
nus campechanus, at oil and gas platforms in the northern 
Gulf of Mexico. Southeast Data, Assessment, and Review, 
SEDAR31-DW26, 23 p. [Available from website.] 
our study cannot be explained on the basis of dietary 
composition reported in the literature because Atlan- 
tic mackerel would have been the expected preferred 
bait type. Although the most likely explanation is gape 
limitation, another possible explanation is that red 
drum were outcompeted for hooks baited with Atlantic 
mackerel and opportunistically fed on northern short- 
fin squid. However, it does not appear that red drum 
were outcompeted because all sets where red drum 
were captured had relatively low catch rates of other 
fish species. 
There was a clear decrease in bait preference with 
increasing total catch rates for Atlantic sharpnose, 
blacknose, and sandbar sharks. This trend was most 
obvious for sandbar sharks: on sets with less than 13 
other captured individuals, regardless of species, 100% 
of sandbar sharks were caught on hooks baited with 
Atlantic mackerel. At catch rates of 13 or more indi- 
viduals, regardless of species, on a set, the likelihood 
that sandbar sharks would be captured on hooks baited 
with northern shortfin squid increased. This decrease 
in bait preference indicates that Atlantic sharpnose, 
blacknose, and sandbar sharks become more opportu- 
nistic when in the presence of competitors or that few- 
er hooks baited with Atlantic mackerel were available 
later in the set (as a result of depredation of preferred 
bait types or a captured fish occupying a hook) and late 
arriving individuals did not have an equal number of 
both bait types from which to choose. 
As total catch rates increased, the trend of Atlan- 
tic sharpnose, blacknose, and sandbar sharks moved 
toward no preference for a particular bait type (i.e., 
IBP approached 0) and the trend of red snapper moved 
toward a preference for northern shortfin squid (i.e., 
IBP<0). This result indicates that sharks were still 
actively selecting hooks baited with Atlantic mackerel 
despite more hooks baited with northern shortfin squid 
being available. Conversely, the trend in bait prefer- 
ence of red snapper at increasing total catch rates in- 
dicates that they were feeding opportunistically on the 
most abundant bait type available. This latter point 
can be more clearly demonstrated by comparing the 
IBP values of the Atlantic sharpnose shark with those 
of the red snapper. On longline sets with greater than 
25 individuals captured, IBP values were exclusively 
greater than 0 for the Atlantic sharpnose shark and 
less than 0 for red snapper. Another possible explana- 
tion for the shift toward a reduced preference for At- 
lantic mackerel at high catch rates could be differences 
in retention rates of the 2 bait types as hook soak time 
increased. However, there was no significant difference 
in the distribution of soak times for hooks retrieved 
with whole bait present for each bait type. 
Beyond species-specific dietary preferences, it is pos- 
sible that differences in foraging strategies among the 
species we examined, at least in part, led to differences 
in catch rates of fish species on the 2 bait types. All 
shark species that we examined are active, roaming 
predators. Speed et al. (2010) estimated that the home 
range (excluding seasonal migrations) of small-bodied 
