128 
Fishery Bulletin 119(2—3) 
Digestion code 
O41 
2 
3 
4 
Figure 4 
Proportion of fish prey found in stomachs of red snapper 
(Lutjanus campechanus) that were assigned to each of 4 
digestion codes used to qualitatively assess the condition of 
fish prey. The codes are (1) fresh, easy to identify visually; 
(2) partially digested: some skin or scales remain, and many 
identifiable features remain; (3) mostly digested: most iden- 
tifiable features absent, with flesh attached to vertebra; and 
(4) severely digested: only hard parts (e.g., otoliths or verte- 
bra) remain. Red snapper were sampled along the Atlantic 
coast of the southeastern United States in 2017 and 2018. 
weight (%W=21.25%). A total of 19 different species of fish 
were identified as prey. The most frequently consumed fish 
species were the bluespotted searobin (Prionotus roseus) 
(%FO=6.67%), snake eels (Ophichthus spp.) (%#FO=3.81%), 
porgy species (Stenotomus spp.) (%FO=3.81%), the inshore 
lizardfish (S. foetens) (%FO=3.81%), and the tomtate (Hae- 
mulon aurolineatum) (%FO=2.86%). 
Fish species formed the most important prey category, on 
the basis of IRI values across all size classes of red snapper, 
especially for the size classes of 300-500 mm TL (59.26%) 
and 701-900 mm TL (61.06%), in comparison with the size 
class of 501-700 mm TL (34.49%) (Fig. 6). Shrimp species 
composed a prey category that was more important in the 
diet of the size classes of 300-500 mm TL (IRI=30.14%) 
and 501-700 mm TL (IRI=28.85%) than in the diet of 
the size class of 701-900 mm TL (IRI=2.17%). Crab spe- 
cles were more important in the diet for the size classes 
of 501-700 mm TL (IRI=30.08%) and 701-900 mm TL 
(31.82%) than in the diet for the size class of 300-500 mm 
TL (IRI=8.08%). Fish species formed the most important 
prey category, according to the IRI, for red snapper cap- 
tured at depths <30 m (74.12%) and at depths of 31-60 m 
(44.64%), but shrimp species were the dominate prey at 
depths >60 m (65.46%) (Fig. 7). 
The slope of the fit of a linear model to data for the last 
5 randomly sampled stomachs in the prey species accumu- 
lation curve was 0.32; therefore, the curve was not consid- 
ered to reach an asymptote (Fig. 8). According to the 
first-order jackknife estimator, approximately 107 differ- 
ent prey species would be expected to have been identified, 
indicating that we taxonomically described ~64% of the 
diet of red snapper along the Atlantic coast of the south- 
eastern United States. 
Discussion 
In our study, we used DNA barcoding to supplement 
visual identification of prey items to improve taxonomic 
resolution of the diet composition of red snapper along the 
Atlantic coast of the southeastern United States. We were 
able to identify a total of 19 fish prey species, using DNA 
barcoding. If we had relied on visual methods alone, we 
would have identified only 2 species and described only 
10% of the total species richness of fish prey. Currently, 
the fishery management plan for the snapper-grouper 
complex in the Atlantic Ocean off the southeastern United 
States manages only 3 of these 19 species: the vermilion 
snapper (Rhomboplites aurorubens), the red porgy (Pagrus 
pagrus), and Stenotomus sp. The %W for both vermilion 
snapper and red porgy was <1% and for Stenotomus sp. 
was <6% in the diet of red snapper from the region in our 
study (Table 1). 
Our findings agree with results of DNA barcoding 
studies done in the Gulf of Mexico that found negligible 
feeding on vermilion snapper (%W=1.01%), red porgy 
(%W=0.00%), and Stenotomus sp. (%W=1.31%) (Tarnecki 
and Patterson, 2015; Szedlmayer and Brewton, 2019). 
Further, feeding behavior related to ontogeny (i.e., size) of 
red snapper in our study was similar to observations of the 
diet of red snapper in the Gulf of Mexico, including that 
the largest fish consumed primarily fish and crab species 
(Wells et al., 2008). In other diet studies for red snapper in 
the Gulf of Mexico (McCawley and Cowan, 2007; Tarnecki 
and Patterson, 2015) significant consumption (>20%) of 
zooplankton, especially by larger fish, was observed. Such 
a level of consumption was not evident in our study, possi- 
bly because of under-representation of larger individuals 
in our study, seasonal abundance of zooplankton that did 
not coincide with the timing of our sampling, or other dif- 
ferences between ecosystems. 
In our study, sequences sampled from most prey assigned 
to a species were >99% similar to reference sequences, 
exceeding the a priori sequence similarity threshold of 
98% for species-level resolution. Given that Ward et al. 
(2005) reported average interspecific distances of 9.93% 
for marine fish species within the same genus and that 
sequences from the 2 most closely related species found in 
our study (both in the genus Synodus) were >19% dissim- 
ilar, we are confident that the 98% threshold for assigning 
a species in our study was appropriate and conservative for 
the goal of limiting false-positive species identifications. 
The inability to genetically distinguish between specimens 
in the genera Ophidion and Stenotomus in our study may 
be attributable to incomplete taxonomic coverage in the 
reference databases or to misidentification of the voucher 
specimens from which these reference sequences were gen- 
erated (Stavrou et al., 2018). 
The species accumulation curve did not achieve satu- 
ration, indicating that sampling intensity in our study 
