Willis et al . Feeding behavior of 3 sciaenids along the southeastern United States 
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labile 3 
Results from the simplified Morisita-Horn index used for analysis of 
diet overlap for pairs of 3 species: weakfish (Cynoscion regalis), southern 
kingfish ( Menticirrhus americanus ), and Atlantic croaker ( Micropogonias 
undulatus). An asterisk (*) denotes a value that indicates biologically 
significant potential for diet overlap between species in a pair. Analyses 
were performed for both mean percent weight (%MW) and mean percent 
number (%MN). 
Weakfish Southern kingfish Atlantic croaker 
Predator and and and 
cross pairs southern kingfish Atlantic croaker weakfish 
%MW 0.46 0.74* 0.50 
%MN 0.40 0.56 0.43 
items according to all 3 of the diet metrics analyzed 
(frequency of occurrence, composition by number, and 
composition by weight). Polychaetes were also impor- 
tant, occurring in nearly half of the stomachs for all 
years of this study, compared with polychaetes ranking 
fourth in the diet of southern kingfish in a study in the 
Gulf of Mexico (McMichael and Ross, 1987). Clam si- 
phons were the most frequently occurring prey item in 
our study, but, in another study in Brazil, amphipods 
were the most common prey item in spring, followed by 
polychaetes and mysids (Rodrigues and Vieira, 2010). 
The Gulf of Mexico and Brazilian study defined juve- 
nile fishes as those ranging in TL between 2 and 6 cm, 
but few fishes less than 10 cm TL were observed in 
our study. A possible explanation for the differences in 
diet are ontogenetic changes in foraging behavior and 
swimming ability that, in turn, increase foraging areas 
and feeding opportunities for larger fishes (Graham et 
al., 2007). 
The diet of Atlantic croaker was the most diverse 
of among the diets of the 3 sciaenids and our findings 
are comparable with those of Overstreet and Heard’s 
(1978) study of this species in the Gulf of Mexico. The 
diet patterns that we observed are most similar to 
those of Atlantic croaker captured in nearshore wa- 
ters, at depths consistent with the depth range of our 
sampling. Statistical analyses indicated no seasonal 
shift in diet in either our study or in that of Over- 
street and Heard (1978), but we found that the diet of 
Atlantic croaker included a markedly higher frequen- 
cy of occurrence for echinoderms, specifically ophiu- 
roids, which were present in an average of 16% of 
stomachs, compared with <4% of the stomachs in the 
Gulf of Mexico study (Overstreet and Heard, 1978). 
This difference could be a result of variance in the 
distribution of ophiuroids, which are quite common off 
the southeastern coast of the United States, or may 
be the result of other prey types being more readily 
available to Atlantic croaker populations in the Gulf 
of Mexico. 
Foraging habitats and feeding strategy varied among 
the 3 species in this study. Southern kingfish and At- 
lantic croaker consumed prey that are associated with 
the seafloor, whereas weakfish generally fed on prey 
items that occur in the water column. Furthermore, 
southern kingfish and Atlantic croaker can be charac- 
terized as having a more generalized feeding strategy. 
Despite the variation in feeding strategy, a few prey 
items were consumed by all 3 species, such as the am- 
phipods Erichthonius brasiliensis and Microprotopus 
raneyi and the mysid Promysis atlantica. Mysids were 
the most frequently consumed individual prey item 
for both southern kingfish and Atlantic croaker, and 
the second-most frequently consumed individual prey 
item of weakfish. Some animals, such as most mysid 
species, exhibit diel vertical migrations, spending day- 
light hours on the seafloor and migrating toward the 
surface at dusk to forage throughout the night or vice 
versa (Robertson and Howard, 1978). These vertical mi- 
gration patterns provide an opportunity for predatory 
fishes to encounter and consume prey that may only 
temporarily dwell in their foraging habitat (Goldman 
and Sedberry, 2010), therefore, creating an opportunity 
for diet overlap between bottom-feeding fishes and wa- 
ter-column-feeding fishes. 
The 3 species examined here did not exclusively em- 
ploy a single feeding strategy (e.g., generalist or spe- 
cialist). Individuals of all 3 species consumed specific 
prey items, but, at the population level, each species 
showed a proclivity to feed opportunistically — a finding 
that could be interpreted as indicating that they fed 
on whatever was both available and abundant. In com- 
parison with the populations of the other 2 fish spe- 
cies, the weakfish population showed a trend toward 
more specialized feeding, shifting to more mobile, pe- 
lagic prey earlier in their ontogeny. Weakfish also have 
the potential to reach the greatest size, and changes 
in their diet as they grow would be expected to reduce 
diet overlap with species that have a smaller terminal 
size (Schoener, 1974; Werner and Gilliam, 1984). Alter- 
natively, the morphological features of the 3 species in- 
dicates that weakfish would be more likely to feed in 
