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Fishery Bulletin 114(3) 
Percent composition or frequency 
Figure 2 
Percent frequency of occurrence (%F), percent composition by 
number (%N), and percent composition by weight (%W) of prey 
types present in the diet of 140 red porgy {Pagrus pagrus) cap- 
tured in the South Atlantic Bight from 2009 through 2011. Prey 
items consumed by fewer than 5% of predators are not included. 
Miscellaneous=fish scales, foraminifera, eggs, macroalgae, and 
sediment. 
Pi = (XSi/5:St)*ioo, (1) 
where Sj = the sum of prey i; and 
St = the sum of all prey items found in only 
those predator guts that contained prey i. Percent com- 
position by weight was the summed variable. On the 
graph that results from this method (Amundsen et ah, 
1996, fig. 3), the percent abundance, which increases 
along the diagonal from the lower left to the upper 
right corner, provides a measure of prey importance, 
with dominant prey on the top and rare or unimport- 
ant prey on the bottom. The vertical axis represents 
feeding strategy: specialization versus generalization. 
Prey points on the upper part of the graph represent 
prey on which predators have specialized, and prey 
positioned on the bottom half of the graph have been 
eaten occasionally or infrequently. 
Results 
Unidentified prey items were often encountered be- 
cause both species bite or grind their food instead of 
consuming it whole. Fortunately, the majority of prey 
have parts that are resistant to digestion, making 
them easily identifiable on the basis of characteristic 
parts. For example, crab claws and legs, pieces of echi- 
noderm test and spines, and pieces of barnacles were 
often seen in stomach contents. A full listing 
of prey items for both species is available in 
Suppl. Tables 1 and 2 [Online]. 
Red porgy 
From 2009 through 2011, gut contents from 
140 red porgy were collected. Lengths of red 
porgy ranged from 274 to 508 mm TL. Sample 
sizes were low at the extremes of our sampling 
range (i.e., 34°N and 27°N). 
General diet description Red porgy had a di- 
verse diet, composed of 188 different taxa 
that belong to 18 taxonomic groupings: deca- 
pods, bivalves, polychaetes, gastropods, bryo- 
zoans, unidentified crustaceans, echinoderms, 
bony fishes, barnacles, miscellaneous (e.g., fish 
scales and foraminifera), tunicates, amphipods, 
squid, cnidarians, stomatopods, isopods, ostra- 
cods, and protochordates. Decapods, barnacles, 
and bivalves were the main prey of red porgy, 
accounting for 44%, 20%, and 11% of the diet 
by weight, respectively (Fig. 2). The most fre- 
quently consumed decapods were parthenopid 
crabs (29%), portunid crabs (28%), calappid 
crabs (28%), and shrimps (28%). The most fre- 
quently consumed bivalve was the painted egg- 
cockle {Laevicardium pictum) (7%). Although 
polychaetes were consumed by 50% of red por- 
gy, this taxon accounted for only 6% by weight 
and 8% by number. Other groups that were 
frequently consumed included gastropods (46%), bryo- 
zoans (45%), echinoderms (33%), and bony fishes (32%); 
however, these species contributed little by weight. 
Ontogenetic, temporal and spatial changes in diet We 
determined that 6% of the total variability in the diet 
data was explained by the CCA. The first and second 
canonical axes accounted for 51% and 22%, respective- 
ly, of the constrained variation. Of the 4 environmental 
variables, depth and season were the most important 
(P<0.001), followed by length (P<0.05) (Fig. 3). 
Although decapods were consumed in all seasons, 
fewer were consumed in the summer (29%) when bar- 
nacles were the primary food source (43%) (Fig. 4A). In 
the spring, red porgy consumed mostly decapods (50%) 
and bivalves (11%). In the autumn, decapods (53%) and 
polychaetes (20%) were the primary prey types. 
Red porgy captured on the inner shelf (depths: 20.1- 
50.0 m) consumed a higher percentage of barnacles and 
bivalves than did their counterparts on the outer shelf, 
but decapods dominated diets of red porgy regardless 
of depth. Outer shelf red porgy also consumed bony 
fishes and polychaetes (Fig. 4B). 
Decapods were the dominant prey at all latitudes, 
but fewer of them were consumed in the middle lati- 
tudes (31-32°N) (Fig. 4C). Red porgy captured at the 
middle latitudes (31-32°N) consumed barnacles (27%) 
and bivalves (11%) in addition to decapods. Barnacles 
